Dissipation and Efficacy of Pendimenthalin, Prodiamine, Dithiopyr and Bensulide As Affected by Dose and Application Timing for C

Home , Benfluralin, Bensulide, Clomazone, Dithiopyr, Mesotrione

DISSIPATION AND EFFICACY OF PENDIMENTHALIN, PRODIAMINE, DITHIOPYR AND BENSULIDE AS AFFECTED BY DOSE AND APPLICATION TIMING FOR CRABGRASS ( DIGITARIA SP ) CONTROL IN A TURFGRASS ENVIRONMENT

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By Alejandra A. Acuña, M.S.

* * * * * The Ohio State University 2009

Dissertation Committee: Approved by Dr David Gardner, Adviser Dr Karl Danneberger, Adviser Dr John Street Dr Jim Metzger ------Dr Ed McCoy Horticulture and Crop Science Graduate Program

ABSTRACT

The dissipation of herbicides in a turfgrass environment is important to determine potential water and soil contamination and verify the actual herbicide concentration in the soil to assure long term weed control. Knowledge of herbicide dissipation and the effect of dose and application timing on weed control would help turf managers to better understand herbicide dynamics, and as a result schedule their herbicide application to improve weed control in the turf environment. Pendimethalin ( N-(1-ethylpropyl)-2,6- dinitro-3,4-xylidine), Prodiamine (1,3-Benzenediamine, 2,6-dinitro-N1,N1- dipropyl-4-

(trifluoromethyl)), Bensulide [S-(O,O-diisopropyl phosphorodithioate) ester of N-(2- mercapto) benzenesulfonamide] and Dithiopyr [ S,S -dimethyl 2-(difluoromethyl)-4-(2- methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate] were applied to a

Kentucky bluegrass turf at 2288 ga.iha -1,737.08 g a.i. ha -1,11339.75 g a.i ha -1 and 421.88 g a.i ha -1,respectively,either once, twice (applications were separated 30 days) or using half of the cited doses twice (separated 30 days). All herbicides and doses were applied in autumn 2007 and again in spring 2008. The design of the experiment was completely randomized with three replicates per treatment. The whole experimental area was seeded with crabgrass ( Digitaria sp) at 1.2 kg ha-1 before herbicide application. Soil temperature and moisture were measured during the experiment. Soil samples were taken from each individual plot: 0, 4, 8, 16, 32, 36, 40, 48, 64 and 128 days after initial treatment (DAT).

Each soil sample was divided in three sections: verdure-thatch, 0 to 5 cm and 5 to 10 cm.

Herbicide was extracted from each section and quantified using a gas chromatograph with a NPD detector, using benfluralin (N-butyl-N-ethyl-2, 6-dinitro-4-(trifluoromethyl) aniline) as the internal standard. Herbicide efficacy was measured every 15 days counting number of crabgrass plants per square meter starting on May 1, 2008 until September 30,

2008. More herbicide was detected in the verdure and thatch layer. The amount of herbicide detected in the soil at 32 DAT date of the second application, was not double of the dose applied. Herbicide dissipation was quicker in spring than in autumn, mainly due to differences in soil temperature and moisture. In Autumn, more herbicide was detected at the end of the study (128 DAT) compared to Spring. Differences in herbicide efficacy were detected at the end of the season (September 30, 2008), dithiopyr provided better crabgrass control was offered by regardless of season of application. No statistical differences in crabgrass count were detected due to herbicide dose. However, 0 crabgrass plants per m 2 were observed when full followed by full recommended dose was applied.

These studies indicated the influence of soil temperature and moisture on herbicide rate of dissipation and the effect of the turfgrass environment in decreasing reported herbicides half lives.

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Dedicated to my son Jose Miguel and daughters Magdalena Francisca and Antonia Teresa with all my love

ACKNOWLEDGMENTS

I want to thank Dr Karl Danneberger for believing in me and giving me opportunities in the turf area, thanks Dr David Gardner for being my adviser and working with me in this intense process of becoming a PhD. Thanks to Dr Jim Metzger for his patience and the time he took to explain laboratory methods. I thank Dr John Street for all his support and explanation in the field. I also wish to thank my soil professor Dr Ed

McCoy who gave me knowledge and guidance. A special thank you to Phil Young and

Mark Rosenthal; who helped me with the sampling process and collection.

Thanks to Deborah Holdren for introducing me to the pesticide application techniques.

Thanks to Matt Williams for your support and for monitoring my irrigation and sensors in the field. Thanks to Jim Vent for his help and time. I also like to thank Luke Case for guiding me with the use of soil sensors and statistics.Thanks to my laboratory coworkers

Aneta Studzinska and Ed Nangle for all their support and encouraging words. I want to make a special recognition to the staff of the C. Wayne Ellen Plant and Pest diagnostic clinic at OSU, especially to Nancy Taylor for all her time and dedication to my research project.Finally thanks to my M Sc adviser Dr Hannah Mathers, husband Dr Samuel

Contreras and my parents Abraham Acuña and Ercilia Estrella for encouraging me to continue my studies and for their examples of hard work.

This research was supported by the Department of Horticulture and Crop Science at The Ohio State University, Ohio Turfgrass Foundation and chemical companies.

VITA

August 27, 1974……………………….Born-Santiago, Chile.

1997……………………………………Licenciado en Agrorrecursos,

Pontificia Universidad Católica de Chile

1999……………………………………Ingeniero Agrónomo.

Pontificia Universidad Católica de Chile

2000……………………………………Research and Development Monsanto-Chile

2004………………………………… Visiting scholar, The Ohio State University,

Biotechnology Center (Dr. Erich Grotewold lab)

2007………………………………….. Master of Science, The Ohio State University

2005-present Graduate Teaching & Research Associate,

The Ohio State University

PUBLICATIONS

Acuña, A. and Mathers, H. 2005. Extension outreach for Hispanic workers: Ohio and beyond. HortScience 40(4):1063. Acuña, A. and Mathers, H. 2006. Influence of DNA herbicides on overwintering oak seedlings. Proceedings of the sixtieth annual meeting of the Northeastern Weed Science society. Northeastern Weed Science Society. Acuña, A. and Mathers, H. 2006. Implementing and assessing an onsite bilingual educational program for Hispanic nursery workers in Ohio. HortScience 41(4): 1055- 1056.

Acuña, A., and Mathers, H. M. 2009. Implementing and assessing an Onsite bilingual educational program for Hispanic nursery workers in Ohio. In preparation for publication in the June issue of the Journal of Environmental Horticulture . Label JEH 08-13. Acuña,A. and Mathers, H. M. 2009. Multistate survey of nursery workforce: OH, MI, DE, TN, FL, IN, KY, AZ and RI. Journal of Environmental Horticulture . In review.

H. M. Mathers, A. Acuña, D. Long, B. K. Behe, A. W. Hodges, J. J. Haydu, U. K. Schuch, S. S.Barton, J. H. Dennis, B. K. Maynard, C. R. Hall, R. McNeil, and T. Archer. 2009. Nursery Worker Turnover and Language Proficiency. HortScience. In review. Acuña, A., Gardner , D., S., Danneberger, T., K.2009. Soil organic matter content, herbicide and dose tested by the bioassay technique. International Turfgrass Society Research Journal, accepted.

FIELDS OF STUDY

Major Field: Horticulture and Crop Science

vii

TABLE OF CONTENTS

Abstract……………………………………………………………………………………ii Dedication………………………………………………………………………………iv Acknowledgements………………………………………………………………………v Vita………………………………………………………………………………………vi List of Tables……………………………………………………………………………...x List of Figures……………………………………………………………………………xii

GENERAL INTRODUCTION…………………………………………………………1 CHAPTER 1 LITERATURE REVIEW…………………………………………………3 FACTORS THAT AFFECT PERSISTENCE OF HERBICIDES IN TURF……3 Turf canopy and thatch……………………………………………………4 Biological decomposition…………………………………………………5 Transfer processes…………………………………………………………6 Soil temperature…………………………………………………………7 Soil moisture………………………………………………………………8 PREVIOUS PESTICIDE DISSIPATION RESEARCH BY HERBICIDE………8

DITHIOPYR………………………………………………………………………8

PENDIMETHALIN……………………………………………………………10

PRODIAMINE…………………………………………………………………12

BENSULIDE………………………………………………………………….....13 PREVIOUS RESEARCH ON EFFICACY FOR CRABGRASS CONTROL …14 Crabgrass control using preemergence herbicides………………………14 PRODIAMINE…………………………………………………………..16 DITHIOPYR……………………………………………………………17 BENSULIDE……………………………………………………………18 PENDIMETHALIN……………………………………………………19 viii

BIBLIOGRAPHY………………………………………………………20

CHAPTER 2 DISSIPATION AND EFFICACY OF PENDIMETHALIN AND PRODIAMINE Abstract…………………………………………………………………………26 Introduction………………………………………………………………………28 Materials and Methods…………………………………………………………30 Field Procedures…………………………………………………………30 Sampling and Analysis of Pesticides……………………………………35 Results……………………………………………………………………………37 Discussions………………………………………………………………………55 BIBLIOGRAPHY………………………………………………………………57

CHAPTER 3 DISSIPATION AND EFFICACY OF BENSULIDE Abstract…………………………………………………………………………59 Introduction………………………………………………………………………60 Materials and Methods…………………………………………………………63 Field procedures…………………………………………………………63 Sampling and Analysis of Pesticides……………………………………64 Results……………………………………………………………………………67 Discussion………………………………………………………………………76 BIBLIOGRAPHY………………………………………………………………77

CHAPTER 4 DISSIPATION AND EFFICACY OF DITHIOPYR Abstract…………………………………………………………………………79 Introduction………………………………………………………………………80 Materials and Methods…………………………………………………………81 Field Procedures………………………………………………………81 Sampling and Analysis of Pesticides……………………………………83 Results……………………………………………………………………………85 Discussion………………………………………………………………………94 BIBLIOGRAPHY………………………………………………………………96 COMPLETE BIBLIOGRAPHY…………………………………………………99

LIST OF TABLES

Table 1. Analysis of Variance (ANOVA) on pendimethalin concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT)…………………………………………………………………………………….41 Table 2. Mean concentration of pendimethalin residues over time in different seasons of applications………………………………………………………………………………43 Table 3. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different pendimethalin doses applied on Autumn 2007 and Spring 2008………………………………………………………………………………………44 Table 4. Analysis of Variance (ANOVA) on prodiamine concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT)…………………………………………………………………………………….49 Table 5. Mean concentration of prodiamine residues over time in different seasons of applications………………………………………………………………………………50

