Weed Management in Bollgard II® XtendFlexTM Cotton
by
Justin L. Spradley, B.S.
A Thesis
In
Crop Science
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE
Approved
Dr. J. Wayne Keeling Co-Chair of Committee
Dr. Peter A. Dotray Co-chair of Committee
Dr. Jason E. Woodward
Dr. Guy H. Loneragan
Dr. Mark Sheridan Dean of the Graduate School
May, 2014 Copyright 2014, Justin L. Spradley Texas Tech University, Justin L. Spradley, May 2014
ACKNOWLEDGMENTS
I first thank Jesus for His divine love, creation, and being my savior. I would like to thank my wife Cryctal for all the sacrifices she has made in order for me to accomplish my work, and my daughter Saige for her sacrifice of time with her daddy.
I would like to thank Drs. Wayne Keeling and Peter Dotray for allowing me the opportunity to work with their programs. I also thank them for the many hours spent on my trials and thesis work. I have learned a tremendous amount from these gentlemen and appreciate greatly who they are.
I would also like to thank Dr. Jason Woodward for all the time he has spent with me in and out of class and at work as well. I gained knowledge of plant pathology from this man, the number one plant pathologist. I thank Dr. Guy
Loneragan for being part of my committee and a friend at Texas Tech. I thank you for your time reviewing my work as well as being the professional animal scientist you are.
I thank my co-workers and fellow graduate students for the hard work they offered in the field and assisting me on thesis challenges. Co-workers Jacob Reed,
Justin Cave, Joel Webb, Shay Morris, Misha Manuchehri, and Rand Merchant helped greatly with field operations, spraying, statistics, data collection, and harvest and deserve many thanks for their time and effort. I thank everyone mentioned for being the best leaders, mentors, and friends a man can have.
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I thank Texas Tech University and Texas A&M AgriLife Research for the opportunity and resources to earn a degree and conduct this research. The faculty and staff of both institutions have been wonderful and I appreciate the support they have provided.
Special recognition goes to Monsanto for providing partial funding for this research. I am very thankful for their guidance and support. The people at Monsanto have been a pleasure to work with.
I also thank my mom Sharron and dad Danny Spradley for all they have done for me. Without their knowledge and wisdom I would not be the man I am today. My brother Dillon for always being there when one is in need. My sister Laurie for being the rock she is. I thank all my extended family for all their love and support.
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TABLE OF CONTENTS
ACKNOWLEDGMENTS ...... ii
ABSTRACT ...... vi
LIST OF TABLES ...... viii
I. INTRODUCTION ...... 1
II.LITERATURE REVIEW ...... 4
History of Weed Management in Cotton ...... 4
Palmer amaranth...... 14
Ivyleaf Morningglory ...... 15
Glyphosate-tolerant Cotton ...... 17
Glufosinate-tolerant Cotton ...... 20
Dicamba-tolerant Cotton ...... 22
III.MATERIALS AND METHODS ...... 25
Field Studies ...... 25
Palmer amaranth, devil’s-claw, and silverleaf nightshade control 2010 ...... 26
Palmer amaranth control 2011 ...... 27
Palmer amaranth and red morningglory control 2012 ...... 27
iv Texas Tech University, Justin L. Spradley, May 2014
2012 Bollgard II® XtendFlexTM Cotton POST – Palmer amaranth and
devil’s-claw control ...... 28
Ivyleaf morningglory control 2012 ...... 28
IV.RESULTS AND DISCUSSION ...... 38
Field Studies ...... 38
Palmer amaranth Glover 2010 ...... 38
Devil’s-claw Glover 2010 ...... 41
Silverleaf nightshade Glover 2010 ...... 42
Palmer amaranth 2011 ...... 43
Palmer amaranth Lorenzo, TX 2012 ...... 47
Red morningglory Lorenzo, TX 2012 ...... 49
Palmer amaranth Glover Farm 2012 ...... 50
Devil’s-claw Glover Farm 2012 ...... 51
Palmer amaranth control Lubbock Station (301) Farm 2012 ...... 52
Ivyleaf morningglory I control Lubbock Station (301) Farm 2012 ...... 53
Ivyleaf morningglory II control Lubbock Station (301) Farm 2012 ...... 54
V. SUMMARY AND CONCLUSIONS ...... 68
LITERATURE CITED ...... 73
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ABSTRACT
Bollgard II® XtendFlexTM cotton could improve management of many problem annual and perennial weeds on the Texas High Plains. Weed species including Palmer amaranth (Amaranthus palmeri S. Wats.), devil’s-claw (Proboscidea louisanica
Thell.), silverleaf nightshade (Solanum elaeagnifolium Cav.), ivyleaf morningglory
(Ipomoea hederacea Jacq.), and red morningglory (Ipomoea coccinea L.) are not always effectively controlled with glyphosate [N-(phosphonomethyl)glycine] alone, but residual herbicides such as trifluralin [2,6-dinitro-N,N-dipropyl-4-
(trifluoromethyl(benzenamine)] combined with dicamba [3,6-dichloro-2- methoxybenzoic acid], glufosinate-ammonium [2-amino-4-
(hydroxymethylphosphinyl)butanoic acid monoammonium salt] or glyphosate may improve control. Bollgard II® XtendFlexTM technology may acknowledge the utility of alternative modes of action in managing identified glyphosate-resistant Palmer amaranth and other weed populations.
The objectives of the studies were to 1) evaluate dicamba applied preemergence (PRE) and postemergence (POST) alone or in combination with glufosinate or glyphosate for Palmer amaranth, devil’s-claw, and ivyleaf morningglory control in Bollgard II® XtendFlexTM cotton, 2) compare Palmer amaranth control with dicamba-based treatments in Bollgard II® XtendFlexTM cotton to standard weed management programs in cotton, and 3) determine cotton response to glyphosate, glufosinate, and dicamba and lint yield in Bollgard II® XtendFlexTM cotton.
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Field trials were conducted in 2010, 2011 and 2012 at the Texas A&M
AgriLife Research and Extension Center in Lubbock, TX and near Lorenzo, TX in
2012 to assess the control of the aforementioned weed species in Bollgard II®
XtendFlexTM cotton. Evaluations were made in plots with or without trifluralin preplant incorporated (PPI) followed by (fb) dicamba, glufosinate, or glyphosate applied either alone or tank-mixed in different combinations. Preemergence treatments included glyphosate and dicamba alone and in combination. The treatments that followed a PRE application were applied at timings that included early-postemergence (EPOST), delayed early-postemergence (D-EPOST), postemergence, mid-postemergence (MPOST), and layby.
Results indicated that >90% Palmer amaranth control was achieved when dicamba was applied PRE and EPOST and fb glufosinate MPOST 14 days after treatment (DAT). Glyphosate applied PRE, POST, and MPOST resulted in the greatest control of devil’s-claw 14 DAT; whereas silverleaf nightshade control was similar for all 14 DAT MPOST treatments and ranged from 65 to 83%. Trifluralin
PPI fb glyphosate + dicamba or glyphosate + dicamba + acetochlor EPOST fb glyphosate or glyphosate + dicamba MPOST controlled ivyleaf morningglory greater than all other treatments. Furthermore, results from these studies indicate that a system-based approach combining glufosinate with dicamba, glyphosate, or acetochlor early in the season was needed to effectively control red morningglory.
.
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LIST OF TABLES
3.1. Monthly rainfall distribution for the years 2010, 2011, 2012 and
the 30 year average for Lubbock, TX...... 31
3.2. Application description for Palmer amaranth and devil’s-claw
control in Bollgard II® XtendFlexTM cotton 2010...... 32
3.3. Application description for Palmer amaranth control in Bollgard
II® XtendFlexTM cotton 2011...... 33
3.4. Application description for Palmer amaranth and red
morningglory in POST treatments in Bollgard II®
XtendFlexTM cotton 2012 (Lorenzo, TX)...... 34
3.5. Application description for Palmer amaranth and devil’s-claw in
Bollgard II® XtendFlexTM cotton POST treatments 2012
(Glover Farm)...... 35
3.6. Application description for ivyleaf morningglory control in
morningglory I trial 2012...... 36
3.7. Application description for ivyleaf morningglory control in
morningglory II trial 2012...... 37
4.1. Palmer amaranth control at the Glover Farm in Lubbock, TX 2010...... 56
4.2. Devil's-claw control at the Glover Farm in Lubbock, TX 2010...... 57
4.3. Silverleaf nightshade control at the Glover Farm in Lubbock, TX
2010...... 58
viii Texas Tech University, Justin L. Spradley, May 2014
4.4. Palmer amaranth control EPOST and D-EPOST at the Glover
Farm in Lubbock, TX, 2011...... 59
4.5. Palmer amaranth control MPOST and cotton yield at the Glover
Farm in Lubbock, TX 2011...... 60
4.6. Palmer amaranth control at Lorenzo, TX 2012...... 61
4.7. Red morningglory control at Lorenzo, TX 2012...... 62
4.8. Palmer amaranth control at the Glover Farm in Lubbock, TX
2012...... 63
4.9. Devil's-claw control at the Glover Farm in Lubbock, TX 2012...... 64
4.10. Palmer amaranth control (Morningglory I trial) on the Texas
A&M AgriLife Research and Extension Center field 301
Lubbock, TX 2012...... 65
4.11. Ivyleaf morningglory control (Morningglory I trial) on the Texas
A&M AgriLife Research and Extension Center field 301
Lubbock, TX 2012...... 66
4.12. Ivyleaf morningglory control (Morningglory II trial) on the
Texas A&M AgriLife Research and Extension Center
field 301 Lubbock, TX 2012...... 67
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CHAPTER I
INTRODUCTION
The Texas High Plains (THP) is the largest cotton (Gossypium hirsutum L.) growing region in the United States. From 2010 to 2012, this region accounted for approximately 33% of the cotton hectares planted and 20% of the total bales were produced in the country (NASS 2013). Production in this region varied from 5.3 million bales in 2010 to 1.83 million bales in 2011. According to Roy (2011), approximately 50% of cotton hectares planted on the THP were abandoned in 2011due to a record-breaking drought. Cotton production increased to 2.92 million bales in
2012 an increase of 1.09 million bales over 2011.
Cotton producers on the THP traditionally rely on preplant incorporated (PPI) and preemergence (PRE) herbicides with in-season cultivation to control weeds.
Current management strategies for control of Amaranthus spp. and Ipomoea spp. depend on cultivation and chemical methods (Reed 2012). With the development of
Roundup Ready® (glyphosate-tolerant) cotton in 1997, effective control of many troublesome annual and perennial weeds was achieved with postemergence-topical
(POST) and postemergence-directed (PDIR) applications of glyphosate. Joy et al.
(2008) found that glyphosate POST effectively controlled Palmer amaranth, devil’s- claw, ivyleaf morningglory, and silverleaf nightshade on the THP. Due to the effectiveness of glyphosate POST, the use of residual herbicides and cultivation has declined. In the past 10 years, cultivation has declined on farms in the THP.
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In 2006, Roundup Ready® Flex cotton was registered in the United States
(Cerny et al. 2010), allowing POST glyphosate applications throughout the growing season. Such applications further reduce the need for residual herbicides and cultivation. It was estimated that 97% of United States cotton hectares and 90% of
THP cotton hectares was planted with glyphosate-tolerant varieties in 2012 (USDA-
AMS 2012). GlyTol® cotton varieties, which contain genes that confer glyphosate tolerance in both vegetative and reproductive tissues was released by Bayer
CropScience in 2011 (Reed 2012). Cultivars containing bialaphos resistance from incertion of the (BAR) gene were commercially released in 2004 and branded
“LibertyLink®” cotton by Bayer CropScience (Devine et al. 1993). In 2011, less than
3% of cotton hectares planted in the United States was LibertyLink® cultivars.
GlyTol® + LibertyLink® technology followed that same year, offering similar opportunities to manage glyphosate-resistant weeds with an alternative mode of action
(Anonymous 2011). Bollgard II® XtendFlexTM is the latest technology by Monsanto allowing for additional modes of action to combat the rising glyphosate resistant issues.
In Texas alone, Amaranthus spp. infests approximately 2 million hectares of cropland (Byrd 2000). Palmer amaranth (Amaranthus palmeri S. Wats.) has been the dominant problem weed on the THP for many years. Amaranthus spp. has been one of the top five weed pests in the United States cotton resulting in significant yield losses annually. Cotton weed control programs are often designed to first control
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Palmer amaranth followed by other weed species of less importance. Control of
Palmer amaranth with glyphosate is highly effective, but current recommendations encourage use of a soil-applied residual herbicide in a glyphosate-based system to prevent the development of resistant weeds (Reed 2012). The identification of glyphosate-resistant Palmer amaranth biotypes in this region in 2011 has led cotton producers to re-evaluate weed management programs that relied exclusively on glyphosate, and return to using a system of residual herbicides and cultivation.
New technologies such as GlyTol® + LibertyLink® and Bollgard II®
XtendFlexTM cotton cultivars can be an important component to manage increasing numbers of glyphosate-resistant Palmer amaranth. Season-long control (90%) of glyphosate resistant Palmer amaranth required application of glufosinate, dicamba, or tank-mixes thereof in a timely manner (less than 15 to 20 cm in height) (Dodds et al.
2012). The objectives of these studies were to evaluate potential of PRE and POST dicamba applications in dicamba tolerant (Bollgard II® XtendFlexTM) cotton for control of problem weeds in the area, including Palmer amaranth, devil’s-claw
(Proboscidea louisianica Thell.), and ivyleaf morningglory (Ipomoea hederacea
Jacq.).
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CHAPTER II
LITERATURE REVIEW
History of Weed Management in Cotton
Weeds are defined as any plant growing where they are not wanted (Zimdahl
2007). As the definition implies, weeds affect crops and can include native or non- native species (Verheye 2010). In human agricultural pursuits, mankind has contended with undesirable species of plants (Robbins et al. 1942). Such unwanted plants interfere with agricultural operations, increase labor, add to costs, and reduce yields (Robbins et al. 1942).
