Template B V3.0 (Beta): Created by J. Nail 06/2015 Impact of Neonicotinoids in Mid-South Row Crop Systems by TITLE PAGE John Ha

Template B v3.0 (beta): Created by J. Nail 06/2015

Impact of neonicotinoids in mid-south row crop systems

By TITLE PAGE John Hartley North

A Thesis Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Agricultural Life Science in the Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology

Mississippi State, Mississippi

May 2016

2016

Impact of Neonicotinoids in Mid-South Row Crop Systems

By APPROVAL PAGE John Hartley North

Approved:

______Angus L. Catchot Jr. (Co-Major Professor)

______Jeffrey Gore (Co-Major Professor)

______Donald R. Cook (Committee Member)

______Darrin M. Dodds (Committee Member)

______Fred R. Musser (Committee Member)

______Michael A. Caprio (Graduate Coordinator)

______George M. Hopper Dean College of Agriculture and Life Sciences

Name: John Hartley North ABSTRACT Date of Degree: May 6, 2016

Institution: Mississippi State University

Major Field: Agricultural Life Science

Major Professors: Dr. Angus L. Catchot Jr. and Dr. Jeffrey Gore

Title of Study: Impact of Neonicotinoids in Mid-South Row Crop Systems

Pages in Study: 133

Candidate for Degree of Master of Science

Neonicotinoid seed treatments are widely used and highly effective against early

season insect pests of all row crops throughout the Mid-South region of the United States.

An analysis was performed to determine the value of neonicotinoid seed treatments

across multiple trials in soybean, Glycine max L.; corn, Zea mays L.; cotton, Gossypium

hirsutum L.; and sorghum, Sorghum bicolor L. production systems across the mid-

southern region. Neonicotinoid seed treatments provided significant yield and economic

increases when utilized the majority of the time. A second experiment was performed to

determine the value of various insecticide classes when utilized in an overall systems

approach when managing cotton insect pest in the Delta and Hills region of Mississippi.

When all classes of insecticides were used in rotation, significant yield and economic benefits were observed in the Delta Region compared to treatment scenarios where some

insecticide classes were omitted.

DEDICATION

This research is dedicated to my parents, Peggy North and Jeff North for the

unconditional love and support throughout my life and during my time at Mississippi

State University. I would not be where I stand today without your love and support that

you have showed me through the years. I’m thankful for all you have done for me and

words cannot express how much I have learned from each of you. You have instilled

honest values and a hard work ethic that I have carried with me throughout my life and

will continue to do so in the future. I would also like to thank God for the strength he has

given me throughout my life and his patience. God has truly blessed me by surrounding

me with outstanding mentors in my life and I have learned to never take a sunrise or sunset for granted.

I also dedicate this research to Bruce Pittman of Coila, MS and Terry Ozborn of

Canton, MS. Words cannot express what these two men have meant to me in my life. I

feel honored to have grown up around them and witnessed there diligence in all aspects

of life. I cherish their friendship and support they have displayed for me all through the

years.

ACKNOWLEDGEMENTS

I sincerely thank my major advisors, Dr. Angus Catchot and Dr. Jeff Gore for giving me the opportunity to work towards a Master’s degree in entomology which has been a lifelong dream of mine to follow in my father’s footsteps. The guidance and support you have given me while working under you will be forever invaluable. The guidance you have given me while conducting research and writing my thesis has made a tremendous impact on my life as well. Words cannot express how much I have enjoyed working for you and what this experience has meant to me. I respect both of you very much and truly honored to have had the opportunity to learn from your diligence and knowledge in agriculture and everyday life. I’m honored to have been associated with two outstanding professionals and proud to call you my friends. I will be forever in your debt for the opportunity you have given me, as well as, the patience and support you have greeted me with. I would also like to thank my other graduate committee members, Dr.

Don Cook, Dr. Fred Musser, and Dr. Darrin Dodds for your guidance and support you have given me throughout my time at Mississippi State University.

I would like to thank Dr. Scott Stewart, Dr. Gus Lorenz, Dr. David Kerns, Chip

Graham, and Bobby Hendrix for their professional assistance throughout the completion of this project. Special thanks to Dung Bao and Boise Stokes for their assistance with all research plots, as well as, fellow graduate students and summer employees.

iii

TABLE OF CONTENTS

DEDICATION ...... ii

ACKNOWLEDGEMENTS ...... iii

LIST OF TABLES ...... vii

CHAPTER

I. INTRODUCTION ...... 1

Neonicotinoids ...... 1 Origin of Neonicotinoids ...... 1 Neonicotinoid Mode of Action ...... 1 Use of Neonicotinoids Worldwide ...... 2 Use of Neonicotinoids in the United States ...... 3 Risks of Neonicotinoid Insecticides ...... 3 Advantages of Neonicotinoid Insecticides ...... 5 Soybean ...... 6 Growth Stages and Maturity Groups of Soybean ...... 6 Soybean and U.S. Soybean Production ...... 6 Soybean production in the Mid-South Region ...... 7 Early Season Insect Management in Soybean with Neonicotinoids ...... 8 Mid-Late Season Insect Management in Soybean with Neonicotinoids ...... 9 Corn ...... 9 Corn and U.S. Corn Production ...... 9 Corn Production in the Mid-South Region ...... 10 Growth Stages and Development of Corn ...... 10 Early Season Insect Management in Corn with Neonicotinoids ...... 10 Cotton ...... 12 Cotton and U.S. Cotton Production ...... 12 Cotton Production in the Mid-South ...... 13 Growth Stages of Cotton ...... 13 Early Season Insect Management in Cotton with Neonicotinoids ...... 15 Mid-Late Season Insect Management in Cotton with Neonicotinoids ...... 16 Grain Sorghum ...... 19 Grain Sorghum and U.S. Grain Sorghum Production ...... 19 Grain Sorghum Production in the Mid-South ...... 19 iv

Growth Stages of Grain Sorghum ...... 20 Early Season Insect Management in Grain Sorghum with Neonicotinoids ...... 21 Mid-Late Season Insect Management in Grain Sorghum ...... 22 Justification for Further Research ...... 23 References ...... 24

II. VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-SOUTH SOYBEAN (GLYCINE MAX L.) PRODUCTION SYSTEMS ...... 35

Abstract ...... 35 Introduction ...... 36 Methods and Materials ...... 38 Results and Discussion ...... 40 References ...... 50

III. VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-SOUTH CORN (ZEA MAYS L.) PRODUCTION SYSTEMS ...... 53

Abstract ...... 53 Introduction ...... 54 Methods and Materials ...... 57 Results and Discussion ...... 59

IV. VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-SOUTH COTTON (GOSSYPIUM HIRSUTUM L.) PRODUCTION SYSTEMS ...... 72

Abstract ...... 72 Introduction ...... 73 Methods and Materials ...... 75 Results and Discussion ...... 78 References ...... 88

V. VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-SOUTH GRAIN SORGHUM (SORGHUM BICOLOR L.) PRODUCTION SYSTEMS ...... 92

Abstract ...... 92 Introduction ...... 93 Materials and Methods ...... 96 Results and Discussion ...... 98

VI. QUANTIFYING THE VALUE OF INSECTICIDE CLASSES IN MISSISSIPPI COTTON (GOSSYPIUM HIRSUTUM L.) ...... 109

Abstract ...... 109 Introduction ...... 110 Materials and Methods ...... 113 Results and Discussion ...... 116 References ...... 128

VII. SUMMARY ...... 132

LIST OF TABLES

1.1 Cotton Development Stages ...... 14

1.2 Grain Sorghum Growth Stages ...... 21

2.1 Values used to calculate net economic returns in each state for each year...... 45

2.2 Mean yields (SEM) and net economic returns (SEM) of soybean treated with a neonicotinoid seed treatment (Neonicotinoid IST) compared with those not treated with insecticide (Untreated) across the Mid-South Region from 2005-2014...... 47

2.3 Mean (SEM) yields and net economic returns (SEM) of soybean treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each state in the Mid- South from 2005-2014...... 47

2.4 ANOVA table for soybean yields and net economic returns across the Mid-South for each year (2005-2014)...... 48

2.5 Mean (SEM) yields and net economic returns of soybean treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across the Mid-South region from 2005-2014...... 49

3.1 Cost of neonicotinoid insecticide treated corn seed ...... 63

3.2 Price received for corn by state and year used to calculate net economic returns in each state for each year ...... 64

3.3 Mean yields (SEM) and net economic returns (SEM) of corn treated with a neonicotinoid seed treatment compared with those not treated with insecticide across the Mid-South Region from 2001-2014...... 66

3.4 Mean (SEM) yields and net economic returns (SEM) of corn treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each state in the Mid-South from 2001-2014...... 66 vii

3.5 ANOVA table for corn yields and net economic returns across the Mid-South for each year (2001-2014)...... 67

3.6 Mean (SEM) yields and net economic returns of corn treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across the Mid-South region from 2001-2014...... 68

4.1 Values used to calculate net economic returns in each state for each year ...... 82

4.2 Insecticide seed treatment (Gaucho 600 or Cruiser 5FS) price ha-1 for each state...... 84

4.3 Mean yields (SEM) and net economic returns (SEM) of cotton treated with a neonicotinoid seed treatment (Neonicotinoid IST) compared with those not treated with insecticide (Untreated) across the Mid-South Region from 1996-2014...... 84

4.4 Mean (SEM) yields and net economic returns (SEM) of cotton treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each state in the Mid-South from 1996-2014...... 85

4.5 ANOVA table for cotton yields and net economic returns across the Mid-South for each year (1996-2014)...... 86

4.6 Mean (SEM) yields and net economic returns of cotton treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across the Mid-South region from 2005-2014...... 87

5.1 Mean yields (SEM) and net economic returns (SEM) of grain sorghum treated with a neonicotinoid seed treatment compared with those not treated with insecticide across Mississippi from 2014- 2015...... 102

5.2 Mean (SEM) yields and net economic returns (SEM) of grain sorghum treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each location in Mississippi from 2014-2015...... 103

5.3 ANOVA table for grain sorghum yields and net economic returns across Mississippi for each year (2014-2015)...... 104

viii

5.4 Mean (SEM) yields and net economic returns of grain sorghum treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across Mississippi from 2014-2015...... 105

6.1 Insecticide applications for 2014 Starkville (hills) Location...... 119

6.2 Insecticide applications for 2014 Stoneville (delta) Location...... 120

6.3 Insecticide applications for 2015 Starkville (hills) Location...... 122

6.4 Insecticide applications for 2015 Stoneville (delta) Location...... 123

6.5 Insecticide prices used to calculate net economic returns in Mississippi for each year...... 124

6.6 2014 Starkville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South...... 125

6.7 2015 Starkville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South...... 125

6.8 2014 Stoneville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South...... 126

6.9 2015 Stoneville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South...... 127

CHAPTER I

INTRODUCTION

Neonicotinoids

Origin of Neonicotinoids

Neonicotinoids were first developed in the 1980s and became commercially available in 1991. Neonicotinoids can be classified into one of three chemical groups, the

N-nitroguanidines (imidacloprid, thiamethoxam, clothianidan, and dinotefuran), nitromethylenes (nitenpyram) and N-cyanoamidines (acetamiprid and thiacloprid)

(Jeschke et al. 2011). The first available neonicotinoid compound, imidacloprid, was commercially sold by (Bayer Cropscience, Research Triangle Park, NC). Neonicotinoids

have been the fastest growing class of insecticides within the past three decades since the

introduction of the pyrethroids (Nauen and Bretschneider 2002).

Neonicotinoid Mode of Action

Neonicotinoids are active across a broad spectrum of insects, especially piercing-

sucking insects. They act on the central nervous system by blocking the postsynaptic

nicotinic acetylcholine receptor (nAChRs) openings causing overstimulation of nerve

cells resulting in paralysis and death (Bai et al. 1991, Liu and Casida 1993, Chao et al.

1997, Wollweber and Tietjen 1999, Zhang et al. 2000, Nauen et al. 2001). The

neonicotinoid class of insecticides are popular because of their low mammalian toxicity

and relative safety for humans compared to other insecticide classes (Tomizawa and 1

Casida 2003). There is little or no cross resistance to other insecticide classes including pyrethroids, chlorinated hydrocarbons, organophosphates (OPs), or carbamates.

Neonicotinoid insecticides are labeled for use in numerous agronomic crops and have replaced other insecticide classes with broader spectrums of activity (Denholm et al.

2002). Insecticides are classified based on their mode of action (MOA) as defined by the

Insecticide Resistance Action Committee (IRAC) for resistance management purposes in

an integrated pest management program (Nauen et al. 2001). Neonicotinoids, as a class,

are extremely water soluble. As a result, they are readily absorbed by plants and

transported through the xylem. Circulation of these compounds through the xylem

provides protection against multiple sap-feeding insects and other common early season soil insects (Magalhaes et al. 2009). They are most commonly used in agricultural crops

as seed treatments, in-furrow sprays/soil drenches, and foliar applications. When utilized

as a seed treatment or in-furrow spray, the compound is absorbed through the roots and

moved throughout the plant. This systemic activity generally provides 14 to 21 days

control of many of the early season pests in major agronomic crops, however, their presence can exceed 1,000 days in soil in some instances (Bonmatin et al. 2015).

Use of Neonicotinoids Worldwide

Neonicotinoids are the most widely used class of insecticides globally. They make up one quarter of all insecticides used. Neonicotinoids are registered in over 120 countries and have a total market value of $2-6 billion. Imidacloprid is the most widely used insecticide in the neonicotinoid class with 41% market share and is ranked second among all agricultural chemicals used around the world (Jeschke et al. 2011, Pollack

2011). 2

Use of Neonicotinoids in the United States

Neonicotinoids are used throughout the United States on numerous agronomic crops. Approximately 60% of neonicotinoid insecticide use is targeting early season insect pests and applied as seed treatments. However they are also commonly used as in-

furrow sprays or broadcast foliar sprays throughout the Mid-South region of the United

States. The Mid-South region of the United States includes Arkansas, Louisiana,

Mississippi, western Tennessee, and extreme southeast Missouri (Bootheel) (Stewart et

al. 2014). Neonicotinoid insecticides are commonly utilized throughout this region on

corn, Zea mays L.; cotton, Gossypium hirsutum L.; rice, Oryza sativa L.; soybean,

Glycine max L.; grain sorghum, Sorghum bicolor L.; wheat, Triticum aestivum L.; and

peanut, Arachis hypogaea L. The Mid-South region of the United States is a temperate

climate with annual rainfall from 127 to 165 cm annually (MSU 2016). This

environment tends to lead to higher insect pest pressure than other regions in the U.S.

Although use of neonicotinoid insecticides as seed treatments do provide control of many

early season insect pest, some believe that neonicotinoid insecticides automatically

applied as seed treatments is not consistent with an integrated pest management philosophy (Metcalf and Luckmann 1994). Some studies suggest that neonicotinoid use is linked to environmental contamination and decline of pollinators leading to widespread

public scrutiny, as well as the ban of neonicotinoids in certain countries (Krupke et al.

2012, Yang et al. 2008, Hopwood et al. 2012, Hardstone and Scott 2010, EPA 2014).

Risks of Neonicotinoid Insecticides

There are several risks to the widespread adoption of the neonicotinoid class of

insecticides including; long half-life in the soil, potential leaching into groundwater, and 3

potential contribution to the decline in pollinator populations. Sur and Stork (2003)

observed that when applied to the soil/seed, the crop only absorbs about 20% of the

neonicotinoid active ingredient. This results in approximately 80% of the active not

being available to the plant in contrast with foliar sprays to the target crop which

generally exceeds 50% absorption in some studies (Graham-Bryce 1977).

Neonicotinoids can readily leach through the soil profile or be lost in run-off depending on rainfall and slope of the field (Scorza et al. 2004, Anhalt et al. 2008, Selim et al. 2010,

Thuyet et al. 2012). However, the majority of the neonicotinoid active ingredients eventually bind to soil particles, thereby reducing the potential of leaching through the

soil profile. Factors that can increase sorption include percent organic matter, clay

content, and desorption from the soil which is dependent on temperature (Cox et al. 1997,

1998a, b, c; Broznic and Milin 2012, Broznic et al. 2012).

Of the 80 to 90% of the active ingredient applied to seed which is not taken up by

the plant; a small amount (<2%) is lost in dust particles at planting (Tapparo et al. 2012).

Farmers commonly apply talc or graphite as a seed lubricant to pneumatic planters.

These compounds are applied directly to the seed in the hoppers to facilitate flow through the seed tubes into the soil. When seeds are treated with neonicotinoids, the seed coatings may flake off and be discharged from the planter with the lubricant. These

neonicotinoid coated particles may drift to nearby flowers where bees or other insects could be foraging. This is a common practice when planting agronomic row crops throughout North America (Krupke et al. 2012). This route of contact is a potential link

to declining populations of honeybee, Apis mellifera L., because of direct exposure to the

compounds (Marzaro et al. 2011, Tapparo et al. 2012).

Advantages of Neonicotinoid Insecticides

Although neonicotinoids have garnered much public attention due to their negative properties, there are many benefits to agricultural and horticultural producers as well as homeowners. Neonicotinoid insecticides provide effective control of a number of insect pests that infest major agronomic crops. Insecticide seed treatments provide control of early season pests that infest soybean (Baur et al. 2000) and are widely used throughout the Mid-South in all row crops. Neonicotinoids are active against both above-

ground and below-ground insects when applied as seed treatments because they are

absorbed into plant tissues (Maienfisch et al. 2001). Longevity in the soil plays a crucial

role in the efficacy of these insecticides on early season pests of row crops.

In cotton, Neonicotinoids provide effective control of tarnished plant bug, Lygus

lineolaris (Palisot de Beauvois). Tarnished plant bug is an economically important pest

of cotton and prefers to feed on small to medium sized flower buds (squares) of cotton

(Tugwell et al. 1976). Lygus feeding causes square abscission and can result in yield

losses (Layton 2000). Feeding on older flower buds damages anthers resulting in

abnormal flowers. Severely damaged flower buds will not pollinate resulting in abnormal bolls that eventually abscise (Pack and Tugwell 1976). Transgenic Bacillus thurengiensis (Bt) cotton and successful boll weevil, Anthonomus grandis grandis

(Boheman); eradication has led to reduced pesticide applications in cotton. However, the widespread applications of malathion for boll weevil eradications appears to have led to development of increased insecticide resistance in the tarnished plant bug in the Mid-

South (Snodgrass et al. 2009). High levels of resistance are currently observed to pyrethroids in Arkansas, Louisiana, and Mississippi in tarnished plant bugs. Resistance

to pyrethroids was first documented in 1995 (Snodgrass 1996) and spread across the Mid-

South by 1999 (Snodgrass and Scott 1999, Snodgrass and Scott 2000). Resistance to the

neonicotinoids has not been documented with tarnished plant bug and these insecticides

continue to provide economic benefits where they are utilized.

Soybean

Growth Stages and Maturity Groups of Soybean

Soybean is sensitive to photoperiod and flowering triggers as day length declines.

There are eleven maturity groups of soybean that range from 00, 0, and I through IX

(Pedersen 2004). Maturity groups are defined by the amount of daylight required to initiate flowering. Soybean can be defined as determinate growth habits, in which

vegetative growth stops at beginning of flowering or indeterminate growth habit where

vegetative growth progresses after beginning of flowering (Kogan and Turnipseed 1980).

The most common soybean maturity groups produced in the Mid-South include Groups

IV and V (Heatherly 1999). Currently, 70% of soybean hectares planted in Mississippi

are earlier maturing indeterminate varieties (Irby 2015, personal communication).

Soybean and U.S. Soybean Production

Currently, the U.S. is the second largest exporter of soybean in the world.

Soybean was first introduced to the United States in the mid-1770s from China as a

ballast in returning clipper ships and has since become a major commodity to the

agriculture industry in the United States (Smith 1994). Soybean production on a large

scale did not begin until the 20th century in the U.S. Higher yielding varieties and

favorable market prices have led to increased soybean production in recent years (USDA

- NASS 2015). In 2004, the U.S. harvested 30 million ha-1 of soybean that accounted for

a total producer value of $17.9 billion (NASS-USDA 2004). In 2014, the U.S. harvested

an all-time high of 33 million ha-1 (NASS-USDA 2014). Currently, the U.S. is the

leading soybean producer in the world followed by Brazil and Argentina (Wilcox 2004).

Soybean production in the Mid-South Region

The agricultural landscape across the Mid-South region has changed significantly in the past decade. In Mississippi for example, there were a total of 486,000 ha of cotton

grown in 2006 compared to 162,000 ha of cotton in 2014 (USDA-NASS 2014). The

decline of cotton acreage has resulted in the increased production of soybean throughout

the region. Also, many producers have switched from determinate maturity group (MG)

VI and VII cultivars to indeterminate maturity group IV and V cultivars. Historically,

determinant soybean varieties were planted later in the growing season usually late-May

to mid-July. At those later planting dates, soybeans often experienced drought conditions

and high temperatures during the pod and seed development stages, reducing yield

potential. The earlier planted soybean systems have been utilized to avoid drought

conditions and extensive heat, thereby increasing yield potential (Kane and Grabau 1992,

Bowers 1995, Heatherly 1999, Sweeney et al. 1995). Many growers have adopted the

early soybean production system (ESPS) where early maturing, indeterminate soybean

varieties are planted from March through early May (Heatherly 1999). Early soybean

planting minimizes the occurrence and impact of late season insect pests and allows more

time for harvest (Baur et al. 2000). The early soybean production system has been

important for maximizing yield potential in Arkansas, Louisiana, Mississippi, and

Tennessee. 7

Early Season Insect Management in Soybean with Neonicotinoids

Soybean production in the United States has changed dramatically over the last decade. Higher yielding varieties and higher grain market prices have resulted in many

farmers planting less cotton and more grains in the Mid-South region with the major

agronomic row crop consisting of soybean. Adoption of the ESPS has resulted in greater

yields and increased profits for growers in the Mid-South (Heatherly 1999). This has

also shifted some of the focus from late season insect pests to early season pests. Insect

pests of economic importance during the early season include bean leaf beetle, Cerotoma

trifurcata (Forster); white grubs, Phyllophaga and Cyclocephala species; wireworms,

Melanotus spp., Limonius spp., and Agiotes mancus (Say); lesser cornstalk borer,

Elasmopalpus lignosellus (Zeller); three cornered alfalfa hopper, Spissistilus festinus

(Say); and multiple species of thrips (Davis et al. 2009, 2010). Thrips species on soybean

include: Frankliniella fusca (Hinds), F. occidentalis (Pergande), F. tritici (Fitch), and

Neohydatothrips (Serico-thrips) variabilis (Beach), (Irwin et al. 1979; Chamberlin et al.