Table 6. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different prodiamine doses applied on Autumn 2007 and Spring 2008………………………………………………………………………………………54

Table 7. Analysis of Variance (ANOVA) on bensulide concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT)…………………………………………………………………………………….67

Table 8. Mean concentration of bensulide residues over time in different seasons of applications………………………………………………………………………………...72

Table 9. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different bensulide doses applied on Autumn 2007 and Spring 2008………………………………………………………………………………………75

Table 10. Analysis of Variance (ANOVA) on dithiopyr concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT)…………………………………………………………………………………….87 x

Table 11. Mean concentration of dithiopyr residues over time in different seasons of applications………………………………………………………………………………88

Table 12. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different dithiopyr doses applied on Autumn 2007 and Spring 2008……………………...... 93

LIST OF FIGURES

Figure 1.Soil temperature from date of herbicide application to last sample collection for autumn and spring applications. Herbicides application dates were 8 October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15 May 2008 (spring applications)……………………………………………………………………………...32

Figure 2.Soil moisture from date of herbicide application to last sample collection for autumn 07 and spring 08 applications. Herbicides application dates were 8 October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15 May 2008 (spring applications)……………………………………………………………………...33

Figure 3. Rainfall from date of herbicide application to last sample collection date, herbicide application dates were 8 October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15 May 2008 (spring applications)……………………………………………………………………………...34

Figure 4. Distribution of pendimethalin residues (mg kg dry soil -1) among verdure- thatch, 0 to 5 cm and 5 to 10 cm soil layers over time, columns followed by the same letter are not significantly different at p=0.05……………………………………………………………………………………42

Figure 5.Dissipation curve for pendimethalin applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2007………………………………………………………………………………………45

Figure 6.Dissipation curve for pendimethalin applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008………………………………………………………………………………………46

Figure 7. Distribution of prodiamine residues (mg kg dry soil -1) among verdure-thatch, 0 to 5 cm and 5 to 10 cm soil layers over time. Columns followed by the same letter are not significantly different at p=0.05……………………………………………………………………………………51

Figure 8. Dissipation curve for prodiamine applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2008………………………………………………………………………………………52

xii

Figure 9. Dissipation curve for prodiamine applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008………………………………………………………………………………………53

Figure 10. Distribution of bensulide residues mg kg dry soil -1 among verdure-thatch, 0 to 5 cm and 5 to 10 cm soil layers over time. Columns followed by the same letter are not significantly different at p=0.05……………………………………………………………………………………71

Figure 11.Dissipation curve for bensulide applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2007………………………………………………………………………………………73 Figure 12.Dissipation curve for bensulide applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008………………………………………………………………………………………74

Figure 13. Distribution of dithiopyr residues (mg kg dry soil -1) among verdure-thatch, 0 to 5 cm and 5 to 10 cm soil layers over time. Columns followed by the same letter are not significantly different at p=0.05……………………………………………………………………………………86

Figure 14.Dissipation curve for dithiopyr applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2007………………………………………………………………………………………87

Figure 15.Dissipation curve for dithiopyr applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008………………………………………………………………………………………88

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GENERAL INTRODUCTION

Knowledge of herbicide fate and the effect of dose and application timing on weed control help turf managers to better understand herbicide dynamics, and as a result schedule their herbicide applications to get better weed control in the turf environment.

Herbicides are used in turf to help achieve a homogenous and a visually attractive sport or residential turf area for the purpose of controlling weeds. Preemergence herbicides suppress weed seed germination and need to be incorporated into the soil after their application. Due to the interaction between soil and herbicide, it is important to recognize which factors affect the rate of degradation of herbicides.

In general, pesticides in soils are transformed by chemical, photochemical, and biological reactions. At and near the soil surface, volatilization, photolysis and runoff events will influence dissipation. However, once below the soil surface, chemical and biological degradation are the main processes involved in the transformation of pesticides. Biological degradation, either complete mineralization or partial decay to form metabolites, is the critical process controlling the ultimate fate of pesticides in the soil

(Nash, 1988). Extensive literature reviews on soil and herbicide dissipation are provided by Walker (1987), Nash (1988), Weber (1990) and Monaco et al (2002).

The purpose of this study was to investigate the possible association between crabgrass (Digitaria sp) control and herbicide residue levels following applications of different herbicides either in autumn or spring. The effect of applying the herbicide as a single dose or in sequential applications was also studied.

CHAPTER 1

REVIEW OF LITERATURE

FACTORS THAT AFFECT PERSISTENCE OF HERBICIDES IN TURF

The persistence of herbicides should be long enough to achieve effective weed control followed by quick dissipation in the soil to an inactive component (Monaco et al,

2002). In the case of preemergence herbicide applications, timing is critical and results vary with factors such as soil type, soil moisture and temperature and herbicide characteristics.

Several processes are involved in the persistence of herbicides in turf. Physical removal can occur via runoff, volatilization and infiltration into soil. Portions of the pesticides that infiltrate may leave the system via leaching. In addition, herbicides can be degraded by sun light (photolysis), water (hydrolysis), other chemical reactions, and microbial activity in the turf and soil layers (Magri and Haith, 2009)

The following sections will review the factors, pertinent to this research, that contribute to herbicide persistence in turf.

Turf canopy and thatch

During herbicide application the turf canopy, also called verdure, intercepts an important amount of product thus differences in herbicide sorption and degradation between turf and bare soil have been reported in the literature (Gardner, 2000)

In addition the dense canopy of turf forms an underlying layer called thatch, a layer of dead and living stems and roots between the green vegetation and soil surface (Gardner and Brandham, 2001).

Turf canopy and thatch contain large amounts of organic carbon, which strongly adsorb pesticides and impede further movement to the soil. Strong retention in foliage and thatch is arguably the most important factor governing pesticide dissipation in turf systems. It makes the pesticides less susceptible to physical removal by runoff, infiltration, and volatilization, and exposes them to large and highly active microbial populations that reside in these layers of vegetative material (Magri and Haith, 2009).

Organic matter plays a prominent role in pesticide adsorption by soils (Calvet,

1989; Gerstl, 1990; Arienzo et al., 1994). According to Calvet (1989) the effect of adsorption on organic matter is difficult to assess because two types of results are often reported: organic matter behaves as an adsorbent and thus reduces the rate of degradation and on the other hand, organic matter acts as a nutritive substrate for microorganisms and this favors degradation.

Preemergence herbicides have been found to be more phytotoxic when applied to thatch-containing than thatch-free Kentucky bluegrass turf (Hurto, 1978).

Laboratory and field studies have shown that verdure and thatch layers strongly sorb organic compounds and have an influence on the fate of pesticides applied to turfgrass (Niemczyk and Krause, 1994; Dell et al., 1994; Lickfeldt and Branham, 1995;

Gardner et al., 2000; Gardner and Branham, 2001)

Retention of pesticides by thatch may result in reduced mobility of pesticides applied to turfgrass (Stahnke et al., 1991; Smith and Bridges, 1996) and/or increase the degradation rate (Roy et al., 2001). Further analysis on the effect of dose and season of herbicide application on herbicide dissipation and its relationship with herbicide efficacy in a turfgrass environment needs to be investigated.

Biological decomposition

The living fraction of the soil is composed of bacteria, fungi, algae, nematodes,

protozoa and worms; this fraction drives the biochemical reactions that occur in the soil.

The primary microorganisms important for herbicide decomposition are bacteria and

fungi. The rate at which these microorganisms will grow depends on the characteristics of

the herbicide, specifically, its chemical structure, temperature, water and oxygen

available in the soil. A warm, moist, well aerated, fertile soil is most favorable for higher

populations and activity of microorganisms. Under these conditions microbes can quickly

decompose most organic herbicides (Monaco et al, 2002).

Measurements of soil microbial biomass (Anderson, 1981; Anderson, 1984) or soil respiration (Walker and Brown, 1981; Walker and Thompson, 1977) have shown to correlate with rates of degradation of several herbicides. The biological activity of most herbicides applied at rates recommended for cultivated crops is less than 12 months

(Monaco et al, 2002)

Transfer processes

The transfer processes related to this research are sorption by soil mineral and organic matter and volatility. The relative importance of each process is controlled by the chemistry of the pesticide and environmental variables (Kenna, 1995).

The tendency of a pesticide to leach is strongly dependent upon the interaction of the pesticide with solids within the soil. Sorption includes adsorption and absorption, the first refers to the binding of a pesticide to the surface of a soil particle; the second one implies that the pesticide penetrates into a soil particle. The absorbed or adsorbed pesticide is often referred to as bound residue and is generally unavailable for microbial degradation or pest control (Kenna, 1995).Factors that contribute to sorption of pesticides are herbicide characteristics and soil properties.

There are three herbicide characteristics related with herbicide sorption and volatilization: K D, K OC and vapor pressure. The partition coefficient K D is the ratio of the

amount of herbicide bound to soil to the amount left in the water surrounding the soil, the

smaller the K D value, the greater the concentration of herbicide in the solution.

The soil sorption index is referred to as the K OC values, which is the K D value normalized to the organic carbon content of the soil. K OC is an expression of the tendency 6 for herbicide sorption by soil organic carbon (organic matter). The smaller the K OC the

less likely is that the herbicide will be absorbed by the soil and thus the greater potential

for leaching (Monaco et al., 2002).

Volatilization is the process by which chemicals are transformed from a solid or

liquid into gas, and is usually expressed in units of vapor pressure. Pesticide volatilization

increases as the vapor pressure increases. As temperature increases, vapor pressure

increases and the chance for volatilization loss. Immediate irrigation is usually

recommended to reduce the loss of highly volatile pesticides (Kenna, 1995).

Soil temperature

Soil temperature or time of year affects herbicide dissipation; generally, within

field soil ranges, the higher the temperature the more rapid the dissipation (Nash, 1988).

There is often a two to three fold increase in half life of herbicides with a 10°C decrease

in temperature (Briggs, 1983; Walker, 1978).

Harris et al (1969) worked with atrazine (2-chloro-4 ethylamine-6-

isopropilamino-S-triazine) and fenac ((2, 3, 6-trichlorophenyl) acetic acid) in twelve

locations in the United States and Puerto Rico and found that decreasing temperature

tended to make the herbicides more persistent. However, the data were quite variable and

the variations were often unexplainable.