Palmer amaranth (Amaranthus palmeri S. Wats.) and devil’s-claw
(Proboscidea louisianica Thell.) are native to North America; whereas silverleaf nightshade (Solanum elaeagnifolium Cav.) is native to South America (Bryson and
DeFelice 2009). Less than 3,000 of the more than 30,000 species of plants found throughout the world are considered weeds in any crop (Buchanan 1992). Weeds may reduce seed cotton yields, quality of cotton fiber, and increase production costs (costs of hand weeding, mechanical tillage, fertilizer, and herbicides). They can impede efficient irrigation and water management, reduce market value of the land, serve as hosts and habitats for insects, disease-causing organisms, nematodes, rodents, and may cause allergenic reactions in humans (Shaw 1964).
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Weed control received little attention and was poorly researched until the late
1800’s and early 1900’s (Verheye 2010). During this time weed control was accomplished with seedbed preparation (Kelton and Price 2011). This was accomplished with very little equipment and intensive labor.
Weeds may be classified as annuals, biennials, and perennials. An annual is a plant that completes its life cycle from seed to seed in less than one year or in one growing season. Summer annuals germinate in spring, grow in summer, flower, and then die in fall; thus, go from seed to seed in one growing season. Examples of annual weeds are common cocklebur (Xanthium strumarium L.) and redroot pigweed
(Amaranthus retroflexus L.). Biennials live more than one but not more than two years, and examples are musk thistle (Carduus nutans L.) and common mullein
(Verbascum thapsus L.). Perennials are usually divided into two groups: simple and creeping. Simple perennials spread by seed and by vegetative reproduction and my regenerate from damaged shoots (Zimdahl 2007). Two simple perennials found on the
THP are common dandelion (Taraxacum officinale F.H Wigg.) and curly dock (Rumex crispus L.). Creeping perennials such as field bindweed (Convolvulus arvensis L.) reproduce by seed and by vegetative reproductive organs that include stolons, rhizomes, tubers, aerial bulblets, and bulbs (Zimdahl 2007).
Some examples of weeds that were troublesome in the 1800’s and early 1900’s were Canada thistle (Cirsium arvense L.), buffalobur (Solanum rostratum Dunal), horseweed (Conyza canadensis L.), cutleaf nightshade (Solanum triflorum Nutt.), and 5 Texas Tech University, Justin L. Spradley, May, 2014
tumbling pigweed (Amaranthus albus L.). Many weed species were brought to the
United States from other countries. These weeds include, but are not limited to puncturevine (Tribulus terrestris L.), johnsongrass (Sorghum halepense L.), and field bindweed (Convolvulus arvensis L.). Later, weeds such as Russian thistle (Salsola iberica Sennen & Pau), kochia (Kochia scoparia L.), ivyleaf morningglory (Ipomoea hederacea Jacq.), Palmer amaranth (Amaranthus palmeri S. Wats.), woollyleaf bursage (Ambrosia grayi A. Nels.), and Texas blueweed (Helianthus ciliaris DC.) became troublesome weeds (Reed 2012).
In general, weed species are prolific seed producers and allow for large amounts of seed, allowing for high germination and plant numbers in a field (Robbins et al. 1942). They grow easily in drought conditions and in different soil types. These plants may also live for long periods of time and spread rapidly. Weeds vary in size, form, and behavior (Robbins et al. 1942). These different attributes help weeds to survive in cultivated crops. Higher water uptake and development of larger canopy for light interception are the result of weeds growing fast. The faster a weed grows the faster it can form a canopy over a crop and shade desirable plant species. Some weeds are closely related to crop species, and a number of species that are weedy in certain situations may be useful forage plants in others (Robbins et al. 1942).
Weeds can adapt to different conditions for suitable growth and development as well as seed dispersal. Seeds can be dispersed by wind, water, animals, humans, or other forms of movement that promote seed relocation. With several weed species, 6 Texas Tech University, Justin L. Spradley, May, 2014
the seeds are structured such that wind can easily carry them across fields. The species that have an umbel inflorescence seed head is an example of seed easily carried by the wind. Some weeds have hooks or spines that can stick to animal fur and humans, and can be dispersed by means other than wind. Tumbleweeds exhibit special adaptation for seed dispersal by wind. Typical tumbleweeds, such as Russian thistle and tumbling pigweed (Amaranthus albus L.), are comprised of many branches and are rounded in outline. When mature, these plants break off near the soil-line base and the entire plant rolls or “tumbles” with the wind, scattering its seeds as it travels
(Robbins et al. 1942).
Water is another method of seed dispersal. Irrigation water is a most important factor in the dissemination of weed seed in the irrigated sections of the western states
(Robbins et al. 1942). Irrigation water will relocate seeds to lower lying areas of the field. Furrow watering will allow weeds to germinate heavily in the furrows making cultivation difficult.
Seeds of different weed species can remain dormant for a long period of time, thus ensuring the survival of the species over time. Under conditions favorable to germination, only a fraction of seeds may germinate the first year; whereas many may remain dormant and germinate in succeeding years (Robbins et al. 1942). Seeds that become buried deep in the soil may survive for many years. Many weeds have the ability to survive adverse conditions, and may reproduce under harsh climatic and soil conditions that are too severe for the crop plants (Robbins et al. 1942). 7 Texas Tech University, Justin L. Spradley, May, 2014
There are limited methods of weed removal that were utilized to control weed populations in different fields throughout the 1800’s. A few of the methods include mechanical, biological, and chemical. Mechanical methods of weed control include manual labor, such as hand pulling and hoeing. Physical removal of weeds by soil disturbance prior to planting, and by hoeing and hand-weeding during crop growth are undoubtedly the oldest forms of agricultural weed management (Liebman 2001).
Jethro Tull was the first to design a weed control method of soil disturbance in order to allow crop plants to gain the nutrients they needed (Timmons 2005). Later in the
1800’s horse drawn plows were used to till the ground for weed control.
Biological control utilizes a pest with nature to introduced enemies (Zimdahl
2007). It can be successful over the long term because once an organism is released it may be self-perpetuating, and control will continue without further human intervention. An advantage of biological control is it doesn’t require chemicals, but a disadvantage would be that results are slow and not guaranteed (Zimdahl 2007).
Chemicals have been used since the 1950’s to control weeds. Chemical control is killing pests with chemicals. An advantage is the reduction of energy cost compared to mechanical control. Some disadvantages are non-target damage which could consist of killing beneficial organisms. Chemicals are high in cost and this hurts the producer financially. One of the most current disadvantages is selection of resistant weeds over time and potential crop injury following application. Salt, ash, and various industrial by-products have been applied to roadsides, fence rows, and 8 Texas Tech University, Justin L. Spradley, May, 2014
pathways to rid them of vegetation (Robbins et al. 1942). Selective herbicidal action was unknown at this point. Little progress was made in the scientific investigation or the practical use of herbicides until the latter part of the nineteenth century; however, the newly developing science of chemistry eventually found many applications in industry and agriculture (Robbins et al. 1942). The Bordeaux mixture which is comprised of sulfur and lime together in water was discovered for use in plant diseases, especially fungi. Copper salts have also been used to control broadleaf weeds.
By 1900, solutions of sodium nitrate, ammonium sulphate, and potassium salts were successful as selective herbicides, and the practice of spraying for the control of mustards and other common grain weeds soon spread throughout Europe and the
British Isles (Robbins et al. 1942). Changes in weed management practices accelerated after the 1930’s. The validity of the discipline of weed science was boosted with the synthesis of 2,4-D (2,4-dichlorophenoxyacetic acid) in 1941. When
2,4-D appeared on the market, it offered users an inexpensive option of weed control that could be applied at relatively low rates and in many agricultural settings (Ross and Lembi 1999).
Rotation practices were largely replaced by monoculture systems and chemical weed control by the 1940’s (Appleby 2005); however, crop rotation had become an integral part of weed management in organic farming, as well as integrated weed management practices in conventional farming systems. In the United States, row 9 Texas Tech University, Justin L. Spradley, May, 2014
cropping began with horse drawn equipment, which made management of weeds easier in the field. Farmers could remove weeds in the furrows next to the crop, allowing the crop access to water and nutrients needed for survival. Row cropping became the standard practice of farming especially after advances in machinery technology. In the mid 1940’s, new types of equipment such as cultivators, shredders, disks, listers, moldboard plows, and sweeps replaced hand-labor and improved the amount and type of work that could be done in cotton fields (Smith 1950). The use of farm laborers started to diminish about this time as farm machinery started to take the jobs of people. This event changed the economy as manual workers had to go to cities to look for work.
In the 1950’s weed control was the last key needed to complete mechanization of cotton production (McWhorter and Abernathy 1992). The cost of weed control by method of hand hoeing ranged between $494 and $741 an hectare. It was noted that not until manual labor was completely eliminated would the efficiencies and economics inherent in mechanization be fully realized (McWhorter and Abernathy
1992). An integral part of this mechanization was use of preemergence (PRE) chemicals and postemergence (POST) herbicidal oils (Crowe et al. 1953). Dinoseb (2- sec-butyl-4,6-dinitrophenol) is an alkanolamine salt that was used in the early 1950’s as a PRE. Dinoseb treatments were found to injure and kill cotton in several states, so it was not commonly used (McWhorter and Abernathy 1992).
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The first herbicide treatment recommended for weed control in cotton was postemergence-directed (PDIR) sprays of herbicidal oils, such as naphthas in 1950
(Talley 1950). These compounds are petroleum-based comprised of 18 to 25% aromatic structures and were extremely effective at the time; however management was difficult as the sides of the beds had to remain flat and undisturbed for the duration of the crop season. Furthermore, rainfall would delay application of oils rendering control less effective. The cost of the herbicide was about 5 to 7 cents per liter, but the rising cost of petroleum caused this herbicide to diminish at the end of the
1950’s and 1960’s (McWhorter and Abernathy 1992).
Chlorpropham [1-methylethyl N-(3-chlorophenyl) carbamate], diuron [N’-(3,4- dichlorophenyl)-N,N-dimethylurea], and dalapon (2,2-dichloropropanoic acid) were developed in the 1950’s as selective herbicides. Chlorpropham and dalapon were phytotoxic to cotton and were not used often. Soil applications of diuron, applied PRE at 0.56 to 1.68 kg ai ha-1, provided 70 to 90 % control of a large number of grasses and broadleaf weeds, and the results obtained were usually more consistent and longer lasting than with chlorpropham or dinoseb (McWhorter and Abernathy 1992).
Dicamba (3,6-dichloro-2-methoxybenzoic acid) is a broadleaf herbicide that was not used in cotton. It was invented by S. B. Richter and the United States patent
(3,013,054) was awarded in 1958 (Senseman and Armbrust 2007).
Research and development of new herbicides accelerated in the 1960’s. New herbicides such as DSMA (disodium methylarsonate) [CH3AsNa2O3], MSMA 11 Texas Tech University, Justin L. Spradley, May, 2014
(monosodium methyl arsenic acid) [CH4AsNaO3], norea [3-(3a,4,5,6,7,7a-hexahydro-
4,7-methanoindan-S-yl)-1,1-dirnethyl urea], and trifluralin [2,6-dinitro-N,N-dipropyl-
4-(trifluoromethyl)benzenamine] were developed in 1963. Trifluralin was a PRE herbicide that controlled annual grasses and broadleaf weeds in different crops.
Trifluralin applied preplant incorporated (PPI) before cotton was planted effectively controlled many troublesome broadleaf weed species. Monosodium methyl arsenic acid allowed for POST applications to control annual grasses, johnsongrass, and nutsedge (Cyperus spp.) with minimal crop injury (Buchanan 1992). The arsenicals continued to be used on about 242,800 to 323,750 hectares in Texas from 1965 to
1970 (McWhorter and Abernathy 1992).
Both PRE and POST herbicides were used across all cotton hectares in the southeast and midsouth. During the mid-1970s, five new dinitroanilines herbicides were introduced and competed with the use of trifluralin. Butralin [4-(1,1- dimethylethyl)-N-(methylpropyl)-2-6-dinitro-benzenamine], fluchloralin [N-(2- chlorethyl)-2-6-dinitro-N-propyl-4-(trifluoromethyl)analine], dinitramine [N3,N3- diethyl-2,4-dinitro-6-(trifluoromithyl)-1,3benzenediamine], pendimethalin [N-(1- ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and profluralin [N-
(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine]. All five of these herbicides were similar in soil residual properties and weed control in cotton.
Glyphosate [N-(phosphonomethyl)glycine] was introduced in 1971 and quickly became the most effective material available for spot treatment of johnsongrass and 12 Texas Tech University, Justin L. Spradley, May, 2014
other weeds that escaped PRE and POST treatments (McWhorter and Abernathy
1992). Glyphosate is a highly effective POST herbicide for broadleaf weed control in crops including Palmer amaranth. Keeling et al. (1998) found that glyphosate controlled Palmer amaranth escapes after applications of soil-applied residual herbicides and suppressed perennial weeds in glyphosate-tolerant cotton. These herbicides continued to be used throughout the 1970’s for weed control in cotton.
The 1980’s was a time of economic pressure and adverse weather conditions.
The same herbicides were used during this time and some were discontinued.
Metolachlor [(RS)-2-Chloro-N-(2-ethyl-6-methylphenyl)-N-(1-methoxypropan-2- yl)acetamide], sethoxydim [2-[1-(ethoxyimino)butyl]-5-[2-(ethylithio)propyl]-3- hydroxy-2-cyclohexen-1-one], and fluazifop [(2R)-2-[4-[[5-(trifluoromethyl)-2- pyridinyl]oxy]phenoxy]propanoic acid] were introduced in the 1980’s, but did not replace fluchloralin, dinitramine, and profluralin that were discontinued in terms of hectares covered on the THP (McWhorter and Abernathy 1992).
Scientists began developing genetically-modified (GM) herbicide-tolerant cotton cultivars in 1995 (Anonymous 2014). Tobacco (Nicotiana tabacum L.) was the first GM plant that was tolerant to herbicides (Fralye et al. 1983). The first genetically modified tobacco field trials were conducted in France and the United States in 1986
(James and Krattiger 1996). Tomatoes (Solanum lycopersicum L.), potatoes (Solanum tuberosum L.), and rapeseed (Brassica napus L.) were other crops under GM development (James and Krattiger 1996). 13 Texas Tech University, Justin L. Spradley, May, 2014
Glyphosate-resistant cotton cultivars were released for commercial use in 1997 with enhanced glyphosate-resistant cultivars released in 2006 (Cerny et al. 2010). In
2010, Roundup Ready® cotton cultivars were planted to over 91% of cotton hectares in the United States (USDA-AMS 2010). The ammonium salt of glufosinate was reported as an herbicide in 1981 (Senseman and Armbrust 2007). Ammonium salt of glufosinate is classified as an amino acid inhibitor, which inhibits glutamine synthetase activity and restricts the production of glutamine, the enzyme that converts glutamate and ammonia to glutamine. It is applied POST and is a non-selective herbicide that controls a broad spectrum of annual and perennial grass and broadleaf weeds.