1992; Davis et al. 2009, 2010).

The impact of early season insect pests tends to be magnified at early planting

dates because of slower seedling growth rates (Baur et al. 2000). Early season insect

pests can have a significant effect on plant densities and health ultimately impacting yield

potential. Neonicotinoid insecticide seed treatments provide good control of the early

season insect pest complex that soybean plantings commonly encounter throughout the

Mid-South annually. Neonicotinoid seed treatments are currently used on the majority of soybeans in the Mid-South region. The systemic nature of these compounds when

applied as a seed treatment plays a major role in their efficacy against early season

soybean pests by protecting against above ground pests as well as below ground

(Maienfisch et al. 2001).

Mid-Late Season Insect Management in Soybean with Neonicotinoids

Although neonicotinoid insecticide seed treatments are used extensively in Mid-

South soybean production systems, benefits of foliar applications have also been

documented. Their efficacy against a wide spectrum of piercing and sucking insects establishes them as a vital alternative in the Mid-South region of the U.S., especially when resistance to other insecticide classes is documented (Nauen and Elbert 2003).

However, because of their widespread usage and adoption globally, overuse has raised

serious concerns around resistance developing with this class of chemistry as well.

Corn

Corn and U.S. Corn Production

Corn is thought to have originated from a wild annual grass known as teosinte

Zea, from Mexico and Central America (Galinat 1988). Years of breeding has resulted in

the current hybrids that now make up the number one crop grown around the world and

in North America (Mangelsdorf 1986). In 2004, the U.S. harvested 29.8 million ha of

corn that accounted for a total producer value of $24.3 billion. In 2013, the U.S.

harvested 34.4 million ha making it the number one crop grown in the U.S. In 2013, corn

production jumped to a $62.7 billion total producer value with a total of 865.2 billion kg

harvested (USDA-NASS 2014). Increased corn production is correlated with increased

commodity prices of grain in recent years.

Corn Production in the Mid-South Region

Since the decline of the area planted to cotton over the past 10 years in the Mid-

South region of the U.S., the area planted to corn has increased along with soybean.

Other crops commonly grown in the region include cotton, rice, grain sorghum, wheat,

and peanuts. Corn is typically the first crop planted throughout the region because of its ability to germinate and grow at cooler temperatures relative to other crops. There are

multiple advantages to early planting. They include minimal harvesting conflict with

other row crops during the growing season, less water management, reduced

susceptibility from insects, viruses, and timely harvest (Espinoza 2008).

Growth Stages and Development of Corn

Corn is an annual grass that responds to timely rainfall and optimal growing

conditions. It develops from a single seed made up of the pericarp, endosperm, and

embryo. Once the seed is planted it takes anywhere from 5-21 days for emergence

depending on depth of seed, moisture, and temperature of soil (Espinoza 2008).

Early Season Insect Management in Corn with Neonicotinoids

Higher yielding hybrids and favorable market prices have led to increased corn

production in the U.S. (USDA – NASS 2015). Optimum planting dates for corn vary

between regions of the United States due to different temperatures and length of optimal

growing conditions for increased yield potential (Bruns 2003). Seeds and seedlings are

more vulnerable to a number of early season pests at earlier planting dates compared to

later planting dates (Higgins 1994). These insects can reduce plant densities and early

season growth, thereby reducing overall yield potential (Higgins 1994).

Several at-planting insecticides are currently labeled for corn production. Early season insect management techniques have progressively changed within the past 20

years. For instance, applications of broad spectrum insecticides applied over the top or

in-furrow have been replaced with the use of insecticide treated corn seed (Elbert et al.

2008). Nearly all corn seed currently planted is treated with a neonicotinoid insecticide

treatment (Haire 2014). Imidacloprid (Gaucho 600, Bayer Cropscience, Research

Triangle Park, NC), thiamethoxam (Cruiser 5FS, Syngenta Crop Protection, Greensboro,

NC), and clothianidan (Poncho 600, Bayer Cropscience, Research Triangle Park, NC)

are the most common neonicotinoid seed treatments applied to corn seed. Over 18

million hectares of corn was treated with a neonicotinoid insecticide seed treatment

between 2009 and 2011 (Brassard 2012). Neonicotinoid seed treatments are systemic in

nature and provide protection against most of the soil insect complex as well as many

above ground pests that attack corn shortly after emergence (Hopwood et al. 2012).

Longevity in the soil also contributes to the efficacy of these insecticides on early season

corn pests (Maienfisch et al. 2001).

Early season insect pests observed in Mid-South corn production include seedcorn

maggot, Delia platura (Meigen); white grubs, Phyllophaga spp; Japanese beetle, Popillia

japonica (Newman); southern corn rootworm, Diabrotica undecimpunctata howardi

(Barber); wireworms, Melanotus spp. and other spp. also; lesser cornstalk borer,

Elasmopalpus lignosellus (Zeller); corn root aphid, Aphis middletoni (Thomas);

greenbug, Schizaphis graminum (Rondani); corn leaf aphid, Rhopalosiphum maidis (F.);

bird cherry-oat aphid, Rhopalosiphum padi (L.); billbugs, Sphenophorus spp; chinch bug,

Blissus leucopterus leucopterus (Say); black cutworm, Agrotis ipsilon (Hufnagel); and 11

sugarcane beetle, Euetheola humilis rugiceps (LeConte) (Steffey et al. 1999, Akin et al.

2012). Wireworm and corn rootworm are common pests of corn seed and seedlings,

feeding directly on the seed or on the primary and secondary roots. Root tissue loss may

cause instability in the corn plant and can cause the plant to lodge making harvest

difficult. Damaged corn roots result in reduced water and nutrient uptake, reduced root and plant growth, and yield losses. The impact of early season insect pests in corn can be

more severe when soil conditions are dry due to compound stresses (Jeschke et al. 2011).

Cotton

Cotton and U.S. Cotton Production

There are five cultivated species of Gossypium including G. hirsutum L., G.

barbadense L., G. arboreum L., G. herbaceum L. and G. ianceolatum Todaro.

Gossypium hirsutum and G. barbadense are the only species cultivated in the United

States (Stalker 1980).

In 2000, 5.3 million ha of cotton were harvested in the U.S. for a total producer value of $4.2 billion. In 2013, 3 million ha were harvested at a value of $5.2 billion

(USDA-NASS 2014). Even though the producer value was higher in 2013 due to higher market prices and yield, the total area harvested in the U.S. was 43% less than it wa s in

2000. The Mid-South region is ideal for cotton production due to the temperate climate

and 139.7 to 152.4 cm of annual rainfall. The recent decline in area planted to cotton

over the last decade is directly related to the increased costs of production and increased

grain prices.

Cotton Production in the Mid-South

Because of the temperate environment in the Mid-South region, growers have the flexibility to grow a wide variety of crops. This allows them to capitalize on market prices and take advantage of rotational benefits of alternate crops. Cotton production has been drastically reduced in the region since 2006 for many reasons, but cotton prices relative to input costs have primarily driven the decline. Cotton producers in the Delta region also experience tremendous insect pest pressure often making 8 to 12 insecticide applications for control of tarnished plant bug alone (Gore, personal communication). In more recent years, herbicide resistance in key weed species has also increased cotton production costs.

Growth Stages of Cotton

Cotton is a perennial, dicotyledonous plant with an indeterminate growth habit

(Silvertooth et al. 1999). During the early growth stages of cotton, above ground plant

development is slow. Cotton development can be accurately predicted based on degree

day models (Jenkins 1990). These models are based on accumulation of heat units

(DD60s) which is the calculation of daily high and low temperatures divided by two

minus 60 (Kerby et al. 1987) (Table 1.1). The minimum temperature for physiological

development is 15.5˚ Celsius or 60˚ Fahrenheit. In cotton, planting to harvest requires

approximately 2600 heat units to reach physiological maturity

Table 1.1 Cotton Development Stages

Growth Stage Days Heat Units-DD60s Planting to Emergence 4 to 9 50 to 60 Emergence to First Square 27 to 38 425 to 475 Square to Flower 20 to 25 300 to 350 Planting to First Flower 60 to 70 775 to 850 Flower to Open Boll 45 to 65 850 to 950 Planting to Harvest Ready 130 to 160 2200 to 2600 Source: National Cotton Council of America 2015

There are five main growth stages of cotton including seedling germination and

emergence, seedling establishment, leaf area and canopy development, flowering and boll

development, and physiological maturation as described by Jenkins (1990). At flower

initiation (first flower on 50% of plants) growth is measured by node counts above the

upper-most first position white flower (Bourland et al. 1992). Germination and root

emergence occurs approximately on the third day after planting. Germination occurs

when water is imbibed through the chalazal aperture. Six days after planting, cotton

seedling emergence is initiated as the hypocotyl arch raises above ground. Cotyledons

unfold around the seventh day after planting depending on weather conditions. Ten days

after planting the taproot will reach anywhere from six to twelve inches in length.

Approximately fourteen days after planting, the first true leaf will begin to unfold and

photosynthesis will begin. Reproductive growth stages are initiated approximately thirty-

five days after planting and the first flower bud (square) will appear. The first occurrence

of a white flower occurs around 65 days after planting. Peak flower generally occurs

around 93 days after planting. Fiber and boll development is maximized during full

bloom. Around 110 days after planting, the first boll will begin to crack (Jenkins et al.

1990).

Early Season Insect Management in Cotton with Neonicotinoids

Cotton is an intensely managed crop for insect pests throughout the year. Thrips are the primary pest of seedling cotton and are typically the first insects to feed on cotton after plants emerge. Also, while other pests of cotton are regional in occurrence and distribution, thrips are found extensively across the Cotton Belt and can require treatment across the entire region (Stewart et al. 2013). The primary thrips species that infest cotton seedlings in the U.S. include tobacco thrips, Frankliniella fusca (Hinds); flower

thrips, Frankliniella tritici (Fitch); western flower thrips, Frankliniella occidentalis

(Pergande); onion thrips, Thrips tabaci (Lindeman); and soybean thrips, Neohydatothrips

variabilis (Beach), (Leigh et al. 1996, Albeldano et al. 2008). However, tobacco thrips

are the primary thrips species observed on seedling cotton throughout the Mid-South

(Reed and Jackson 2002, Cook et al. 2003, Stewart et al. 2013). Injury, due to feeding,

causes yellowing, stunting, a reduction in plant vigor, and occasionally plant mortality

(Davidson et al. 1979). Injury from thrips feeding results in delayed plant maturity and

decreased yields (Gaines 1934, Dunham and Clark 1937, Bourland et al. 1992, Parker et

al. 1992, Herbert 1998, Leonard et al. 1999, Van Tol and Lentz 1999, Lentz and Van Tol

2000). In instances with heavy infestations, crop maturity to harvest can be delayed for

more than two weeks (Gaines 1934, Dunham and Clark 1937, Bourland et al. 1992,

Parker et al. 1992, Watts 1937). Delayed crop maturity can prolong the time when the crop is susceptible to other insects throughout the growing season and lead to increased production costs (Stewart et al. 2013). Also, by prolonging the required growing season, adverse weather conditions can be experienced before defoliation and harvest (Morris

1963, Gipson and Joham 1968). Previous research has shown an increase in yields when

thrips were controlled in seedling cotton (Davis et al. 1966, Davis and Cowan 1972,

Burris et al. 1989, Herbert 1998, Van Tol and Lentz 1999, Lentz and Van Tol 2000, Cook

et al. 2011). In 2001, 93% of the cotton grown in the United States was infested with

thrips, leading to an estimated loss of 235,996 bales (Williams 2002). Each year, around

three million hectares of cotton is treated for thrips at an estimated costs of $81 million

(Williams 2001). Therefore, many producers utilize insecticide seed treatments to help

manage early season insect pests and decrease risk of stand loss and delayed crop

maturity.

Early season insect pests observed in Mid-South cotton production includes

tobacco thrips, Frankliniella fusca (Hinds); cotton aphid, Aphis gossypii (Glover); cutworm, Agrotis ipsilon (Hufnagel); and three cornered alfalfa hopper, Spissistilus

festinus (Say). Cotton seedlings are extremely susceptible to early season insect pests,

especially thrips, from emergence to approximately the fourth true leaf stage. This time

interval is generally two to three weeks depending on weather conditions and plant

growth. Thrips control is commonly achieved with use of preventative at-planting

neonicotinoid insecticide seed treatments (Cook et al. 2011). Neonicotinoids are active

against both above-ground and below-ground insects because of their systemic ability to

be absorbed into plant tissue. Longevity in the soil also contributes to the efficacy of

these insecticides on early season pests of seedling cotton (Maienfisch et al. 2001).

Mid-Late Season Insect Management in Cotton with Neonicotinoids

The primary mid-late season pests of cotton in the Mid-South include tarnished

plant bug, Lygus lineolaris (Palisot de Beauvois); bollworm, Heliocoverpa zea (Boddie);

and tobacco budworm, Heliothis verescens (Fabricius); cotton aphid; and twospotted 16

spider mite, Tetranychus urticae Koch. Tarnished plant bug and other Lygus species feed

on a wide range of plants, including cotton. They feed on the plant during the

reproductive stages throughout the entire growing season (Snodgrass et al. 1984, Young

1986). Neonicotinoids are an important class of insecticides for tarnished plant bug

management in the Mid-South region of the United States. Tarnished plant bug is an

economically important pest of cotton and feeds on small to medium sized squares

(Tugwell et al. 1976). Lygus feeding causes square abscission and results in a direct yield

loss (Layton 2000). Feeding on older squares causes damage to the developing anthers

located in the flower bud. This results in abnormal flowers and may impact pollination

(Pack and Tugwell 1976).

Transgenic Bt cotton and boll weevil, Anthonomus grandis grandis (Boheman),

eradication has led to fewer insecticide applications in cotton. However, widespread use

of ULV malathion for boll weevil eradication is believed to have selected for resistance

to organophosphates in the tarnished plant bug (Snodgrass and Scott 2003). Widespread

resistance has resulted in an increased pest status for tarnished plant bugs in the Mid-

South region of the United States (Snodgrass et al. 2009). High levels of resistance are currently observed to pyrethroids in Arkansas, Louisiana, and Mississippi in tarnished

plant bugs. Resistance to pyrethroids was first documented in 1995 (Snodgrass 1996)

and spread across the Mid-South by 1999 (Snodgrass and Scott 1999, Snodgrass and

Scott 2000). Also, resistance to the organophosphate class of insecticides including

acephate, was first reported in 2001 (Snodgrass and Scott 2002) and spread across the

Mid-South by 2008 (Snodgrass et al. 2009).

Resistance to acephate also leads to resistance to other organophosphate/carbamate insecticides that are currently utilized in cotton to manage tarnished plant bug (Snodgrass et al. 2009). Widespread resistance to most classes of insecticides makes management of tarnished plant bug with currently labeled insecticides difficult (Gore et al. 2012). Resistance to organophosphates and pyrethroids has resulted

in the neonicotinoid insecticide class becoming a valuable alternative control option for

tarnished plant bug during pre-flowering and flowering stages of cotton development.

The two most common neonicotinoid insecticides utilized for tarnished plant bug control

in cotton are imidacloprid (Admire Pro, Bayer CropScience, Research Triangle Park, NC)

and thiamethoxam (Centric, Syngenta Crop Protection, Greensboro, NC) (Gore et al.

2012).

There are multiple foliar control options for tarnished plant bug in the Mid-South.

Rotating modes of action or tank mixing multiple modes of action is a commonly

recommended practice. Tarnished plant bug resistance to insecticides has evolved from

the mid-1990s and has become a major concern for cotton pest managers, especially in

the mid-southern region of the United States due to increased spray applications.

Responses to insecticide resistance are typically to increase dosages, number of

applications, and rotation of chemical classes (National Research Council 1986). Higher

rates of acephate and dicrotophos are being applied to control tarnished plant bug in the

Mississippi Delta due to resistance and as a result have become less consistent in

controlling Lygus throughout the Mid-South (Gore et al. 2007). In contrast there has

been tolerance found in tarnished plant bugs but no documented resistance to

neonicotinoids in cotton. Currently, Mississippi recommends a fully integrated IPM

approach to tarnished plant bug management which includes, early planting, hairy leaf varieties, blocking cotton away from corn, insecticide rotation and tank mixing insecticides, reduced nitrogen, and intensive scouting (Gore et al. 2013).

Grain Sorghum

Grain Sorghum and U.S. Grain Sorghum Production

Grain sorghum is primarily produced on the hot, dry plains located from Texas to

South Dakota because it is drought tolerant and well suited for moderately arid

environments and non-irrigated fields (Carter et al. 1989). In 2004, there were 2.6

million ha of sorghum harvested with a total producer value of $843.3 million. The area planted to grain sorghum has not changed over the last 10 years (USDA-NASS 2015).

Kansas and Texas are currently the leading producers of grain sorghum in the United

States (USDA-NASS 2014).

Grain Sorghum Production in the Mid-South

Arkansas and Louisiana are the leading grain sorghum producing states in the

Mid-South followed by Mississippi. In 2013, 118.1 ha of grain sorghum were harvested from Arkansas, Louisiana, and Mississippi which had a total producer value of $151.1 million. In 2014, the area harvested was 148.1 ha. In recent years, grain sorghum has found a fit in the Mid-South and some producers have increased its production. Grain sorghum fits well on non-irrigated marginal ground and is a good rotation crop where nematodes or resistant weeds occur (USDA-NASS 2014).

Growth Stages of Grain Sorghum

Emergence of sorghum seedlings occurs between five to ten days after planting depending on soil temperature and soil moisture (Table 1.2). After emergence, the plant

develops through numerous stages of vegetative growth until reaching the flag leaf stage.

The flag leaf stage is described as the last leaf to emerge from the whorl and it is located

directly below the panicle. Emergence of flag leaf initiates the boot stage of the sorghum

plant. At boot stage the plant has attained maximum leaf area and has accumulated 60%

of its total dry matter. The panicle emerges from the whorl and is followed by the

beginning of flowering and seed set. Sorghum is considered heading when 50% of the plants across the field have fully emerged panicles. Flowering occurs from the top of the

panicle to the bottom of panicle over a period of several days. Thirty to 45 days after

flowering are generally required to reach physiological maturity (black layer). Black

layer refers to a black colored region located on the sorghum kernel where attached in the floret near the base of the kernel (Gerik et al. 2003).

Table 1.2 Grain Sorghum Growth Stages

Growth Approximate Days Identifying Characteristics Stage After Emergence 0 0 Emergence. Coleoptile visible at soil surface 1 10 Collar of 3rd leaf visible 2 20 Collar of 5th leaf visible 3 30 Growing point differentiation. Approximately 8 leaf stage by previous criteria 4 40 Final leaf visible in whorl 5 50 Boot. Head extended into flag leaf sheath 6 60 Half-bloom. Half of the plants at some stage of bloom 7 70 Soft dough 8 85 Hard dough 9 95 Physiological maturity. Maximum dry matter accumulation Source: Vanderlip, R. L. and H. E. Reeves 1972.

Early Season Insect Management in Grain Sorghum with Neonicotinoids

Early season insect pests observed in grain sorghum production include

wireworms, Melanotus spp., Limonius spp., and Agiotes mancus (Say); white grubs,

Phyllophaga spp. and Cyclocephala spp.; black cutworm, Agrotis ipsilon (Hufnagel);

chinch bug, Blissus leucopterus (Say); and multiple aphid species. Aphids that feed on

grain sorghum include: greenbug, Schizaphis graminum (Rondani); corn leaf aphid,

Rhopalosiphum maidis (Fitch); and sugarcane aphid, Melanaphis sacchari (Zehntner).

Within the Mid-South region of the United States, the primary aphid pest since 2014, has been the sugarcane aphid (Catchot 2016, personal communication).

Sugarcane aphid can colonize sorghum seedlings 2-3 weeks after emergence

resulting in economic damage and populations increase throughout the entire growing

season (van Rensburg 1973a). Sugarcane aphid colonization can occur rapidly reaching

as many as 30,000 aphids on a single sorghum plant (Setokuchi 1977). However, 2-3

weeks after peak sugarcane aphid populations occur, aphid densities rapidly decline due to winged dispersal from high aphid densities and poor health of the sorghum plant (van

Rensburg 1973b). Significant population increases occur from the boot to soft dough stage which is 40 to 70 days after planting and from heading to harvest which occurs 60 to 100 days after planting (Fang 1990). Temperature and relative humidity also have

significant effects on sugarcane aphid densities (Mote 1983, Waghmare et al. 1995). It

has also been noted that aphid populations can increase more rapidly under irrigation

compared to non-irrigated fields (Balikai 2001).