Roy et al. (2001) working with dicamba (3,6-dichloro-2-methoxybenzoic acid)

found that increasing temperature from 4 to 20°C resulted in a decrease of the half life of

dicamba ranging from 2.0 to 3.7 times. Ou (1984) found that the degradation rate of 2,4-

D in two soils was reduced at 35°C compared with 25°C. 7

Weber (1990) asserted that herbicide degradation occurs at a higher rate under warm soil conditions than under cool conditions.

Soil moisture

Soil water content directly influences soil oxygen content and microbial activity and therefore can influence pesticide persistence (Veeh et al., 1996)

Decreasing soil moisture generally decreases the rate of degradation of pesticides

under aerobic soil conditions. This is especially true when the soils are almost air-dried.

The reasons for the decreased rates of degradation are reduced activity of the

microorganisms and increased sorption of the pesticide. However, in some instances

where chemical decomposition is being catalyzed at the soil surface, decreased moisture

may increase the rate of decomposition of the pesticide (US EPA, 1988).

The response of degradation to differences in soil moisture level tends to be more

variable than the response to changes in temperature (Walker et al, 1983).

Weber (1990) in his extensive review on the behavior of dinitroanilines in soil

pointed out that herbicides are degraded more under moist soil conditions than under dry

conditions; and thus carryover, if it occurs, usually occurs following a dry season.

PREVIOUS PESTICIDE DISSIPATION RESEARCH BY HERBICIDE

Dithiopyr

Dithiopyr [ S,S -dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-

(trifluoromethyl)-3,5-pyridinedicarbothioate] is the active ingredient in the formulated herbicide Dimension, marketed by Monsanto Co. (St. Louis, MO). It is registered for use in the control of crabgrass ( Digitaria spp) in turfgrass (including greens) (Enache and

Ilnicki, 1991).

The low water solubility (1.38 mg/kg), high octanol−water partition coefficient

(Kow = 56 250), and organic carbon partition coefficient ( Koc = 1920) suggest a high potential of dithiopyr retention within the thatch, mat, and surface soil (Schleicher et al.,

1995).

Dithiopyr has a vapor pressure of 5.3 × 10 -6 kPa (Schleicher et al., 1995),

pesticides with vapor pressures ≥ 5.2 × 10 -9 kPa at 25 °C have been classified as

moderately to highly volatile in the field (Kennedy and Talbert, 1977).

Dithiopyr it is rapidly lost by photodegradation and volatilization following

application to the sod and soil surface. The degradation of dithiopyr after entry into the

root media is mediated by biotic and abiotic factors and occurs at a much slower rate

compared to loss by volatilization (Hong and Smith, 1996). These authors showed that

dithiopyr losses increased in response to higher temperatures and increasing time after

application and that the loss is probably due to volatilization from the surface of the soil.

Adams and Cowell (1990) reported a range of half-lives for dithiopyr, in soil under turfgrass in United States, from 4 to 49 days.

Dithiopyr dissipation occurs in the field with vegetation coverage with a half-life of between 17 and 61 days depending on soil composition, weather conditions and formulation applied. Three major metabolites of dithiopyr (the normal acid, reverse acid and diacid metabolites) are formed and dissipated within 365 days. (EPA, 1991)

Schleicher et al. (1995) estimated the half-life for dithiopyr in soil under turfgrass at Mead, NE to be 35 days. Hong and Smith (1996) calculated half-lives for dithiopyr ranged from 68.8 days (20 °C) to 39.2 days (35 °C) in simulated golf course greens root media, in the dark and in absence of oxygen.

Pendimethalin

Pendimethalin (N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine) is a selective herbicide used to control most annual grasses and certain broadleaf weeds in field corn, potatoes, rice, cotton, soybeans, tobacco, peanuts, and sunflowers. It is used both pre-emergence and early post-emergence (Etoxnet, 2009).

Pendimethalin is one of the less volatile dinitroaniline herbicides, and its dissipation in soil is dependent on microbial decomposition (Parochetti and Dec 1978;

Walker and Bond 1977; Weber 1990).

Factors that affect pendimethalin dissipation are organic matter content, soil temperature, soil moisture content, and aerobic conditions (Zimdahl et al. 1984; Weber

1990).

Pendimethalin is moderately persistent, with an estimated average soil half-life of

60 days (Wauchope, 1990). However, the rate of degradation varies with edaphic and

climatic conditions. Soil temperature, moisture, and type have been found to influence

pendimethalin persistence in the field (Kennedy, 1977). Walker and Bond (1977) found

differences in pendimethalin half lives, in a sandy loam soil was 98 days at 30°C but was

409 days at 10°C.

Stahnke et al. (1991) found that pendimethalin leachability is low, with greater

herbicide retention in the thatch layer of turf. No half life was reported in this study.

Kulschrestha and Singh (1992) found a half-life for Pendimethalin of 33 days in

flooded soil compared to 52 days in non flooded soil. Schleicher et al (1995) reported a

half life of 23 days for their study done in a perennial ryegrass turf during two years.

Zimdahl et al. (1984) working with pendimethalin fate in three different types of

soils found that pendimethalin half life is 47 days. Starret et al (1996) working with the

same herbicide in a Kentucky bluegrass turf found that pendimethalin is less likely to be

leached than other pesticides. Berayon and Mercado (1983) found that the persistence of

pendimethalin in different soil types is affected by rate of application and moisture

regime under greenhouse conditions. Niemczyk and Krause (1994) working with

premergent herbicides found that pendimethalin is less mobile than bensulide.

The European Commission (2003) reports a half life of pendimethalin in the range of 30-150 days in soil residue studies performed in Germany, The Netherlands, UK, and

South Africa, however higher values were sporadically observed.

Prodiamine

Prodiamine (N3, N3 -Di-n-propyl-2,4-dinitro-6-(trifluoromethyl)-m- phenylenediamine) is a selective dinitroaniline herbicide that provides long term control of many annual grass weeds such as large crabgrass, smooth crabgrass, and annual bluegrass in established turf (Fermanian and Haley,1994 a).

The primary route of dissipation is photolysis (United States Department of

Energy, 2006). Prodiamine degrades rapidly in the light in both water (t 1/2 of 0.3 hours at

pH 5) and soil (t 1/2 of 50 hours) (Syngenta, 2009)

Being a dinitroaniline, prodiamine has a low water solubility and high potential of hydrogen bonding, becoming strongly sorbed by soil (Weber, 1990).Reported half-life value for prodiamine is 120 days (Weber, 1990).

Photodecomposition of dinitroaniline herbicide vapors occur readily in the atmosphere when the chemicals leave the soil and occurs to a lesser extent when the chemicals are applied preemergence and are adsorbed (Weber, 1990)

According to Weber (1990), degradation of the dinitroaniline herbicides in soils is primarily by microbiological processes. Fungi appear to be the major microbial species involved.

In general, dinitroaniline herbicides have a long persistence or low dissipation rate that is favorable for long weed term control (Fermanian and Haley, 1994 b)

Bensulide

Bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl) benzenesulfonamide] is a premergent herbicide which provides effective control of annual grasses including crabgrass, Poa annua and goosegrass as well as certain broadleaf weeds in greens, tees and bentgrass fairways. Fall application provides control next spring (PBI Gordon Corporation, 2009).

Menges and Tamez (1974) working in movement and persistence with bensulide and trifluralin found that the persistence of bensulide, was not affected by depth of incorporation into soil; most of the bensulide activity was unaffected by a trace of rainfall and remained in the original soil zone of incorporation one week after application. No herbicide activity was present after 6 months, regardless of rate of application or depth of incorporation. This study indicated no appreciable bensulide activity 12 months after application.

Mazur et al (1969) working with 22 seedling species using bensulide, found that the two highest rates of this herbicide, 34 and 51 kg ha-1, were detected down to 7.6 cm.

This indicates that bensulide, which is only slightly soluble in water, does move in soil, although the highest concentrations were found near the surface. This could be the result of higher rates of the herbicide saturate the soil colloids in the upper soil layer, which

13 would permit further movement of unabsorbed herbicide to lower levels in the soil. Other authors considered leaching a not important mechanism of movement in soil for bensulide (Anderson et al, 1968; Harris, 1967; Horowitz et al, 1974; Koren, 1972;

Menges and Hubbard, 1970, Miller et al, 1975).

Although the environmental fate data base for bensulide is not complete,

information from acceptable laboratory studies indicates bensulide is persistent. Neither

abiotic hydrolysis nor photolysis is major degradation processes in soil. The main route

of dissipation of bensulide appears to be aerobic soil metabolism with a reported half-life

of 1 year. Under aerobic conditions it appears that mineralization of bensulide to CO 2, and immobilization as unextractable residues are the major mechanisms of dissipation in the soil. Under anaerobic soil conditions bensulide did not degrade. Based on the lack of degradation under laboratory conditions, it is predicted that bensulide will be extremely persistent in anaerobic terrestrial ecosystems (The Royal Society of Chemistry, 1991).

PREVIOUS RESEARCH ON EFFICACY FOR CRABGRASS CONTROL

Crabgrass control using premergence herbicides

Crabgrasses (Digitaria sp.) are seed propagated summer annual grasses (Hafliger

and Scholtz 1980; Webster 1987; Webster and Hatch, 1990). They are native to Europe

and currently are widely disseminated from latitudes 50 N to 40 S. Among the 60 species

in the genus, 13 are considered weeds in the United States, the most common being

smooth crabgrass (Digitaria ischaemum ) and large crabgrass (Digitaria sanguinalis ) 14

(Mitich, 1988). These species differ in leaf architecture and in the location and the amount of hairs. Large crabgrass has pubescent leaves and sheaths in both seedling and adult stages as a difference with smooth crabgrass, which generally lacks hairs (Kim et al,

2002).

Several physiological and ecological traits contribute to the successful adaptation of crabgrasses in agronomic and turfgrass systems. Crabgrasses are prolific seed producers; a single plant may produce up to 188,000 seeds (Peters and Dunn, 1971).

Additionally, crabgrasses tolerate a variety of crop management systems, including cultivation and mowing. Having a C4 photosynthetic pathway, crabgrasses can tolerate hot, dry conditions, and are very competitive during the summer when C3 plants such as cool season turfgrasses, are under stress (Danneberger, 1993).