Palmer amaranth
Palmer amaranth is one of the most troublesome, economically, and yield damaging agronomic weeds (Ward et al. 2013). Numerous factors have enabled
Palmer amaranth to become such a dominant and difficult-to-control weed, including its rapid growth rate, high fecundity, genetic diversity, and its ability to tolerate adverse conditions. (Ward et al. 2013).
Palmer amaranth is an annual forb capable of growing 2 m tall and native to the area encompassing northwestern Mexico and southern California to New Mexico and Texas (Sauer 1957). Palmer amaranth started to spread beyond its original range in the early 20th century, probably because of human activity transporting seeds or
14 Texas Tech University, Justin L. Spradley, May, 2014
creating new habitats through agricultural expansion. It was first reported in Virginia in 1915, Oklahoma in 1926, and Southern Carolina in 1957 (Culpepper et al. 2010).
The genus Amaranthus belongs to the family Amaranthaceae and contains approximately 75 species worldwide (Ward et al. 2013). Palmer amaranth is one of the distinct subgroup of 10 dioecious species within Amaranthus that are native only to North America (Steckel 2007). Because of its large and aggressive growth, Palmer amaranth detrimentally affects crops growth and yield by competing effectively for light, water, space, and nutrients (Rowland et al. 1999). It can produce hundreds of thousands of seed per plant, which may remain dormant in the soil for years (Keeley et al. 1986). The amount of time seed lay dormant is hard to determine because of factors such as light, dark, time, moisture, and temperature.
A survey conducted in 1995 reported that the Amaranthus genus infested approximately 33,600 ha of Oklahoma cotton and caused a 13% lint yield reduction
(Byrd et al. 1996). In Texas, annual yield loss has ranged from as high as 38% in
1980 to recent estimates of 12% in 2001 (Byrd et al. 1996).
Ivyleaf Morningglory
Ivyleaf morningglory is a climbing, twisting, and tangling annual member of the family Convolvulaceae (Reed 2012). Stems are usually highly branched and can grow up to three meters long. This plant is distinguished by its pubescent leaves and stems, blue to purplish flowers, long sepals, and lobed leaves (Bryson and DeFelice
15 Texas Tech University, Justin L. Spradley, May, 2014
2009). It will intertwine itself around cotton stalks, stems, and leaves and finally out- compete cotton plants. Ipomoea species have been cited as one of the most common and most troublesome weeds in United States cotton production since at least 1973
(Murray et al. 1992). Since 1978, species have been one of the top five most abundant weeds in United States cotton production with annual yield losses ranging from 9 to
21% (Reed 2012).
Ivyleaf morningglory causes severe yield loss in cotton, as well as making harvest difficult if not impossible. Keeley et al. (1986) reported that 1 plant per 2 m of row caused total crop loss. Lint yield reductions of 5.9% were recorded at Perkins for each weed up to 10 m (Rogers et al. 1996). Morningglory plants that emerged in June caused an 11% reduction in yield. At densities greater than 8 plants per meter, mechanical harvest was not possible (Rogers et al. 1996).
Common cotton preplant herbicide programs do not easily control morningglory species. Preplant incorporated and PRE followed by POST and PDIR are among the most effective ways to control morningglory during the season.
Herbicides such as prometryn [N,N’-bis(1-methylethyl)-6-(methylthio)-1,3,5-triazine-
2,4-diamine], diuron [N’-(3,4-dichlorophenyl)-N,N-dimethylurea], linuron [N’-(3,4- dichlorophenyl)-N-methoxy-N-methylurea], fluometuron [[N,N-dimethyl-N’-[3- trifluoromethyl)phenyl]urea]], pyrithiobac-sodium [[sodium 2-chloro-6-[(4,6- dimethoxy-2-pyrimidinyl)thio]benzoic acid]] , oxyfluorfen [2-chloro-1-(3-ethoxy-4- nitrophenoxy)-4-(trifluoromethyl)benzene], clomazone [[2-[(2-chlorophenyl)methyl]- 16 Texas Tech University, Justin L. Spradley, May, 2014
4,4-dimethyl-3-isoxazolidinone]], lactofen [2-ethoxy-1-methyl-2-oxoethyl 5-[2- chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate], fomesafen [5-[2-chloro-4-
(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide], flumioxazin [2-[7- fluoro-3,4-dihydro-3-oxo-4-(2-propynyl)-2H-1,4-benzoxazin-6-yl]-4,5,6,7-tetrahydro-
1H-isoindole-1,3(2H)-dione], and trifloxysulfuron [[N-[(4,6-dimethoxy-2- pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-2-pyridinesulfonamide]] may be used to control morningglories, but generally must be applied PPI, PRE or PDIR and have the potential to injure cotton if applied to coarse soils or unfavorable environmental conditions (Reed 2012). Residual effects may injure crops planted in years later after some of these herbicides are applied. Preplant incorporated and PRE applications are beneficial for morningglory control later in the season.
Glyphosate-tolerant Cotton
Glyphosate is a non-selective POST herbicide that has been used to control over 300 annual, perennial, and biennial herbaceous grasses, sedges, and broadleaf weeds as well as woody brush and trees for more than 30 year period Franz et al.
(1997) noted that glyphosate controls 74 of the 76 world’s worst weeds (Holm et al.
1977). Glyphosate is available in many formulations, such as isopropylamine salt, potassium salt, ammonium salt, diammonium salt, and sesquisodium salts and as an acid. Adjuvants may alter activity biologically depending on the formulation type.
17 Texas Tech University, Justin L. Spradley, May, 2014
Glyphosate competes with the substrate phosphoenolpyruvate (PEP) at the 5- enolpyruvylshikimate-3-phosphate synthase (EPSPS) (EC 2.5.1.26) enzyme-binding site in the chloroplast to inhibit the shikimate pathway (Green 2007). Essential aromatic amino acids tryptophan, tyrosine, and phenylalanine are products of the shikimate pathway (Green 2007). The mode of action of glyphosate is slow. This causes phytotoxcity to be slow, which results in effective translocation of the herbicide throughout the plant. When the shikimate pathway is deregulated plant death occurs.
Attempts to discover glyphosate resistance in crops with conventional breeding failed (Padgette et al. 1995) and discovery of a glyphosate-resistant EPSPS with sufficient catalytic activity to provide adequate functioning was very difficult (Kishore et al. 1992). A more successful method is the CP4 gene that was found from an
Agrobacterium, which is the source of resistance in glyphosate-resistant crops.
Concerns about the sustainability of weed control programs have been a major issue for herbicide-resistant crop systems (Green 2007). Weeds will eventually circumvent any control strategy (Shaner 2000). Growers that make numerous applications of glyphosate year after year on the same field lead to resistance. This is done because glyphosate has a large range of crop use. This intensive use of glyphosate across wide areas has resulted in extremely high selection pressure and aided the evolution of glyphosate-resistant weeds (Culpepper 2006). Producers must implement other means of weed control such as use of other herbicides modes of
18 Texas Tech University, Justin L. Spradley, May, 2014
action or other systems in order to cut down on glyphosate resistance. Control tactics cannot stay static and remain effective.
The first transgenic cotton cultivars became commercially available in 1995 with the introduction of bromoxynil [3,5-dibromo-4-hydroxybenzonitrile] herbicide- resistant cultivars BXN 57 and BXN 58 (Collins 1996). Glyphosate-tolerant cotton
(MON 1445) was available in 1996 followed by the introduction of Roundup Ready® cotton in 1997 (Reed 2012). When applications of glyphosate applied over the top of
Roundup Ready® cotton, yield loss would not occur unless glyphosate was applied after the fourth leaf stage (Reed 2012). This technology led to a reduction in cultivation, but did not eliminate it for producers. In 2006, Roundup Ready® Flex cotton was fully approved and released in the United States (Cerny et al. 2010).
Roundup Ready® Flex cotton is a cultivar that producers may apply glyphosate over the top of the crop at any stage and yield loss will not occur. This variety was derived after further research which evaluated enhanced EPSP synthase expression. This research was done so glyphosate could be applied over the top of cotton at any leaf stage for greater weed control throughout the season. This cultivar selection is more beneficial because the technology is utilized for a longer period and less machinery across a field is necessary.
GlyTol® cotton cultivars were released in 2011. This technology also gives producers flexibility with application timings. GlyTol® cultivars arose from events that also had glyphosate tolerance in both vegetative and reproductive tissues but used 19 Texas Tech University, Justin L. Spradley, May, 2014
a double mutant 5-enol pyruvylshikimate-3-phosphate synthase (2mEPSPS) gene to encode for the double mutant 5-enol pyruvylshikimate-3-phosphate synthase
(2mEPSPS) protein (Reed 2012).
Several million hectares of transgenic cotton has been planted in the United
States since 1997. Glyphosate resistance became well-known because of its ease of use and wide range of weed control. Reported POST applications of glyphosate effectively controlled Palmer amaranth, devil’s-claw, ivyleaf morningglory, and silverleaf nightshade in West Texas (Joy et al. 2008). Glyphosate resistance cultivars are stepping stones leading into the cotton transgenic world.
Glufosinate-tolerant Cotton
Glufosinate is a non-selective POST herbicide commonly used for the control of most annual and perennial grasses and broadleaf weeds (Ahrens et al. 1994).
Glufosinate is a POST herbicide that produces its toxic effect to plants by inhibiting glutamine synthetase (Wendler et al. 1990; Wild and Wendler 1991). Inhibition of this enzyme causes a buildup of ammonia, injury symptoms within 3 to 5 days, and ultimately plant death (Steckel et al. 1997). Glufosinate is an amino acid inhibitor.
Both ammonia buildup and the eventual disruption of photosystem I and photosystem
II reactions cause the decoupling of photophosphorylation and cell membrane lipid peroxidation and eventually plant death (Senseman and Armbrust 2007).
20 Texas Tech University, Justin L. Spradley, May, 2014
Herbicide translocation within the plant is especially important for control of older plants or perennial species (Steckel et al. 1997). Glufosinate has a phosphoric acid group similar to glyphosate, but has been reported to have limited movement in the phloem because it causes rapid phytotoxcity (Bromilow et al. 1993).
Glufosinate tolerance was achieved by insertion and expression of the bialaphos resistance gene (bar gene) isolated from Streptomyces hygroscopicus (Blair-
Kerth et al. 2001). The bar gene, which is responsible for coding for the phosphinothricin acetyl transferase (PAT) enzyme, detoxifies the L-isomer of glufosinate into an inactive acetylated derivative (Tsaftaris 1996). The bar gene was introduced into cotton Coker 312 using Agrobacterium-mediated infection. The
Tobacco Mosaic Virus played a role in the gene code for cotton Coker 312. In 1997, the bar gene was successfully inserted in ‘Coker 312’ cotton and the resulting cultivar was found to be highly tolerant to topical applications of glufosinate (Blair-Kerth et al.
2001).
LibertyLink® cotton came on the market in 2004 (Reed 2012). Cultivars
LibertyLink® and WideStrike® were tested for over the top applications of glufosinate.
Injury up to 30% has been reported from over-the-top applications of glufosinate on
WideStrike® cultivars (Culpepper et al. 2009). Bayer CropScience, as well as other agencies, do not recommend applying glufosinate to WideStrike® cultivars due to injury.
21 Texas Tech University, Justin L. Spradley, May, 2014
Cotton cultivars containing both GlyTol® and LibertyLink® traits were developed and commercialized as GlyTol® + LibertyLink® (GL) cotton in 2011 (Reed
2012). GlyTol® + LibertyLink® cultivars introduced a broader spectrum of weed control. This technology combines the use of glyphosate and glufosinate in one cultivar. These herbicides may be applied over the top of the crop and no injury or yield loss will occur (Reed 2012). They may be applied alone or in a combination giving another tool that should delay the development of glyphosate-resistant weeds
(Reed 2012). The use of both of these herbicides helps with both Palmer amaranth and morningglory species in the same fields. Glufosinate may not have the same efficacy on the THP as in some regions of the United States that have a higher relative humidity level. Low relative humidity decreased control of Palmer amaranth, redroot pigweed (Amaranthus retroflexus L.), and common waterhemp (Amaranthus rudis
Sauer) by glufosinate (Coetzer et al. 2009).
Dicamba-tolerant Cotton
Dicamba is a benzoic acid derivative. It can be applied preplant and PRE at
0.56 kg ae/ha in corn, POST at 0.28 kg ae/ha in corn and sorghum, preharvest in sorghum at 0.28 kg ae/ha (Texas and Oklahoma only), POST at 0.07 to 0.14 kg ae/ha in small grains POST at 0.28 to 2.24 kg ae/ha in pasture and rangeland, POST at 0.28 to 0.56 kg ae/ha in asparagus (California, Oregon, and Washington only), and POST at
0.28 to 1.1 kg ae/ha in turf (Senseman and Armbrust 2007).
22 Texas Tech University, Justin L. Spradley, May, 2014
Dicamba has a mechanism of action similar to that of endogenous auxins indole acetic acid (IAA), but the true mechanism is not well understood. The specific cellular or molecular binding site relevant to the action of IAA and the auxin- mimicking herbicides has not been identified (Senseman and Armbrust 2007). The primary action of these compounds appears to affect cell wall plasticity and nucleic acid metabolism (Senseman and Armbrust 2007).
Dicamba is absorbed through the roots, stems, and leaves. It is translocated symplasticly and apoplasticly and accumulates in the growing points. Plants will show twisting and curling of the leaves and petioles. This herbicide has a residual that will last approximately a week, but this is very dependent on soil moisture and temperature. Dicamba has a half-life of <14 days under conditions amenable to rapid metabolism (Senseman and Armbrust 2007).
It has been only in the last few years that research has been done in dicamba tolerant cotton. There is a cultivar being researched that has a triple stacked gene
Bollgard II® XtendFlexTM, this is for the purpose of even broader spectrums of weed control. These cultivars may come on the market between 2015 and 2016.