Sugarcane aphid damage in sorghum depends on population densities and

infestation duration. Sugarcane aphids feed on the abaxial surface of older sorghum leaves. Plant responses from sugarcane aphid feeding include purple leaf discoloration, chlorosis, necrosis, stunting, delayed flowering, and poor grain fill (Narayana 1975).

Injury from sugarcane aphid feeding reduces plant biomass, grain yield, and grain quality

(Van den Berg et al. 2003, Singh et al. 2004). Indirect injury due to sugarcane aphid feeding results from excessive honeydew excreted on the lower leaves below where the aphids are located. This results in sooty molds which accumulate on the honeydew excreted by sugarcane aphids (Narayana 1975, Villanueva et al. 2014). Accumulation of honeydew and sooty mold reduces plant photosynthesis and clogs harvest machinery

making harvest of grain difficult (Villanueva et al. 2014).

Mid-Late Season Insect Management in Grain Sorghum

Mid to late season insect pests of grain sorghum include sorghum midge,

Contarinia sorghicola (Coquillet) and the sorghum headworm complex including fall

armyworm, Spodoptera frugiperda (J. E. Smith); corn earworm, Helicoverpa zea

(Boddie); sorghum webworm, Nola sorghiella (Riley). Sorghum midge is the most damaging pest of sorghum worldwide (Young and Teetes 1977). Female sorghum midge

oviposit in individual spikelets of flowering sorghum. Each larva will develop in an

individual seed resulting in failure of kernel development (Tao et al. 2003). The sorghum

headworm complex comprises the majority of late season pests of heading sorghum

during post anthesis. Yield losses are estimated over $80 million dollars due to sorghum

headworms in the U.S. (Teetes 1982). Corn earworm and fall armyworm are generally

the most damaging species in the sorghum headworm complex in grain sorghum (Wilde

2007).

Justification for Further Research

The objective of this research project is to determine the value of neonicotinoid

insecticides in major agronomic crops in the Mid-South region. All available

unpublished data was solicited from Louisiana, Arkansas, Mississippi, and Tennessee for

soybean, corn, and cotton and analyzed to determine economic benefits within the region.

Because little data existed for grain sorghum, we conducted numerous trials during 2014

and 2015 in Mississippi to generate data on the value of neonicotinoid seed treatments to

include in the analysis. There are a number of insecticide classes used in the current

integrated pest management programs throughout the Mid-South region in cotton. This

research also attempts to assign a value to whole classes of chemistry by excluding

classes in an overall management program in cotton to provide input to the

Environmental Protection Agency (EPA) for consideration during the insecticide

chemistry review process. 23

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CHAPTER II

VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-

SOUTH SOYBEAN (GLYCINE MAX L.) PRODUCTION SYSTEMS

Abstract

Early season insect management is complex in the Mid-South region of the U.S.

A complex of multiple pest species generally occurs simultaneously at sub-threshold levels in most fields. Neonicotinoids are the only insecticide seed treatment widely used in soybean, Glycine max L., production. An analysis was performed on 170 trials conducted in Arkansas, Louisiana, Mississippi, and Tennessee from 2005 through 2014 to determine the impact of neonicotinoid seed treatments in soybean. The analysis compared soybean seed treated with a neonicotinoid insecticide and a fungicide to soybean seed only treated with the same fungicide. When analyzed by state, soybean yields were significantly greater in all states when neonicotinoid seed treatments were used compared to fungicide only treatments. Soybean treated with neonicotinoid treatments yielded 112.0 kg ha-1, 203.0 kg ha-1, 165.0 kg ha-1, and 70.0 kg ha-1, higher than fungicide only treatments for Arkansas, Louisiana, Mississippi, and Tennessee, respectively. Across all states, neonicotinoid seed treatments yielded 132.0 kg ha-1 with fungicide only treated seed. Net returns from neonicotinoid seed treatment usage were

$1,203 per ha-1 compared to $1,172 per ha-1 for fungicide only treated seed across the

Mid-South. However, economic returns for neonicotinoid seed treatments were

significantly greater than fungicide only treated seed in four out of ten years. When analyzed by state economic returns for neonicotinoid seed treatments were significantly greater than fungicide only treated seed in Louisiana and Mississippi. These data show that in some areas and years, neonicotinoid seed treatments provide significant economic benefits in Mid-South soybean.

Introduction

Soybean production in the Mid-southern United States has changed considerably in recent years. The Mid-southern region includes Arkansas, Louisiana, Mississippi, western Tennessee, and extreme southeast Missouri. Higher yielding varieties and favorable market prices have led to increased soybean hectares (USDA - NASS 2015).

Many growers have adopted the early soybean production system (ESPS) where early maturing, indeterminate soybean varieties are planted from March through early May

(Heatherly 1999). Historically, soybean producers planted soybean later, often experiencing drought conditions and high temperatures during the pod and seed development stages, reducing yield potential. The early production system was developed to avoid drought conditions and extensive heat, thereby increasing yield potential throughout the Mid-South (Kane and Grabau 1992, Bowers 1995, Heatherly

1999, Sweeney et al. 1995). In soybean, the price of seed in addition to the price of other inputs has increased in recent years. Technology fees associated with herbicide tolerance

(Rawlinson and Martin 1998) and increased weed management costs to combat herbicide resistant weeds (Bradley et al. 2000, Johnson et al. 2000) has led to a greater investment at the time of planting. Therefore, many producers have adopted insecticide seed treatments to help manage early season insect pests and decrease the risk of stand loss 36

and replanting. These assumptions were made by producers without sufficient evidence and a comprehensive analysis of the benefits of insecticide seed treatments needs to be conducted in the Mid-South.

These changes in soybean production practices and the subsequent increased yield

potential has led to increased management for insect, disease, and weed pests. Early

season insect pests observed in Mid-South soybean production include bean leaf beetle,

Cerotoma trifurcata (Forster); white grubs, Phyllophaga spp. and Cyclocephala spp.; wireworms, Melanotus spp., Limonius spp., and Agiotes mancus (Say); lesser cornstalk

borer, Elasmopalpus lignosellus (Zeller); three-cornered alfalfa hopper, Spissistilus

festinus (Say); grape colaspis, Colaspis brunnea (Fabricius); pea leaf weevil, Sitona lineatus L.; and multiple species of thrips (Davis et al. 2009, 2010). Thrips species that feed on soybean include: Frankliniella fusca (Hinds), F. occidentalis (Pergande), F.

tritici (Fitch), and Neohydatothrips (Serico-thrips) variabilis (Beach) (Irwin et al. 1979;

Chamberlin et al. 1992; Davis et al. 2009, 2010). Soybean insect infestations throughout

the seedling stage tend to be greater and more detrimental to yield potential in the early

season production system (Baur et al. 2000). These early season soybean pests can have

a significant effect on plant population densities and health which can effect yield.

Additionally, a complex of multiple species at sub-threshold levels commonly infests

soybean seedlings in the Mid-South making scouting and treatment decisions difficult.

Neonicotinoid insecticide seed treatments provide control of early season pests that infest

soybean (Baur et al. 2000) and are widely used throughout the Mid-South in all row

crops. Neonicotinoids are active against both above-ground and below-ground insects

because of their systemic ability to be absorbed into plant tissue (Maienfisch et al. 2001).

Longevity in the soil plays a major role in the efficacy of these insecticides on early

season soybean pests. While many experiments have been previously conducted on

neonicotinoid seed treatments in soybean, there is a shortage of published data on the

value of neonicotinoid insecticide seed treatments in soybean production systems in the

Mid-South. Therefore, an analysis of previous unpublished research with neonicotinoid

insecticide seed treatments across the Mid-South region was conducted to determine the

value of neonicotinoid insecticide seed treatments in soybean production systems.

Methods and Materials

Numerous efficacy trials were conducted at the University of Arkansas, Louisiana

State University, Mississippi State University, and the University of Tennessee from

2005 to 2014 to estimate the impact of neonicotinoid insecticide seed treatments on insect

pest populations and soybean yield.

These experiments included a neonicotinoid seed treatment with a base fungicide.

The neonicotinoids were imidacloprid (Gaucho 600, Bayer CropScience, Research

Triangle Park, NC), or thiamethoxam (Cruiser 5FS, Syngenta Crop Protection,

Greensboro, NC). Gaucho 600 is applied at 0.0747 to 0.2336 mg ai/seed (Anonymous

2015a). Cruiser 5FS is typically applied at 0.0756 to 0.1512 mg ai/seed (Anonymous

2015b). In all tests, a base fungicide treatment without an insecticide was included. The

base fungicide was the same for both the insecticide seed treatments and the fungicide

only treatment within a test. All available unpublished data from University research and

extension specialists within each state that met the above criteria were included in the

analysis. Tests were implemented as a randomized complete block design with

replications that varied across states from four to nine repeated blocks with one test 38

consisting of only one replication. Plot sizes ranged from 4 to 16 rows by 12.2 to 30.5

meters long and planted on 76.2 to 101.6 centimeter centers. Various measurements were

taken to evaluate insect control. These included but were not limited to actual insect

counts, damage ratings, stand counts, plant height, plant vigor, and etc. Evaluations of

insect control were not standardized across experiments and varied based on soybean

growth stage, location, and year. Timings and methods of evaluation were not

consistently recorded across tests and are not included in this analysis. Overall, the most

common insect group evaluated included thrips, but other insects observed included

various soil insects, threecornered alfalfa hopper, bean leaf beetle, grape colaspis, and pea

leaf weevil. In most experiments, insect populations consisted of a complex of multiple

species occurring simultaneously or in sequence throughout seedling growth.

Tests were harvested at physiological maturity and this was the only dependent

variable that was recorded in a consistent manner. Experiments were conducted at

multiple locations within each state across the Mid-South. Twenty-four tests were

conducted at three locations in Arkansas. They included the Lon Mann Cotton Research

Station (Marianna, AR), the University of Arkansas at Pine Bluff (Pine Bluff, AR) and

Phillips County, Arkansas (Helena, AR). Twenty-four tests were conducted in Louisiana

at the LSU AgCenter Macon Ridge Research Station (Winnsboro, LA). Seventy-three

tests were conducted in Mississippi at multiple locations including the R.R. Foil Plant

Science Research Center (Starkville, MS), the Delta Research and Extension Center

(Stoneville, MS), the Brown Loam Experiment Station (Raymond, MS), North

Mississippi Research and Extension Center (Verona, MS), as well as several producer

fields throughout the state. Forty-nine tests were conducted in Tennessee at the West

Tennessee Research and Education Center (Jackson, TN) and at the Milan Research and

Education Center (Milan, TN).

Yield and economic data were analyzed with a mixed model analysis of variance

(PROC MIXED SAS ver. 9.3; SAS Institute; Cary, NC). Year, location and replication

nested within year and location were considered random effects, and treatments were

considered fixed effects. Residual plots and normal distribution plots were generated to

verify that data met ANOVA assumptions. Means were separated using Fisher’s

Protected LSD procedure at the 0.05 level of significance. Economic data were

determined using yield for each treatment and the price of soybean seed (harvested grain)

in that particular year and state based on data from the National Agricultural Statistics

Service (Table 1) (NASS 2015). Insecticide seed treatment prices were obtained through

personal correspondence from Bayer CropScience. The costs of the insecticide seed

treatments were accounted for during economic analyses. To calculate gross economic

returns, the yield of each treatment was multiplied by the average price received (Table

1) for the state and year of that trial. The cost of the seed treatment was then subtracted

from the gross economic return to give the net economic return for each treatment.

Results and Discussion

A total of 170 experiments were conducted over the ten year period in Arkansas,

Louisiana, Mississippi, and Tennessee. There was a significant difference in mean soybean yield among treatments where there was a neonicotinoid seed treatment applied

(F = 25.71; df = 2, 169; P < 0.01). Thiamethoxam and imidacloprid resulted in significantly greater yields compared to fungicide seed treatment alone. There were no differences in yield between the thiamethoxam and imidacloprid treatments. Yields of 40

soybean treated with thiamethoxam or imidacloprid averaged 3,172 ± 1.1 kg ha-1 and

3,158 ± 1.1 kg ha-1, respectively. Because no differences were observed between

thiamethoxam and imidacloprid, a separate analysis was done where data for

thiamethoxam and imidacloprid seed treatments were pooled and comparisons were made

between soybean with a neonicotinoid seed treatment and soybean without an insecticide

seed treatment. Averaged across all trials, soybean yield following a neonicotinoid seed

treatment was significantly (F = 51.07; df = 1, 1269; P < 0.01) greater than yields of

soybean where a neonicotinoid seed treatment was not used (Table 2). The average

difference in yield was 135 kg ha-1 across all trials. There also was a significant

difference in mean returns in dollars per hectare between treatments (F = 17.86; df = 1,

1269; P < 0.01) (Table 2). Across years and locations, returns for soybean that received a neonicotinoid seed treatment were greater than where no insecticide seed treatment was

used. The neonicotinoid seed treatment resulted in a $33 per hectare return over soybean

where no insecticide seed treatment was used.

When analyzed by state for the years 2005 to 2014, there were significant

differences in mean soybean yield among treatments for each state (Arkansas: F = 5.42;

df = 1, 155; P = 0.02; Louisiana: F = 17.66; df = 1, 179; P < 0.01; Mississippi: F = 26.67;

df = 1, 554; P < 0.01, and Tennessee: F = 5.18; df = 1, 376; P = 0.02). Plots planted with

a neonicotinoid seed treatment produced significantly greater yields than plots planted with no insecticide seed treatment (Table 3). Soybean seed treated with a neonicotinoid seed treatment resulted in 112.0, 203.0, 165.0, and 70.0 kg ha-1 more yield than fungicide

only seed treatment in Arkansas, Louisiana, Mississippi, and Tennessee, respectively.

Significant differences in net economic returns were observed between soybean that

received a neonicotinoid seed treatment and soybean with no insecticide seed treatment in

Louisiana (F = 5.32; df = 1, 177; P = 0.02) and Mississippi (F = 13.37; df = 1, 558; P <

0.01) (Table 3). No differences in mean economic returns between treatments were

observed in Arkansas (F = 2.15; df = 1, 154; P = 0.14) or Tennessee (F = 0.21; df = 1,

375; P = 0.65).

When analyzed by year, there was a significant difference in yields between seed

treated with a neonicotinoid and those only treated with fungicide in six out of ten years

(Table 4). Soybean yield in 2005, 2006, 2007, 2008, 2011, and 2012, were significantly

greater where a neonicotinoid seed treatment was used compared to where no insecticide

seed treatment was used (Table 5). However, significant economic returns between the

treatments were only observed in four years out of ten (2006, 2007, 2008, 2012).

Numerous experiments have investigated the impact of neonicotinoid seed

treatments on soybean yield in the U.S. (Cox et al. 2008, Magalhaes et al. 2009, Cox and

Cherney 2011, Reisig et al. 2012, Seagraves and Lundgren 2012). In general, those

studies showed little to no benefit to using a neonicotinoid seed treatment in soybean.

For instance, Reisig et al. (2012) showed that neonicotinoid seed treatments reduced adult

thrips numbers three weeks after planting; however, there were no significant differences

in yield. Similarly, Cox et al. (2008) and Cox and Cherney (2011) found that insecticide

seed treatments did not increase soybean yield. These data indicate that an

insecticide/fungicide seed treatment is not required for soybean production in the

northeastern United States. However, other studies have shown that neonicotinoid seed

treatments prevented losses of soybean yields in the U.S. (McCornack and Ragsdale

2006, Johnson et al. 2008 and 2009, McCarville et al. 2014). In general, those studies

showed yield responses to neonicotinoid seed treatments compared to untreated soybean seed. Buehring et al. (2015) investigated the yield response of three different soybean maturity groups at three different planting dates to insecticide seed treatments and found that there was no interaction between seed treatments and planting date. Averaged across locations, planting dates, and maturity groups, soybean with an insecticide seed treatment resulted in yields that were significantly greater than the fungicide only treatment. Their results were similar to the current study with a reported 222 kg/ha-1 difference.

Out of the 170 neonicotinoid insecticide seed treatment trials conducted across the

Mid-South, 67% displayed a positive yield response when a neonicotinoid seed treatment was used from 2005-2014. The overall average soybean yield response to neonicotinoid seed treatments was 132.0 kg ha-1 and ranged from a loss of -742.6 kg ha-1 to an increase

of 2,527 kg ha-1. The 2,527 kg ha-1 advantage at one location was due to pea leaf weevil,

Sitona lineatus L., damage in the fungicide only plots. When net returns were calculated across the Mid-South region; 60% of the trials had a positive net return from using neonicotinoid seed treatments with an average increased return of $94.00 per hectare.

This analysis was conducted on previous research with neonicotinoid insecticide seed treatments throughout the Mid-South with the goal of determining the value of

neonicotinoid insecticides as a seed treatment in soybean. These 170 experiments were

analyzed from the production years of 2005 to 2014 and data indicates that neonicotinoid seed treatments may provide a yield and economic benefit in soybean production systems throughout the Mid-South region a majority of the time. However, significant differences

in net economic returns were only observed in Louisiana and Mississippi when analyzed

by state and in four out of ten years when analyzed by year. Neonicotinoid seed

treatments are currently used on more than 50% of soybean production in the Mid-South

region (Musser et al. 2013). This high adoption rate can be attributed to better stand

establishment, more vigorous seedling growth, yield advantages, and risk management

aversion. Many producers report more uniform emergence, less stand loss, and fewer

replants since adoption of insecticide seed treatments in the Mid-South region. Our

results demonstrate significant yield and economic increases in some situations resulting

from the use of neonicotinoid seed treatments in Mid-South soybean production. Because

these benefits are likely the result of management of a complex of multiple pest species

that usually occur at sub-threshold levels individually and because those complexes are

difficult to predict at the time of planting, at-planting insecticides (including seed

treatments) are broadly recommended for soybean integrated pest management in the

Mid-South. As such, producers may elect to use or not use seed treatments based on

commodity prices, tillage and cover crop practices, previous field history, or personal

preference.

Table 2.1 Values used to calculate net economic returns in each state for each year.

Arkansas Insecticide Seed Treatment Year $/Kg Kg/ha-1 Price/ha-1 2005 $0.22 2,285 $17.29 2006 $0.24 2,352 $17.29 2007 $0.33 2,419 $17.29 2008 $0.35 2,554 $17.29 2009 $0.35 2,520 $19.76 2010 $0.40 2,352 $16.67 2011 $0.45 2,587 $16.67 2012 $0.52 2,923 $16.67 2013 $0.48 2,923 $16.67 2014 $0.48 3,360 $16.67

Louisiana Insecticide Seed Treatment Year $/Kg Kg/ha-1 Price/ha-1 2005 $0.22 2,285 $17.29 2006 $0.22 2,419 $17.29 2007 $0.31 2,890 $17.29 2008 $0.35 2,218 $17.29 2009 $0.35 2,621 $19.76 2010 $0.39 2,755 $16.67 2011 $0.44 2,419 $16.67 2012 $0.53 3,125 $16.67 2013 $0.49 3,259 $16.67 2014 $0.49 3,830 $16.20

Mississippi Insecticide Seed Treatment Year $/Kg Kg/ha-1 Price/ha-1 2005 $0.22 2,453 $16.80 2006 $0.23 1,747 $16.80 2007 $0.31 2,722 $16.80 2008 $0.34 2,688 $16.80 2009 $0.34 2,554 $19.20 2010 $0.38 2,587 $16.20 2011 $0.44 2,621 $16.20 2012 $0.53 3,024 $16.20 2013 $0.48 3,091 $16.20 2014 $0.48 3,494 $16.20

Table 2.1 (Continued)

Tennessee Insecticide Seed Treatment Year $/Kg Kg/ha-1 Price/ha-1 2005 $0.21 2,554 $16.80 2006 $0.23 2,621 $16.80 2007 $0.38 1,277 $16.80 2008 $0.35 2,285 $16.80 2009 $0.36 3,024 $19.20 2010 $0.41 2,083 $16.20 2011 $0.45 2,150 $16.20 2012 $0.54 2,554 $16.20 2013 $0.48 3,125 $16.20 2014 $0.49 3,091 $16.20 Source: USDA-NASS 2015

Table 2.2 Mean yields (SEM) and net economic returns (SEM) of soybean treated with a neonicotinoid seed treatment (Neonicotinoid IST) compared with those not treated with insecticide (Untreated) across the Mid-South Region from 2005-2014.

Treatment Kg ha-1 $/ha-1 Untreated1 3,032 b (75.0) b 1,172 b (39.5) b Neonicotinoid IST2 3,167 a (75.6) a 1,205 a (39.3) a P value P > F P < 0.01 P < 0.01 Means within a column and treatment followed by the same letter are not significantly different, P < 0.05. 1Treated with a fungicide seed treatment but not an insecticide. 2Treated with the same fungicide as the untreated, but also included either thiamethoxam or imidacloprid.

Table 2.3 Mean (SEM) yields and net economic returns (SEM) of soybean treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each state in the Mid-South from 2005-2014.