Crabgrasses are considered to be more problematic in turf than in other cropping systems (Kim et.al., 2002).The use of preemergence herbicides for selective control of annual grass weeds, including large crabgrass and smooth crabgrass has become an important component in turfgrass management programs (Bhowmik, 1987; Bingham and

Schmidt, 1964). High quality turf on athletic fields, golf courses, lawns, and other turfgrass areas usually require herbicides for crabgrass control during the spring and summer months (Johnson, 1997).

It is recommended that preemergence herbicides be applied approximately two weeks before expected germination of annual grassy weeds. Predicting crabgrass seed

15 germination can be difficult because of inconsistent spring weather. This is also the busiest time of the year for professional turf managers (Reicher and Throssell, 1993).

Two strategies of preemergence herbicides applications are commonly used in the turfgrass industry: late fall application and early spring application.

Reicher and Throssell (1993) working with pendimethalin, prodiamine and dithiopyr found when herbicides were applied at the lowest rate there were no differences in crabgrass control among application rates. When averaged across application date, prodiamine and dithiopyr applied at 0.6 kg h -1 resulted on better crabgrass control than

pendimethalin at 1.7 kg h -1 , however when these herbicides were applied at the highest rate there were no statistical differences in crabgrass control.

Prodiamine

Prodiamine is a commonly used crabgrass premergence herbicide (McCurdy et al,

2008). Prodiamine applied March 15 to April 26, in Knoxville, TN, controlled smooth crabgrass greater than 90%. However, control decreased to 55% when prodiamine was applied on May 24 (McCurdy et al, 2008).

Large crabgrass control was better when prodiamine was applied at 0.3 kg aiha -1 at the end of February followed by MSMA (monosodium acid methanearsonate) at 1.1 kg aiha -1 than when prodiamine was applied alone at 0.8 kg aiha -1 (Johnson, 1996).

Large crabgrass control was 88% in common bermudagrass when treated with either prodiamine, dithiopyr and pendimethalin at the recommended rates during the first year and followed by reduced rates in the second year (Johnson,1997). According to

16 these results the recommended rates of these herbicides are not needed annually for large crabgrass control.

Using sequential (one in March followed by another 2 months later) applications of Barricade 65 WG (prodiamine) in a tall fescue turf showed excellent crabgrass control

(≥ 95% control) 4 months after initial application.

Sybouts (1987) found that Prodiamine has superior weed control performance than pendimethalin 27 weeks after spring application. The same author reported that prodiamine applied at 1.12 kg ha-1 provides longer control of smooth crabgrass and annual bluegrass than the normal rates used for bensulide, oxadiazon, oryzalin and pendimethalin.

Most effective weed control in turf grasses will be obtained when prodiamine is

activated by at least 0.5 inch of rainfall or irrigation prior to weed germination and within

14 days following application (Novartis Crop Protection, Inc.1998).

An extensive review of Prodiamine efficacy is provided by Bhowmik and

Bingham (1990) in which they review the phytotoxicity and efficacy of dinitroanilines

applied in cool season turfgrases.

Dithiopyr

Dithiopyr was specifically developed for control of annual grasses and annual

broadleaf weeds in established turfgrasses. It is absorbed primarily by roots and shoots

and to a lesser extent by foliage (Enache and Ilnicki, 1991). Kaufman (1991), Rossi et al.

(1988) and (Enache and Ilnicki, 1991) reported that dithiopyr efficacy is better when

17 applied preemergence. Enache and Ilnicki (1991) found that dithiopyr applied at doses ranged from 0.43 to 0.56 kg ai ha -1 has an excellent potential for crabgrass control

regardless of the time of application. Bhowmik and O’Toole (1991) evaluated Dithiopyr

applied at 0.3, 0.6, 0.8, 1.1, 1.7 and 2.2 kg ha -1 for large crabgrass control. 12 to 14 weeks

after treatment the control was excellent with all treatments. Reicher and Throssell (1993)

found season long control of crabgrass with Dithiopyr applied either in late fall or early

spring at 0.6 kg a.iha-1

Bensulide

Evaluating bensulide for control of crabgrass in established bentgrass turf,

Bingham and Schmidt (1967) obtained almost complete control when applied at 16.8 kg ha-1 during four years of experiment.

Watschke et al (1974) evaluating seven experimental and four commercial preemergence crabgrass herbicides found that the 3.6 formulation of bensulide was superior in control at both rates than the 7 percent formulation. In the same experiment they showed that bensulide was superior in crabgrass control than benefin.

In a seven-year crabgrass control study, Hall et al. (1974) found bensulide and tricalcium arsenate controlled crabgrass best. Callahan et al (1983) over 9 years working with bensulide applied preemergence at 11 and 22 kg ha-1, controlled 94 to 100% of large crabgrass ( Digitaria sanguinalis ).

Pendimethalin

There were no differences in crabgrass control among application dates, when herbicides (pendimethalin, prodiamine and dithiopyr) were applied at the low rate. The high rates of these herbicides provided more effective and more consistent control of crabgrass (Johnson, 1997).

Large crabgrass control was >80% in common bermudagrass when treated with pendimethalin, prodiamine and dithiopyr between others, at the recommended rates during the first year and followed by reduced rates the second year (Johnson, 1997).

Pendimethalin 1.71% granular provided better weed control than pendimethalin

60% wettable powder at all rates, irrigation events, and years (Gasper,

1994).Pendimethalin 60 DG applied sequentially, in April and again in May (1.5+1.5 lb/acre) provided an excellent control of smooth crabgrass (>90%), the same percentage of control was reported for Prodiamine in sequential application(0.5+0.75 lb/a) , oxidiazon (single application,3 lb/a) and benefin+trifluralin (sequential application 2 + 1 lb/a) (Dernoeden and Davis,1988).

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CHAPTER 2

DISSIPATION AND EFFICACY OF PENDIMETHALIN AND PRODIAMINE

ABSTRACT

The use of herbicides for selective preemergence control of crabgrass ( Digitaria sp.) is an important component of turfgrass management programs. This study was conducted to determine the efficacy and dissipation dynamics of two dinitroaniline herbicides, pendimethalin (N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine) and prodiamine

(1,3-Benzenediamine, 2,6-dinitro-N1,N1- dipropyl-4-(trifluoromethyl)), under different dose and timings of application (autumn and spring). Herbicides were applied at three rates (maximum label rate applied twice at 30 days interval, half label rate applied twice at 30 days interval and maximum label rate applied once) and application times (autumn and spring). The design of the experiment was completely randomized with three replicates per treatment. The whole experimental area was seeded with crabgrass

(Digitaria sp) prior to herbicide application. Soil temperature and moisture were measured during the experiment. Soil samples were taken from each individual plot 0, 4,

8, 16, 32, 36, 40, 48, 64 and 128 days after initial treatment. Each soil sample was divided into three sections: verdure-thatch, 0 to 5 cm and 5 to 10 cm and assayed for pendimethalin or prodiamine. More herbicide was detected in verdure and thatch than in the other two sections (0 to 5 cm and 5 to 10 cm).

Rate of pendimethalin dissipation was higher in spring than in autumn,

Prodiamine was more rapidly dissipated than pendimethalin in both seasons. However, no differences, between seasons, in the amount of prodiamine in soil were detected at

128DAT. The amount of herbicide detected at 32 DAT (date of the second application) was not twice the dose applied for both seasons. Excellent crabgrass control (0 crabgrass plants per m 2) was obtained when herbicides were applied in spring using the higher dose

twice.

INTRODUCTION

Dinitroanilines are a class of premergence herbicides used to control a wide spectrum of weeds in turfgrasses (Bhowmik and Bingham, 1990) . Dinitroaniline herbicides prevent tubulin from polymerizing into microtubules, and in this way they inhibit mitosis (Hatzinikolaou et al, 2004).

Pendimethalin ( N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine) is a dinitroaniline herbicide used to control most annual grasses and certain broadleaf weeds in field corn, potatoes, rice, cotton, soybeans, tobacco, peanuts and sunflowers. It is used both preemergence, that is before weed seeds have sprouted, and early postemergence

(Extoxnet, 1993).

Prodiamine (1,3-Benzenediamine, 2,6-dinitro-N1,N1- dipropyl-4-

(trifluoromethyl)) is a dinitroaniline herbicide used for selective preemergence control of

grass and broadleaf weeds in established turf grasses (excluding golf course putting

greens), lawns and sod nurseries; landscape ornamentals; established perennial and

wildflower plantings (Syngenta Crop Protection, 2009). The use of preemergence

herbicides for selective control of annual grass weeds such as smooth crabgrass has

become an important component of turfgrass management programs (Bhowmik, 1987,

Bingham and Schmidt, 1964). The efficacy of these herbicides can be influenced by

season of application (Fermanian and Haley, 1994; Johnson, 1997).

Early spring application of prodiamine resulted in better smooth crabgrass control than late spring applications (McCurdy et al, 2008).

Split application is a technique of chemical (fertilizers, herbicides mainly) use in crop production, which consists in the sequential application of the same component in a given area. Sequential applications (first in March and the second 60 days later) of prodiamine in a tall fescue turf resulted in excellent crabgrass control ( ≥ 95%) 4 months

after initial application (Johnson, 1997). However, Throssell and Weisenberger (1999),

working with prodiamine and pendimethalin applied in spring to control crabgrass in a

Kentucky bluegrass turf in Indiana found that treatments applied as split applications

provided much less crabgrass cover than a single application when the same total of

active ingredient per acre was applied.

Johnson (1975) working with purple nutsedge control with bentazon [3-isopropyl-

1H-2,1,3-benzothiadiazin-4(3H)one 2,2-dioxide] and perfluidone {1,1,1-trifluoro-N-[2- methyl-4-(phenylsulfonyl) phenyl] methanesulfonamide} applied in five different species of turfgrasses found that spring applications of bentazon better controlled nutsedge than late summer ones. However, with perfluidone, better control occurred in summer.

Various experiments have been done measuring the efficacy of herbicides applied as split or single application and in different season. However, limited research has been done on single versus split application of premergence herbicides controlling crabgrass

(Digitaria sp ). The objective of this study was to associate crabgrass control with herbicide residue level under different pendimethalin and prodiamine doses and application timings (autumn and spring).