Glyphosate-resistant Palmer amaranth can be controlled with these different modes of action. Use of the dicamba resistance trait alone or in combination with other herbicide resistance traits will allow rotation of herbicides or use of mixtures of herbicides that will greatly suppress several present or future herbicide-resistant weeds
(Behrens et al. 2007). Researchers at the University of Nebraska discovered the gene 23 Texas Tech University, Justin L. Spradley, May, 2014
that provides tolerance to dicamba in broadleaf agronomic crops. These researchers isolated soil bacteria at a dicamba manufacturing plant that detoxifies dicamba. This gene is known as the dicamba monooxygenase (DMO) gene and has imparted tolerance to dicamba of up to 5.6 kg ai ha-1 in soybeans and up to 28 kg ai ha-1 in tobacco (Behrens et al. 2007).
Dicamba/glyphosate/glufosinate tolerant cotton demonstrated excellent tolerance to dicamba, glufosinate, and glyphosate alone and in tank-mixture (Dodds et al. 2012). Season-long control (90%) of glyphosate-resistant Palmer amaranth required applications of glufosinate, dicamba, or tank-mixes thereof in a timely manner (less than 15 to 20 cm in height) (Dodds et al. 2012). Residual herbicides will be vital for a total resistant weed control program. Therefore, the objectives of the studies were to 1) evaluate dicamba applied PRE and POST alone or in combination with glufosinate or glyphosate for Palmer amaranth, devil’s-claw, and ivyleaf morningglory control in Bollgard II® XtendFlexTM cotton, 2) compare Palmer amaranth control with dicamba-based treatments in Bollgard II® XtendFlexTM cotton to standard weed management programs in cotton, and 3) determine cotton response and lint yield in Bollgard II® XtendFlexTM cotton.
24 Texas Tech University, Justin L. Spradley, May, 2014
CHAPTER III
MATERIALS AND METHODS
Field Studies
Field trials were conducted in 2010, 2011, and 2012 at the Texas A&M
AgriLife Research and Extension Center in Lubbock, TX and near Lorenzo, TX in
2012 to assess Palmer amaranth (Amaranthus palmeri S. Wats.) and ivyleaf morningglory (Ipomoea hederacea L.) control in Bollgard II® XtendFlexTM cotton.
Evaluations were made to plots with or without trifluralin [2,6-dinitro-N,N-dipropyl-4-
(trifluoromethyl(benzenamine)] preplant incorporated (PPI) followed by (fb) dicamba
[3,6-dichloro-2-methoxybenzoic acid], glufosinate-ammonium [2-amino-4-
(hydroxymethylphosphinyl)butanoic acid monoammonium salt], or glyphosate [N-
(phosphonomethyl)glycine] applied either alone or tank-mix in different combinations.
Preemergence (PRE) treatments included glyphosate and dicamba alone and in combination. The treatments that followed a PRE application were applied at timings that included early-postemergence (EPOST), delayed early-postemergence (D-
EPOST), postemergence (POST), mid-postemergence (MPOST), and layby.
The soil at the Lubbock trial locations is Acuff clay loam, with organic matter
<1% and pH 7.9. The soil at Lorenzo is Amarillo fine sandy loam, with organic matter 0.8% and pH 7.8. Bollgard II® XtendFlexTM cotton was planted at a depth of
25 Texas Tech University, Justin L. Spradley, May, 2014
3.8 cm on 102 cm rows. Planting dates were May 12 in 2010, May 23 in 2011, and
May 9 in 2012 at Lubbock. The planting date at Lorenzo, TX was May 25, 2012.
Plots, 4 rows by 11 m in length, were arranged in a randomized complete block design with 4 replications. Rainfall amounts totaled 695 mm in 2010, 172 mm in
2011, and 251 mm in 2012. Additional irrigation was applied in all years, except
2010. In 2011, due to record low rainfall 406 mm of irrigation was applied in-furrow to produce the crop. In 2012, rainfall was below average and 305 mm of irrigation was applied (Table 3.1).
Herbicide applications were made using a tractor-mounted, compressed-air or
-1 CO2-pressurized backpack sprayer, calibrated to deliver 150 L ha . Sprayers were equipped with Air Induction Extended Range (AIXR TeeJet®) 11002 flat fan nozzles
(Spraying Systems Co., North Avenue Glendale Heights, IL 60139). These nozzles provided medium droplet size to reduce drift. All applications were made at 5 km/hr at 241 kPa. Herbicide applications and timings are summarized in (Tables 3.1 to 3.7).
Palmer amaranth, devil’s-claw, and silverleaf nightshade control 2010
Palmer amaranth treatments in 2010 included glyphosate at 0.87 kg ae ha-1, glufosinate at 0.59 kg ai ha-1, dicamba at 0.56 kg ae ha-1, and a non-treated control.
Glyphosate and dicamba were applied PRE alone or in combination. One treatment contained fomesafen [5-[2-chloro-4-(trifluoromethyl) phenoxy]-N-(methylsulfonyl)-2- nitrobenzamide] at 0.28 kg ai ha-1 14 days before planting. Fluometuron [N,N-
26 Texas Tech University, Justin L. Spradley, May, 2014
dimethyl-N’-[3-(trifluoromethyl)phenyl]urea] was applied PRE at 1.12 kg ai ha-1.
Early-postemergence treatments were applied when weed sizes reached 5 to 10 cm in height, whereas D-EPOST and MPOST treatments were applied when weed sizes reached 10 to 15 cm and 15 to 20 cm, respectively. Layby treatments, which included a combination of diuron at 1.12 kg ai ha-1 and MSMA (monosodium methylarsonate) at 2.24 kg ai ha-1, were applied to all plots (Table 4.1). Applications were made when weeds were 10 to 15 cm tall.
Palmer amaranth control 2011
In 2011, Palmer amaranth control treatments included glyphosate at 0.87 kg ae ha-1, glufosinate at 0.42 kg ai ha-1, and dicamba at 0.56 kg ae ha-1. Trifluralin was applied PPI at 0.84 kg ai ha-1 and dicamba was applied PRE at 0.56 kg ae ha-1. One treatment included fluometuron PRE at 1.12 kg ai ha-1 and pyrithiobac-sodium
[sodium 2-chloro-6-[(4,6-dimethoxy-2-pyrimidenyl)thio]benzoic acid] D-EPOST at
0.035 kg ai ha-1. The EPOST and MPOST treatments were applied to weeds at heights of 5 to 10 cm and 10 to 20 cm, respectively (Table 4.4).
Palmer amaranth and red morningglory control 2012
All treatments received a blanket application of trifluralin PPI at 0.84 kg ae ha-1
(Table 4.5). Dicamba was applied PRE at rates of 1X (0.56 kg ai ha-1), 1.5X, and 2X.
Acetochlor (Warrant™) was applied PRE at 1.5 kg ai ha-1 in one treatment and POST
27 Texas Tech University, Justin L. Spradley, May, 2014
and MPOST in other treatments. Glyphosate at 0.87 kg ae ha-1, glufosinate at 0.42 kg ai ha-1, acetochlor 1.26 kg ai ha-1, and dicamba at 0.56 kg ae ha-1 were applied the same as the previously described trials. Weeds were evaluated in this experiment included Palmer amaranth, red morningglory (Ipomoea coccinea L.), and Russian thistle (Salsola iberica Sennen & Pau). Postemergence treatments were applied to weeds 5 to 10 cm in height, whereas MPOST treatments were applied to weeds 10 to
20 cm in height (Table 4.5).
2012 Bollgard II® XtendFlexTM Cotton POST – Palmer amaranth and
devil's-claw control
Trials in 2012 received a PPI application of trifluralin [2,6-dinitro-N,N-
-1 dipropyl-4-(trifluoromethyl)benzenamine] at 0.84 kg ai ha or dicamba at 0.56 kg ae ha-1 or in combination as dicamba + glyphosate at 0.56 + 0.84 kg ha-1 EPOST or
MPOST. Glufosinate at 0.59 kg ai ha-1 and acetochlor at 1.26 kg ai ha-1 were applied
EPOST (Table 4.7). Palmer amaranth height was 5 to 10 cm at the EPOST and
MPOST timings and devil’s-claw (Proboscidea louisianica Thell.) was at 5 to 10 cm at EPOST and 15 to 20 cm at MPOST (Table 3.5).
Ivyleaf morningglory control 2012
Ivyleaf morningglory trials received treatments glyphosate at 0.84 kg ae ha-1, glufosinate at 0.58 kg ai ha-1, and dicamba at 0.56 kg ae ha-1. Trifluralin PPI was
28 Texas Tech University, Justin L. Spradley, May, 2014
applied to the entire morningglory I trial except for the untreated check. It was not applied on any of the plots in the Morningglory II trial. Early-postemergence treatments were applied when ivyleaf morningglory was 5 to 10 cm in height and
MPOST treatments were applied when weeds were 15 to 20 cm in height.
To evaluate control of ivyleaf morningglory, plots received either no PPI or a
PPI application of trifluralin at 0.84 kg ae ha-1 and an EPOST and MPOST treatment.
Preemergence treatments were applied at planting and POST treatments were applied when weeds were 5 to 10 cm in height.
Ivyleaf morningglory trials received a PPI application of trifluralin at 0.84 kg ha-1. Incorporation of PPI herbicide was done with a spring-tooth in a one pass operation at a depth of 13 cm. Postemergence applications were applied later.
Percent weed control was recorded 7, 14, and 21 days after treatment (DAT).
Control was visually estimated using a scale of 0 to 100 with 0 meaning no control and 100 meaning total control as indicated by plant death (Reed 2012). In 2010,
Palmer amaranth density was estimated at 929 cm2 per plot (meaning a 929cm2 device was place in plots and weeds were counted).
Devil’s-claw and silverleaf nightshade (Solanum elaeagnifolium Cav.) assessments were made utilizing the same scale. In 2011, Palmer amaranth assessments and density were recorded and yield recorded. Crops and trials suffered from extreme heat, wind, and lack of moisture in 2011. Weather conditions in 2012 were more closely related to an average year on the THP, where climate and rain were 29 Texas Tech University, Justin L. Spradley, May, 2014
not extreme. Densities of Palmer amaranth, devil’s-claw, red morningglory, ivyleaf morningglory, and Russian thistle were estimated in 2012 enumerating each species in an area two rows by 12.2 m.
Plots were harvested with a John Deere 7445 two-row cotton stripper, which recorded cotton weights from individual plots. The 2011 Palmer amaranth trial was harvested on October 10. Harvest in 2012 was donee on October 5, 2012 for Bollgard
II® XtendFlexTM cotton POST trial and on October 25, 2012 for the evaluation of
POST Treatments trial. Ivyleaf morningglory trials were not harvested.
For all experiments, a univariate analysis was performed on all responses in order to test for s variance. Data were subjected to ANOVA using the GLIMMIX procedure of SAS 9.3 (SAS Institute Inc., SAS Campus Drive, Cary, NC 27513) to determine application differences. Means were separated using GLIMMIX at an alpha level of p=0.05. Replication was considered a random variable in each experiment.
Data were not combined over years due to variable weather conditions each year.
30 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.1. Monthly rainfall distribution for the years 2010, 2011, 2012 and the 30 year average for Lubbock, TX.
Year 2010 2011 2012 30 yr avg mm January 43 4 0 17 February 56 20 17 19 March 77 9 28 27 April 118 0 20 34 May 29 7 38 57 June 65 0 38 81 July 181 1 17 46 August 31 9 22 45 September 24 32 67 65 October 66 34 5 47 November 2 7 0 23 December 0 49 17 22 Total 692 172 269 483 aAbbreviations: mm, millimeters; yr, year; avg, average.
31 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.2. Application description for Palmer amaranth and devil’s-claw control in Bollgard II® XtendFlexTM cotton in 2010.
PREa EPOST D-EPOST MPOST LAYBY
Application date May 12 June 4 June 14 June 21 July 19
Air temperature (°C) 28 27 26 23 23
Relative humidity (%) 31 52 52 72 65
Wind speed (kph) 9 9 3 3 2
Soil temperature (°C) 26 22 27 21 24
Cloud cover (%) 10 0 95 10 0
Palmer amaranth height at - 5 to 10 10 to 15 10 to 20 30 to 35 application (cm)
Devil’s-claw height at application - 5 to 10 10 to 15 15 to 20 20 to 30 (cm)
Crop stage at application - 2-nodes 2 to 4 nodes 6 to 8 nodes midbloom aAbbreviations: PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early-postemergence; MPOST, mid- postemergence; °C, degrees Celsius; kph, kilometers per hour; cm, centimeters. 32 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.3. Application description for Palmer amaranth control in Bollgard II® XtendFlexTM cotton 2011.
PPIa PRE EPOST D-EPOST MPOST LAYBY
Application date April 1 May 23 June 10 June 21 July 5 July 26
Air temperature (°C) 17 34 28 21 28 29
Relative humidity (%) 38 18 48 4 43 31
Wind speed (kph) 8 4 11 12 8 16
Soil temperature (°C) 13 29 28 25 27 26
Cloud cover (%) 0 0 0 0 80 0
Weed height at application - - 5 to 10 10 to 15 5 to 10 5 to 10 (cm)
Crop stage at application - - 2-nodes 2 to 4 nodes 6 to 8 nodes midbloom aAbbreviations: PPI, preplant incorporated; PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early- postemergence; MPOST, mid-postemergence; °C, degrees Celsius; kph, kilometers per hour; cm, centimeters.
33 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.4. Application description for Palmer amaranth and red morningglory in POST treatments in Bollgard II® XtendFlexTM cotton in 2012 (Lorenzo, TX).
PREa EPOST MPOST
Application date May 25 June 26 July 31
Air temperature (°C) 33 37 30
Relative humidity (%) 25 15 47
Wind speed (kph) 6 9 5
Soil temperature (°C) 27 31 25
Cloud cover (%) 5 0 0
Palmer amaranth height at - 5 to 10 5 to 10 application (cm) Red morningglory height at - 2 to 3 5 to 8 application (cm) Crop stage at application - 2-nodes 6 to 8 nodes aAbbreviations: PRE, preemergence; EPOST, early-postemergence; MPOST, mid-postemergence; °C, degrees Celsius; kph, kilometers per hour; cm, centimeters. 34 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.5. Application description for Palmer amaranth and devil’s-claw in Bollgard II® XtendFlexTM cotton POST treatments in 2012 (Glover Farm).