Year Treatment Kg ha-1 $/ha-1 Untreated 3,003 b (248.1) b 1,270 a (125.6) a Arkansas Neonicotinoid IST 3,115 a (247.1) a 1,299 a (125.9) a P > F 0.02 0.14 Untreated 2,842 b (226.0) b 1,022 b (98.3) b Louisiana Neonicotinoid IST 3,045 a (224.7) a 1,065 a (97.9) a P > F <0.01 0.02 Untreated 2,936 b (109.0) b 1,070 b (54.9) b Mississippi Neonicotinoid IST 3,101 a (107.8) a 1,120 a (54.5) a P > F <0.01 <0.01 Untreated 3,281 b (124.6) b 1,349 a (72.4) a Tennessee Neonicotinoid IST 3,351 a (123.7) a 1,354 a (72.2) a P > F 0.02 0.65 Means within a column and state followed by the same letter are not significantly different, P < 0.05.

Table 2.4 ANOVA table for soybean yields and net economic returns across the Mid- South for each year (2005-2014).

Year Yield Returns F-value 7.2 1.48 2005 df 1, 32.9 1, 32.8 P-value 0.01 0.23 F-value 20.14 5.62 2006 df 1, 183 1, 183 P-value 0.01 0.01 F-value 8.17 3.88 2007 df 1, 63.3 1, 63.4 P-value 0.01 0.05 F-value 18.62 11.74 2008 df 1, 211 1, 211 P-value 0.01 0.01 F-value 0.15 0.34 2009 df 1, 92.7 1, 92.5 P-value 0.70 0.56 F-value 1.71 0.28 2010 df 1, 202 1, 202 P-value 0.19 0.60 F-value 6.90 3.41 2011 df 1, 159 1, 158 P-value 0.01 0.06 F-value 10.06 7.34 2012 df 1, 199 1, 199 P-value 0.01 0.01 F-value 0.27 1.78 2013 df 1, 125 1, 125 P-value 0.61 0.18 F-value 2.97 1.74 2014 df 1, 68 1, 68 P-value 0.08 0.19

Table 2.5 Mean (SEM) yields and net economic returns of soybean treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across the Mid-South region from 2005-2014.

Year Treatment Kg ha-1 $/ha-1 Untreated 3,212 b (313.5) 694 a (63.6) 2005 Neonicotinoid IST 3,360 a (312.9) 709 a (63.5) P > F 0.01 0.23 Untreated 2,945 b (199.2) 669 b (45.7) 2006 Neonicotinoid IST 3,112 a (198.4) 689 a (45.5) P > F 0.01 0.01 Untreated 2,931 b (396.4) 943 b (109.1) 2007 Neonicotinoid IST 3,146 a (394.6) 990 a (108.3) P > F 0.01 0.05 Untreated 2,559 b (180.4) 890 b (62.4) 2008 Neonicotinoid IST 2,800 a (178.0) 956 a (61.6) P > F 0.01 0.01 Untreated 3,537 a (178.0) 1,239 a (66.7) 2009 Neonicotinoid IST 3,560 a (176.2) 1,227 a (66.1) P > F 0.70 0.56 Untreated 3,094 a (190.7) 1,212 a (73.4) 2010 Neonicotinoid IST 3,165 a (188.2) 1,223 a (72.4) P > F 0.19 0.60 Untreated 3,040 b (302.9) 1,353 a (135.9) 2011 Neonicotinoid IST 3,168 a (301.8) 1,393 a (135.4) P > F 0.01 0.06 Untreated 3,180 b (206.6) 1,691 b (110.6) 2012 Neonicotinoid IST 3,396 a (204.4) 1,790 a (109.4) P > F 0.01 0.01 Untreated 3,234 a (207.8) 1,555 a (98.6) 2013 Neonicotinoid IST 3,212 a (206.9) 1,528 a (98.2) P > F 0.61 0.18 Untreated 2,949 a (368.2) 1,406 a (175.5) 2014 Neonicotinoid IST 3,097 a (365.8) 1,460 a (174.4) P > F 0.08 0.19 Means within a column and year followed by the same letter are not significantly different, P < 0.05.

References

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CHAPTER III

VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-

SOUTH CORN (ZEA MAYS L.) PRODUCTION SYSTEMS

Abstract

Neonicotinoid seed treatments are one of several effective control options used in corn, Zea mays L., production in the Mid-South for early season insect pests. An analysis was performed on 91 insecticide seed treatment trials from Arkansas, Louisiana,

Mississippi and Tennessee to determine the value of neonicotinoids in corn production systems across the Mid-South region of the United States. The analysis compared neonicotinoid insecticide treated seed plus a fungicide to seed only treated with fungicide. When analyzed by state, corn yields were significantly higher when neonicotinoid seed treatments were used compared to fungicide only treatments in

Mississippi and Louisiana. Corn treated with neonicotinoid seed treatments yielded

111.0, 1,093.0, 416.0, and 140.0 kg ha-1, higher than fungicide only treatments for

Arkansas, Louisiana, Mississippi, and Tennessee, respectively. Across all states, neonicotinoid seed treatments resulted in 700.0 kg ha-1 more yield compared to fungicide only treated corn seed. Net returns for corn treated with neonicotinoid seed treatment were $1,446 per ha-1 compared to $1,390 per ha-1 for fungicide only treated corn seed across the Mid-South. Economic returns for neonicotinoid seed treated corn were significantly greater than fungicide only treated corn seed in eight out of fourteen years.

When analyzed by state, economic returns for neonicotinoid seed treatments were significantly greater than fungicide only treated seed in Louisiana. These data show that in some areas and years, neonicotinoid seed treatments provide significant yield and economic benefits in Mid-South corn.

Introduction

Corn production in the Mid-South region of the United States has changed considerably in recent years. Higher yielding hybrids and favorable market prices have led to increased corn production (USDA – NASS 2015). Corn is typically the first major agronomic crop planted in the Mid-South region of the United States beginning around early March and extending through mid-April (Cartwright et al. 2003, Purcell et al.

2003).

Early season insect pests observed in Mid-South corn production include seedcorn maggot, Delia platura (Meigen); white grubs, Phyllophaga spp; Japanese

beetle, Popillia japonica (Newman); southern corn rootworm, Diabrotica

undecimpunctata howardi (Barber); wireworms, Melanotus spp. and other spp. also; lesser cornstalk borer, Elasmopalpus lignosellus (Zeller); corn root aphid, Aphis

middletoni (Thomas); greenbug, Schizaphis graminum (Rondani); corn leaf aphid,

Rhopalosiphum maidis (F.); bird cherry-oat aphid, Rhopalosiphum padi (L.); billbugs,

Sphenophorus spp; chinch bug, Blissus leucopterus leucopterus (Say); black cutworm,

Agrotis ipsilon (Hufnagel); and sugarcane beetle, Euetheola humilis rugiceps (LeConte)

(Steffey et al. 1999, Akin et al. 2012, Catchot et al. 2013). Wireworms and corn

rootworms are key pests of corn seed and seedlings in many regions of the U.S., feeding

on the primary and secondary roots. Root tissue loss causes instability in the corn plant 54

and can cause the plant to lodge (Higgins 1994). Also, damaged corn roots are less efficient for water and nutrient uptake resulting in stunted plant growth and yield losses.

These are exacerbated in dry soil conditions and can be detrimental to corn production across the United States (Jeschke et al. 2011).

Numerous at planting insecticides are currently labeled for corn production. At

planting insecticide options consist of neonicotinoid seed treatments, or in-furrow/banded

applications of organophosphate or pyrethroid insecticides. Early season insect

management techniques have progressively changed within the past two decades. In

2008 for instance, in-furrow applications were already being replaced with the use of

insecticide treated corn seed (Elbert et al. 2008).

Nearly all corn seed is currently treated with a neonicotinoid insecticide (Haire

2014). Imidacloprid (Gaucho 600, Bayer Cropscience, Research Triangle Park, NC),

thiamethoxam (Cruiser 5FS, Syngenta Crop Protection, Greensboro, NC), and

clothianidin (Poncho 600, Bayer Cropscience, Research Triangle Park, NC) are the

neonicotinoid seed treatments commonly applied to corn seed. Use of insecticide seed

treatments across the United States is higher in corn than other crops relative to the

percentage of hectares treated. Over 18 million ha of corn were treated with a

neonicotinoid insecticide seed treatment between 2009 and 2011 (Brassard 2012). Since

2011, around 80% of corn seeds are coated with a neonicotinoid seed treatment in the

United States (Douglas and Tooker 2015). Neonicotinoid insecticides are moved

systemically through the plant when applied as a seed treatment to corn. This provides a

high degree of efficacy on early season insect pests feeding on seedling corn both above

and below the soil surface (Hopwood et al. 2012).

Longevity in the soil also plays a major role in the efficacy of these insecticides on early season corn pests (Maienfisch et al. 2001). However, there are some alternative at-planting insecticides for corn that are effective against early season pests. Bifenthrin

(Capture LFR, FMC Corporation, Philadelphia, PA), chlorpyrifos (Lorsban 15G, Dow

Chemical Company, Midland, MI), and terbufos (Counter 15G, BASF Corporation,

Research Triangle Park, NC) are the most common at-planting non-neonicotinoid insecticides used.

Pyrethroids, organophosphates, and neonicotinoids provide similar control of the

early season pest complex in corn (Pike et al. 1993, Sloderbeck et al. 1996, Wilde 1997,

Tharp et al. 2000, Kuhar et al. 2003). Although there are several options for at-planting

insecticides to control the early season pest complex in corn, most producers have opted

to use the neonicotinoid seed treatments because of their ease of use and reduced risk to

pesticide handlers compared to the organophosphates and pyrethroids.

The use of neonicotinoids and their potential association with declines in

pollinator populations have raised questions about the future use of this class of

chemistry (Spivak et al. 2011, vanEngelsdorp et al. 2009). While many experiments have

been previously conducted on neonicotinoid seed treatments in corn, there is a shortage

of published data on the value of neonicotinoid insecticide seed treatments in corn

production systems in the Mid-South. Therefore, an analysis of previous research with

neonicotinoid insecticide seed treatments across the Mid-South region was conducted to

determine their value to corn production systems in the region.

Methods and Materials

To determine the impact of neonicotinoid seed treatments on corn yields, an analysis was done on 91 trials conducted in Arkansas, Louisiana, Mississippi, and

Tennessee from 2001 to 2014. All experiments included a neonicotinoid seed treatment with a base fungicide. The neonicotinoids were imidacloprid (Gaucho 600, Bayer

Cropscience, Research Triangle Park, NC), thiamethoxam (Cruiser 5FS, Syngenta Crop

Protection, Greensboro, NC), or clothianidin (Poncho, Bayer Cropscience, Research

Triangle Park, NC). Neonicotinoid seed treatments were applied to corn seed at rate ranges from of 0.13 to 1.34 mg ai per kernel. In all tests, a base fungicide treatment without an insecticide was included as an untreated comparison. A common base fungicide was used for both the insecticide seed treatments and the fungicide only treatment within each trial. All available unpublished data from University research and extension specialists within each state that met the above criteria were included in the analysis.

The experimental design for each individual experiment was a randomized complete block design with four to six replications. Plot ranged from 4 to 16 rows wide on 76.2 to 101.6 centimeter centers by 12.2 to 30.5 meters long. Measurements to evaluate insect control included but were not limited to actual insect counts, damage ratings, stand counts, plant height, plant vigor and etc. These measurements varied considerably based on insect species occurrence, corn growth stage, location, and year.

Timings and methods of evaluation were not consistently recorded across experiments and therefore are not included in this analysis. In most experiments, insect populations consisted of a complex of multiple species occurring simultaneously or in sequence

throughout seedling growth. The most common insects observed included soil insects.

Other insects observed included corn billbug, lesser cornstalk borer, and chinch bug.

All experiments included in this analysis were harvested at physiological

maturity. Grain weight and moisture content were recorded and all yields were corrected

to 15% moisture and converted to kg of grain per hectare. Yield was the only dependent

variable that was recorded in a consistent manner.

Of the 91 total experiments, eight trials were conducted at two locations in

Arkansas. They included the Northeast Research and Extension Center (Keiser, AR) and

Southeast Research and Extension Center (Rowher, AR). Forty-nine trials were

conducted in Louisiana at the LSU AgCenter Macon Ridge Research Station (Winnsboro,

LA). Twenty-four trials were conducted in Mississippi at multiple locations including

the R.R. Foil Plant Science Research Center (Starkville, MS), the Delta Research and

Extension Center (Stoneville, MS), the Brown Loam Experiment Station (Raymond, MS)

as well as several producer fields throughout the state. Ten trials were conducted in

Tennessee at the West Tennessee Research and Education Center (Jackson, TN) and at

the Milan Research and Education Center (Milan, TN).

Yield and economic data were analyzed with a mixed model analysis of variance

(PROC MIXED SAS ver. 9.4; SAS Institute; Cary, NC). Year, location and replication

nested within year and location were considered random effects, and treatments were

considered fixed effects for overall analysis. Analysis was also performed on yield and

economic data by year and state. Residual plots and normal distribution plots were

generated to verify that data met ANOVA assumptions. Means were separated using

Fisher’s Protected LSD procedure at the 0.05 level of significance. Insecticide seed

treatment prices were obtained through personal correspondence from Bayer

CropScience. The costs of the insecticide seed treatments were accounted for during

economic analyses (Table 3.1) and based on 79,040 plants ha-1. Economic data were

determined using yield for each treatment and the price of corn seed (harvested grain) in

that particular year and state based on data from the National Agricultural Statistics

Service (Table 3.2) (NASS 2015). To calculate gross economic returns, the yield of each

treatment was multiplied by the average price received (Table 3.2) for the state and year

of that trial. The cost of the seed treatment was then subtracted from the gross economic

return to give the net economic return for each treatment.

Results and Discussion

A total of 91 experiments were conducted over the fourteen year period in

Arkansas, Louisiana, Mississippi, and Tennessee. There was a significant difference in mean corn yield among treatments where there was a neonicotinoid seed treatment applied (F= 32.95; df = 3, 672; P < 0.01). There were no differences in yield between the imidacloprid, thiamethoxam, or clothianidin treatments. Yields of corn treated with

imidacloprid, thiamethoxam or clothianidin averaged 9,406.0 kg ha-1, 9,137 kg ha-1 and

9,245.0 kg ha-1, respectively, compared to 8,528 kg ha-1 for the fungicide only treatment.

Because no differences were observed between imidacloprid, thiamethoxam, or clothianidin, a separate analysis was conducted where data for imidacloprid, thiamethoxam, and clothianidin seed treatments were pooled and comparisons were made between corn with a neonicotinoid seed treatment and corn without a neonicotinoid seed treatment. Averaged across all experiments, corn yield with a neonicotinoid seed treatment was significantly (F = 95.55; df = 1, 670; P < 0.01) greater than yields of corn 59

where a neonicotinoid seed treatment was not used (Table 3.3). The average difference in yield was 700.0 kg ha-1 higher compared to the base fungicide only treated seed. There also was a significant difference in mean economic returns between treatments (F =

19.82; df = 1, 662; P < 0.01) (Table 3.3). The neonicotinoid seed treatment resulted in a

$56.00 per hectare return over corn where no insecticide seed treatment was used.

When analyzed by state for the years 2001 to 2014, there were significant

differences in mean corn yield among treatments for Louisiana (F = 219.58; df = 1, 315;

P < 0.01) and Mississippi (F = 5.71; df = 1, 190; P < 0.01). In those states, corn planted

with a neonicotinoid seed treatment produced greater yields than corn planted with no insecticide seed treatment (Table 3.4). Corn seed treated with a neonicotinoid seed treatment resulted in 1,094.0 and 401.0 kg ha-1 more yield than fungicide only seed

treatment in Louisiana and Mississippi, respectively. Significant differences in net

economic returns were observed between corn that received a neonicotinoid seed

treatment and corn with no insecticide seed treatment only in Louisiana (F = 104.02; df =

1, 302; P < 0.01) (Table 3.4). No differences in mean economic returns between

treatments were observed in (Arkansas: F = 0.94; df = 1, 91.1; P = 0.33; Mississippi: F =

1.85; df = 1, 189; P = 0.17; and Tennessee: F = 0.01; df = 1, 74.6; P = 0.92).

When analyzed by year, there was a significant difference in yields between seed

treated with a neonicotinoid and those only treated with fungicide in eight out of fourteen

years (Table 3.5). Corn yield in 2001, 2002, 2004, 2005, 2006, 2007, 2008 and 2014,

were significantly greater where a neonicotinoid seed treatment was used compared to

where no insecticide seed treatment was used (Table 3.6). Also, significant economic

returns were observed in years where there was a significantly greater corn yield (2001,

2002, 2004, 2005, 2006, 2007, 2008, and 2014).

Numerous experiments have investigated the impact of neonicotinoid seed treatments on corn yield in the U.S. (Wilde et al. 2004, Mullin et al. 2005, Kabaluk and

Ericsson 2007). In general, those studies showed reduced insect numbers and improved yields with a neonicotinoid seed treatment in corn. For instance, Wilde et al. (2004) showed that systemic seed treatments reduced early season infestations of seedling pests and yield increases were associated with where a neonicotinoid seed treatment was applied. Mullin et al. (2005) found that imidacloprid, thiamethoxam, and clothianidin at rates used commercially provided 90% mortality of corn rootworm within one day in laboratory bioassays. Also, Kabaluk and Ericsson (2007) found increases in stand density and seedling growth where clothianidin was present. These data indicate that an insecticide/fungicide seed treatment can in fact provide control of early season insect pests attacking corn throughout different regions of the United States.

Out of the 91 experiments conducted across the Mid-South, 82% displayed a numerically positive yield response when a neonicotinoid seed treatment was used from

2001-2014. The overall average corn yield response to neonicotinoid seed treatments was 700.0 kg ha-1 and ranged from a loss of -2,030.0 kg ha-1 to an increase of 3,593.0 kg

ha-1. When net economic returns were calculated across the Mid-South region; 79% of

the locations had a numerically positive return from using neonicotinoid seed treatments.

This analysis was conducted on previous unpublished research with neonicotinoid

insecticide seed treatments throughout the Mid-South with the goal of determining the

value of neonicotinoid insecticides as a seed treatment in corn. These 91 experiments

were analyzed from the production years of 2001 to 2014 and data indicates that neonicotinoid seed treatments provided a yield and economic benefit in corn production systems throughout the Mid-South region a majority of the time. However, significant differences in net economic returns were only observed in Louisiana when analyzed by state and in eight out of fourteen years when analyzed by year. Neonicotinoid seed treatments are currently used on a majority of corn hectares planted in the Mid-South.

This high adoption rate can be attributed to better stand establishment, more vigorous

seedling growth, yield advantages, and risk management. Field corn does not have the

ability to compensate as well from early season stand loss compared to cotton and

soybeans making early season insect control very important (Bailey and Pedigo 1986).

Sampling below ground insects prior to planting is difficult and not always predictive of

risk in the Mid-South region. Also, there are no rescue treatments available in corn if soil

insect pests are causing economic damage after the crop has been planted. Because corn

is planted early, and often in cool soils, initial emergence and growth can be slow.

Damage from the soil insect complex is often not immediate and visual symptomology

may not be observed until several weeks after planting. Research has shown yield losses

associated with delayed planting of as much as 62.7 kg ha-1 per day after optimal planting

dates. Even timely replants can result in substantial losses in yield for producers. For

these reasons, most producers utilize at planting insecticides or seed treatments to protect

against stand loss and promote early season growth and vigor in corn throughout the Mid-

South region.

Table 3.1 Cost of neonicotinoid insecticide treated corn seed

Insecticide Rate Insecticide Seed Treatment Price/ha-1 (mg ai per seed) 0.125 $8.40 0.13 $8.72 0.16 $10.74 0.22 $14.77 0.25 $16.80 0.32 $21.49 0.34 $22.82 0.35 $23.51 0.45 $30.23 0.50 $33.59 0.60 $40.31 0.64 $42.98 1.05 $43.97 1.125 $47.13 1.25 $52.36 1.34 $56.12 Source: Bayer CropScience

Table 3.2 Price received for corn by state and year used to calculate net economic returns in each state for each year

Arkansas Year $/Kg Kg/ha-1 2001 $0.08 9,101 2002 $0.10 8,411 2003 $0.09 8,787 2004 $0.09 8,787 2005 $0.08 8,222 2006 $0.11 9,164 2007 $0.15 10,608 2008 $0.17 9,540 2009 $0.15 9,289 2010 $0.18 9,415 2011 $0.25 8,850 2012 $0.27 11,172 2013 $0.20 11,675 2014 $0.16 11,737 Louisiana Year $/Kg Kg/ha-1 2001 $0.09 9,289 2002 $0.09 7,595 2003 $0.09 8,411 2004 $0.10 8,473 2005 $0.09 8,536 2006 $0.11 8,787 2007 $0.15 10,231 2008 $0.18 9,038 2009 $0.14 8,285 2010 $0.19 8,787 2011 $0.24 8,473 2012 $0.27 10,859 2013 $0.20 10,859 2014 $0.16 11,486

Table 3.2 (Continued)

Mississippi Year $/Kg Kg/ha-1 2001 $0.08 8,160 2002 $0.09 7,532 2003 $0.09 8,348 2004 $0.10 8,348 2005 $0.09 7,909 2006 $0.11 6,716 2007 $0.14 9,289 2008 $0.18 8,787 2009 $0.15 8,034 2010 $0.17 8,536 2011 $0.25 8,034 2012 $0.27 10,356 2013 $0.20 11,047 2014 $0.17 11,612 Tennessee Year $/Kg Kg/ha-1 2001 $0.08 8,285 2002 $0.10 6,716 2003 $0.09 8,222 2004 $0.09 8,787 2005 $0.08 8,160 2006 $0.12 7,846 2007 $0.15 6,653 2008 $0.18 7,406 2009 $0.14 9,289 2010 $0.19 7,344 2011 $0.26 8,222 2012 $0.29 5,335 2013 $0.19 9,792 2014 $0.15 10,545 Source: USDA-NASS 2001-2014

Table 3.3 Mean yields (SEM) and net economic returns (SEM) of corn treated with a neonicotinoid seed treatment compared with those not treated with insecticide across the Mid-South Region from 2001-2014.