MATERIALS AND METHODS

Field Procedures

Field experiments were conducted in Kentucky bluegrass (Poa pratensis ) turf at

the The Ohio Turfgrass Foundation Research & Education Facility in Columbus, Ohio

during autumn 2007 and spring 2008. The turfgrass area was prepared and dethatched

with a Bluebird dethatcher/Lawn Comb (BlueBird Beatrice, Nebraska) and seeded with smooth crabgrass ( Digitaria ischaemum ) at 1.2 kg ha-1 the third week of September

2007. Adequate turfgrass recovery time was allowed before herbicide application. The soil was a Brookston silty-clay loam (fine, loamy, mixed, mesic Typic Argiaquoll) with

21% sand, 44% silt, 36% clay, 6.4% organic matter, pH 7.0 , cation exchange capacity

(CEC) of 11.7 meq/100g.

Field plots were 1.7 m2 with a 0.9 m border and were arranged in a randomized

complete block design with treatments replicated three times.

Herbicide efficacy ratings were taken every two weeks from 1 May to 30

September, 2008 and were based on total crabgrass plant counts (number per m2, with a

minimum of 0 and a maximum of 16) and visual percentage of weeds cover (minimum of

0% and maximum of 100%).

Pendimethalin (Pendulum 3.3 EC, BASF Corporation Agricultural Products, 26

Davis Drive, Research Triangle Park, NC 27709) was applied to the plots at either 2288 g 30 a.i ha -1 (full dose) or, 1144 g a. i ha -1 (half dose). Treatments were full dose, followed 32

days later by a second full dose application, half dose followed 32 days later by a second

half dose and full dose applied once, corresponding to the first application.. Dates of

application were 8 October 2007 and 12 November 2007 (autumn applications) and 15

April 2008 and 15 May 2008 (spring applications). Prodiamine (Barricade 65 WG,

Syngenta Crop Protection, Inc., P.O. Box 18300, Greensboro, NC 27419) was applied to

the plots at 737.08 g a.i. ha -1 (full dose) and 368.54 g a.i. ha -1 ha (half dose).Treatments and dates of applications were the same as for Pendimethalin. No history of previous herbicide application existed in the experimental area.

Applications were made with a CO 2-pressurized backpack sprayer at 40 psi (R&D

Sprayers, Opelousas, LA) equipped with 2-6503 flat fan nozzles (Teejet, Wheaton, IL) nozzles height of 40 cm, with an effective spray width of 3 feet with water as carrier.

Both herbicides were applied in 7.57 liters/ 93 m 2, following irrigation of 1.3 cm immediately after treatment. The experimental area was mowed once a week at 5 cm with a Walker mower with catcher (Walker Manufacturing Co , Fort Collins, Co) and clippings collected. The site was irrigated as necessary to avoid wilt and soil temperature

(Figure 1) and soil moisture (Figure 2) were measured once per hour using four 250 Data

Logger Temp/RH (Spectrum Technologies, Inc. Plainfield, IL) installed in each side of the experimental area, each of them had one soil temperature sensor and one Watermark sensor, installed at 10 cm depth. Data from sensors was processed using Spec 7 Basic

Software (Spectrum Technologies, Inc. Plainfield, IL). In addition, natural precipitation was measured (Figure 3).

30.00

Autumn 07 Spring 08 25.00

20.00

15.00

10.00 Soil temperature °C temperature Soil

5.00

0.00 0 16 32 48 64 80 96 112 128

-5.00 Days After Treatment

Figure 1 .Soil temperature (mean of 4 sensors installed at 10 cm depth) from date of herbicide application to last sample collection for autumn and spring applications. Herbicide application dates were 8 October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15 May 2008 (spring applications).

Soil moisture autumn 07 250.00 Soil moisture spring 08

200.00

150.00

100.00

Soil moisture tension (cbars) moisture Soil 50.00

0.00 0 16 32 48 64 80 96 112 128 Days After Treatment

Figure 2 .Soil water suction (mean of 4 sensors installed at 10 cm depth) from date of herbicide application to last sample collection for autumn 07 and spring 08 applications. Herbicides application dates were 8 October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15 May 2008 (spring applications).

9.00 Precip AU 07 (mm) 8.00 Precip SP 08 (mm) 7.00

6.00

5.00

4.00

Rainfall(mm) 3.00

2.00

1.00

0.00 0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128

Days After Treatment

Figure 3 . Rainfall from date of herbicide application to last sample collection date. Herbicide application dates were 8 October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15 May 2008 (spring applications).

Sampling and analysis of pesticides

Soil samples were randomly taken 0 (2 hours after herbicide application), 4, 8, 16,

32, 36, 40, 48, 64 and 120 days after treatment (DAT), using a lever action hole cutter

(Par-Aide Products Co., Lino Lakes, Minnesota). Each soil sample was partitioned into verdure and thatch, 0 to 5 cm, and 5 to 10 cm soil depth sections. Samples were weighed, placed in 16 oz. glass jars and covered with aluminum foil, and stored at -20°C until residue analysis.

For herbicide analysis, each soil section was thawed and a representative 20 g sample was placed in a 500 ml Erlenmeyer flask, and extracted by shaking with 100 mL ethyl acetate for 3 hours in a platform shaker (Lab-line Instruments, Inc. Melrose Park.

IL. 60160) at 200 RPM. The extract was vacuum filtered by passing through Whatman

G6 glass fiber filter paper. The Ethyl acetate was removed by rotary evaporation

(Rotavapor RE 121, Buchi, Switzerland) at 40° C. The evaporatory flask was rinsed 3 times with 3 mL of dichloromethane each time, the rinsate was transferred to a 10 ml

Reacti-Vial (Thermo-Fisher Scientific, Rockford, IL) . The Dichloromethane was evaporated to a final volume of 2 ml using a Reacti-Vap, Evaporating Unit (Pierce Model

18780, Rockford, Illinois). The concentrate was passed through a 0.45 um nylon membrane filter (Gelman Sciencies, Ann Harbor, MI). Two milliliters of the extract were transferred to an autosampler vial for analysis by gas chromatography (Model 6890

Universal, Agilent technologies, Wilmington, DE) with a Nitrogen Phosphorus Detector

(NPD).

Pendimethalin was separated on capillary column model Agilent 19091S-433,

HP-5 MS (5%-Phenyl)-Methyl Siloxane, 30 m nominal length, 0.25 mm nominal diameter, 0.25 um nominal film thickness in a constant flow mode of 1.0 mL min -1, an average velocity of 30 cm sec -1 and a nominal initial pressure of 27.58 psi. Oven initial

temperature was 150°C and final temperature was 250°C. Initial temperature of inlet was

250°C. The NPD detector temperature was 325°C. Carrier gas was He (64.8 mL min -1).

-1 1 Detector gases were air (60.0 mL min ) and H 2 (3 mL min- ). Injection of samples was

splitless with initial temperature of 250°C and a pressure of 27.57 psi. Residues were

quantified by peak area measurement in comparison with Benfluralin (N-butyl-N-ethyl-2,

6-dinitro-4-(trifluoromethyl) aniline) as an internal standard peak area following

calculations detailed by Agilent (1998).

Prodiamine was separated on capillary column model Agilent 19091S-433, HP-5

MS (5%-Phenyl)-Methyl Siloxane, 30 m nominal length, 0.25 mm nominal diameter,

0.25 um nominal film thickness in a constant flow mode of 1.0 mLmin -1, an average

velocity of 30 cmsec -1 and a nominal initial pressure of 18.43 psi. Oven initial

temperature was 180°C and final temperature was 250°C.Initial temperature of inlet was

230°C. The NPD detector temperature was 300°C. Carrier gas was He (63.9 mL min -1).

-1 -1 Detector gases were air (60.0 mL min ) and H 2 (3 mL min ). Inlet was in splitless mode with initial temperature of 230°C and a pressure of 18.42 psi.

Residues were quantified by peak area measurement in comparison with

Benfluralin as internal standard peak area. One injection of 1 uL was made for each extract. Calibration standards were included every sixth extract. Control samples fortified

36 at 1000 ppm and 100 ppm, plus a method blank was included with each batch of 50 samples. Recovery calculations were made using EPA (2007) formulas.

Pendimethalin recovery from verdure and thatch, 0 to 5 cm and 5 to 10 cm soil

averaged 117% on day 0 with a coefficient of variation of 16%. Prodiamine recovery from verdure and thatch, 0 to 5 cm and 5 to 10 cm soil averaged 110% on day 0 with a coefficient of variation of 9.5%.

Concentrations of the herbicide were calculated on a basis of grams per kilogram

of dry soil section. Calibration standards were made following EPA (2007) protocols.

Active ingredients to prepare calibration standards (Chem Service,West Chester, PA)

were included every after six samples.

Analysis of variance (ANOVA) was conducted on the data using SAS © (SAS ©

Institute Inc., Cary, NC, 2002) GLM procedure. Treatment means were compared to the

control using Fisher’s least significant difference test (lsd) with α=0.05.

RESULTS

Pendimethalin dissipation

Calculated half lives for the first part of autumn (0 to 16 DAT) were lower than

those calculated for the second part (32 to 128 DAT). The half lives calculated for the

first part of autumn were: 6 ( R2=0.67, P=0.18), 7 ( R2=0.23, P=0.16) and 6

(R2=0.79, P=0.11) days for full following full dose, single full dose and half plus half

dose, respectively. For the second part of autumn (32 to 128 DAT) calculated half lives

37 were higher 30( R2=0.14, P=0.47) and 17( R2=0.13, P=0.48) days for full following full dose and half plus half dose, respectively. Half lives for spring showed the same tendency as for autumn, lower half lives for the first part of the season (0 to 16 DAT) but higher for the second part (32 to 128 DAT).Calculated half lives for spring 0 to 16 DAT were

27( R2=0.5, P=0.29),57( R2=0.48, P=0.02) and 12( R2=0.65, P=0.19) days, for full following full dose, single full dose and half plus half dose, respectively. On the contrary half lives for the second part of spring, 32 to 128 DAT, were 86.5 (R2=0.58, P=0.07) and

80( R2=0.75, P=0.02) days for full following full dose and half plus half dose, respectively, were higher.

Soil section was a significant factor on all dates (Table 1). More pendimethalin was detected in verdure and thatch section than in the other two sections (0 to 5 cm and 5 to 5 cm) (Figure 4).

Season was a significant factor on 0, 8, 16, 32, 36, 40, 48 and 128 DAT (Table 2).

The amount of herbicide as active ingredient (a.i) applied at Day 0 was 1.76 mg a.i/soil core (full dose) and 0.88 mg a.i./soil core (half dose); and as can be seen on Figures 5 and

6 the amount of herbicide recovered (full dose) at 0 DAT in autumn was higher than in spring 1.4 mg versus 0.9 mg, the same happened with half dose.