PREa EPOST MPOST
Application date March 28 June 15 July 12
Air temperature (°C) 26 23 28
Relative humidity (%) 49 62 47
Wind speed (kph) 3 16 5
Soil temperature (°C) 26 21 27
Cloud cover (%) 40 5 0
Palmer amaranth height at - 5 to 10 5 to 10 application (cm) Devil’s-claw height at - 5 to 10 15 to 20 application (cm) Crop stage at application - 2-nodes 6 to 8 nodes aAbbreviations: PRE, preemergence; EPOST, early-postemergence; MPOST, mid-postemergence; °C, degrees Celsius; kph, kilometers per hour; cm, centimeters. 35 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.6. Application description for ivyleaf morningglory control in morningglory I trial in 2012.
PREa EPOST MPOST
Application date March 28 June 15 July 12
Air temperature (°C) 26 31 32
Relative humidity (%) 43 44 42
Wind speed (kph) 6 11 5
Soil temperature (°C) 24 23 27
Cloud cover (%) 40 20 10
Ivyleaf morningglory height at - 5 to 10 7 to 10 application (cm) aAbbreviations: PRE, preemergence; EPOST, early-postemergence; MPOST, mid-postemergence; °C, degrees Celsius; kph, kilometers per hour; cm, centimeters.
36 Texas Tech University, Justin L. Spradley, May, 2014
Table 3.7. Application description for ivyleaf morningglory control in morningglory II trial in 2012.
EPOSTa
Application date June 26
Air temperature (°C) 31
Relative humidity (%) 34
Wind speed (kph) 11
Soil temperature (°C) 27
Cloud cover (%) 0
Ivyleaf morningglory height at application (cm) 8 to 10 aAbbreviations: PRE, preemergence; EPOST, early-postemergence; °C, degrees Celsius; kph, kilometers per hour; cm, centimeters.
37 Texas Tech University, Justin L. Spradley, May, 2014
CHAPTER IV
RESULTS AND DISCUSSION
Field Studies
Palmer amaranth Glover 2010
There was an abundance of Palmer amaranth in this trial due to above average rainfall totaling 692 mm in 2010 (Table 3.1). All dicamba PRE treatments controlled
Palmer amaranth 100% at 21 DAT. These results are similar to Samples et al. (2012) who reported all PRE applications containing dicamba resulted in 90 to 99% Palmer amaranth control. Dicamba PRE controlled Palmer amaranth better than glyphosate
PRE (23%) 21 DAT (Table 4.1). Fomesafen at 0.28 kg ha-1 applied 14 days before planting (DBP) and S-metolachlor at 0.87 kg ae ha-1 applied early preplant (EPP) followed by (fb) fluometuron at 1.12 kg ha-1 PRE controlled Palmer amaranth 95 to
99%. Likewise, Samples (2012) reported early preplant applications of fomesafen at
0.14 kg ai ha-1 + dicamba 1.12 kg ai ha-1 resulted in greater than 96% Palmer amaranth
-1 control five weeks after treatment in Mississippi. Dicamba at 0.56 kg ai ha PRE fb glufosinate at 0.59 kg ai ha-1 EPOST controlled Palmer amaranth 99% 7 DAT.
Dicamba PRE fb dicamba EPOST provided complete control. Fomesafen applied 14
DBP fb fluometuron PRE fb glyphosate + S-metolachlor EPOST controlled Palmer amaranth 98% 7 DAT. All treatments of dicamba or glyphosate + dicamba PRE fb 38 Texas Tech University, Justin L. Spradley, May, 2014
glufosinate, dicamba, or glufosinate + dicamba EPOST controlled Palmer amaranth 95 to 100% 7 DAT (Table 4.1).
Dicamba PRE fb glufosinate, dicamba, or a combination of the two EPOST applications provided Palmer amaranth control between 87 and 94% 14 DAT.
Fomesafen applied 14 DBP fb fluometuron PRE fb glyphosate + S-metolachlor
EPOST controlled Palmer amaranth 99%, which was greater than glyphosate + dicamba PRE fb dicamba EPOST fb glufosinate MPOST (81%) 14 DAT (Table 4.1).
Dicamba PRE fb glufosinate EPOST fb glufosinate MPOST controlled Palmer amaranth greater than glyphosate PRE fb dicamba EPOST fb glufosinate MPOST
(68%) 14 DAT. Glyphosate PRE fb glufosinate EPOST fb glufosinate MPOST did not effectively control Palmer amaranth (18%) 14 DAT. In contrast, Barker et al.
(2005) reported that glufosinate provided broad-spectrum control of broadleaf weeds early-season. For example, control of Palmer amaranth was greater than 90% for all
EPOST fb POST treatments except glufosinate fb glufosinate (80%). Glufosinate in combination with dicamba or glyphosate was more effective than glufosinate alone in this case.
Glyphosate + dicamba PRE fb dicamba or glufosinate + dicamba delayed early-postemergence (D-EPOST) controlled Palmer amaranth at least 97% 14 DAT.
This control was greater than the control following S-metolachlor PPI and fluometuron
PRE fb pyrithiobac D-EPOST (91%) 14 DAT. Dicamba and glufosinate + dicamba
D-EPOST resulted in 99% Palmer amaranth control 21 DAT. Glufosinate and 39 Texas Tech University, Justin L. Spradley, May, 2014
pyrithiobac applied D-EPOST were less effective 21 DAT 83 and 88% control, respectively, but Dotray et al. (2007) reported that glufosinate + pyrithiobac applied
EPOST fb glufosinate + pyrithiobac MPOST, and pyrithiobac applied PRE fb sequential glufosinate applications EPOST and MPOST controlled Palmer amaranth at least 95%.
Dicamba alone or in combination with glyphosate or glufosinate fb glufosinate
MPOST resulted in 85 to 96% Palmer amaranth control 7 DAT. Dicamba PRE fb dicamba EPOST fb glufosinate MPOST resulted in 95 and 96% Palmer amaranth control 14 DAT. All treatments that received glufosinate or glyphosate MPOST controlled Palmer amaranth 80 to 92% 14 DAT, except glyphosate PRE fb glufosinate
EPOST fb glufosinate MPOST, which led to 25% control of this weed.
These results indicate that effective (>90%) season-long Palmer amaranth control was achieved when dicamba was applied once PRE or EPOST and fb glufosinate MPOST 14 DAT. This shows the use of this technology may allow control of glyphosate-resistant Palmer amaranth on the THP. This control was greater than glyphosate applied PRE alone or in combination with dicamba fb glufosinate
EPOST and MPOST (80 to 81%) 14 DAT. Similar control (83%) was achieved when glyphosate was applied alone PRE, EPOST, and MPOST 14 DAT. Likewise, glyphosate alone and glyphosate + dicamba PRE fb dicamba EPOST fb glufosinate
MPOST achieved 81 and 88% Palmer amaranth control, respectively. Less effective
40 Texas Tech University, Justin L. Spradley, May, 2014
control (25%) was achieved when glyphosate was applied PRE fb glufosinate EPOST fb glufosinate MPOST 14 DAT.
Devil’s-claw Glover 2010
All EPOST treatments of glufosinate, glyphosate, dicamba, and glufosinate + dicamba controlled devil’s-claw at least 93%, whereas fomesafen applied 14 DBP fb fluometuron PRE fb glyphosate + S-metolachlor EPOST provided 68% control 21
DAT (Table 4.2). Burns et al. (2002) stated that trifluralin fb glufosinate POST controlled devil’s-claw 95%. Glyphosate + dicamba PRE fb glufosinate + dicamba D-
EPOST controlled devil’s-claw 96% 14 DAT (Table 4.2). All other D-EPOST treatments were less effective (<80%) 14 DAT. Glyphosate + dicamba PRE fb glufosinate + dicamba D-EPOST controlled devil’s-claw 89%, which was greater than control achieved following glyphosate + dicamba PRE fb dicamba D-EPOST (56%)
21 DAT (Table 4.2). In contrast, the latter program was reported to provide season- long control (100%) of devil’s-claw in the THP (Joy et al. 2008).
Glyphosate PRE fb glufosinate EPOST fb glufosinate MPOST was 98% effective in controlling devil’s-claw and similar control was observed when the following treatments were applied: glyphosate + dicamba PRE fb glufosinate EPOST fb glufosinate MPOST (93%) 7 DAT. Glyphosate PRE fb glyphosate EPOST fb glyphosate MPOST controlled devil’s-claw 99%, which was more effective than
41 Texas Tech University, Justin L. Spradley, May, 2014
glyphosate alone and glyphosate + dicamba PRE fb glufosinate EPOST fb glufosinate
MPOST (93%) 14 DAT (Table 4.2).
Glyphosate applied PRE, POST, and MPOST achieved the greatest control
≥99% 14 DAT. Greater than 90% season-long control may be achieved with these systems. Glyphosate alone or in combination with dicamba PRE fb glufosinate
EPOST fb glufosinate MPOST was less effective (91 to 93%) 14 DAT
Silverleaf nightshade Glover 2010
When evaluating treatments 21 DAT, ineffective silverleaf nightshade control was observed following fomesafen applied 14 DBP fb fluometuron PRE fb glyphosate
+ S-metolachlor EPOST (averaging 40%). These results are similar to Burns et al.
(2002) who also observed poor silverleaf nightshade control (35%) using trifluralin fb glufosinate. In comparison, plots receiving glyphosate PRE fb glyphosate EPOST controlled silverleaf nightshade 76% (Table 4.3). All other EPOST treatments controlled silverleaf nightshade between 87 to 93% during this timeframe. Sequential applications are needed 21 days after the application EPOST in order to maintain good control. Silverleaf nightshade was controlled 91 to 95% 14 DAT following glyphosate
+ dicamba PRE fb glufosinate and glufosinate + dicamba D-EPOST, respectively.
Control following glyphosate + dicamba PRE fb dicamba D-EPOST was moderately effective (79%). In contrast, Joy et al. (2008) stated that 2003 mid-season control of silverleaf nightshade averaged between 89 to 96% with glyphosate applied as needed.
42 Texas Tech University, Justin L. Spradley, May, 2014
Glyphosate + dicamba PRE fb glufosinate + dicamba or dicamba D-EPOST controlled silverleaf nightshade 70 to 73% 21 DAT. This control was greater than glyphosate + dicamba PRE fb glufosinate D-EPOST (27%).
Silverleaf nightshade control ranged from 85 to 93% for all treatments seven days after the MPOST treatments, except for glyphosate PRE fb glyphosate EPOST fb glyphosate MPOST, which controlled this weed 76%. These results suggest that the addition of dicamba PRE and EPOST may increase control by approximately 9% 7 days after the MPOST application. Dicamba PRE fb glufosinate + dicamba EPOST fb glufosinate MPOST controlled silverleaf nightshade 93 and 83% 7 and 14 DAT, respectively. Silverleaf nightshade control with all treatments was similar 14 DAT and ranged from 65 to 83%. Therefore, in order to achieve greater control, dicamba maybe needed as a tankmix partner with glufosinate MPOST (Table 4.3).
Palmer amaranth 2011
Palmer amaranth was controlled 93 to 99% with dicamba PRE fb glyphosate + dicamba EPOST 14 DAT (Table 4.4). Dicamba PRE fb glyphosate + dicamba
EPOST provided greater control (99%) than glufosinate EPOST with no PRE application (92%). Glufosinate + dicamba EPOST controlled Palmer amaranth 92% whereas the control for dicamba PRE fb dicamba EPOST was less effective (85%) 14
DAT. Glufosinate EPOST or following dicamba PRE controlled this weed 68 to 71%
7 DAT and 50 to 53% 14 DAT, but dicamba PRE fb glufosinate + dicamba EPOST
43 Texas Tech University, Justin L. Spradley, May, 2014
provided 94% control 14 DAT. Similar control (99%) was observed following trifluralin PPI fb glyphosate + dicamba, trifluralin PPI fb glyphosate, dicamba PRE fb glyphosate + dicamba, and glyphosate + dicamba EPOST 14 DAT (Table 4.4).
Trifluralin PPI fb glyphosate + dicamba EPOST resulted in 99% control of Palmer amaranth 14 DAT, and dicamba PRE fb glufosinate + dicamba EPOST controlled this weed 93%. Trifluralin PPI fb glyphosate + dicamba EPOST was 99% effective in controlling Palmer amaranth (Table 4.4).
Trifluralin PPI fb glyphosate + dicamba EPOST and dicamba PRE fb glufosinate + dicamba EPOST controlled Palmer amaranth 98 and 83%, respectively,
21 DAT (Table 4.4). Ineffective control was observed from all programs containing glufosinate EPOST (3%) 21 DAT.
Trifluralin PPI fb fluometuron PRE fb pyrithiobac D-EPOST controlled
Palmer amaranth 80%, 7 DAT (Table 4.4). Dicamba PRE fb glyphosate + dicamba D-
EPOST controlled this weed 93%, 14 DAT. All treatments 21 days after treatment D-
EPOST controlled Palmer amaranth <75%.
Palmer amaranth control 7 to 21 DAT ranged from 93 to 99% for treatments where trifluralin was applied PPI. Trifluralin PPI fb glyphosate + dicamba EPOST fb glyphosate + dicamba MPOST resulted in complete Palmer amaranth control 7, 14, and 21 DAT (Table 4.5). Trifluralin PPI fb glyphosate + dicamba EPOST fb glyphosate + dicamba MPOST controlled Palmer amaranth 99% 7 DAT, which was greater than dicamba PRE fb dicamba EPOST fb glufosinate MPOST (79%). 44 Texas Tech University, Justin L. Spradley, May, 2014
Trifluralin PPI fb glyphosate EPOST fb glyphosate MPOST provided greater control
(99%) than dicamba PRE fb dicamba EPOST fb glufosinate MPOST (76%).