Treatment Kg ha-1 $/ha-1 Untreated1 8,528 (140.8) b 1,390 (32.3) b Neonicotinoid IST2 9,228 (103.9) a 1,446 (23.5) a P value P > F P < 0.01 P < 0.01 Means within a column and treatment followed by the same letter are not significantly different, P < 0.05. 1Treated with a fungicide seed treatment but not an insecticide. 2Treated with the same fungicide as the untreated, but also included either imidacloprid, thiamethoxam, or clothianidin.

Table 3.4 Mean (SEM) yields and net economic returns (SEM) of corn treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each state in the Mid-South from 2001-2014.

State Treatment Kg ha-1 $/ha-1 Untreated1 8,990 (386.0) a 1,732 (117.1) a Arkansas Neonicotinoid IST2 9,101 (266.1) a 1,669 (64.6) a P > F 0.70 0.33 Untreated1 7,845 (161.7) b 1,088 (32.6) b Louisiana Neonicotinoid IST2 8,939 (128.2) a 1,188 (26.2) a P > F <0.01 <0.01 Untreated1 9,035 (271.1) b 1,678 (56.4) a Mississippi Neonicotinoid IST2 9,451 (197.7) a 1,719 (40.8) a P > F <0.01 0.17 Untreated1 10,263 (532.2) a 1,905 (85.8) a Tennessee Neonicotinoid IST2 10,403 (367.1) a 1,903 (65.7) a P > F 0.37 0.92 Means within a column and state followed by the same letter are not significantly different, P < 0.05. 1Treated with a fungicide seed treatment but not an insecticide. 2Treated with the same fungicide as the untreated, but also included either imidacloprid, thiamethoxam, or clothianidin.

Table 3.5 ANOVA table for corn yields and net economic returns across the Mid- South for each year (2001-2014).

Year Yield Returns F-value 50.21 23.99 2001 df 1, 7 1, 7 P-value 0.01 0.01 F-value 36.45 30.67 2002 df 1, 11 1, 11 P-value 0.01 0.01 F-value 3.26 1.27 2003 df 1, 17.4 1, 17.3 P-value 0.08 0.27 F-value 48.41 28.95 2004 df 1, 65.8 1, 65.7 P-value 0.01 0.01 F-value 52.28 18.57 2005 df 1, 29.4 1, 27.3 P-value 0.01 0.01 F-value 48.49 31.20 2006 df 1 1, 65 P-value 0.01 0.01 F-value 70.45 38.84 2007 df 1, 53.2 1, 53.2 P-value 0.01 0.01 F-value 25.44 16.07 2008 df 1, 85.4 1, 85.6 P-value 0.01 0.01 F-value 0.08 0.04 2009 df 1, 52.3 1, 52.3 P-value 0.77 0.83 F-value 0.75 0.02 2010 df 1, 76.2 1, 76.1 P-value 0.38 0.87 F-value 0.72 1.64 2011 df 1, 64.4 1, 64.3 P-value 0.40 0.20 F-value 1.69 0.05 2012 df 1, 56.4 1, 56.4 P-value 0.19 0.81 F-value 2.27 0.40 2013 df 1, 43 1, 43 P-value 0.13 0.52 F-value 14.18 6.51 2014 df 1, 39.4 1, 39.4 P-value 0.01 0.01

Table 3.6 Mean (SEM) yields and net economic returns of corn treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across the Mid-South region from 2001-2014.

Year Treatment Kg ha-1 $/ha-1 Untreated 6,091 (282.1) b 528 (24.4) b 2001 Neonicotinoid IST 7,698 (228.8) a 624 (19.8) a P > F 0.01 0.01 Untreated 4,081 (378.3) b 386 (35.7) b 2002 Neonicotinoid IST 6,055 (184.6) a 541 (16.2) a P > F 0.01 0.01 Untreated 7,315 (331.4) a 691 (31.3) a 2003 Neonicotinoid IST 7,988 (241.1) a 729 (21.8) a P > F 0.08 0.27 Untreated 8,474 (246.4) b 814 (23.2) b 2004 Neonicotinoid IST 9,695 (138.5) a 904 (12.5) a P > F 0.01 0.01 Untreated 7,774 (269.9) b 689 (23.9) b 2005 Neonicotinoid IST 8,983 (150.4) a 754 (15.5) a P > F 0.01 0.01 Untreated 8,006 (518.2) b 893 (59.8) b 2006 Neonicotinoid IST 9,483 (329.6) a 1022 (38.3) a P > F 0.01 0.01 Untreated 11,104 (264.8) b 1,661 (39.6) b 2007 Neonicotinoid IST 12,150 (191.2) a 1,778 (28.5) a P > F 0.01 0.01 Untreated 7,106 (184.4) b 1,258 (33.5) b 2008 Neonicotinoid IST 8,014 (132.2) a 1,387 (23.7) a P > F 0.01 0.01 Untreated 9,348 (657.8) a 1,355 (95.2) a 2009 Neonicotinoid IST 9,466 (485.3) a 1,343 (70.3) a P > F 0.77 0.83 Untreated 8,352 (490.2) a 1,511 (89.5) a 2010 Neonicotinoid IST 8,569 (370.0) a 1,518 (68.1) a P > F 0.38 0.87 Untreated 8,821 (389.5) a 2,190 (98.7) a 2011 Neonicotinoid IST 8,524 (287.7) a 2,079 (73.6) a P > F 0.40 0.20 Untreated 6,458 (364.8) a 1,769 (96.2) a 2012 Neonicotinoid IST 6,666 (257.8) a 1,780 (68.2) a P > F 0.19 0.81 Untreated 11,290 (430.0) a 2,228 (77.4) a 2013 Neonicotinoid IST 11,670 (309.1) a 2,260 (57.0) a P > F 0.13 0.52 Untreated 10,686 (419.6) b 1,799 (71.5) b 2014 Neonicotinoid IST 11,412 (294.9) a 1,883 (51.5) a P > F 0.01 0.01 Means within a column and year followed by the same letter are not significantly different, P < 0.05.

References

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CHAPTER IV

VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-

SOUTH COTTON (GOSSYPIUM HIRSUTUM L.) PRODUCTION SYSTEMS

Abstract

Neonicotinoid insecticides are currently one of two classes of chemicals available as a seed treatment for growers to control early season insect pests in cotton, Gossypium hirsutum L., in the Mid-South, and they are used on nearly 100 percent of the cotton hectares. An analysis was performed on 102 neonicotinoid insecticide seed treatment trials from Arkansas, Louisiana, Mississippi, and Tennessee to determine the value of neonicotinoid seed treatments in cotton production systems across the Mid-South region of the United States. The analysis compared neonicotinoid insecticide seed treatments plus a fungicide to seed only treated with fungicide. When analyzed by state, cotton yields were significantly greater in each state when neonicotinoid seed treatments were used compared to fungicide only treatments. Cotton treated with neonicotinoid treatments yielded 84.0 kg ha-1, 149.0 kg ha-1, 117.0 kg ha-1, and 140.0 kg ha-1, higher than fungicide only treatments for Arkansas, Louisiana, Mississippi, and Tennessee, respectively. Across all states, neonicotinoid seed treatments yielded an additional 127.0 kg ha-1 compared to fungicide only treated seed. Average net returns from cotton with a neonicotinoid seed treatment was $1,849 per ha-1 co mpared to $1,686 per ha-1 for cotton with fungicide only treated seed across the Mid-South. Economic returns for

neonicotinoid seed treatments yielded significantly greater than fungicide only treated

seed in ten out of fifteen years. When analyzed by state, economic returns for

neonicotinoid seed treatments were significantly greater than fungicide only treated seed

in every state of the Mid-South. These data show that neonicotinoid seed treatments

provide significant yield and economic benefits in Mid-South cotton compared to

fungicide only treated seed.

Introduction

Thrips are routine pests of seedling cotton and are typically the first insect producers experience during any given growing season (Cook et al. 2011). While other

seedling pests of cotton are regional in occurrence and distribution, thrips are found

across the Cotton Belt and can require treatment across the entire region (Stewart et al.

2013). Thrips species that primarily infest cotton seedlings in the U.S. include tobacco

thrips, Frankliniella fusca (Hinds); flower thrips, Frankliniella tritici (Fitch); western

flower thrips, Frankliniella occidentalis (Pergande); onion thrips, Thrips tabaci

(Lindeman); and soybean thrips, Neohydatothrips variabilis (Beach) (Leigh et al. 1996,

Albeldano et al. 2008). However, tobacco thrips are the primary thrips species observed

on seedling cotton throughout the Mid-South (Reed and Jackson 2002; Cook et al. 2003;

Stewart et al. 2013). Injury from thrips feeding causes yellowing, stunting, reduced plant

vigor, and occasionally plant mortality that results in delayed plant maturity and

decreased yields (Davidson et al. 1979, Leonard et al. 1999). Also, significant delays in

cotton maturity due to thrips feeding have been observed (Gaines 1934, Dunham and

Clark 1937, Bourland et al. 1992, Parker et al. 1992, Herbert 1998, Van Tol and Lentz

1999, Lentz and Van Tol 2000). In instances where heavy infestations occur, crop 73

maturity to harvest can be delayed for more than two weeks (Gaines 1934, Dunham and

Clark 1937, Bourland et al. 1992, Parker et al. 1992). Delayed crop maturity can prolong the interval in which the crop is susceptible to other insects throughout the growing season and lead to increased production costs (Stewart et al. 2013). Delayed maturity can also make the crop more susceptible to late season cool temperatures and adverse weather such as heavy rains associated with tropical systems (Morris 1963, Gipson and Joham

1968). Previous research has shown an increase in yields when thrips were controlled in seedling cotton (Cook et al. 2011, Davis et al. 1966, Davis and Cowan 1972, Burris et al.

1989, Herbert 1998, Van Tol and Lentz 1999, Lentz and Van Tol 2000). In 2014, 71% of

the cotton infested in the United States was treated for thrips, leading to an estimated loss

of 150,479 bales (Williams 2015). Thrips are the second most damaging cotton pest in

the United States behind tarnished plant bug, Lygus lineolaris (Palisot de Beauvois)

(Williams 2015), therefore, many producers utilize insecticide seed treatments to manage

early season insect pests, and to decrease the risk of stand loss, delayed crop maturity,

and yield losses.

Cotton seedlings are extremely susceptible to early season insect pests, especially

thrips, from emergence to approximately the fourth true leaf stage. This time interval is

generally two to three weeks depending on weather conditions and plant growth. Thrips

control is commonly achieved with use of preventative at-planting insecticide treatments

(Cook et al. 2011) such as aldicarb (Temik 15G, Bayer CropScience, Research Triangle

Park, NC) and acephate (Orthene 90S or 97S, AMVAC Chemical Corporation, Newport

Beach, CA); seed treatments including acephate, imidacloprid (Gaucho 600, Bayer

CropScience, Research Triangle Park, NC), and thiamethoxam (Cruiser 5FS, Syngenta

Crop Protection, Greensboro, NC) and foliar insecticides (Kerns et al. 2009, Kerns and

Cattaneo 2009, Parker et al. 2009, Bacheler and Reisig 2010, Catchot et al. 2010, Greene

2010, Herbert 2010, Pollet et al. 2010, Reed et al. 2010, Roberts et al. 2010, Stewart et al.

2010, Studebaker et al. 2010). However, in 2010 Bayer CropScience terminated the

marketing of aldicarb leading to increased adoption of the neonicotinoid seed treatments

(Catchot et al. 2014). Previous experiments in Virginia have shown yield responses for

controlling early season pests of cotton seedlings where 220 insecticide treatments

(including foliar, in-furrow, and seed applied) tested over a five-year period from 1997-

2001 showed an average yield increase of 381 kg lint/ha over non-treated controls

(Herbert 2002). Also, in-furrow applications of aldicarb and seed treatments containing

imidacloprid in North Carolina and Virginia resulted in average yield increases of 483

and 614 kg lint ha-1 respectively (Herbert et al. 2007).

There are multiple factors that increase the severity of thrips damage to seedling cotton such as environmental conditions, herbicide injury, and chemical applications for thrips control (Copeland et al. 2015). While many experiments have been previously conducted on neonicotinoid seed treatments in cotton, there is little published data on the value of neonicotinoid insecticide seed treatments in cotton production systems in the

Mid-South. Therefore, an analysis of previous unpublished research with neonicotinoid insecticide seed treatments across the Mid-South region was conducted to determine the value of neonicotinoid insecticide seed treatments in cotton production systems.

Methods and Materials

Data were requested from University cooperators at the University of Arkansas,

Louisiana State University, Mississippi State University, and the University of 75

Tennessee. The data received were from small plot replicated trials conducted in each of those states from 1996 - 2014 to estimate the impact of neonicotinoid insecticide seed treatments on insect pest populations and cotton yield.

All experiments included a neonicotinoid seed treatment with a base fungicide

compared to seed treated with the same fungicide. The neonicotinoid was imidacloprid

(Gaucho 600, Bayer CropScience, Research Triangle Park, NC), or thiamethoxam

(Cruiser 5FS, Syngenta Crop Protection, Greensboro, NC). Imidacloprid was applied at

0.375 mg ai/seed (Anonymous 2015a). Thiamethoxam was applied at 0.30 to 0.34 mg

ai/seed (Anonymous 2015b). The base fungicide was the same for both the insecticide

seed treatments and the fungicide only treatment within a test. All tests were conducted

as a randomized complete block design with four to six replications. Plot sizes ranged

from 4 to 16 rows by 12.2 to 30.5 meters long and planted on 96.52 to 101.6 centimeter

centers. Various measurements were taken to evaluate insect control. These included but

were not limited to actual insect counts, damage ratings, stand counts, plant height, plant

vigor and etc. Evaluations of insect control were not standardized across experiments

and varied based on insect species occurrence, cotton growth stage, location, and year.

Timings and methods of evaluation were not consistently recorded across tests and are

not included in this analysis. Overall, the most common insect evaluated included thrips,

but other insects observed included various soil insects, three cornered alfalfa hopper, and

cutworm. In most experiments, insect populations consisted of a complex of multiple

species occurring simultaneously or in sequence throughout seedling growth.

All trials were harvested with a mechanical cotton picker modified for small plot

research when the last harvestable boll had opened. Experiments were conducted at

multiple locations within each state across the Mid-South. Sixteen tests were conducted at three locations in Arkansas. They included the Lon Mann Cotton Research Station

(Marianna, AR), the University of Arkansas at Pine Bluff (Pine Bluff, AR) and Phillips

County, Arkansas (Helena, AR). Thirty tests were conducted at two locations in

Louisiana. They included the LSU AgCenter Macon Ridge Research Station

(Winnsboro, LA) and Northeast Research Station (St. Joseph, LA). Thirty-four tests were conducted in Mississippi at multiple locations including the R.R. Foil Plant Science

Research Center (Starkville, MS) and the Delta Research and Extension Center

(Stoneville, MS). Twenty-two tests were conducted in Tennessee at the West Tennessee

Research and Education Center (Jackson, TN).

Yield and economic data were analyzed with a mixed model analysis of variance

(PROC MIXED SAS ver. 9.3; SAS Institute; Cary, NC). Year, location and replication nested within year and location were considered random effects, and treatments were considered fixed effects. Means were separated using Fisher’s Protected LSD procedure at the 0.05 level of significance. Economic data were determined using yield for each treatment and the price of cottonseed (harvested lint) in that particular year and state based on data from the National Agricultural Statistics Service (Table 4.1) (NASS 2015).

Insecticide seed treatment prices were obtained through personal correspondence from

Bayer CropScience. The costs of the insecticide seed treatments were accounted for during economic analyses. To calculate gross economic returns, the yield of each treatment was multiplied by the average price received for the state and year of that trial.

The cost of the seed treatment was then subtracted from the gross economic return to give the net economic return for each treatment (Table 4.2).

Results and Discussion

A total of 102 experiments were conducted over the fifteen year period in

Arkansas, Louisiana, Mississippi, and Tennessee. There was a significant difference in mean cotton lint yield among treatments where there was a neonicotinoid seed treatment applied (F = 62.41; df = 2, 1042; P < 0.01). Thiamethoxam and imidacloprid resulted in significantly greater yields compared to fungicide only treated cottonseed but did not

differ significantly from each other. Lint yields of cotton treated with thiamethoxam or

imidacloprid averaged 1,270 and 1,294 kg ha-1, compared to 1,160 kg ha-1 for the base

fungicide only. Because no differences were observed between thiamethoxam and

imidacloprid, a separate analysis was conducted where data for thiamethoxam and

imidacloprid seed treatments were pooled and comparisons were made between cotton

with a neonicotinoid seed treatment and cotton without an insecticide seed treatment.

Averaged across all trials, cotton yields with a neonicotinoid seed treatment were

significantly (F = 122.05; df = 1, 1038; P < 0.01) greater than yields where a

neonicotinoid seed treatment was not used (Table 4.3). The average difference in yield

was 127.0 kg ha-1 across all trials. There was also a significant difference in net economic returns between treatments (F = 88.16; df = 1, 1038; P < 0.01) (Table 4.3).

The neonicotinoid seed treatment resulted in a $164.00 per hectare return over cotton where no insecticide seed treatment was used.

When analyzed by state for the years 1996 to 2014, there were significant differences in mean cotton yield among treatments for each state (Arkansas: F = 5.68; df

= 1, 147; P < 0.01; Louisiana: F = 55.35; df = 1, 306; P < 0.01; Mississippi: F = 34.25; df

= 1, 325; P < 0.01 and Tennessee: F = 36.99; df = 1, 262; P < 0.01). Plots planted with a

neonicotinoid seed treatment produced significantly greater yields than plots planted with

no insecticide seed treatment in each state (Table 4.4). Cottonseed treated with a

neonicotinoid seed treatment resulted in 84.0, 149.0, 117.0, and 140.0 kg ha-1 more yield

than fungicide only seed treatments in Arkansas, Louisiana, Mississippi, and Tennessee,

respectively. Significant differences in net economic returns were observed between

cottonseed that received a neonicotinoid seed treatment and cottonseed with no

insecticide seed treatment in each state (Arkansas: F = 3.72; df = 1, 148; P < 0.05;

Louisiana: F = 36.06; df = 1, 305; P < 0.01; Mississippi: F = 28.67; df = 1, 327; P < 0.01;

Tennessee: F = 27.39; df = 1, 257; P < 0.01). Cottonseed treated with a neonicotinoid

seed treatment resulted in $105.00, $185.00, $170.00, and $165.00 ha-1 more return than fungicide only seed treatments in Arkansas, Louisiana, Mississippi, and Tennessee (Table

4.4).

When analyzed by year, there were significant differences in yields between seed treated with a neonicotinoid and those only treated with fungicide in ten out of fifteen years (Table 4.5). Cotton yields in 1997, 2002, 2003, 2005, 2006, 2007, 2008, 2011,

2013, and 2014, were significantly greater where a neonicotinoid seed treatment was used compared to where no insecticide seed treatment was used (Table 4.6). Also, there was a significant difference in net economic returns between seed treated with a neonicotinoid and those only treated with fungicide in the ten years that had significant yield responses

(Table 4.6).

Overall, neonicotinoid seed treatments had a positive effect on lint yields and economic returns. Numerous experiments have investigated the impact of neonicotinoid seed treatments on cotton yields across the U.S. Those experiments also resulted in

significant yield increases from the use of a neonicotinoid seed treatment (Graham et al.

1995, Copeland 2015). Copeland (2015) showed that imidacloprid seed treatments reduced immature thrips numbers and damage from the one to four leaf stage and imidacloprid seed treatments resulted in significantly higher cotton lint yields (2586 kg ha-1) compared to cotton seed treated only with a fungicide (2343 kg ha-1). Similarly,

Graham et al. (1995) found that imidacloprid seed treatments significantly increased

cotton lint yields compared to untreated cotton seed.

Out of the 102 neonicotinoid insecticide seed treatment trials conducted across the

Mid-South, 75% displayed a positive numerical yield response when a neonicotinoid seed

treatment was used from 1996-2014. The overall average cotton lint yield response to

neonicotinoid seed treatments was 127.0 kg ha-1 and ranged from a loss of -302.7 kg ha-1

to an increase of 882.4 kg ha-1. When net returns were calculated across the Mid-South

region; 73% of the trials had a positive net return from using neonicotinoid seed

treatments with an average increased return of $164.00 ha-1. These results were likely

due to early season thrips infestations. In Mississippi, a total of 5,057 bales were lost

from tobacco thrips damage on seedling cotton (Williams 2013).

This analysis was conducted on unpublished small-plot research with insecticide

seed treatments throughout the Mid-South with the goal of determining the value of

neonicotinoid insecticides as a seed treatment in cotton. These 102 experiments were

analyzed from the production years of 1996 to 2014 and data indicates that neonicotinoid

seed treatments provided a yield and economic benefit in cotton production systems

throughout the Mid-South region in all states the majority of the time. Significant yield

responses were observed in Arkansas, Louisiana, Mississippi, and Tennessee. Also,

significant differences in net economic returns were observed in Arkansas, Louisiana,

Mississippi, and Tennessee when analyzed by state and in ten out of fifteen years when analyzed by year. Neonicotinoid seed treatments are currently used on 99% of cotton planted in the Mid-South region. This high adoption rate is mainly attributed to nearly a

100% likelihood of thrips infestations in cotton across the region during the seedling stage. Many producers report more uniform emergence, less stand loss, lower production

costs (due to less likelihood of flaring secondary pests than foliar sprays), and faster crop

maturity when using insecticide seed treatments at-planting. Currently at-planting

insecticides (including seed treatments) are broadly recommended for cotton in the Mid-

South.