More herbicide was detected in spring treatments than autumn between 8 to 32

DAT treatments (Table 2). However at the end of the season (128 DAT) more herbicide was detected following autumn treatments (Table 2). Even though dose was not a significant factor through both seasons (Table 1), at the beginning (0 DAT) and at the end

128 (DAT) was significant, showing more herbicide per kg of dry soil at the highest dose

(full plus full) (Figures 5 and 6).

Rate of degradation from 0 DAT to 16 DAT was higher in autumn than in spring

(Figures 5 and 6).The amount of herbicide detected at 32 DAT ( date of the second application) was not twice the dose applied (3.52 mg/soil core full dose and 1.76 mg/soil core half dose) for both seasons. Again, the rate of degradation from 32 DAT to 128 DAT was higher in autumn than in spring (Figures 2 and 3).

Pendimethalin efficacy

Season and dose were significant factors in crabgrass control (Table 3). Better efficacy of crabgrass control with pendimethalin was obtained when it was applied in spring and at the higher dose twice with 0 crabgrass plants per m 2 in all dates of

evaluation (Table 3).

Days After Treatment (DAT) Source DF 0 4 8 16 32 36 40 48 64 128 ______p>F ______Season 1 0.0150 0.3070 0.0310 0.0001 0.0049 0.1213 0.0006 0.0574 0.6880 0.0002 Replication*Season 4 0.8902 0.2757 0.8329 0.3887 0.3098 0.2866 0.1297 0.5427 0.5464 0.1102 Soil Section (SS) 2 <0.0001 <0.0001 0.0491 <0.0001 <0.0001 <0.0001 <0.0001 0.0042 <0.0001 0.0006 Dose 2 0.0552 0.3762 0.3603 0.8059 0.0009 <0.0001 0.0267 0.3962 0.1530 0.4799 SS*Dose 4 0.0034 0.3993 0.3767 0.9581 <0.0001 <0.0001 0.0168 0.4210 0.5713 0.4361 SS*Season 2 0.0014 0.4718 0.2905 <0.0001 0.0006 <0.0001 <0.0001 0.0232 0.9005 0.0051 Dose*Season 2 0.7559 0.2787 0.4631 0.8100 0.0103 <0.0001 0.0320 0.4645 0.9789 0.6069 SS*Dose*Season 4 0.1484 0.1999 0.3079 0.8958 0.0019 <0.0001 0.0210 0.4183 0.8840 0.6299

Table 1. Analysis of Variance (ANOVA) on pendimethalin concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT) .

1.00

0.90 a verdure-thatch 0.80 a 0-5 0.70 a a

0.60 5-10

0.50 a a 0.40

0.30 a a

mg pendimethalin/kg dry soil mg 0.20 b 0.10 b b a a b b b b b b b b b b b b b b 0.00 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 4 . Distribution of pendimethalin residues (mg kg dry soil -1) among verdure - thatch, 0 to 5 cm and 5 to 10 cm soil layers over time. Columns followed by different letters are significantly different at p=0.05.Columns without l etters were not significantly different.

Season Days After treatment (DAT) 0 4 8 16 32 36 40 48 64 128

______-1 Pendimethalin detected mg kg dry soil ______

AU 07 0.34 a 0.26 a 0.05 b 0.04 b 0.44 a 0.22 a 0.03 a 0.05 b 0.02 a 0.04 a SP 08 0.21 b 0.21 a 0.20 a 0.17 a 0.11 b 0.38 a 0.26 b 0.29 b 0.02 a 0.001 b

Table 2. Mean concentration of pendimethalin (mg kg-1 dry soil) residues over time in different seasons of applications. 43

Factor 30 Jul 2008 15 Aug 2008 30 Aug 2008 15 Sep 2008 30 Sep 2008 Treatment Dose Season Number % Number % Number % Number % Number % crabgrass crabgrass crabgrass/ crabgrass crabgrass/ crabgrass crabgrass/ crabgrass crabgrass/ crabgrass /m 2 coverage m2 coverage m2 coverage m2 coverage m2 coverage Pendulum 2.3 kg a.i ha-1 Au 22 b 15 44 b 23 33 b 21 66 b 40 99 b 35 3.3 EC Pendulum 2.3 kg a.i ha-1+2.3 Au 11 b 6 22 b 13 33 b 19 66 b 35 88 b 52 3.3 EC kg a.i ha-1 Pendulum 1.14 kg a. i ha-1 Au 11 b 4 22 b 10 33 b 21 55 b 29 66 b 38 3.3 EC +1.14 kg a. i ha-1 Control Au 88 a 47 110 a 67 88 a 50 165 a 94 132 a 75

Pendulum 2.3 kg a.i ha-1 Sp 11 b 2 33 c 21 33 b 17 66 b 38 55 b 40 3.3 EC Pendulum 2.3 kg a.i ha-1+2.3 Sp 0 b 0 0 c 0 0 c 0 0 c 0 0 c 0 3.3 EC kg a.i ha-1 Pendulum 1.14 kg a. i ha-1 Sp 0 b 0 11 c 4 0 c 2 33 b 17 33 c 21 3.3 EC +1.14 kg a. i ha-1 Control Sp 110a 63 132 a 73 176 a 100 176 a 98 165 a 92

Analysis of Variance 44

Source p>F

Treatment ** ** ** ** **

Dose NS NS NS NS NS

Season NS NS * NS *

Season*Dose NS NS NS NS NS

Treatment * Dose NS NS ** NS **

Table 3. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different pendimethalin doses applied on Autumn 2007 and Spring 2008. Significance taken at P=0.05, NS† indicates no significance, ** indicates significance at 0.005,* indicates significance at 0.05. Numbers in the same column followed by different letters are significantly different at p=0.05

0.6

0.5 2.3 kg a.i ha-1+2.3 kg a.i ha-1 (2x)AU

0.4 2.3 kg a.i ha -1(1x)AU

1.14 kg a. i ha-1 +1.14 kg a. i ha-1(1x)AU 0.3

0.2 m pendimethalin/kg dry soil m 0.1

0 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 5 . Dissipation curve for pendimethalin applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2007.Error bars represent standard error of the mean (n=3).Dates of application for autumn were 8 October 2007 and 12 November 2007

2.3 kg a.i ha-1+2.3 kg a.i ha-1 3.00 (2x)SP 2.3 kg a.i ha -1(1x)SP 2.80

2.60 1.14 kg a. i ha-1 +1.14 kg a. i ha-1(1x)SP 2.40

2.20

2.00

1.80

1.60

1.40

1.20

1.00

mg pendimethalin/kg dry soil mg 0.80

0.60

0.40

0.20

0.00 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 6 . Dissipation curve for pendimethalin applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008. Dates of application for spring were 15 April 2008 and 15 May 2008.

Prodiamine dissipation

Calculated half lives for the first part of autumn (0 to 16 DAT) were lower than those calculated for the second part (32 to 128 DAT). The half lives calculated for the first part of autumn were: 2.5 (R2=0.46, P=0.31), 105 (R2=0.11,P=0.33) and 2

(R2=0.47,P=0.31) days for full following full dose, single full dose and half plus half

dose, respectively. For the second part of autumn (32 to 128 DAT) calculated half lives

were higher 300 (R2=0.11, P=0.51) and 208 (R2=0.05, P=0.66) days for full following

full dose and half plus half dose, respectively.

Half lives for spring showed the same tendency as for autumn, lower half lives for

the first part of the season (0 to 16 DAT) but higher for the second part (32 to 128

DAT).Calculated half lives for spring 0 to 16 DAT were 26(R2=0.39, P=0.37), 75

(R2=0.15, P=0.26) and 7 (R2=0.10, P=0.67) days, for full following full dose, single full

dose and half plus half dose, respectively. On the contrary half lives for the second part of

spring, 32 to 128 DAT, were 185 ( R2=0.14, P=0.45) and 135 (R2=0.28, P=0.27) days for

full following full dose and half plus half dose, respectively, were higher.

Soil section was a significant factor on all dates (Table 3), an exception were 4

and 8 DAT where the amount of herbicide detected was low. More prodiamine was

detected on verdure and thatch section than in the other two sections (0 to 5 cm and 5 to 5

cm) (Figure 4).

Season of application was a significant factor at 0, 16, 32, 36, 40 DAT but not at

the end (128 DAT) of the season (Table 3). Through the 128 DAT more herbicide was

47 detected in spring treatments than in autumn. However, no difference in herbicide content was detected at the end of the season (128 DAT) (Table 4).

Dissipation curves for prodiamine showed differences in the amount of herbicide detected at 0 DAT, autumn treatments showed 50% less herbicide than spring treatments, however dissipation curves from 0 to 16 DAT were similar showing a quick dissipation on time. After the second application (32 DAT) an increase of the herbicide detected was noted in both seasons (Figures 8 and 9).

Days After Treatment (DAT) Source DF 0 4 8 16 32 36 40 48 64 128 ______p>F

Season 1 0.0283 0.3167 0.1520 0.0068 0.0335 0.0395 0.0280 0.1497 0.0478 0.3429 Replication*Season 4 0.1113 0.4149 0.5894 0.4309 0.0493 0.9982 0.4827 0.8356 0.1119 0.4329 Soil Section (SS) 2 <0.0001 0.3353 0.5052 0.0499 0.0129 0.0159 <0.0001 0.0061 0.0535 0.0219 Dose 2 0.0063 0.3963 0.4976 0.5225 0.4927 0.9110 0.0014 0.9522 0.3398 0.3246 SS*Dose 4 0.0010 0.4466 0.3561 0.8460 0.5822 0.9833 0.0001 0.9952 0.7464 0.2763 SS*Season 2 0.0104 0.3670 0.5056 0.0579 0.0135 0.0169 0.0103 0.1296 0.0977 0.3719 Dose*Season 2 0.1929 0.3888 0.5012 0.5421 0.4900 0.9120 0.1444 0.6523 0.4730 0.6228 SS*Dose*Season 4 0.1668 0.4359 0.3544 0.8362 0.5785 0.9847 0.1098 0.7837 0.8475 0.8852

49 Table 4. Analysis of Variance (ANOVA) on prodiamine concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT).

Season Days After treatment DAT 0 4 8 16 32 36 40 48 64 128 ______Prodiamine detected mg kg -1 dry soil----______AU 07 0.13253b 0.00029a 0.00089a 0.00010b 0.00062b 0.00023b 0.0001856b 0.001204a 0.00113b 0.002422a SP 08 0.28615a 0.01290a 0.07223a 0.03405a 0.08913a 0.02748a 0.007351a 0.004861a 0.02300a 0.005687a

Table 5. Mean concentration of prodiamine (mg kg -1 dry soil) residues over time in different seasons of application. 50

0.70

a 0.60

0.50 verdure-thatch 0-5 cm

0.40 5 to 10 cm

0.30

0.20 mg prodiamine/kg dry soil prodiamine/kg mg

a 0.10 a a a a a b a a a a b b b b b b b a 0.00 a a a b b b b b bb b 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 7. Distribution of prodiamine residues mg*kg dry soil -1 among verdure-thatch, 0 to 5 cm and 5 to 10 cm over time. Columns followed by different letters are significantly different at p=0.05.Columns without letters were not significantly different.