Trifluralin PPI fb glyphosate EPOST fb glyphosate MPOST controlled Palmer amaranth 99% 14 DAT and 95% 21 DAT. Joy et al. (2008) reported that all weed management systems containing glyphosate controlled Palmer amaranth 90 to 100% regardless of application timing or rate. Dicamba PRE fb dicamba EPOST fb glufosinate MPOST controlled this weed 75% 14 and 21 DAT (Table 4.5). Trifluralin
PPI fb glyphosate + dicamba EPOST fb glyphosate + dicamba MPOST and dicamba
PRE fb glyphosate + dicamba EPOST fb glyphosate + dicamba MPOST provided complete Palmer amaranth control whereas glyphosate + dicamba EPOST fb glyphosate MPOST controlled this weed 89% 14 DAT. Dotray et al. (2000) reported that glyphosate controlled Palmer amaranth 85 to 90% late-season. They also found that Palmer amaranth control improved to 94 to 100% when pyrithiobac was tank- mixed with glyphosate. In this study, the three systems listed above had greater control than glufosinate + dicamba EPOST fb glufosinate MPOST. Mid- postemergence applications of glufosinate alone controlled Palmer amaranth < 75% 7,
14, and 21 DAT with the exception of dicamba PRE fb glyphosate + dicamba EPOST fb glufosinate MPOST, which provided 96, 93, and 91% Palmer amaranth control, respectively.
Effective season-long Palmer amaranth control (>94%) was achieved when dicamba was applied PRE fb glufosinate + dicamba EPOST fb glyphosate + dicamba 45 Texas Tech University, Justin L. Spradley, May, 2014
MPOST 21 DAT (Table 4.5). When trifluralin or dicamba was applied PPI or PRE fb glyphosate + dicamba EPOST and MPOST, complete to near complete control was achieved 21 DAT. Trifluralin PPI fb glyphosate EPOST and MPOST provided similar controls (95%) 21 DAT. These results suggest that greater control was observed with glyphosate compared to those that included glufosinate EPOST or
MPOST 21 DAT. Palmer amaranth control following dicamba PRE fb dicamba
EPOST fb glufosinate MPOST was 75% 21 DAT, which was less effective than the preceding treatments. Dicamba PRE fb glufosinate EPOST and MPOST was less effective (34%) than with the addition of dicamba EPOST (59%) 21 DAT. Similar results was observed when glufosinate was applied alone EPOST and MPOST (40%).
46 Texas Tech University, Justin L. Spradley, May, 2014
Plots treated with glyphosate + dicamba EPOST fb glufosinate MPOST yielded 1122 kg ha-1,where Palmer amaranth was controlled 86 to 89% 7, 14, and 21
DAT (Table 4.5). Plots treated with trifluralin PPI fb glyphosate EPOST fb glyphosate MPOST had greater yield (842 kg ha-1) than plots treated with dicamba
PRE fb glufosinate EPOST fb glufosinate MPOST (390 kg ha -1) (Table 4.5). Plots treated with dicamba PRE fb glyphosate + dicamba EPOST fb glufosinate or glyphosate + dicamba MPOST produced an average yield between 872 and 890 kg ha-1. Trifluralin PPI fb fluometuron PRE fb pyrithiobac D-EPOST treated plots yielded 646 kg ha-1, which was greater than yield from plots treated with dicamba PRE
-1 fb dicamba EPOST fb glufosinate MPOST (324 kg ha ). When glufosinate was applied alone EPOST or D-EPOST, plots yielded <390 kg ha-1.
Palmer amaranth Lorenzo, TX 2012
Trifluralin PPI fb an EPOST treatment of glyphosate, glyphosate + dicamba, or glyphosate + dicamba + acetochlor resulted in 96 to 100% control of Palmer amaranth
7, 14, and 21 DAT (Table 4.6). In contrast, Samples et al. (2012) reported that fluometuron, acetochlor, or prometryn alone resulted in less than 75% control of
Palmer amaranth five weeks after treatment. Trifluralin PPI fb dicamba at 1.0X (0.56 kg ai ha-1) to 1.5X PRE controlled Palmer amaranth between 51 and 68% 7 DAT and
57% 21 DAT; whereas trifluralin PRE fb dicamba EPOST at 2.0X rate achieved 83 to
47 Texas Tech University, Justin L. Spradley, May, 2014
87% control 7, 14, and 21 DAT. Trifluralin PPI fb glufosinate EPOST controlled
Palmer amaranth 61 to 65% over these same observation times.
Several treatments containing glyphosate and/or dicamba MPOST provided total control of Palmar amaranth 7 and 14 days after MPOST treatments.
Preemergence treatments with dicamba at 1X, 1.5X, or 2X with or without acetochlor were more effective MPOST than EPOST. Palmer amaranth was controlled 82 to
89% following 1.0X, 1.5X and 2.0X applications of dicamba MPOST 7 DAT.
Trifluralin PPI fb glufosinate EPOST fb glufosinate MPOST was more effective at controlling Palmer amaranth 7 (88%) and 14 (89%) DAT compared to trifluralin PPI fb glufosinate EPOST fb glyphosate MPOST (≤50%).
The results in this trial indicate that trifluralin PPI fb glufosinate alone EPOST and MPOST was less effective (35%) than trifluralin PPI fb glufosinate EPOST fb glyphosate MPOST (89%) 14 DAT. Overall, greater Palmer amaranth control was achieved when glufosinate was combined with trifluralin, glyphosate, dicamba, or acetochlor in any combination PPI, EPOST and MPOST 14 DAT than that of glufosinate alone at those timings. For example, trifluralin PPI fb dicamba + glufosinate EPOST fb glyphosate + dicamba MPOST resulted in total Palmer amaranth control 21 DAT (Table 4.6).
Plots treated with trifluralin PPI fb acetochlor PRE fb glyphosate MPOST yielded 1268 kg ha-1, which was greater than plots treated with trifluralin PPI fb glyphosate EPOST fb glyphosate MPOST (941 kg ha-1) (Table 4.6). Plots treated with 48 Texas Tech University, Justin L. Spradley, May, 2014
trifluralin PPI fb acetochlor PRE fb glyphosate MPOST yielded 1268 kg ha -1, which was greater than trifluralin PPI fb glyphosate + dicamba + acetochlor EPOST fb glyphosate + dicamba MPOST plots (1159 kg ha-1).
Red morningglory Lorenzo, TX 2012
Trifluralin PPI fb glyphosate + dicamba EPOST controlled red morningglory
(Ipomoea coccinea L.) 96 to 98% 7 DAT (Table 4.7). This control was greater than control observed following glufosinate EPOST alone (65%) 7 DAT. Glyphosate + dicamba + acetochlor EPOST resulted in 94 to 97% red morningglory control, which is greater than the control observed following trifluralin PPI fb glyphosate + acetochlor (86%) 7 DAT. These treatments provided similar control 14 (84 to 99%) and 21 DAT (83 to 100%). Trifluralin PPI fb glufosinate EPOST controlled red morningglory 65% 7 DAT, and this combination achieved 58 to 62% and 58 to 63% control 14 and 21 DAT, respectively. Trifluralin PPI fb dicamba at 1.0X, 1.5X, and
2.0X PRE controlled red morningglory 38 to 63% 7 DAT. Likewise, red morningglory control following EPOST treatments were similar 14 (39 to 59%) and 21 DAT (38 to
57%) (Table 4.6). The most effective treatments for red morningglory control were trifluralin PPI fb glyphosate + dicamba + acetochlor EPOST, which resulted 100% control of red morningglory 21 DAT. Trifluralin PPI fb glyphosate EPOST controlled red morningglory similar to trifluralin PPI fb glyphosate + acetochlor.
49 Texas Tech University, Justin L. Spradley, May, 2014
These results indicate that effective control of red morningglory early-season involves glufosinate combined with dicamba, glyphosate, or acetochlor in a system.
Flushes of red morningglory were limited at the Lorenzo location due to low seed numbers and environmental conditions.
Palmer amaranth Glover Farm 2012
Total Palmer amaranth control was achieved with trifluralin PPI fb glyphosate or any combination of glyphosate + dicamba +acetochlor EPOST and MPOST 7, 14, and 21 DAT (Table 4.8). The addition of soil residual herbicides such as trifluralin
PPI, metolachlor POST, or pyrithiobac POST reduced the number of in-season glyphosate applications by one (from three to two) for season-long Palmer amaranth control (Joe et al. 2008). Trifluralin PPI fb dicamba + glufosinate EPOST had greater control (99%) than trifluralin PPI fb glufosinate EPOST (91%) 21 DAT. Trifluralin
PPI fb dicamba + glufosinate EPOST fb glyphosate + dicamba MPOST controlled
Palmer amaranth at least 99% 7 and 21 DAT. Trifluralin PPI fb glufosinate EPOST fb glufosinate MPOST controlled Palmer amaranth 91% 14 and 21 days after the EPOST treatment. This treatment when applied MPOST controlled Palmer amaranth 98% and was similar compared to any other treatment combination with the exception of trifluralin alone PPI (92%) 21 DAT.
The Palmer amaranth was controlled 100% 21 days after MPOST for 10 of the
12 treatments. Treatments that were less effective include trifluralin PPI fb
50 Texas Tech University, Justin L. Spradley, May, 2014
glufosinate EPOST and MPOST (98%) as well as trifluralin alone PPI (92%) 21 DAT.
These results indicate greater than 92% control was achieved when additional applications of dicamba, glyphosate or glufosinate were applied following trifluralin
PPI 21 days after the MPOST treatments.
Plots treated with trifluralin PPI fb glyphosate + dicamba EPOST fb glyphosate + dicamba MPOST produced the most cotton (1256 kg ha-1) (Table 4.8).
All yields except for trifluralin PPI fb glyphosate EPOST fb glyphosate MPOST (397 kg ha-1), and trifluralin PPI fb glyphosate + acetochlor EPOST fb glyphosate + dicamba MPOST (359 kg ha-1) were similar (Table 4.8).
Devil’s-claw Glover Farm 2012
Trifluralin PPI alone did not control devil’s-claw; however, previous studies have shown that trifluralin fb glyphosate controlled devil’s-claw at least 93% by
Dotray et al. (2000). All treatments in this study except trifluralin PPI fb glufosinate
EPOST fb glufosinate MPOST and trifluralin PPI fb glufosinate EPOST fb glyphosate
MPOST controlled devil’s-claw at least 95% EPOST and MPOST (Table 4.9).
Devil’s-claw control of >90% has been achieved with POST treatments based either on cotton growth stage or as populations dictated “as needed” applications (Joy et al.
2005). Trifluralin PPI fb glufosinate EPOST fb glufosinate MPOST and trifluralin
PPI fb glufosinate EPOST fb glyphosate MPOST treatments controlled devil’s-claw
51 Texas Tech University, Justin L. Spradley, May, 2014
75% to 100% 7, 14, and 21 DAT (Table 4.9). Devil’s-claw was controlled 100%with all treatments except for trifluralin alone PPI (0%) MPOST 21 DAT.
Palmer amaranth control Lubbock Station (301) Farm 2012
In 2012, glyphosate EPOST and trifluralin PPI fb glyphosate EPOST controlled Palmer amaranth 86 and 90%, respectively, 14 DAT (Table 4.10).
Trifluralin PPI fb glyphosate + dicamba EPOST provided complete control, which was greater than glyphosate EPOST (88%) 21 DAT. Trifluralin PPI fb glyphosate + dicamba EPOST combinations achieved 99 to 100% control 7, 14, and 21 DAT.
Trifluralin PPI fb glyphosate or glyphosate + dicamba + acetochlor EPOST controlled
Palmer amaranth at least 96% 7 DAT, 97 to 99% 14 DAT, and 94 to 99% 21 DAT
(Table 4.10). This control was greater than control observed following trifluralin PPI fb glufosinate (65 to 69%) or dicamba + glufosinate (84 to 92%) EPOST 7, 14, and 21
DAT.
Trifluralin PPI fb glufosinate EPOST fb glyphosate MPOST controlled Palmer amaranth 86 and 90% 14 and 21 DAT, respectively. This control was similar to trifluralin PPI fb glufosinate EPOST fb glufosinate MPOST (62 to 63%) (Table 4.10).
Palmer amaranth control following trifluralin PPI fb glufosinate EPOST fb glufosinate
MPOST was greater (63%) than trifluralin PPI (53%) 21 DAT. It was beneficial to have trifluralin PPI followed by a sequential treatment to improve control.
52 Texas Tech University, Justin L. Spradley, May, 2014
This trial suggests that effective (>98%) season-long Palmer amaranth control is possible with all treatments except glufosinate applied alone EPOST or MPOST.
Less effective control was achieved when trifluralin PPI fb glufosinate EPOST and
MPOST (63%) when compared to trifluralin PPI fb glufosinate EPOST fb glyphosate
MPOST (90%) 21 DAT. Trifluralin applied alone resulted in 53% control when evaluated 21 days after the MPOST timings.
Ivyleaf morningglory I control Lubbock Station (301) Farm 2012
Ivyleaf morningglory was controlled ≥99% 14 and 21 DAT following trifluralin PPI fb glyphosate + dicamba EPOST. Likewise, trifluralin PPI fb glyphosate + dicamba + acetochlor EPOST controlled this weed at least 97%. This level of control was greater than that observed following trifluralin PPI fb dicamba + glufosinate EPOST (89%) 14 and 21 DAT (Table 4.11). All of the above EPOST combinations controlled ivyleaf morningglory 93 to 98% 7 DAT (Table 4.11).
Trifluralin PPI fb glufosinate EPOST controlled this weed (90%) greater than glyphosate (83%) 7 DAT. Trifluralin PPI fb glufosinate EPOST provided greater ivyleaf morningglory control 14 and 21 DAT (68 to 70%) compared to glyphosate
EPOST (44 to 45%). Trifluralin PPI did not control ivyleaf morningglory when evaluated following EPOST and MPOST treatments.
Complete ivyleaf morningglory control was achieved 14 and 21 days after the
MPOST timing with trifluralin PPI fb dicamba + glufosinate EPOST fb glyphosate +
53 Texas Tech University, Justin L. Spradley, May, 2014
dicamba MPOST. Similar control (97%) was observed following trifluralin PPI fb glyphosate alone or glyphosate + acetochlor EPOST fb glyphosate + dicamba MPOST
7 DAT and total control was observed 14 and 21 DAT. Trifluralin PPI fb glyphosate
+ dicamba EPOST fb glyphosate + dicamba MPOST controlled ivyleaf morningglory
99% 7, 14, and 21 DAT (Table 4.11). Culpepper and York (1998) reported that early, mid-, and late-POST applications of glyphosate controlled tall (Ipomoea purpurea L.
Roth) and pitted (Ipomoea lacunose L.) morningglory 100%.