Table 4.1 Values used to calculate net economic returns in each state for each year

Arkansas Year $/Kg Kg/ha-1 1996 $1.49 2,133 1997 $1.44 2,252 2001 $0.61 2,222 2002 $0.98 2,343 2003 $1.37 2,464 2004 $0.90 2,997 2005 $1.03 2,733 2006 $1.02 2,811 2007 $1.27 2,881 2008 $1.05 2,723 2009 $1.38 2,201 2010 $1.62 2,811 2011 $2.08 2,499 2012 $1.57 2,863 2013 $1.75 3,048 2014 $1.69 3,210 Louisiana Year $/Kg Kg/ha-1 1996 $1.49 1,875 1997 $1.43 1,959 2001 $0.61 1,560 2002 $0.97 1,929 2003 $1.34 2,602 2004 $0.91 2,333 2005 $1.03 2,362 2006 $1.01 2,545 2007 $1.25 2,736 2008 $1.15 1,550 2009 $1.38 2,004 2010 $1.78 2,265 2011 $2.05 2,276 2012 $1.52 2,744 2013 $1.72 3,290 2014 $1.76 3,150

Table 4.1 (Continued)

Mississippi Year $/Kg Kg/ha-1 1996 $1.49 2,203 1997 $1.43 2,425 2001 $0.58 1,934 2002 $0.97 2,174 2003 $1.33 2,513 2004 $0.90 2,755 2005 $1.01 2,311 2006 $0.99 2,230 2007 $1.27 2,599 2008 $1.05 2,451 2009 $1.44 1,808 2010 $1.74 2,672 2011 $2.15 2,561 2012 $1.67 2,728 2013 $1.79 3,237 2014 $1.76 3,183 Tennessee Year $/Kg Kg/ha-1 1996 $1.49 1,644 1997 $1.43 1,781 2001 $0.67 2,053 2002 $0.99 1,994 2003 $1.25 2,168 2004 $0.89 2,421 2005 $1.03 2,281 2006 $1.02 2,542 2007 $1.22 1,520 2008 $1.09 2,446 2009 $1.43 2,268 2010 $1.85 2,273 2011 $2.06 2,142 2012 $1.62 2,545 2013 $1.76 2,295 2014 $1.76 2,354

Table 4.2 Insecticide seed treatment (Gaucho 600 or Cruiser 5FS) price ha-1 for each state.

Year Neonicotinoid IST Price ($ ha-1) 1996 16.77 1997 16.77 2001 16.77 2002 16.77 2003 16.77 2004 15.73 2005 15.73 2006 15.73 2007 15.73 2008 16.07 2009 16.07 2011 12.10 2012 12.10 2013 12.10 2014 12.10

Table 4.3 Mean yields (SEM) and net economic returns (SEM) of cotton treated with a neonicotinoid seed treatment (Neonicotinoid IST) compared with those not treated with insecticide (Untreated) across the Mid-South Region from 1996-2014. Treatment Kg ha-1 $/ha-1 Untreated1 1,160 (37.2) b 1,686 (78.4) b Neonicotinoid IST2 1,287 (36.5) a 1,849 (77.7) a P value P > F P < 0.01 P < 0.01 Means within a column and treatment followed by the same letter are not significantly different, P < 0.05. 1Treated with a fungicide seed treatment but not an insecticide. 2Treated with same fungicide as the untreated, but also included either thiamethoxam or Imidacloprid

Table 4.4 Mean (SEM) yields and net economic returns (SEM) of cotton treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each state in the Mid-South from 1996-2014.

Year Treatment Kg ha-1 $/ha-1 Untreated 1,237 (98.8) b 1,834 (208.9) b Arkansas Neonicotinoid IST 1,321 (96.7) a 1,939 (206.5) a P > F 0.01 0.05 Untreated 1,035 (73.0) b 1,406 (152.1) b Louisiana Neonicotinoid IST 1,184 (72.0) a 1,591 (151.9) a P > F 0.01 0.01 Untreated 1,195 (62.9) b 1,916 (134.0) b Mississippi Neonicotinoid IST 1,312 (61.7) a 2,086 (132.5) a P > F 0.01 0.01 Untreated 1,222 (69.6) b 1,603 (134.3) b Tennessee Neonicotinoid IST 1,362 (67.9) a 1,768 (132.7) a P > F 0.01 0.01 Means within a column and state followed by the same letter are not significantly different, P < 0.05.

Table 4.5 ANOVA table for cotton yields and net economic returns across the Mid- South for each year (1996-2014).

Year Yield Returns F-value 0.00 0.01 1996 df 1, 7 1, 7 P-value 0.98 0.94 F-value 6.19 4.72 1997 df 1, 31 1, 31 P-value 0.01 0.03 F-value 0.07 0.34 2001 df 1, 7 1, 7 P-value 0.80 0.57 F-value 26.53 21.28 2002 df 1, 47 1, 47 P-value 0.01 0.01 F-value 10.05 8.74 2003 df 1, 45.5 1, 45.5 P-value 0.01 0.01 F-value 1.62 0.86 2004 df 1, 37.6 1, 37.6 P-value 0.21 0.35 F-value 27.34 22.99 2005 df 1, 52.2 1, 52.3 P-value 0.01 0.01 F-value 25.78 17.72 2006 df 1, 155 1, 155 P-value 0.01 0.01 F-value 10.32 8.96 2007 df 1, 56.9 1, 56.9 P-value 0.01 0.01 F-value 37.28 32.86 2008 df 1, 99.3 1, 99.7 P-value 0.01 0.01 F-value 2.00 2.80 2009 df 1, 23 1, 23 P-value 0.17 0.10 F-value 57.89 55.28 2011 df 1, 63.1 1, 63.1 P-value 0.01 0.01 F-value 0.03 0.14 2012 df 1, 114 1, 114 P-value 0.86 0.71 F-value 9.67 8.44 2013 df 1, 175 1, 175 P-value 0.01 0.01 F-value 11.78 10.72 2014 df 1, 118 1, 118 P-value 0.01 0.01

Table 4.6 Mean (SEM) yields and net economic returns of cotton treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across the Mid-South region from 2005-2014.

Treatment Kg ha-1 $/ha-1 Year Untreated 1,581 (239.3) a 2,370 (358.8) a 1996 Neonicotinoid IST 1,577 (211.9) a 2,348 (317.7) a P > F 0.99 0.94 Untreated 1,367 (229.1) b 1,956 (327.9) b 1997 Neonicotinoid IST 1,459 (228.1) a 2,071 (326.4) a P > F 0.01 0.03 Untreated 1,177 (94.3) a 729 (58.4) a 2001 Neonicotinoid IST 1,155 (80.7) a 699 (50.0) a P > F 0.80 0.57 Untreated 921 (39.1) b 893 (37.9) b 2002 Neonicotinoid IST 1,086 (31.8) a 1,037 (30.8) a P > F 0.01 0.01 Untreated 1,057 (268.3) b 1,419 (360.3) b 2003 Neonicotinoid IST 1,243 (265.9) a 1,653 (357.0) a P > F 0.01 0.01 Untreated 1,151 (236.4) a 1,032 (211.3) a 2004 Neonicotinoid IST 1,217 (233.9) a 1,075 (209.1) a P > F 0.21 0.35 Untreated 1,232 (100.4) b 1,272 (102.9) b 2005 Neonicotinoid IST 1,418 (98.5) a 1,448 (102.9) a P > F 0.01 0.01 Untreated 900 (58.5) b 912 (59.9) b 2006 Neonicotinoid IST 987 (57.4) a 985 (58.9) a P > F 0.01 0.01 Untreated 894 (106.2) b 1,114 (132.0) b 2007 Neonicotinoid IST 1,058 (102.3) a 1,307 (127.0) a P > F 0.01 0.01 Untreated 1,010 (152.7) b 1,094 (169.0) b 2008 Neonicotinoid IST 1,294 (151.1) a 1,386 (167.3) a P > F 0.01 0.01 Untreated 1,312 (104.6) a 1,878 (149.7) a 2009 Neonicotinoid IST 1,251 (100.0) a 1,774 (143.1) a P > F 0.17 0.10 Untreated 1,009 (115.9) b 2,126 (225.4) b 2011 Neonicotinoid IST 1,252 (114.2) a 2,622 (221.6) a P > F 0.01 0.01 Untreated 1,418 (109.9) a 2,250 (171.1) a 2012 Neonicotinoid IST 1,416 (107.6) a 2,229 (167.3) a P > F 0.86 0.78 Untreated 1,326 (106.1) b 2,340 (188.2) b 2013 Neonicotinoid IST 1,421 (104.1) a 2,496 (184.7) a P > F 0.01 0.01 Untreated 1,298 (80.1) a 2,290 (141.6) b 2014 Neonicotinoid IST 1,448 (75.3) a 2,542 (133.2) a P > F 0.01 0.01 Means within a column and year followed by the same letter are not significantly different, P < 0.05.

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CHAPTER V

VALUE OF NEONICOTINOID INSECTICIDE SEED TREATMENTS IN MID-

SOUTH GRAIN SORGHUM (SORGHUM BICOLOR L.)

PRODUCTION SYSTEMS

Abstract

Neonicotinoids are currently the most common at-planting insecticide used in grain sorghum, Sorghum bicolor (L.) Moench, in the Mid-South. Experiments were conducted on nine trials in Mississippi during 2014 through 2015 to determine the impact of neonicotinoid seed treatments on yield of grain sorghum. The analysis compared grain sorghum treated with a neonicotinoid insecticide and a fungicide to grain sorghum seed only treated with the same fungicide. Neonicotinoid seed treatments yielded an average of 1,013 kg ha-1 higher than fungicide only treated seed. Average net returns from neonicotinoid seed treatments usage were $543.00 per ha-1 compared to $398.00 per ha-1

for fungicide only treated seed. However, when analyzed by trial, grain sorghum yield,

was significantly higher in only four out of nine tests compared to base fungicide only

treated seed. Economic returns for neonicotinoid seed treatments were significantly

higher than fungicide only treated seed in only three out of nine experiments across

Mississippi. When analyzed across all tests there was an overall significant increase in

yield and net return where a neonicotinoid seed treatment was utilized. These data

indicate that neonicotinoid insecticide seed treatments can provide yield and economic benefits in grain sorghum production systems in some situations throughout Mississippi.

Introduction

Production of grain sorghum, Sorghum bicolor (Moench) fluctuates drastically

from year to year in the Mid-Southern United States depending on market value. The

area planted to grain sorghum increased substantially in 2014 and 2015 because of an

increase in the price received and a subsequent decrease in the prices of corn, Zea mays

L. (USDA – NASS 2015). Grain sorghum is considered a good rotational crop and is

commonly rotated with cotton and soybean. It is typically planted at a depth of 3.2 to 3.8

cm when soils are 17.7˚ to 21.1˚ C. Although grain sorghum is considered a fairly

drought tolerant crop, it can benefit from early planting due to more abundant rainfall and

lower insect pest pressure, especially in dryland situations (Buntin 2009).

The input costs associated with grain sorghum have increased dramatically over

the past two years due to outbreaks of sugarcane aphid, Melanaphis sacchari (Zehntner),

across the Gulf Coast and Lower Rio Grande Valley in Texas, Louisiana, Mississippi,

and Oklahoma (Villanueva et al. 2014). Multiple applications of higher priced

insecticides such as sulfoxaflor (Transform WGTM, Dow AroSciences, Indianapolis, IN)

and flupyradifuerone (Sivanto®, Bayer Crop Science, Raleigh, NC) are needed to

adequately control this pest that were not previously needed.

Cultural practices including tillage and crop rotation influence the presence and

severity of early season pests (Gregory and Musick 1976, Burton and Krenzer 1985).

Many producers have adopted insecticide seed treatments to help manage early season

insect pests and decrease risk of stand loss and replanting. However, because grain 93

sorghum production is limited in the Mid-South region, there is little published research that address the benefit of using these seed treatments.

Early season insect pests commonly observed in grain sorghum include wireworms, Melanotus spp., Limonius spp., and Agriotes mancus (Say); white grubs,

Phyllophaga spp. and Cyclocephala spp.; black cutworm, Agrotis ipsilon (Hufnagel);

chinch bug, Blissus leucopterus (Say), lesser cornstalk borer, Elasmopalpus lignosellus

(Zeller); red imported fire ant, Solenopsis invicta Buren; and multiple aphid species

(Catchot et al. 2014a). Aphids that commonly feed on grain sorghum include: greenbug,

Schizaphis graminum (Rondani); corn leaf aphid, Rhopalosiphum maidis (Fitch); and

sugarcane aphid, Melanaphis sacchari (Zehntner). Within the Mid-South region of the

United States, the primary aphid pest is the sugarcane aphid.

Sugarcane aphid was discovered into the United States in 1922 in the state of

Florida (Wilbrink 1922). It has only become a pest of sorghum in the U.S. since 2013,

and has now become the most commonly treated pest in grain sorghum since 2014.

Sugarcane aphid colonization of sorghum seedlings 2-3 weeks after emergence results in

economic damage, but populations tend to increase more rapidly after panicle formation

(van Rensburg 1973a). Sugarcane aphid colonization can occur rapidly, reaching as

many as 30,000 aphids on a single sorghum plant (Setokuchi 1977). However, 2-3 weeks

after aphid populations peak, densities rapidly decline due to dispersal of winged

individuals and declining suitability of the sorghum plant (van Rensburg 1973b) and

predation. Significant population increases occur from the boot to soft dough stage

which occurs 40 to 70 days after planting and from heading to harvest which occurs 60 to

100 days after planting (Fang 1990). Temperature and relative humidity can also have

significant effects on sugarcane aphid densities (Mote 1983, Waghmare et al. 1995). It has also been observed that aphid population densities can increase significantly under irrigation compared to non-irrigated fields (Balikai 2001).

Sugarcane aphid damage in sorghum depends on infestation density and duration.

They feed on the abaxial surface of older sorghum leaves. Plant responses from sugarcane aphid feeding include purple leaf discoloration of sorghum seedlings, chlorosis, necrosis, stunting, delayed flowering, and poor grain fill (Narayana 1975).

Severe injury from sugarcane aphid reduces plant biomass, grain yield, and grain quality

(Van den Berg et al. 2003, Singh et al. 2004). Accumulation of excessive amounts of honeydew results in sooty mold that reduces plant photosynthesis and interferes with harvest (Narayana 1975, Villanueva et al. 2014).

Mid to late season insect pests of grain sorghum include sorghum midge,

Contarinia sorghicola (Coquillet) and the sorghum headworm complex including fall armyworm, Spodoptera frugiperda (J. E. Smith); corn earworm, Helicoverpa zea

(Boddie); and sorghum webworm, Nola sorghiella Riley. Sorghum midge is the most damaging pest of sorghum worldwide and attacks pollinating sorghum heads (Young and

Teetes 1977). Female sorghum midge oviposit in individual glumes of flowering sorghum, and each larva develops in an individual seed resulting in failure of kernel development (Tao et al. 2003). The sorghum headworm complex are the most abundant pests found post anthesis. Corn earworm and fall armyworm are the most damaging pest in the sorghum headworm complex in grain sorghum (Wilde 2007). Yield losses are estimated over $80 million dollars annually due to sorghum headworms, in the U.S

(Teetes 1982). While many foliar insecticide experiments have been conducted on

commonly occurring insect pests in sorghum, there is little published data on the value of neonicotinoid insecticide seed treatments in grain sorghum production systems in the

Mid-South, therefore, 9 trials were conducted in 2014-2015 to determine the value of neonicotinoid insecticide seed treatments in cotton production systems.

Materials and Methods

Nine experiments were conducted at Mississippi State University in 2014 and

2015 to estimate the impact of neonicotinoid insecticide seed treatments on insect pest populations and grain sorghum yield. These experiments included a neonicotinoid seed treatment with a base fungicide compared to seed treated with only a base fungicide. The neonicotinoids used were clothianidin (Poncho 600, Bayer CropScience, Research

Triangle Park, NC) and thiamethoxam (Cruiser 5FS, Syngenta Crop Protection,

Greensboro, NC). Poncho 600 was applied at 0.062 to 0.078 mg ai/seed (Anonymous

2015a). Cruiser 5FS was applied at 0.062 to 0.093 mg ai/seed (Anonymous 2015b). The base fungicide was the same for insecticide seed treatments and the fungicide only treatment within a test. Each test was conducted as a randomized complete block design with four to eight replications. Plot sizes were four rows by 7.6 to 12.2 meters long and planted on 96.5 or 101.6 centimeter centers.

In 2014, AG54-00 (Monsanto Company, St. Louis, MO) was planted at 192,000 seed ha-1 at two planting dates in Starkville, MS at the R.R. Foil Plant Science Research

Center (May 8 and July 7) and in Stoneville, MS at the Delta Research and Extension

Center. In 2015, 83P17 (DuPont USA, Wilmington, DE) was planted at 192,000 seed ha-

1 at two planting dates in Starkville, MS (May 6, June 4, and June 29) and Stoneville,

MS. Also, in 2015, 84P80 (DuPont USA, Wilmington, DE) was planted at a seeding rate of 192,000 seed ha-1 only in the Starkville, MS location.

In both years furrow irrigation was utilized at the Stoneville locations while

Starkville was grown under dry land conditions. Plots across all locations were

maintained weed free throughout the growing season using 5.8 liters ha-1 S-metolachlor,

atrazine, and mesotrione (Lexar EZ, Syngenta Crop Protection, Greensboro, NC) and

hand weeding. Fertilizer applications were applied based on soil test recommendation

across each location. Plots were scouted weekly across all locations throughout the

growing season. Insecticides and harvest aids were applied based on Mississippi State

University Extension Service recommendations (Anonymous 2014c; Catchot et al. 2014).

Trials within each location were treated the same, although timing of applications

varied across planting dates due to infestation timings and growth stage. Early season

applications of chlorantraniliprole (Prevathon, DuPont USA, Wilmington, DE) were

applied to control fall armyworm during the vegetative stage when 50% or more plants

reached infestation. Sugarcane aphid was controlled by applying sulfoxaflor (Transform

WG, Dow AgroSciences, Indianapolis, IN). The late season sorghum headworm

complexes were controlled by applying chlorantraniliprole when threshold was reached

for bollworm, webworm, and fall armyworm.

The two center rows of each plot were harvested at the end of the growing season

in 2014 and 2015 and grain yield and moisture were determined for all plots when each

individual test reached physiological maturity (<14% moisture). Grain yields were

corrected to 13% moisture and converted to kg per hectare.

Economic data were determined using yield for each treatment and the price of grain sorghum seed (harvested grain) in that particular year from the Mississippi State

Department of Agricultural Economics Planning Budgets (MSU 2015). Insecticide seed treatment prices were obtained through personal correspondence from Bayer

CropScience. The costs of insecticide seed treatments were accounted for during economic analyses and were set at $17.29 ha-1 for clothianidin and thiamethoxam (Bayer

CropScience). To calculate gross economic returns, the yield of each treatment was multiplied by the average price received for the state and year of the trial. Price received for grain in 2014 and 2015 was $0.17 and $0.13 per kilogram (MSU 2015). The cost of the seed treatment was then subtracted from the gross economic return to give the net economic return for each treatment.

Yield and economic data were analyzed with a mixed model analysis of variance

(PROC MIXED SAS ver. 9.3; SAS Institute; Cary, NC). Year, location and replication nested within year and location were considered random effects, and treatments were considered fixed effects. Residual plots and normal distribution plots were generated to verify that data met ANOVA assumptions. Means were separated using Fisher’s

Protected LSD procedure at the 0.05 level of significance.

Results and Discussion

There was a significant difference in mean grain sorghum yields among treatments. Clothianidin and thiamethoxam treated sorghum seed resulted in significantly higher yields compared to sorghum treated with fungicide alone (F = 4.63; df = 2, 8.83; P < 0.04). Yields of grain sorghum treated with clothianidin and thiamethoxam averaged 3,831 kg ha-1 and 3,539 kg ha-1, respectively, compared to 2,725 98

kg ha-1 for the fungicide only treatment. No differences in yield were observed between the clothianidin and thiamethoxam treatments. Because no differences were observed

between clothianidin and thiamethoxam, a separate analysis was done where data for

clothianidin and thiamethoxam seed treatments were pooled and comparisons were made

between grain sorghum with a neonicotinoid seed treatment and grain sorghum without

an insecticide seed treatment. Averaged across all trials, grain sorghum yield with a

neonicotinoid seed treatment was significantly (F = 9.38; df = 1, 8.63; P < 0.01) greater

than yields of grain sorghum where a neonicotinoid seed treatment was not used (Table

5.1). The average difference in yield was 1,013 kg ha-1 across all trials. There also was a

significant difference in mean returns in dollars per hectare between treatments (F = 6.39;

df = 1, 8.5; P < 0.03) (Table 5.1). Across years and locations, returns for grain sorghum

that received a neonicotinoid seed treatment were $145.00 ha-1 greater than where

fungicide only seed treatment was used.