0.80

0.70 0.737 kg a.i.ha-1+0.737 kg a.i.ha-1 (2x)AU 0.60 0.737 kg a.i.ha-1 (1x)AU 0.50 0.368 kg a.i.ha-1+0.368 kg a.i.ha-1 (1x)AU 0.40

0.30

0.20 mg of prodiamine/kg dry soil of prodiamine/kg mg 0.10

0.00 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 8. Dissipation curve for prodiamine applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2008.Dates of application for autumn were 8 October 2007 and 12 November 2007 .

1.80 0.737 kg a.i.ha-1+0.737 kg 1.60 a.i.ha-1 (2x)AU 0.737 kg a.i.ha -1 (1x)AU 1.40

1.20 0.368 kg a.i.ha-1+0.368 kg a.i.ha-1 (1x)AU 1.00

0.80

0.60

0.40 mg of prodiamine/kg dry soil of prodiamine/kg mg 0.20

0.00 0 4 8 16 32 36 40 48 64 128

Days After Treatment

Figure 9 . Dissipation curve for prodiamine applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008. Dates of application for spring were 15 April 2008 and 15 May 2008.

30 Jul 2008 15 Aug 2008 30 Aug 2008 15 Sep 2008 30 Sep 2008 Treatment Dose Season Number % of Number % of Number % of Number % of Number % of crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass coverage coverage coverage coverage coverage Barricade 0.737.08 kg a.i. ha -1 Au 8b 4.2 26b 14.4 26b 14.4 33b 18.75 44b 25 65WG Barricade 0.737.08 kg a.i ha -1.+ Au 0b 0 3b 2.1 0b 0 0c 0 0b 0 65WG 0.737.08 kg a.i ha -1 Barricade 0.368.54 kg a.i. ha -1 + Au 3b 1.8 8b 4.4 89a 4.4 7bc 3.8 7b 3.8 65WG 0.368.54 kg a.i. ha -1 Control Au 86a 48.1 119a 66.9 89a 50 167a 93.8 133a 75 Barricade 0.737.08 kg a.i. ha -1 Sp 11b 6.3 22b 12.5 22.2b 12.5 18b 10 11b 6.3 65WG Barricade 0.737.08 kg a.i ha -1.+ Sp 0b 0 0b 0 0b 0 0c 0 0b 0 65WG 0.737.08 kg a.i ha -1 Barricade 0.368.54 kg a.i. ha -1 + Sp 0b 0 0b 0 8b 4.4 0c 0 0b 0 65WG 0.368.54 kg a.i. ha -1 Control Sp 111a 62.5 130a 73.1 178a 100 173a 97.5 167a 93.8 Analysis of Variance

Source p>F 54

Treatment ** ** ** ** **

Dose NS NS NS NS NS

Season NS NS * NS NS

Season*Dose NS NS NS NS NS

Treatment * Dose NS NS ** NS NS

Treatment * Season NS NS ** NS NS

Table 6. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different prodiamine doses applied on autumn 2007 and spring 2008. Significance taken at P=0.05, NS† indicates no significance, ** indicates significance at 0.005,* indicates significance at 0.05. Numbers in the same column followed by different letters are significantly different at p=0.05

Prodiamine efficacy

Higher dose of Barricade 65 WG 0.737.08 kg. a.i. ha-1 plus 0.737.08 kg. a.i. ha -1 applied either in autumn or spring showed 100% crabgrass control (Table 5).Half sequential dose applied in spring showed better control than applied on autumn.

DISCUSSION

More pendimethalin was detected in autumn applications at the beginning (0

DAT) and at the end of the season (128 DAT), due to the differences in soil temperature

and moisture between autumn and spring. During spring, soil temperatures were high

( between 15°C to 25°C) and soil moisture low (200cbar) during the first 56 days after

first herbicide application (Figures 1 and 2), accelerating pendimethalin degradation as

reported previously in the literature ( Zimdahl et al.,1984; Veeh et al, 1996; Walker et al,

1983; Weber, 1990).

Prodiamine was more rapidly dissipated than pendimethalin in both seasons. This

can be explained by prodiamine’s susceptibility to photolysis in aqueous solution (EPA,

2002); in addition the amount of prodiamine applied per kilogram of dry soil (0.56 mg

a.i, full dose) was lower than for pendimethalin (1.76 mg a. i., full dose). A second

application of herbicide did not double the amount of herbicide in the soil, for both

herbicides. Half lives (amount of time needed to obtain half of the dose applied) for both

herbicides were lower than those reported in the literature. Weber (1990) reported 122

and 120 days for pendimethalin and prodiamine respectively.

Distribution of pendimethalin through soil profile was similar to that reported by

Stahnke et al., 1991). The majority of the herbicide was found in the verdure-thatch layer.

Similar behavior was observed when analyzing prodiamine (Figure 4).

Due to their low water solubilities and high potential for hydrogen bonding, dinitroaniline herbicides are strongly sorbed to soil (Weber, 1990), this phenomena can be explained because pendimethalin and prodiamine have both two dinitro groups.

Prodiamine data showed a quick dissipation, especially in autumn where a second application was not detected on soil residues. Few residues were found at 128 DAT contrary to the reported by Bohn et al (1985) where half life (in the field reported for prodiamine was 120 days.

Crabgrass coverage was 0%, at the end of the season (30 september 2008), for

prodiamine and pendimethalin applied in Spring in full following full dose, even though

the amount of herbicide detected at 128 DAT was low, but detectable, indicating the

premergence activity of both herbicides during the window of crabgrass seed emergence.

Higher dose (full-following-full) applied early in the season (spring application)

seems to be the better way to control crabgrass using pendimethalin. In the case of

prodiamine no seasonal effect was detected and higherer doses either in autumn or spring

reported near 100% crabgrass control.

Crabgrass control was associated with higher herbicide dose and spring

applications. More herbicide detected in the soil does not necessarily indicate better weed

control, suggesting the importance of preemergence herbicide application timing.

BIBLIOGRAPHY

Agilent. 1998.Understanding your Agilent ChemStation. Available at http://www.chem.agilent.com/Library/usermanuals/Public/G2070- 91125_understanding_e-book.pdf (verified 30 November 2008)

Bhowmik, P. C. 1987. Smooth crabgrass (Digitaria ischaemum) control in Kentucky bluegrass ( Poa pratensis ) turf with bensulide and napropamide. Weed Technol. 1:145- 148.

Bhowmik, P., C. and Bingham,S.,W.1990 . Dinitroanilines in cool-season turf. Weed Technology. 4:387-393

Bingham, S. W., and R. E. Schmidt. 1964. Crabgrass control in turf. Proc. South. Weed Sci. Conf. 17:113-122.

Dernoeden, P., H. 1990. Comparison of Three Herbicides For Selective Tall Fescue Control in Kentucky Bluegrass. Agronomy Journal 82:278-282.

Environmental Protection Agency.2007.Environmental Chemistry Method (ECM).Available at http://www.epa.gov/oppbead1/methods/ecmindex.htm (verified 20 June 2007)

EPA. 2002. Pesticides: Freedom of Information Act (FOIA). Available at http://www.epa.gov/pesticides/foia/reviews/110201/110201-016.pdf (verified 05 March 2009)

Extoxnet.1993. Available at http://pmep.cce.cornell.edu/profiles/extoxnet/metiram- propoxur/pendimethalin-ext.html (verified 02 February 2009)

Fermanian, T.W and Haley J.E.1994.Fall application of prodiamine for spring crabgrass (Digitaria spp .) control. Weed Technology.8 (3): 612-616.

Hatzinikolaou, A.S, Eleftherohorinos, I.G., Vasilakoglou, I.B.2004. Influence of Formulation on the Activity and Persistence of Pendimethalin. Weed Technology.18:397–403.

Johnson B.J.1997. Reduced herbicide rates for large crabgrass (Digitaria sanguinalis) and goosegrass (Eleusine indica) control in bermudagrass (Cynodon dactylon).Weed Science, 45: 283-287.

Johnson B.J.1975.Purple nutsedge control with bentazon and perfluidone in turfgrasses. Weed Science , 23: 349-353

Lockhart, S.J. and Howatt, K.A. 2004. Split Applications of Herbicides at Reduced Rates Can Effectively Control Wild Oat ( Avena fatua ) in Wheat. Weed Technology 18(2):369- 374.

Lycan, D., W. and Hart, S., E. 2006 . Seasonal Effects on Annual Bluegrass ( Poa annua ) Control in Creeping Bentgrass with Bispyribac-Sodium. Weed Technology 20(3):722- 727. McCurdy, J., D. McElroy J., S., Breeden, G.,K., and Kopsell D., A. 2008. Mesotrione plus prodiamine for smooth crabgrass ( Digitaria ischaemum ) control in established bermudagrass turf. Weed Technology 2008 22:275–279.

Syngenta Crop Protection. Material Safety Data Sheet for prodiamine.2009. Available at http://www.syngentaprofessionalproducts.com/prodrender/index.aspx?nav=labels&ProdI D=729&ProdNM=Barricade%2065WG (verified 03 March 2009)

Throssell, C. and Weisenberger, D. Preemergence Crabgrass Control - 1999 (Daniel Turf Center).1999. Available at http://www.agry.purdue.edu/turf/report/1999/page30.pdf (verified 04 March 2009)

CHAPTER 3

DISSIPATION AND EFFICACY OF BENSULIDE

ABSTRACT

Bensulide [S-(O,O-diisopropyl phosphorodithioate) ester of N-(2-mercapto) benzenesulfonamide] is an organophosphate pre-emergence herbicide, and is one of the

few products available for use on bentgrass putting greens to control annual weeds. This

study was conducted to determine the efficacy and dissipation dynamics of the herbicide

bensulide, applied at different rates and seasons of application (autumn and spring).