Trifluralin PPI fb glyphosate + dicamba or glyphosate + dicamba + acetochlor
EPOST fb glyphosate or glyphosate + dicamba MPOST had greater season-long ivyleaf morningglory control than all other treatments. Glyphosate or glufosinate applied alone EPOST and MPOST and following trifluralin PPI resulted in the poorest ivyleaf morningglory control (71 to 74%) 21 DAT. No control was achieved with trifluralin alone throughout the season. Clewis et al. (2006) stated that glyphosate
EPOST controlled Ipomoea spp. no more than 40% late-season. Similarly, Wood et al. (1999) reported that this level of control was not adequate because the vining growth of Ipomoea spp. interferes with harvesting efficiency, thus leading to cotton yield and fiber quality reductions.
Ivyleaf morningglory II control Lubbock Station (301) Farm 2012
Glyphosate + dicamba, glyphosate + dicamba + acetochlor, and dicamba + glufosinate EPOST controlled ivyleaf morningglory 93 to 96%, which was greater
54 Texas Tech University, Justin L. Spradley, May, 2014
than control (86%) from glufosinate treatments alone 7 DAT (Table 4.12).
Glufosinate EPOST controlled ivyleaf morningglory at least 79% 14 DAT and 59% 21
DAT. Early-postemergence applications of glyphosate and glyphosate + acetochlor controlled ivyleaf morningglory 69 to 74% 7 DAT. These treatments were less effective at controlling ivyleaf morningglory compared to glyphosate + dicamba, glyphosate + dicamba + acetochlor, and dicamba + glufosinate EPOST (93 to 96%).
Glyphosate + dicamba, glyphosate + dicamba + acetochlor, and dicamba + glufosinate EPOST resulted in 95 to 99% ivyleaf morningglory control 14 DAT. This control was greater than control achieved following glufosinate (78 to 79%).
Glyphosate EPOST treatments provided 68 to 71% ivyleaf morningglory control and glyphosate + dicamba controlled ivyleaf morningglory 99%. All treatments controlled ivyleaf morningglory better than glyphosate 14 DAT. Glyphosate + dicamba, glyphosate + dicamba + acetochlor (99% to total control) and dicamba + glufosinate
(95%) had the longest residual effects 21 DAT EPOST.
Ivyleaf morningglory was controlled 95 to 100% 21 DAT with glyphosate + dicamba and glyphosate + dicamba + acetochlor EPOST. These treatments provided effective control into the middle part of the growing season. Joy et al. (2005) reported effective ivyleaf morningglory control was achieved with four POST applications of glyphosate applied as needed beginning at the 2-leaf cotton growth stage.
55 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.1. Palmer amaranth control at the Glover Farm in Lubbock, TX in 2010.
Treatments PREd EPOSTe D-EPOSTf MPOSTg EPPa PRE EPOST D-EPOST MPOST 21 DAT 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT (%) - glyc glu - glu 0 c 68 e 18 f 70 e - - - 69 c 25 c - dic glu - glu 100 a 99 ab 87 abc 90 bcd - - - 90 ab 80 b - gly+dic glu - glu 100 a 100 a 72 cde 91 abcd - - - 91 ab 81 b - gly dic - glu 0 c 78 d 74 cde 89 cd - - - 89 ab 84 ab - dic dic - glu 100 a 100 a 92 ab 97 ab - - - 96 a 96 a - gly+dic dic - glu 100 a 99 a 81 bcd 91 abcd - - - 91 ab 88 ab - gly dic - glu 0 c 95 b 68 de 85 d - - - 85 b 81 b - dic glu+dic - glu 100 a 100 a 94 ab 96 ab - - - 96 a 95 a - gly+dic glu+dic - glu 100 a 99 a 90 ab 94 abc - - - 94 a 92 ab - gly+dic - glu - 100 a - - - 83 c 93 bc 83 b - - - gly+dic - dic - 100 a - - - 98 ab 97 ab 99 a - - - gly+dic - glu+dic - 100 a - - - 99 a 99 a 99 a - - - gly gly - gly 23 b 85 c 60 e 93 abc - - - 93 a 83 b fomb flu gly+S-met - - 95 a 98 ab 99 a 98 a - - - - - S-met flu - pyr - 99 a - - - 87 bc 91 c 88 b - - aAbbreviations: EPP, early preplant; PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early-postemergence; MPOST, mid- postemergence; DAT, days after treatment; gly, glyphosate; glu, glufosinate; dic, dicamba; fom, fomesafen; flu, fluometuron; S-met, S-metolachlor; pyr, pyrithiobac. bFomesafen was applied 14 days before planting. cGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, fomesafen 0.28 kg ha-1, fluometuron 1.12 kg ha-1, S- metolachlor 1.38 kg ha-1, and pyrithiobac 0.07 kg ha-1. defgDates applications were applied EPP 4-28, PRE 05-12, EPOST 06-04, D-EPOST 06-14, and MPOST 06-21.
56 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.2. Devil’s-claw control at the Glover Farm in Lubbock, TX in 2010.
Treatments EPOSTd D-EPSOTe MPOSTf EPPa PRE EPOST D-EPOST MPOST 21 DAT 14 DAT 21 DAT 7 DAT 14 DAT (%) - glyc glu - glu 97 a - - 98 a 91 b - dic glu - glu 97 a - - 97 ab 97 ab - gly + dic glu - glu 93 a - - 93 b 93 b - gly dic - glu 96 a - - 96 ab 96 ab - dic dic - glu 96 a - - 95 ab 93 ab - gly + dic dic - glu 96 a - - 96 ab 96 ab - gly dic - glu 95 a - - 95 ab 96 ab - dic glu + dic - glu 97 a - - 97 ab 95 ab - gly + dic glu + dic - glu 95 a - - 95 ab 94 ab - gly + dic - glu - - 80 ab 72 ab - - - gly + dic - dic - - 78 b 56 b - - - gly + dic - glu + dic - - 96 a 89 a - - - gly gly - gly 94 a - - 94 ab 99 a fomb flu gly + S-met - - 68 b - - - - S-met flu - pyr - - 8 c 13 c - - aAbbreviations: EPP, early preplant, PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; gly, glyphosate; glu, glufosinate; dic, dicamba; fom, fomesafen; flu, fluometuron; S-met, S-metolachlor; pyr, pyrithiobac. bFomesafen was applied 14 days before planting. cGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, fomesafen 0.28 kg ha-1, fluometuron 1.12 kg ha-1, S-metolachlor 1.38 kg ha-1, and pyrithiobac 0.07 kg ha-1. defDates applications were applied EPP 04-28, PRE 05-12, EPOST 06-04, D-EPOST 06-14, and MPOST 06-21. 57 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.3. Silverleaf nightshade control at the Glover Farm in Lubbock, TX in 2010.
Treatments EPOSTd D-EPOSTe MPOSTf EPPa PRE EPOST D-EPOST MPOST 21 DAT 14 DAT 21 DAT 7 DAT 14 DAT (%) - glyc glu - glu 91 a - - 93 a 68 a - dic glu - glu 93 a - - 93 a 65 a - gly + dic glu - glu 87 a - - 87 ab 71 a - gly dic - glu 92 a - - 92 a 75 a - dic dic - glu 90 a - - 85 ab 83 a - gly + dic dic - glu 91 a - - 91 a 71 a - gly dic - glu 91 a - - 91 a 80 a - dic glu + dic - glu 93 a - - 93 a 83 a - gly + dic glu + dic - glu 91 a - - 91 a 78 a - gly + dic - glu - - 91 a 27 b - - - gly + dic - dic - - 79 b 73 a - - - gly + dic - glu + dic - - 95 a 70 a - - - gly gly - gly 76 a - - 76 b 71 a fomb flu gly + S-met - - 40 b - - - - S-met flu - pyr - - 0 c 0 b - - aAbbreviations: EPP, early preplant; PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; gly, glyphosate; glu, glufosinate; dic, dicamba; fom, fomesafen; flu, fluometuron; S-met, S-metolachlor; pyr, pyrithiobac. bFomesafen was applied 14 days before planting. cGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, fomesafen 0.28 kg ha-1, fluometuron 1.12 kg ha-1, S-metolachlor 1.38 kg ha-1, and pyrithiobac 0.07 kg ha-1. defDates applications were applied EPP 04-28, PRE 05-12, EPOST 06-04, D-EPOST 06-14, and MPOST 06-21. 58 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.4. Palmer amaranth control EPOST and D-EPSOT at the Glover Farm in Lubbock, TX in 2011.
Treatments EPOSTc D-EPOSTd PPIa PRE EPOST D-EPOST 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT 21 DAT (%) - - glyb - 96 a 94 abc 75 cd - - - - - glu - 69 c 53 e 21 f - - - - - glu + dic - 96 a 92 c 73 d - - - - - gly + dic 97 a 99 ab 91 ab - - - - dic glu - 71 c 50 e 31 e - - - - dic dic - 79 b 85 d 70 d - - - - dic glu + dic - 94 a 94 abc 83 bc - - - - dic gly + dic - 99 a 99 a 91 ab - - - - dic glu - 68 c 50 e 30 ef - - - - dic glu + dic - 96 a 93 bc 78 cd - - - - dic gly + dic - 98 a 98 ab 90 ab - - - - dic - glu - - - 0 b 24 b 20 c - dic - glu + dic - - - 21 b 63 a 63 b - dic - gly + dic - - - 0 b 93 a 69 ab tri - gly - 99 a 99 ab 93 a - - - tri flu - pyr - - - 80 a 69 a 75 a tri - gly + dic - 99 a 99 a 98 a - - - aAbbreviations: PPI, preplant incorporated, PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; gly, glyphosate; glu, glufosinate; dic, dicamba; flu, fluometuron; pyr, pyrithiobac. bGlyphosate was applied at 0.87 kg ae ha-1,glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, fluometuron 1.12 kg ha-1, and pyrithiobac 0.07 kg ha-1. cdDates applications were applied PRE 05-23, EPOST 06-10, and D-EPOST 06-21. 59 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.5. Palmer amaranth control MPOST and cotton yield at the Glover Farm in Lubbock, TX in 2011.
Treatments MPOSTc PPIa PRE EPOST MPOST 7 DAT 14 DAT 21 DAT Yield (%) (kg/ha-1) - - glyb gly 94 bc 96 ab 91 bc 641 bc - - glu glu 26 f 26 f 40 f 0 e - - glu + dic glu 69 e 71 c 59 e 494 cd - - gly + dic glu 86 d 89 b 89 c 1122 a - dic glu glu 24 f 35 e 34 f 390 cd - dic dic glu 73 e 75 d 75 d 324 d - dic glu + dic glu + dic 94 bc 96 ab 90 c 641 bc - dic gly + dic glu 96 abc 93 bc 91 c 890 ab - dic glu gly + dic 92 c 98 ab 92 bc 324 d - dic glu + dic gly + dic 96 abc 99 a 94 abc 653 bc - dic gly + dic gly + dic 99 a 100 a 99 ab 872 ab - dic - - - - - 0 e - dic - - - - - 299 de - dic - - - - - 439 cd tri - gly gly 98 ab 99 a 95 abc 842 ab tri flu - - - - - 646 bc tri - gly + dic gly + dic 100 a 100 a 100 a 805 b aAbbreviations: PPI, preplant incorporated, PRE, preemergence; EPOST, early-postemergence; D-EPOST, delayed early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; gly, glyphosate; glu, glufosinate; dic, dicamba; flu, fluometuron; pyr, pyrithiobac. bGlyphosate was applied at 0.87 kg ae ha-1,glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, fluometuron 1.12 kg ha-1, and pyrithiobac 0.07 kg ha-1. cDates applications were applied MPOST 07-05. 60 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.6. Palmer amaranth control at Lorenzo, Texas in 2012.
Treatments EPOSTd MPOSTe PPIa PREc EPOST MPOST 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT Yield (%) (kg/ha-1) -1 tri dic 0.56 kg/ha - - 51 f 53 e 57 d 82 c 91 bcd 1187 ab -1 tri dic 1.12 kg/ha - - 68 de 57 de 57 d 88 bc 94 abc 1111 abc tri dic 2.24 kg/ha-1 - - 83 bc 88 b 87 b 89 bc 86 d 1127 abc tri act - gly 78 cd 77 c 76 c 95 ab 97 abc 1268 a tri - glyb gly 99 a 98 ab 97 a 99 a 95 a 941 c tri - gly + dic gly 98 a 97 ab 98 a 100 a 100 a 1238 ab tri - gly + dic gly + dic 98 a 98 ab 98 a 100 a 100 a 1203 ab tri - glu glu 63 ef 61 de 61 d 50 d 35 e 1066 bc tri - glu gly 65 def 63 d 61 d 88 bc 89 cd 1153 ab tri - gly + dic + act gly 98 a 98 a 100 a 100 a 100 a 1112 abc tri - gly gly + dic 82 c 96 ab 96 ab 99 a 100 a 1077 bc tri - gly + act gly + dic 96 ab 96 ab 96 ab 99 a 99 ab 1198 ab tri - gly + dic + act gly + dic 96 ab 99 a 100 a 100 a 100 a 1159 ab tri - dic + glu gly + dic 97 a 96 ab 94 ab 99 a 100 a 1160 ab aAbbreviations: PPI, preplant incorporated; PRE, preemergence; EPOST, early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; act, acetochlor; gly, glyphosate; glu, glufosinate; dic, dicamba. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.50 kg ai ha-1. cdeDates applications were applied PRE 05-25, EPOST 06-26, and MPOST 07-31.
61 Texas Tech University, Justin L. Spradley, May, 2014
Table 4.7. Red morningglory control at Lorenzo, Texas in 2012.
Treatments EPOST PPIa PRE EPOST 7 DAT 14 DAT 21 DAT (%) tri dic 0.56 kg/ha-1 - 38 d 55 cd 57 cd tri dic 1.12 kg/ha-1 - 63 c 59 cd 57 cd tri dic 2.24 kg/ha-1 - 45 e 39 d 38 d tri act - 13 e 12 e 14 e tri - glyb 85 ab 86 a 84 ab tri - gly + dic 96 a 96 a 97 a tri - gly + dic 98 a 98 a 97 a tri - glu 65 bc 58 cd 58 cd tri - glu 65 bc 62 bc 63 bc tri - gly + dic + act 97 a 97 a 100 a tri - gly 80 abc 84 ab 83 ab tri - gly + act 86 ab 88 a 89 a tri - gly + dic + act 94 a 99 a 100 a tri - dic + glu 97 a 96 a 94 a aAbbreviations: PPI, preplant incorporated; PRE, preemergence; EPOST, early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; act, acetochlor; gly, glyphosate; glu, glufosinate; dic, dicamba. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.50 kg ai ha-1. cDates applications were applied PRE 05-25 and EPOST 06-26.