When analyzed by trial for the years 2014 to 2015, there were significant differences in mean grain sorghum yield among treatments in four out of nine tests (test

1: F = 52.36; df = 1, 10; P < 0.01; test 2: F = 24.26; df = 1, 10; P < 0.01; test 3: F =

51.97; df = 1, 14; P < 0.01; test 6: F = 7.49; df = 1, 6; P < 0.03) (Table 5.2 and 5.3) Also,

when analyzed by test, there were significant differences in net economic returns in three

out of nine test (test 1: F = 45.85; df = 1, 10; P < 0.01; test 2: F = 21.80; df = 1, 10; P <

0.01; test 3: F = 48.39; df = 1, 14; P = 0.01) (Table 5.2 and 5.3).

When analyzed by year, there was a significant difference in yields between seed treated with a neonicotinoid and those only treated with fungicide in 2014 and 2015

(Table 5.4). However, significant economic returns between the treatments were not

observed in either year.

Numerous experiments have investigated the impact of sugarcane aphid on

sorghum yield throughout regions of the world including Botswana, (Anonymous 1974,

Flattery 1982); Zimbabwe, (Page et al. 1985); and India, (Mote and Kadam 1984, Mote et

al. 1985). In general, those studies showed sorghum yield losses due to sugarcane aphid

infestations and yield losses ranged from minimal to extreme throughout each

experiment. Also, experiments in South Africa, (van Rensburg and van Hamburg 1975,

van Rensburg 1979, van den Berg 2002) observed significant yield losses where no

insecticides were applied. For instance, van Rensburg and van Hamburg (1975), van

Rensburg (1979), and van den Berg (2002) observed yield losses from 46-78% without

insecticide control.

Out of the nine neonicotinoid insecticide seed treatment trials conducted in two

different locations in Mississippi, four out of nine trials displayed a significant positive

yield response when a neonicotinoid seed treatment was used and ranged from a positive

response of 141.0 kg ha-1 to an increase of 2,910.0 kg ha-1. The 2,910.0 kg ha-1

advantage was due to sugarcane aphid damage in the fungicide only plots. In this trial

four of the eight fungicide only treated seed plots did not head due to severe sugarcane

aphid damage even though they were treated with a foliar insecticide at threshold. The

base fungicide plots were treated with dimethoate (Dimethoate 4EC, Drexel Chemical

Company, Memphis, TN) on August 21 and were re-treated for sugarcane aphid August

25 with sulfoxaflor due to poor control from dimethoate. Neonicotinoid insecticide seed

treatment plots were not treated for sugarcane aphid until September 5 and base fungicide

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only plots were re-treated for sugarcane aphid, as well. Across all plots the average grain sorghum yield response to neonicotinoid seed treatments was 1,013 kg ha-1

In summary, when net returns were calculated across individual trials; three out of

nine trials had a significant positive net return from using neonicotinoid seed treatments

with an average increased return of $145.00 per ha-1. These nine experiments were

analyzed from the production years of 2014 and 2015 and data indicates the

neonicotinoid seed treatments provide a yield and economic benefit in grain sorghum

production systems in some situations in Mississippi. Benefits of neonicotinoid seed

treatments include better stand establishment, increased vigorous seedling growth, yield

advantages, and risk management aversion. Seed treatments decrease early season

sugarcane aphid populations and delay spray applications depending on location and

planting date. While individual trials may vary, our results demonstrate an overall

significant yield and economic increase in experiments conducted resulting from the use

of neonicotinoid seed treatments in Mississippi grain sorghum production. Increased

grain sorghum yields in many cases is likely related to controlling sugarcane aphids

during vegetative stages prior to boot. However, due to the inconsistency of sugarcane

aphid infestation timings, neonicotinoid seed treatments are recommended for grain sorghum production in the Mid-South. Although neonicotinoid seed treatments only provided significant positive yield returns in four out of nine tests and significant positive net returns in three out of nine tests, they resulted in positive yield and net returns in

100% of all trials.

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Table 5.1 Mean yields (SEM) and net economic returns (SEM) of grain sorghum treated with a neonicotinoid seed treatment compared with those not treated with insecticide across Mississippi from 2014-2015.

Treatment Yield ( Kg ha-1) Net Return ($/ha-1) Untreated1 2,725 (221.7) b 398 (34.5) b Neonicotinoid IST2 3,737 (168.7) a 543 (29.8) a P value P > F P < 0.01 P < 0.03 Means within a column and treatment followed by the same letter are not significantly different, P < 0.05. 1Treated with a fungicide seed treatment but not an insecticide. 2Treated with the same fungicide as the untreated, but also included either thiamethoxam or clothianidin.

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Table 5.2 Mean (SEM) yields and net economic returns (SEM) of grain sorghum treated with a neonicotinoid seed treatment compared with those not treated with insecticide within each location in Mississippi from 2014-2015.

Test Treatment Kg ha-1 $/ha-1 Untreated 1,464 (84.1) b 248 (14.2) b 1 Neonicotinoid IST 3,053 (202.9) a 500 (34.3) a P > F 0.01 0.01 Untreated 2,172 (293.3) b 368 (49.6) b 2 Neonicotinoid IST 4,132 (268.9) a 689 (45.5) a P > F 0.01 0.01 Untreated 994 (390.6) b 168 (66.1) b 3 Neonicotinoid IST 3,904 (101.5) a 644 (17.1) a P > F 0.01 0.01 Untreated 5,159 (178.3) a 678 (23.4) a 4 Neonicotinoid IST 5,508 (225.0) a 707 (29.5) a P > F 0.27 0.47 Untreated 3,423 (352.6) a 450 (46.3) a 5 Neonicotinoid IST 4,050 (193.5) a 515 (25.4) a P > F 0.17 0.26 Untreated 2,222 (219.9) b 292 (28.9) a 6 Neonicotinoid IST 2,878 (95.2) a 361 (12.5) a P > F 0.03 0.07 Untreated 2,564 (237.4) a 337 (31.2) a 7 Neonicotinoid IST 2,705 (240.6) a 338 (31.6) a P > F 0.68 0.97 Untreated 1,919 (461.1) a 252 (60.6) a 8 Neonicotinoid IST 2,280 (360.5) a 283 (47.4) a P > F 0.55 0.70 Untreated 4,737 (323.7) a 802 (54.8) a 9 Neonicotinoid IST 5,035 (444.9) a 835 (75.3) a P > F 0.59 0.72 Means within a column and state followed by the same letter are not significantly different, P < 0.05.

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Table 5.3 ANOVA table for grain sorghum yields and net economic returns across Mississippi for each year (2014-2015).

Test Yield Returns F-value 52.36 45.85 1 df 1, 10 1, 10 P-value 0.01 0.01 F-value 24.26 21.80 2 df 1, 10 1, 10 P-value 0.01 0.01 F-value 51.97 48.39 3 df 1, 14 1, 14 P-value 0.01 0.01 F-value 1.47 0.57 4 df 1, 6 1, 6 P-value 0.27 0.47 F-value 2.43 1.52 5 df 1, 6 1, 6 P-value 0.17 0.26 F-value 7.49 4.79 6 df 1, 6 1, 6 P-value 0.03 0.07 F-value 0.17 0.00 7 df 1, 8 1, 8 P-value 0.68 0.97 F-value 0.38 0.15 8 df 1, 10 1, 10 P-value 0.55 0.70 F-value 0.29 0.13 9 df 1, 14 1, 14 P-value 0.59 0.72

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Table 5.4 Mean (SEM) yields and net economic returns of grain sorghum treated with a neonicotinoid seed treatment compared with those not treated with insecticide for each year across Mississippi from 2014-2015.

Year Treatment Kg ha-1 $/ha-1 Untreated 2,345 (329.9) b 398 (55.8) a 2014 Neonicotinoid IST 4,032 (195.6) a 665 (33.1) a P > F 0.05 0.06 Untreated 3,063 (279.8) b 403 (36.7) a 2015 Neonicotinoid IST 3,472 (269.1) a 439 (35.3) a P > F 0.03 0.15 Means within a column and year followed by the same letter are not significantly different, P < 0.05.

105

References

Anonymous. 1974. Crop protection in Botswana: biennial report 1971-73. Ministry of Agriculture, Division of Agriculture Research, Gaborone, Botswana.

Anonymous. 2015a. Poncho 600 insecticide product label. EPA Reg. No. 264-789. Research Triangle Park, NC: Bayer CropScience. Pp 4.

Anonymous. 2015b. Cruiser 5FS insecticide product label. EPA Reg. No. 100-941. Greensboro, NC: Syngenta Crop Protection, Inc. Pp 14.

Anonymous. 2014c. Weed Control Guidelines for Mississippi. Mississippi State University Extension Service, Mississippi Agricultural and Forestry Experiment Station. Publication 1532.

Balikai, R. A. 2001. Bioecology and management of the sorghum aphid, Melanaphis sacchari. Ph. D. Thesis, University of Agricultural Sciences, Dharwad, Karnataka, India, pp. 203.

Buntin, G. D. 2009. Grain Sorghum Insect Pests and Their Management. The University of Georgia Cooperative Extension, Griffin, GA. Pp 3.

Burton, R. L. and E. G. Krenzer. 1985. Reduction of greenbug (Homoptera: Aphididae) populations by surface residues in wheat tillage systems. J. Econ. Entomol. 78: 390-394.

Catchot, A. L., C. Allen, D. Cook, D. Dodds, J. Gore, T. Irby, E. Larson, B. Layton, S. Meyers, and F. Musser. 2014a. Insect Management Guide for Agronomic Crops 2014. Mississippi State University Extension Service. Publication 2471. Catchot, A. L., J. Gore, D. Cook, F. Musser, J. Smith, S. Stewart, G. Lorenz, G. Studebaker, S. Akin, R. Leonard, and R. Jackson. 2014b. Yield loss potential of twospotted spider mites in Mid-South cotton. Mississippi State University Extension Service. Publication 2852. Fang, M. N. 1990. Population fluctuation and timing for control of sorghum aphid on variety, Taichung 5. Bull. Taichung Dist. Agric. Improv. Stn. 28, 59-71.

Flattery, K. E. 1982. An assessment of pest damage of grain sorghum in Botswana. Exp. Agric. 18, 319-328.

Gregory, W. W. and G. J. Musick. 1976. Insect management in reduced tillage systems. Bull. Entomol. Soc. Am. 22: 302-304.

Mote, U. N. 1983. Epidemic of delphacids and aphids on winter sorghum. Sorghum Newsl. 26, 76.

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Mote, U. N. and J. R. Kadam. 1984. Incidence of (Aphis sacchari Zehnt) in relation to sorghum plant characters. Sorghum Newsl. 27, 86.

Mote, U. N., M. D. Shindle, D. R. Bapat. 1985. Screening of sorghum collections for resistance to aphids and oily malady of winter sorghum. Sorghum Newsl. 28, 13.

Mississippi State University. 2015. www.agecon.msstate.edu/whatwedo/budgets.asp

Narayana, D. 1975. Screening for aphids and sooty molds in sorghum. Sorghum Newsl. 25, 72.

Page, S. L., C. M. Mguni, S. Z. Sithole. 1985. Pests and diseases of crops in communal areas of Zimbabwe. Overseas Development Administration Technical Report, St. Albans, England.

SAS Institute. 2015. SAS/STAT 9.3 PROC MIXED. SAS Institute, Cary, NC.

Setokuchi, O. 1977. Ecology of Longiunguis sacchari (Zehntner) (Aphididae) infesting sorghums. V. Influence of harvesting time and plant population on the aphid occurrence. Proc. Assoc. Plant Prot., Kyushu 23, 109-112.

USDA-NASS. 2015. Online at http://www.nass.usda.gov/QuickStats/index2.jsp

van den Berg, J. 2002. Resistance of sorghum hybrids of the sorghum aphid, Melanaphis sacchari (Zehntner) (Homoptera: Aphididae). S. Afr. J. Plant Soil 19, 151-155.

van Rensburg, N. J. 1973a. Notes on the occurrence and biology of the sorghum aphid in South Africa. J. Entomol. Soc. S. Afr. 36, 293-298. 107

van Rensburg, N. J. 1973b. Population fluctuations of the sorghum aphid, Melanaphis (Longiunguis) pyrarius (Passerini) forma sacchari (Zehntner). Phytophylactica 5, 127-134.

van Rensburg, N. J. and H. van Hamburg. 1975. Grain sorghum pests: an integrated control approach. In: Proceedings of the First Congress of Entomological Society of Southern Africa, 1975, pp. 151-162. van Rensburg, N. J. 1979. Grain sorghum aphids. Farming in South Africa. Government Printer, Pretoria, South Africa, E. 2.

Waghmare, A. G., M. C. Varshneya, S. V. Khandge, S. S. Thakur, and A. S. Jadhav. 1995. Effects of meteorological parameters on the incidence of aphids on sorghum. J. Mah. Agric. Univ. 20, 307-308.

Wilbrink, G. 1922. An investigation on spread of the mosaic disease of sugarcane by aphids. Medid. Procfst. Java Suikerind 10, 413-456.

Wilde, G. E. 2007. Sorghum insects: ecology and control. In: Encyclopedia of pest management, ed. David Pimentel, Taylor and Francis p. 618-622.

Young, W. R. and G. L. Teetes. 1977. Sorghum entomology. Annu. Rev. Entomol. 22: 193.

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CHAPTER VI

QUANTIFYING THE VALUE OF INSECTICIDE CLASSES IN MISSISSIPPI

COTTON (GOSSYPIUM HIRSUTUM L.)

Abstract

Experiments were conducted to determine the benefit of individual insecticide classes utilized in an overall systems approach to insect management in cotton. Value of insecticide classes were analyzed from four site years in two different locations in

Mississippi from 2014 to 2015. The treatments in this study included cotton treated with all available classes of insecticides, cotton treated with all classes except neonicotinoids, cotton treated with all classes except pyrethroids, cotton treated with all classes except carbamates and organophosphates, and an untreated control. Plots were scouted weekly and insecticide applications were made with the best available insecticides for each treatment when that treatment reached threshold for a particular insect pest. All treatments were sprayed independently of the other treatments. At Starkville, MS (hills) location in 2014 and 2015 there were no significant differences between mean cotton yields and mean economic returns across all treatments. However, at Stoneville, MS

(delta) location in 2014 and 2015 there were significant differences between mean cotton yields where all classes of insecticides were applied compared to the untreated control and where neonicotinoids were excluded. Also there were differences in economic returns where all classes of insecticides were applied compared to the untreated control

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and where neonicotinoids were excluded in 2015 in the Stoneville, MS (delta) location.

At Stoneville, where any class of insecticide was excluded from the trial, a yield loss of

39.0 to 99.0 kg ha-1 was observed with an economic loss of $94.00 to $172.00 ha-1 in

2014. Also, at the same location in 2015, where any class of insecticide was excluded

from the trial; a yield loss of 41.0 to 295.0 kg ha-1 was observed with an economic loss of

$57.00 to $295.00 ha-1. These data show that in areas with high insect pressure, all

insecticide classes, are needed to maximize yield and economic returns in Mid-South

cotton production.

Introduction

Cotton, Gossypium hirsutum L., is an important agronomic crop in the southern

U.S. Because of its indeterminate growth habit, cotton produces flower buds (squares),

flowers, and fruit (bolls) over several weeks during the season. This makes cotton

attractive to numerous insect pests throughout the year. Key insect species that infest

cotton include several thrips species, Frankliniella spp.; (Leigh et al. 1996, Albeldano et

al. 2008), cotton aphid, Aphis gossypii Glover; tarnished plant bug, Lygus lineolaris

(Palisot de Beauvois); banded winged whitefly, Trialeurodes abutiloneus (Haldeman);

silver leaf whitefly, Bemisia argentifolii Bellows and Perring; bollworm, Helicoverpa zea

(Boddie); and tobacco budworm, Heliothis virescens (F.). In addition to being highly

attractive to insect pests, the indeterminate nature (long fruiting period) also makes cotton

susceptible to substantial yield losses from several of those species. In particular,

infestations of thrips during the early seedling stage can significantly reduce yields.

The tarnished plant bug is the most economically important insect pest of cotton

in the Mid-South. It prefers to feed on small to medium sized squares of cotton, but will 110

also feed on larger squares and bolls (Tugwell et al. 1976). Lygus feeding causes squares

to abscise and results in a direct yield losses (Layton 2000). Feeding on older squares

damages the developing anthers and results in abnormal flowers that will not pollinate

properly. When this occurs abnormal bolls are produced that shed from the plant soon

after pollination (Pack and Tugwell 1976). As a result, numerous insecticide applications

are made annually to minimize yield losses from this insect.

High levels of resistance to multiple insecticides have been reported in Arkansas,

Louisiana, and Mississippi. Resistance to the pyrethroids was first documented in 1995

(Snodgrass 1996) and was widespread across the Mid-South by 1999 (Snodgrass and

Scott 1999, Snodgrass and Scott 2000). Also, resistance to multiple organophosphate

insecticides including acephate, was first recorded in 2001 (Snodgrass and Scott 2002)

and was widespread across the Mid-South by 2008 (Snodgrass et al. 2009).

Widespread resistance to organophosphates and pyrethroids and the loss of

aldicarb as an in-furrow treatment has resulted in the neonicotinoid class of insecticides

becoming a valuable control option for multiple pests during the pre-flowering and

flowering stages of cotton development. Neonicotinoids are a class of insecticides that

are relied on heavily by producers throughout the Mid-South because they are highly

effective against a broad spectrum of piercing and sucking insects and can be delivered

by multiple application techniques (Elbert et al. 1998). The two most common

neonicotinoid insecticides utilized in cotton are imidacloprid (Admire Pro® and Gaucho®

Bayer CropScience, Research Triangle Park, NC) and thiamethoxam (Centric 40WG or

Cruiser Syngenta Crop Protection, Greensboro, NC) (Gore et al. 2012). Both of these

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insecticides are utilized as seed treatments for thrips control, and as foliar sprays for

tarnished plant bug control.

Insecticides are an important component of integrated pest management systems

for cotton throughout the United States. However, recent concerns over declining

pollinator health and the potential link to pesticides used in agriculture is threatening the

registrations of several insecticides. Some studies suggests that neonicotinoid use is

associated with environmental contamination and the primary insecticide involved in the

decline of pollinators leading to widespread public scrutiny, as well as the ban of neonicotinoids in certain countries (Krupke et al. 2012, Yang et al. 2008, Hopwood et al.

2012, Hardstone and Scott 2001, EPA 2014). Other risks of neonicotinoids include a long half-life in soil and potential leaching into groundwater (Sur and Stork 2003).

Neonicotinoids are highly water soluble and can readily leach through the soil profile or be lost in run-off depending on amount of rainfall or field slopes (Scorza et al. 2004,

Anhalt et al. 2008, Selim et al. 2010, Thuyet et al. 2012). Also, small amounts of active

ingredients can be lost in dust particles at planting (Tapparo et al. 2012). The use of talc

or graphite as seed lubricants are applied directly to seed in hoppers to facilitate flow

through seed tubes into the soil. On neonicotinoid treated seeds, the seed coatings may

flake off and be lost from the planter with the talc or graphite. Active ingredients can

drift to nearby flowering hosts plants where pollinators may be foraging. This can be a

source of direct exposure to foraging pollinators (Marzaro et al. 2011, Tapparo et al.

2012). Integrated pest management practices are utilized to limit selection pressure to

prevent or delay resistance to insecticide classes (Georghiou and Taylor 1976).

Insecticide resistant management schemes include utilizing insecticide alternatives and

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rotation of chemical insecticide classes, along with implementing an integrated pest

management plan to avoid developing resistance to economically important pests

(Georghiou et al. 1983). Increased tarnished plant bug populations in the region have led

to increased insecticide applications for effective control and higher use rates. To

achieve satisfactory control in areas where resistance is well documented, it is necessary

to rotate chemistries frequently. Recent loss of sulfoxaflor (Transform® WG, Dow

AgroSciences, Indianapolis, IN) due to concerns over safety to honey bees now excludes

a primary sub-group class that was used to control tarnished plant bug effectively. The

ability to utilize all labeled classes of insecticides provides an effective resistant

management plan and typically increases yield while lowering insect control costs. There

is currently little research that attempts to quantify the value of individual classes of

chemistry and how it impacts control of key pests and influences yield of cotton in the

Mid-South. The objectives of this research was to determine the value of insecticide

classes in an overall systems approach to insect management in cotton production

systems in the Mid-South region of the United States.

Materials and Methods

Experiments were conducted in 2014 and 2015 to quantify the value of selected

insecticide classes currently labeled for use in cotton. Cotton seed (2014: DeltaPine 0912

B2RF, 2015: ST 4946 GLB2) were planted May 8, 2014 and May 5, 2015 at the R.R.

Foil Plant Science Research Center in Starkville, MS at a plant population of 135,909

plants ha-1 and May 25, 2014 and May 29, 2015 at the Delta Research and Extension

Center in Stoneville, MS at a rate of 129,111 seed ha-1. Plots were planted as a

randomized complete block design with four replications. Plot sizes were four rows by 113

12.2 meters to 15.2 meters long and planted on 96.5 to 101.6 cm centers. Furrow irrigation was utilized at both locations. Plots across all locations were maintained weed free throughout the growing season using pre-emergence and post-emergence herbicides and hand weeding. Fertilizer applications were applied based on soil test recommendations across each location. Insecticides and harvest aids were applied based on Mississippi State University Extension Service recommendations (Anonymous 2014;

Catchot et al. 2014). Treatments consisted of multiple insecticide use strategies that excluded different classes of insecticides. The exclusion treatments included 1) no neonicotinoid insecticides, 2) no pyrethroid insecticides, and 3) no organophosphate/carbamate insecticides. Additionally, two control treatments were evaluated that included 4) all classes of insecticides and 5) an untreated control. For the untreated control, no insecticides were used throughout the entire growing season. For treatment 1, acephate (Orthene® 97S, AMVAC, Newport Beach, CA) was applied to seed at 0.189 liters cwt-1 seed. For treatments 2-4, imidacloprid (Gaucho 600, Bayer

CropScience, Research Triangle Park, NC) was applied to the seed at 0.379 liters cwt-1.