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Table 4.8. Palmer amaranth control at the Glover Farm in Lubbock, TX in 2012.
Treatments EPOSTc MPOSTd PPIa EPOST MPOST 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT 21 DAT Yield (%) (kg ha-1) tri - - 85 c 93 b 93 b 90 c 94 ab 92 c 588 ab - glyb gly 99 a 99 a 99 a 100 a 78 b 100 a 681 ab tri gly gly 100 a 100 a 100 a 100 a 100 a 100 a 397 b tri gly + dic gly 100 a 100 a 100 a 100 a 100 a 100 a 728 ab tri gly + dic gly + dic 100 a 100 a 100 a 100 a 100 a 100 a 1256 a tri glu glu 88 bc 91 b 91 b 97 b 99 a 98 b 677 ab tri glu gly 92 b 96 ab 97 a 99 a 100 a 100 a 714 ab tri gly + dic + act gly 100 a 100 a 100 a 100 a 100 a 100 a 555 ab tri gly dic 100 a 100 a 100 a 100 a 100 a 100 a 1008 ab tri gly + act gly + dic 100 a 100 a 100 a 100 a 100 a 100 a 359 b tri gly + dic + act gly + dic 100 a 100 a 100 a 100 a 100 a 100 a 654 ab tri dic + glu gly + dic 99 a 95 b 99 a 99 a 100 a 100 a 821 ab aAbbreviations: PPI, preplant incorporated; EPOST, early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; gly, glyphosate; glu, glufosinate; dic, dicamba, act, acetochlor. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.26 kg ai ha-1. cdDates applications were applied PPI 03-28, EPOST 06-15, and MPOST 07-12.
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Table 4.9. Devil’s-claw control at the Glover Farm in Lubbock, TX in 2012.
Treatments EPOSTc MPOSTd PPIa EPOST MPOST 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT 21 DAT (%) tri - - 0 d 0 d 0 d 0 c 0 d 0 b - glyb gly 100 a 100 a 100 a 100 a 100 a 100 a tri gly gly 100 a 100 a 100 a 99 a 100 a 100 a tri gly + dic gly 100 a 100 a 100 a 100 a 100 a 100 a tri gly + dic gly + dic 100 a 100 a 100 a 100 a 100 a 100 a tri glu glu 93 b 88 b 88 b 98 a 99 b 100 a tri glu gly 83 c 75 c 75 c 93 b 98 c 100 a tri gly + dic + act gly 100 a 100 a 100 a 100 a 100 a 100 a tri gly dic 100 a 100 a 99 a 100 a 100 a 100 a tri gly + act gly + dic 100 a 100 a 100 a 100 a 100 a 100 a tri gly + dic + act gly + dic 100 a 100 a 100 a 99 a 99 ab 100 a tri dic + glu gly + dic 99 a 95 ab 95 ab 99 a 100 a 100 a aAbbreviations: PPI, preplant incorporated; EPOST, early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; gly, glyphosate; glu, glufosinate; dic, dicamba, act, acetochlor. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.26 kg ai ha-1. cdDates applications were applied PPI 03-28, EPOST 06-15, and MPOST 07-12.
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Table 4.10. Palmer amaranth control (Morningglory I trial) on the Texas A&M AgriLife Research and Extension Center field 301 Lubbock, TX in 2012.
Treatments EPOSTc MPOSTd PPIa EPOST MPOST 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT 21 DAT (%) tri - - 66 d 70 e 66 d 55 c 52 c 53 d - glyb gly 96 a 86 bc 84 c 99 a 99 a 99 a tri gly gly 99 a 90 b 88 bc 99 a 99 a 98 ab tri gly + dic gly 99 a 99 a 99 a 100 a 99 a 99 a tri gly + dic gly + dic 100 a 100 a 100 a 100 a 99 a 99 a tri glu glu 68 d 69 e 65 d 63 c 62 c 63 c tri glu gly 75 c 76 d 71 d 83 b 86 b 90 b tri gly + dic + act gly 99 a 99 a 99 a 100 a 100 a 100 a tri gly gly + dic 96 a 97 a 94 ab 99 a 100 a 100 a tri gly + act gly + dic 99 a 98 a 97 a 99 a 100 a 100 a tri gly + dic + act gly + dic 99 a 99 a 99 a 100 a 100 a 100 a tri dic + glu gly + dic 92 b 84 c 84 c 98 a 100 a 100 a aAbbreviations: PPI, preplant incorporated; EPOST, early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; gly, glyphosate; glu, glufosinate; dic, dicamba; act, acetochlor. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.26 kg ai ha-1. cdDates applications were applied PPI 03-28, EPOST 06-15, and MPOST 07-12.
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Table 4.11. Ivyleaf morningglory control (Morningglory I trial) on the Texas A&M AgriLife Research and Extension Center field 301 Lubbock, TX in 2012.
Treatments EPOST MPOSTd PPIa EPOST MPOST 7 DAT 14 DAT 21 DAT 7 DAT 14 DAT 21 DAT (%) tri - - 0 h 0 f 0 f 0 f 0 e 0 d - glyb gly 74 g 45 e 44 e 68 de 69 cd 74 bc tri gly gly 83 ef 53 de 50 de 76 cd 81 bc 87 ab tri gly + dic gly 98 ab 99 a 99 a 93 ab 94 a 96 a tri gly + dic gly + dic 99 a 100 a 100 a 99 a 99 a 99 a tri glu glu 90 cd 70 c 68 c 76 cd 74 cd 71 c tri glu gly 86 de 66 c 64 c 63 e 66 d 73 c tri gly + dic + act gly 95 abc 97 ab 97 ab 85 bc 89 ab 94 a tri gly gly + dic 71 g 51 de 50 de 97 a 99 a 100 a tri gly + act gly + dic 76 fg 60 cd 59 cd 93 ab 97 a 96 a tri gly + dic + act gly + dic 95 abc 99 ab 98 ab 99 a 99 a 100 a tri dic + glu gly + dic 93 bcd 89 b 89 b 99 a 100 a 100 a aAbbreviations: PPI, preplant incorporated; EPOST, early-postemergence; MPOST, mid-postemergence; DAT, days after treatment; tri, trifluralin; gly, glyphosate; glu, glufosinate; dic, dicamba; act, acetochlor. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.26 kg ai ha-1. cdDates applications were applied PPI 03-28, EPOST 06-15, and MPOST 07-12.
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Table 4.12. Ivyleaf morningglory control (Morningglory II trial) on the Texas A&M AgriLife Research and Extension Center field 301 Lubbock, TX in 2012.
Treatments EPOSTc EPOSTa 7 DAT 14 DAT 21 DAT (%) glyb 73 c 68 d 65 bc gly 74 c 71 cd 73 b gly + dic 96 a 99 a 100 a gly + dic 95 a 99 a 99 a glu 86 b 78 bc 59 c glu 86 b 79 b 59 c gly + dic + act 95 a 99 a 100 a gly 69 c 66 d 59 c gly + act 69 c 68 d 61 c gly + dic + act 93 a 98 a 99 a dic + glu 96 a 95 a 95 a aAbbreviations: EPOST, early-postemergence; DAT, days after treatment; gly, glyphosate; glu, glufosinate; dic, dicamba; act, acetochlor. bGlyphosate was applied at 0.87 kg ae ha-1, glufosinate 0.59 kg ai ha-1, dicamba 0.56 kg ai ha-1, and acetochlor 1.26 kg ai ha-1. cDates applications were applied EPOST 06-26.
67 Texas Tech University, Justin L. Spradley, May, 2014
CHAPTER V
SUMMARY AND CONCLUSIONS
In 2010, Palmer amaranth (Amaranthus palmeri S. Wats.), devil’s-claw
(Proboscidea louisianica Thell.), and silverleaf nightshade (Solanum elaeagnifolium
Cav.) control was assessed in Bollgard II® XtendFlexTM cotton. All PRE treatments that contained dicamba controlled Palmer amaranth 100% at least 21 days, or until
EPOST applications were used. Similar Palmer amaranth control was observed with the use of fomesafen or S-metolachlor applied early-preplant (14 days before planting) followed by (fb) fluometuron PRE (95 to 99%).
When applied to 5 to 10 cm tall Palmer amaranth dicamba alone, as a PRE fb glufosinate or in combinations EPOST provided >99% control 7 DAT. Fomesafen applied 14 DBP fb fluometuron PRE fb glyphosate + S-metolachlor EPOST consistently controlled Palmer amaranth 7, 14, and 21 DAT EPOST. The addition of glufosinate to dicamba EPOST increased control of 5 to 10 cm tall Palmer amaranth
21 DAT compared to glyphosate PRE fb dicamba EPOST. The greatest Palmer amaranth control was achieved longer in season with dicamba alone and glufosinate+ dicamba D-EPOST, which resulted in 99% control 21 DAT. Glufosinate and pyrithiobac applied D-EPOST were less effective.
Results from Palmer amaranth studies indicated that effective (>90%) season- long Palmer amaranth control was achieved when dicamba was applied once PRE or 68 Texas Tech University, Justin L. Spradley, May, 2014
EPOST and fb glufosinate MPOST 14 DAT. This control was greater than glyphosate applied PRE alone or in combination with dicamba fb glufosinate EPOST and
MPOST. Similar control was achieved when glyphosate was applied alone PRE,
EPOST, and MPOST. Likewise, glyphosate alone and glyphosate + dicamba PRE fb dicamba EPOST fb glufosinate MPOST achieved 81 and 88% Palmer amaranth control, respectively.
In 2011, effective (>94%) season-long control was achieved when dicamba was applied PRE fb glufosinate + dicamba EPOST fb glyphosate + dicamba MPOST
5 to 10 cm Palmer amaranth on the Glover Farm in Lubbock. When trifluralin or dicamba was applied PPI or PRE fb glyphosate + dicamba EPOST and MPOST similar control was observed as well as when trifluralin was applied PPI fb glyphosate
EPOST and MPOST 21 DAT. These treatments conferred greater control of 5 to 10 cm Palmer amaranth than those that included glufosinate applied EPOST or MPOST.
Plots treated with glyphosate + dicamba EPOST fb glufosinate MPOST had cotton yields that closely correlated with the control of Palmer amaranth throughout the season. Cotton yield was correlated with the level of weed control achieved. Plots treated with trifluralin PPI fb glyphosate EPOST fb glyphosate MPOST had greater weed control and yield than plots treated with dicamba PRE fb glufosinate EPOST fb glufosinate MPOST. When plots were treated with glufosinate alone EPOST or D-
EPOST, plots yielded less than those with any other treatment.
69 Texas Tech University, Justin L. Spradley, May, 2014
In 2012, (Glover Farm) MPOST results indicated total control 21 DAT for 10 of the 12 treatments. The two treatments that were less effective on 5 to 10 cm Palmer amaranth included trifluralin PPI fb glufosinate EPOST and MPOST as well as trifluralin alone PPI 21 DAT. All treatments resulted in at least 92% control 21 DAT
MPOST for mid-season control of Palmer amaranth. Plots treated with glyphosate
EPOST fb glyphosate MPOST and trifluralin PPI fb glyphosate +acetochlor EPOST fb glyphosate + dicamba MPOST yielded less than trifluralin PPI fb glyphosate + dicamba EPOST fb glyphosate + dicamba MPOST.
All EPOST treatments in 2010 of glufosinate, glyphosate, dicamba, and glufosinate + dicamba controlled 5 to 10 cm devil’s-claw greater than fomesafen applied 14 DBP fb fluometuron PRE fb glyphosate + S-metolachlor EPOST 21 DAT.
Glyphosate + dicamba PRE fb glufosinate + dicamba D-EPOST controlled devil’s- claw the longest D-EPOST. Glyphosate applied PRE, POST, and MPOST achieved the greatest season-long control on 15 to 20 cm devil’s-claw. In 2012, trifluralin PPI achieved no control of 15 to 20 cm devil’s-claw, but all other treatments achieved total control season-long.
Silverleaf nightshade control was similar following all treatments seven days after the MPOST treatments, except for glyphosate PRE fb glyphosate EPOST fb glyphosate MPOST. This indicates the addition of dicamba PRE and EPOST may increase control, also making another application of a dicamba, glyphosate or glufosinate between the 7 and 14 day interval MPOST for silverleaf nightshade may 70 Texas Tech University, Justin L. Spradley, May, 2014
increase control. Less control was observed late season than early season for silverleaf nightshade.
Ivyleaf morningglory (Ipomoea hederacea Jacq.) control in 2012 at Lubbock
(station) was >99% with glyphosate + dicamba EPOST treatments. The addition of acetochlor to this system had similar results on 8 to 10 cm ivyleaf morningglory.
Glyphosate, glufosinate alone and glyphosate + acetochlor was the least effective on ivyleaf morningglory early season. Trifluralin PPI fb glyphosate + dicamba or glyphosate + dicamba + acetochlor EPOST fb glyphosate or glyphosate + dicamba
MPOST had greater mid-season control of 8 to 10 cm ivyleaf morningglory than any other treatments. Glyphosate or glufosinate applied alone EPOST and MPOST and following trifluralin PPI resulted in the least amount of ivyleaf morningglory control mid-season.
In 2012, results from the Lorenzo, TX trial indicated to effectively control 5 to
10 cm red morningglory (Ipomoea coccinea L.) early season glufosinate needs to be combined with dicamba, glyphosate, or acetochlor in a system. Flushes of red morningglory were limited due to low seed numbers and environmental conditions.
This made it difficult to take ratings for season-long control of red morningglory.
Bollgard II® XtendFlexTM cotton technology has been assessed on the THP in these trials showing similarities and differences in glyphosate, glufosinate, and dicamba application effectiveness when applied to different weed species. The use of this technology has shown results that can help better manage glyphosate resistant 71
Texas Tech University, Justin L. Spradley, May, 2014
Palmer amaranth. Agronomic attributes such as further cotton quality, yield and more weed management data should be collected in order to gain a greater understanding of this new technology and how it can benefit producers on the THP.
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