Each plot was scouted weekly throughout the season to determine populations of

insect pests. Thrips were visually observed by slapping ten plants by hand over a white

box to measure thrips densities on cotton from emergence to four leaf stage

Early season tarnished plant bug populations were measured by taking 25 sweeps

with a standard 38 cm diameter sweep net in each plot during pre-flowering stages.

Sweeps consisted of a back and forth motion across the upper half of the plant on rows 2

and 3 to determine tarnished plant bug populations for management decisions. Also,

measurements of square retention were evaluated to determine a management decision by

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observing the top 3 nodes to determine tarnished squares from Lygus feeding. During the

flowering period, cotton was sampled once per week by laying a 0.76 cm black cloth between rows 2 and 3 and shaking plants on both rows with wooden rods to dislodge tarnished plant bugs from cotton plants. Visually, tarnished plant bug nymphs and adults were counted to determine when to initiate a spray application. Insect pests were sprayed when the average of all four replications of a treatment exceeded the current thresholds based on the 2014 and 2015 Insect Control Guide for Agronomic Crops (Catchot et al.

2014 and 2015). When a particular insect pest exceeded the current threshold, insecticides were selected from the Insect Control Guide for Agronomic Crops in

Mississippi (Catchot et al. 2014) that met the criteria of the treatment for that pest (Tables

6.1-6.4).

The two center rows of each plot were harvested at the end of the growing season

in 2014 and 2015 and seedcotton weights were recorded. Seedcotton yields were

converted to lint yields by taking the weight of the harvest sample and multiplying by

38%. Yields were converted to kg lint ha-1.

Yield and economic data were analyzed with a mixed model analysis of variance

(Proc Mixed SAS ver. 9.3; SAS Institute; Cary, NC). Degrees of freedom were

calculated using Kenward-Roger method. An analysis compared yield of different

insecticide classes across all locations using Proc Mixed. In the model, treatments were considered fixed effects. Rep nested in region was considered a random effect and means were estimated using the Proc Means statement and considered significant at α = 0.05.

Means were separated using Fisher’s Protected LSD procedure at the 0.05 level of significance. Economic data were determined using yield for each treatment and the

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price of cottonseed (harvested lint) in that particular year and state based on data from the

National Agricultural Statistics Service (USDA-NASS 2015). Insecticide seed treatment

prices were obtained through personal correspondence from Bayer CropScience.

Insecticide application costs (Gore 2014, personal communication) (Table 6.5) were

obtained and added to seed treatment costs and accounted for during economic analysis.

Seed treatment costs included $7.41 for acephate and $17.29 for imidacloprid ha-1 for

insecticide treated seed (Gore 2014, personal communication, Bayer CropScience 2014).

For each insecticide application $12.35 ha-1 was added to represent application costs. To

calculate gross economic returns, the yield of each treatment was multiplied by the

average price received in Mississippi during the year of the trial. Price of seed for cotton

in 2014 was $1.56 and in 2015 was $1.53 per kilogram (USDA-NASS 2014-2015). The

cost of the seed treatment and insecticide applications were then subtracted from the

gross economic return to give the net economic return for each treatment.

Results and Discussion

Experiments were conducted over four site years in Starkville, MS and Stoneville,

MS to determine the value of insecticide classes used in an overall systems approach to insect management in cotton production systems in Mississippi. There was a range of insect pressure between two locations and a significant interaction was observed between site year (location by year) and treatment for yield (F = 2.69; df = 12, 48; P < 0.01) so an

analysis was conducted by site year.

The 2014 Starkville (hills) location had no significant differences in mean cotton

yield among treatments (F = 0.40; df = 4, 12; P = 0.80) or economic returns (F = 0.36; df

= 4, 12; P = 0.83) (Table 6.6). Similarly, the 2015 (hills) location had no significant 116

differences in mean cotton yield among treatments (F = 0.78; df = 4, 15; P = 0.55 or

mean economic returns (F = 0.75; df = 4, 15; P = 0.57) (Table 6.7). In both years insect pressure was minimal at the hills locations.

6.2).

In 2014, Stoneville (delta) insecticide class treatments had a significant impact on

mean yield (F = 100.10; df = 4, 12; P < 0.01) (Table 6.8). Use of all classes produced significantly higher yields than untreated control, no neonicotinoids, and no pyrethroids but was not significantly higher than no organophosphates/carbamates. All insecticide treated plots yielded significantly higher than the untreated control. Also, insecticide class had a significant impact on mean economic returns (F = 96.18; df = 4, 12; P <

0.01). Economic returns followed yield data except neonicotinoids did not differ from the

treatment where all classes were used (Table 6.8). In 2015, the insecticide class

treatment had a significant impact on yield in Stoneville when compared to other

treatments (F = 28.81; df = 4, 12; P < 0.01) (Table 6.9). All classes, no pyrethroids, and

no organophosphates/Carbamates yielded higher than the untreated control and when

neonicotinoids were excluded. Similarly, In 2015 Stoneville (delta) significant mean

economic return between classes of insecticides were observed (F = 27.89; df = 4, 12; P

< 0.01) (Table 6.9). Utilization of all classes of insecticides produced the highest mean

cotton yield and mean economic returns in 2014 and 2015 at Stoneville (delta) locations.

The Delta locations required more insecticide applications for multiple cotton

pests throughout the growing season than Hills locations. The Delta region traditionally

experiences much higher pest pressure than the Hill region and this data agrees. Across

all insecticide treatments in both years of the study the Hill region averaged 1.4 tarnished

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plant bug sprays and 1.5 thrips applications (seed treatment + foliar applications).

However, the Delta region averaged 3.4 tarnished plant bug applications, 2.9 thrips application (seed treatment + foliar applications), 0.5 cotton bollworm applications, and

0.5 stink bug applications (Tables 6.1-6.4). Higher plant bug sprays in the Delta region is likely due to insecticide resistance. Resistance levels increase later in the growing season in tarnished plant bug populations making them more difficult to control, especially when populations are high (Snodgrass and Scott 2000), therefore, utilization of all insecticide

classes are beneficial for developing an integrated resistance management plan in cotton

production systems in these areas.

In the Hills location in 2014 and 2015 there were no significant differences

between mean cotton yields and mean economic returns across all treatments. However,

at the Delta locations in 2014 and 2015 there were significant differences when any class

of insecticides were used compared to untreated cotton. In the Delta, where any class of

insecticide was included from the trial, a yield loss of 39.0 to 99.0 kg ha-1 was observed

with an economic loss of $94.00 to $172.00 ha-1 in 2014. Also, at the same location in

2015, where any class of insecticide was included from the trial; a yield loss of 41.0 to

295 kg ha-1 was observed with an economic loss of $57.00 to $295.00 ha-1. These data

show that in areas with high insect pressure and resistance to one or more classes of

chemistryh, including the Mississippi Delta, utilization of all insecticide classes provide

significant yield and economic benefits in Mid-South cotton.

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Table 6.1 Insecticide applications for 2014 Starkville (hills) Location.

Treatment Application Product Common Pest(s) Rate Classification Date Name Name Early Season 0.379 5/8/14 Gaucho Imidacloprid Pests liters/cwt All Classes Tarnished Plant Admire® 0.12 liters 7/3/14 Imidacloprid Bug Pro ha-1 Early Season Orthene® 0.189 5/8/14 Acephate No Pests 97S liters/cwt Neonicotinoids Orthene® 246.2 g/ai 6/4/14 Thrips Acephate 97S ha-1 Early Season 0.379 5/8/14 Gaucho Imidacloprid No OP’s/ Pests liters/cwt Carbamates Tarnished Plant Admire® 0.12 liters 7/3/14 Imidacloprid Bug Pro ha-1 Early Season 0.379 5/8/14 Gaucho Imidacloprid Pests liters/cwt No Pyrethroids Tarnished Plant Admire® 0.12 liters 7/3/14 Imidacloprid Bug Pro ha-1

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Table 6.2 Insecticide applications for 2014 Stoneville (delta) Location.

Treatment Application Product Pest(s) Common Name Rate Classification Date Name Early 0.379 5/25/14 Season Gaucho Imidacloprid liters/cwt Pests Orthene® 246.2 g/ai 6/6/14 Thrips Acephate 90S ha-1 Tarnished Orthene® 800.0 g/ai 7/1/14 Acephate Plant Bug 90S ha-1 0.58 liters Bidrin® 8 Dicrotophos Tarnished ha-1 7/16/14 All Classes Plant Bug Diamond® 0.43 liters Novaluron 0.83 EC ha-1 0.36 liters Bifenthrin bifenthrin Tarnished ha-1 7/22/14 Plant Bug Orthene® 840.0 g/ai Acephate 90S ha-1 Tarnished 0.58 liters Bidrin® 8 Dicrotophos Plant Bug ha-1 8/13/14 0.18 liters Bollworm Karate® Z 08 λ - cyhalothrin ha-1 Early Orthene® 0.189 5/25/14 Season acephate 97S liters/cwt Pests Orthene® 246.2 g/ai 6/18/14 thrips acephate 90S ha-1 Tarnished Orthene® 840.0 g/ai 7/1/14 acephate Plant Bug 90S ha-1 0.58 liters Bidrin® 8 dicrotophos Tarnished ha-1 7/16/14 No Neonicotinoids Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 0.36 liters Bifenthrin bifenthrin Tarnished ha-1 8/5/14 Plant Bug Orthene® 840.0 g/ai acephate 90S ha-1 Tarnished Orthene® 840.0 g/ai acephate Plant Bug 90S ha-1 8/13/14 0.18 liters Bollworm Karate® Z 08 λ - cyhalothrin ha-1

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Table 6.2 (Continued)

Early 0.379 5/25/14 Season Gaucho imidacloprid liters/cwt Pests 0.11 liters 6/6/14 Thrips Radiant™ spinetoram ha-1 Tarnished 0.12 liters 7/1/14 Admire® Pro imidacloprid Plant Bug ha-1 Transform® 0.11 liters No sulfoxaflor Tarnished WG ha-1 OP’s/Carbamates 7/16/14 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 Tarnished Transform® 0.11 liters 8/5/14 sulfoxaflor Plant Bug WG ha-1 Tarnished 0.14 liters Centric WG thiamethoxam Plant Bug ha-1 8/13/14 1.02 liters Bollworm Prevathon® chlorantraniliprole ha-1 Early 0.379 5/25/14 Season Gaucho Imidacloprid liters/cwt Pests Orthene® 246.2 g/ai 6/6/14 Thrips Acephate 90S ha-1 Tarnished 0.12 liters 7/1/14 Admire® Pro Imidacloprid Plant Bug ha-1 Transform® 0.11 liters sulfoxaflor No Pyrethroids Tarnished WG ha-1 7/16/14 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 Tarnished Transform® 0.11 liters 8/5/14 sulfoxaflor Plant Bug WG ha-1 Tarnished Orthene® 840.0 g/ai Acephate Plant Bug 90S ha-1 8/13/14 1.02 liters Bollworm Prevathon® chlorantriniliprole ha-1

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Table 6.3 Insecticide applications for 2015 Starkville (hills) Location.

Treatment Application Product Pest(s) Common Name Rate Classification Date Name Early 0.379 5/4/15 Gaucho imidacloprid Season Pest liters/cwt Orthene® 246.2 g/ai 6/1/15 Thrips acephate 97S ha-1 Tarnished Admire® 0.12 liters All Classes 6/29/15 imidacloprid Plant Bug Pro ha-1 0.14 liters Centric WG thiamethoxam Tarnished ha-1 7/20/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 Early Orthene® 0.189 5/4/15 acephate Season Pest 97S liters/cwt Orthene® 246.2 g/ai 6/1/15 Thrips acephate 97S ha-1 Tarnished Orthene® 840.0 g/ai No Neonicotinoids 6/29/15 acephate Plant Bug 97S ha-1 0.58 liters Bidrin® 8 dicrotophos Tarnished ha-1 7/20/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 Early 0.379 5/4/15 Gaucho imidacloprid Season Pest liters/cwt 0.11 liters 6/1/15 Thrips Radiant™ spinetoram ha-1 No Tarnished Admire® 0.12 liters 6/29/15 imidacloprid OP’s/Carbamates Plant Bug Pro ha-1 Transform® 0.11 liters sulfoxaflor Tarnished WG ha-1 7/20/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 Early 0.379 5/4/14 Season Gaucho imidacloprid liters/cwt Pests Orthene® 246.2 g/ai 6/1/15 Thrips acephate 97S ha-1 No Pyrethroids Tarnished Admire® 0.12 liters 6/29/15 imidacloprid Plant Bug Pro ha-1 Transform® 0.11 liters sulfoxaflor Tarnished WG ha-1 7/20/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1

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Table 6.4 Insecticide applications for 2015 Stoneville (delta) Location.

Treatment Application Product Pest(s) Common Name Rate Classification Date Name Early 0.379 5/29/15 Gaucho imidacloprid Season Pest liters/cwt Orthene® 246.2 g/ai 6/23/15 Thrips acephate 90S ha-1 Tarnished Admire® 0.12 liters 7/7/15 imidacloprid Plant Bug Pro ha-1 Tarnished 0.14 liters 7/10/15 Centric WG thiamethoxam Plant Bug ha-1 All Classes Orthene® 840.0 g/ai acephate 90S ha-1 Tarnished 0.46 liters 7/23/15 Bifenthrin bifenthrin Plant Bug ha-1 Diamond® 0.43 liters novaluron 0.83 EC ha-1 0.58 liters 8/26/15 Stink Bug Bidrin® 8 dicrotophos ha-1 Early Orthene® 0.189 5/29/15 acephate Season Pest 97S liters/cwt Orthene® 246.2 g/ai 6/23/15 Thrips acephate 90S ha-1 Tarnished Orthene® 840.0 g/ai 7/7/15 acephate Plant Bug 90S ha-1 No Neonicotinoids 0.58 liters Bidrin® 8 dicrotophos Tarnished ha-1 7/23/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 0.58 liters 8/26/15 Stink Bug Bidrin® 8 dicrotophos ha-1 Early 0.379 5/29/15 Season Gaucho imidacloprid liters/cwt Pests 0.11 liters 6/23/15 Thrips Radiant™ spinetoram ha-1 Tarnished Admire® 0.12 liters 7/7/15 imidacloprid Plant Bug Pro ha-1 No Tarnished 0.14 liters 7/10/15 Centric WG thiamethoxam OP’s/Carbamates Plant Bug ha-1 Transform® 0.11 liters sulfoxaflor Tarnished WG ha-1 7/23/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 0.46 liters 8/26/15 Stink Bug Bifenthrin bifenthrin ha-1

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Table 6.4 (Continued)

Early 0.379 5/29/15 Season Gaucho imidacloprid liters/cwt Pests Orthene® 246.2 g/ai 6/23/15 Thrips acephate 90S ha-1 Tarnished Admire® 0.12 liters 7/7/15 imidacloprid Plant Bug Pro ha-1 Tarnished 0.14 liters No Pyrethroids 7/10/15 Centric WG thiamethoxam Plant Bug ha-1 Transform® 0.11 liters sulfoxaflor Tarnished WG ha-1 7/23/15 Plant Bug Diamond® 0.43 liters novaluron 0.83 EC ha-1 0.58 liters 8/26/15 Stink Bug Bidrin® 8 dicrotophos ha-1

Table 6.5 Insecticide prices used to calculate net economic returns in Mississippi for each year.

Insecticide Formulation Insecticide Insecticide Rate Insecticide Common Name (g/ai) or (liters) Price $ ha-1 ha-1 Orthene® 97S or 90S acephate 246.2 g/ai 4.07 Admire® Pro imidacloprid 0.12 liters 4.32 Orthene® 97S or 90S acephate 840.0 g/ai 13.90 Bifenthrin bifenthrin 0.36 liters 9.63 Bifenthrin bifenthrin 0.46 liters 15.01 Karate® Z 08 λ - cyhalothrin 0.18 liters 16.07 Diamond® 0.83 EC novaluron 0.43 liters 17.29 Radiant™ spinetoram 0.11 liters 18.52 Centric WG thiamethoxam 0.14 liters 20.50 Bidrin® 8 dicrotophos 0.58 liters 20.89 Transform® WG sulfoxaflor 0.11 liters 25.93 Prevathon® chlorantriniliprole 1.02 liters 43.29

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Table 6.6 2014 Starkville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South.

Treatment Kg ha-1 $ ha-1

Untreated 1,093 (95.1) a 1,706 (148.4) a

No Neonicotinoids 1,230 (179.3) a 1,904 (279.7) a

All Classes 1,253 (42.7) a 1,939 (66.7) a

No Pyrethroids 1,178 (145.0) a 1,822 (226.3) a

No Organophosphates/Carbamates 1,255 (103.1) a 1,942 (160.9) a Means followed by the same letter are not significantly different at (P ≤ 0.05).

Table 6.7 2015 Starkville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South.

Treatment Kg ha-1 $ ha-1

Untreated 1,327 (45.3) a 2,037 (69.5) a

No Neonicotinoids 1,541 (85.7) a 2,273 (131.6) a

All Classes 1, 373 (79.1) a 2,025 (121.4) a

No Pyrethroids 1, 497 (137.4) a 2,209 (211.0) a

No Organophosphates/Carbamates 1, 473 (128.5) a 2,159 (197.3) a Means followed by the same letter are not significantly different at (P ≤ 0.05).

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Table 6.8 2014 Stoneville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South.

Treatment Kg ha-1 $ ha-1

Untreated 1,654 (38.1) c 2,580 (59.5) c

No Neonicotinoids 2,114 (29.8) b 3,144 (46.5) ab

All Classes 2,190 (31.3) a 3,238 (48.8) a

No Pyrethroids 2,091 (27.0) b 3,066 (42.1) b

No Organophosphates/Carbamates 2,151 (42.6) ab 3,139 (66.6) ab Means followed by the same letter are not significantly different at (P ≤ 0.05).

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Table 6.9 2015 Stoneville mean (SEM) yields and net economic returns (SEM) of cotton quantifying neonicotinoids and utilizing insecticide classes throughout production systems in the Mid-South.

Treatment Kg ha-1 $ ha-1

Untreated 796 (28.9) c 1,222 (44.6) c

No Neonicotinoids 1,314 (99.5) b 1,892 (152.9) b

All Classes 1,525 (39.2) a 2,187 (60.3) a

No Pyrethroids 1,483 (86.7) ab 2,123 (133.1) ab

No Organophosphates/Carbamates 1,484 (98.8) ab 2,130 (151.8) ab Means followed by the same letter are not significantly different at (P ≤ 0.05).

127

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CHAPTER VII

SUMMARY

Multiple experiments were conducted across four states from the years 1996 to

2015 to determine the value of neonicotinoid insecticides in row crop production systems

throughout the Mid-South region of the United States. Yields of neonicotinoid seed

treatments were analyzed in soybean, corn, cotton, and grain sorghum and compared to a

base fungicide only seed treatment. Also, four site years of an experiment was conducted

at Starkville, MS (hills) and Stoneville, MS (delta) to quantify the impact of the major

insecticide classes on cotton production systems. Yields and economic returns were analyzed to determine the value of individual classes of chemistry and their impact on pest management strategies in cotton by developing scenarios where certain classes of insecticides were excluded from use season long for insect control when economic thresholds were reached

Over 372 separate experiments were conducted in soybean, corn, cotton, and grain sorghum throughout the Mid-South from 1996 to 2015. Neonicotinoid insecticide seed treatments provided significantly higher yields in soybean, corn, cotton, and grain sorghum production systems throughout the Mid-South region. When analyzed across the Mid-South, neonicotinoid seed treatments provided a significant increase in mean yield of soybean (132.0 kg ha-1), corn (700.0 kg ha-1), cotton (127.0 kg ha-1), and grain

sorghum (1,013.0 kg ha-1) when compared to fungicide only treated seed in those crops.

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Over the 19 year span neonicotinoid insecticide seed treatments provided significant economic returns resulting in a $398.00 ha-1 overall economic return across all crop

production systems analyzed throughout the Mid-South. Economic returns by crop included soybean ($33.00 kg ha-1), corn ($56.00 kg ha-1), cotton ($164.00 kg ha-1), and

grain sorghum ($145.00 kg ha-1). Out of 372 experiments conducted in Arkansas,

Louisiana, Mississippi, and Tennessee; 74% had a positive yield response and 69%

displayed a positive economic return where a neonicotinoid seed treatments was used

compared to fungicide only treated seed in soybean, corn, cotton, and grain sorghum.

The analysis that was conducted across the Mid-South region and represents multiple

landscapes and different environments with a variation of early season insect pests that

infest the crops in this region.

In comparing insecticide classes in cotton, insect populations in Hill region were

minimal compared to the Delta region. Therefore, there were no significant yield or

economic differences between any treatments including the untreated check in the Hills,

but there were significant differences between mean cotton yields and mean economic

returns in the Delta. In the Delta, where any class of insecticide was excluded from the

trial, a yield loss of 39.0 to 295.0 kg ha-1 was observed with an economic loss of $57.00

to $295.00 ha-1. These data show that in areas with high insect pressure availability of all

insecticide classes are needed to maximize yield and economic benefits in Mid-South

cotton. In summary, neonicotinoid insecticides as seed treatments and access to multiple

classes of chemistry are valuable tools in all row crop production systems throughout the

region due to their ability to protect yields and maximize economic profits.

133