Bensulide was applied at three rates (maximum label rate applied twice at 30 days

interval, half label rate applied twice at a 30 day interval, and maximum label rate applied

once) and application timing (autumn and spring).The design of the experiment was

completely randomized with three replicates per treatment. The whole experimental area

was reseeded with crabgrass ( Digitaria sp) before herbicide application. Soil temperature and moisture were measured during the experiment. Soil samples were taken from each individual plot: 0, 4, 8, 16, 32, 36, 40, 48, 64 and 128 days after treatment. Each soil sample was divided in three sections: verdure-thatch, 0 to 5 cm and 5 to 10 cm and assayed for bensulide. More herbicide was detected on the verdure and thatch layer; bensulide dissipation was quicker in spring than autumn, mainly due to differences in soil moisture and temperature. Crabgrass control was better when bensulide was applied in spring mainly because the amount of herbicide remained on soil by May 15 2008 (initial date of crabgrass seed germination in Ohio) was 79% versus less than 29% of bensulide in autumn treatments.

INTRODUCTION

Bensulide [S-(O,O-diisopropyl phosphorodithioate) ester of N-(2-mercapto) benzenesulfonamide] is an organophosphate herbicide. It is used for preemergence control of annual grasses and broadleaf weeds in agricultural crops (60-65% of all use).

Current registered use sites are: carrots, fruiting vegetables, leafy vegetables (mostly head lettuce), dry bulb vegetables (onions), cucurbits (mostly melons), and cole crops

(cauliflower, cabbage, broccoli, broccolini, broccoflower). Products containing bensulide are also intended for outdoor homeowner use on lawns and ornamentals, and application by professional lawncare operators to lawns, ornamentals, parks, and recreation areas

(EPA, 2006).

Bensulide is one of the few products available for use on bentgrass putting greens; it should not be used on newly seeded turf. Recommended use rates for crabgrass control

range from 9 to 13.44 kg.ai ha -1. However, more consistent control of crabgrass will be obtained with two applications of it at rates ranging from 9 to 13.44 kg.ai ha -1 spaced 6 to

8 weeks apart (Hart, 2000).

Niemczyk and Krause (1994) working with preemergence herbicides applied to turfgrass, found that bensulide is more mobile than pendimethalin. Menges and Tamez

(1974) working with different herbicides and soil depth incorporations found that bensulide persists in appreciable amounts in the soil 12 months after treatment.

Bingham and Schmidt (1967) working with granular and emulsifable formulations

of bensulide found large amounts of the granular formulations eleven months after the

fourth annual application; detectable quantities were obtained to depths of 12.75 cm.

However, the emulsifiable concentrate treatments did not persist for eleven months following the fourth application in detectable quantities in the soil.

Although the environmental fate data base for bensulide is not complete,

information from acceptable laboratory studies indicates bensulide is highly persistent in

both plants and soils (U.S. Public Health Service, 1995; EPA, 2007). The main route of

dissipation of bensulide appears to be aerobic soil metabolism with a reported half-life of

1 year. Under aerobic conditions it appears that mineralization of bensulide to CO 2, and immobilization as unextractable residues are the major mechanisms of dissipation in the soil. Under anaerobic soil conditions bensulide did not degrade. Based on the lack of degradation under laboratory conditions, it is predicted that bensulide will be extremely persistent in anaerobic terrestrial ecosystems (EPA, 2007).

In studies cited by EPA (2002) bensulide dissipation data were not acceptable because of insufficient reporting of test parameters in 8 different studies. The field dissipation half-life of bensulide was reported to range from 8-34 days in studies conducted in California and from 91-210 days in studies conducted in Mississippi. In none of the studies was a consistent decline of parent compound observed. In another unacceptable but upgradeable field dissipation study, calculated first-order half-lives for bensulide in the top 6 inches of soil were 106.8 days (registrant-calculated) and 80.4 days

(EPA reviewer-calculated). Bensulide and its degradate bensulide oxon were found only in the top 6 inches of the soil. These field dissipation data contrast with the laboratory data but do indicate qualitatively that bensulide will be persistent, although not to the extent indicated in the laboratory.

In the upgradeable field study with the 106.8 day half-life, the deficiencies were in reporting ancillary data and not in the conduct of the study. Canadian studies indicated a half life for bensulide up to 363 days in the aerobic soil conditions (Pest Management

Regulatory Agency, Health Canada, 2004)

Bensulide does not evaporate easily and leaches very little in sand, clay, or organic soils because it strongly binds to the top 0 to 2 inches of soil. However, it can be carried off site with sediment or dust. Bensulide is slowly broken down by soil microorganisms. The rate of degradation increases with increasing soil temperature and organic matter, but decreases with increasing basicity (U.S. Public Health Service, 1995)

Crabgrass species (Digitaria spp.) have an excellent susceptibility to bensulide

when it is applied before seed emergence (Breeden and Brosnan, 2009).Used at

recommended doses bensulide provides an excellent crabgrass control (Bingham and

Schmidt, 1967; Watschke et al., 1974; Hall et al., 1974 and Callahan et al., 1983).

Various experiments have been done measuring the efficacy of herbicides applied

as split or single application and in different seasons; however, limited research has been

done on single versus split application of premergence herbicides controlling crabgrass

(Digitaria sp ). The objective of this study was to associate crabgrass control with

herbicide residue level following application of different rates of bensulide applied either

once or as a split application. Difference in seasons of application (autumn and spring)

was also studied to determine if crabgrass control could be achieved with an autumn

application.

MATERIALS AND METHODS

Field Procedures

Field experiments were conducted in Kentucky bluegrass turf at the The Ohio

Turfgrass Foundation Research & Education Facility in Columbus, Ohio during autumn

2007 and spring 2008. The turfgrass area was prepared and dethatched with a Bluebird

dethatcher/Lawn Comb (BlueBird Beatrice, Nebraska) and over seeded with smooth crabgrass ( Digitaria ischaemum ) at 1.2 kg ha-1 on September 15, 2007. Adequate turfgrass recovery time was allowed before herbicide application. The soil was a

Brookston silty-clay loam (fine, loamy, mixed, mesic Typic Argiaquoll) with 21% sand,

44% silt, 36% clay, 6.4% organic matter, pH 7.0 , cation exchange capacity (CEC) of 11.7

meq/100g.Field plots were 1.7 m2 with a 0.9 m border and were arranged in a randomized complete block design with treatments replicated three times. Herbicide efficacy ratings were taken every two weeks from 1 May to 30 September, 2008 and were based on total crabgrass plant counts (number per m2, with a minimum of 0 and a maximum of 16) and visual percentage of weeds coverage (minimum of 0% and maximum of 100%).

Bensulide (Bensumec 4LF, pbi Gordon Corporation 1217 West 12 th Street, Kansas City

Missouri) was applied to the plots at either 11339.75 g a.i ha -1 (full dose) or 5669.88 g a. i ha -1 (half dose). Treatments were full dose followed 32 days later by a second full dose application, half dose followed by half dose and full dose applied once. Dates of application were 8 October 2007 and 12 November 2007 (autumn applications) and 15

April 2008 and 15 May 2008 (spring applications).

Applications were made with a CO 2-pressurized backpack sprayer at 40 psi (R&D

Sprayers, Opelousas, LA) equipped with 2-6503 flat fan nozzles (Teejet, Wheaton, IL) nozzles height of 40 cm, with an effective spray width of 3 feet with water as carrier.

Both herbicides were applied in 2 liters of water with irrigation of 1.3 cm immediately after treatment.

The experimental area was mowed once a week at 5 cm with a Walker mower

with catcher (Walker Manufacturing Co, Fort Collins, Co) and clippings collected. The

site was irrigated as necessary to avoid wilt and soil temperature (Figure 1) and soil

moisture (Figure 2) were registered once per hour using four 250 Data Logger Temp/RH

(Spectrum Technologies, Inc. Plainfield, IL) installed in each side of the experimental

area. Each of them had one external soil temperature sensor and one watermark soil. Data

from sensors was processed using Spec 7 Basic Software (Spectrum Technologies, Inc.

Plainfield, IL). In addition natural precipitation was measured (Figure 3).

Sampling and analysis of pesticides

Soil samples were randomly taken 0 (2 hours after herbicide application), 4, 8, 16,

32, 36, 40, 48, 64 and 120 days after treatment (DAT), using a lever action hole cutter

(Par-Aide Products Co., Lino Lakes, Minnesota). Each soil sample was partitioned into

verdure and thatch, 0 to 5 cm, and 5 to 10 cm soil depth sections. Samples were weighed,

placed in 16 oz. glass jars and covered with aluminum foil, properly labeled and stored at

-20°C until residue analysis.

For herbicide analysis, each soil section was thawed and a representative 20 g sample was placed in a 500 ml Erlenmeyer flask, herbicide was extracted from the soil by shaking with 100 mL ethyl acetate for 3 hours on a platform shaker (Lab-line

Instruments, Inc. Melrose Park. IL 60160) at 200 RPM. The extract was vacuum filtered by passing through Whatman G6 glass fiber filter paper. The flask was rinsed 3 times with 5 ml of ethyl acetate, swirling the flask and pouring rinsate through the filter. Ethyl acetate was removed by rotary evaporation (Rotavapor RE 121, Buchi, Switzerland) at

40° C, using a water bath (Buchi 461, Switzerland).The evaporatory flask was rinsed 3 times with 3 mL of Dichloromethane each time, the rinsate was transferred to a 10 ml

Reacti-Vial (Thermo-Fisher Scientific, Rockford, IL) . The Dichloromethane was evaporated to a final volume of 2 ml using a Reacti-Vap, Evaporating Unit (Pierce Model

18780, Rockford, Illinois). The concentrate was passed through a 0.45 um nylon membrane filter (Gelman Sciencies, Ann Harbor, MI). Two millimeters of the extract were transferred to an autosampler vial for analysis by gas chromatography (Model 6890

Universal, Agilent technologies, Wilmington, DE) with a Nitrogen Phosphorus Detector

(NPD).

Bensulide was separated on capillary column model Agilent 19091S-433, HP-5

MS (5%-Phenyl)-Methyl Siloxane, 30 m nominal length, 0.25 mm nominal diameter,

0.25 um nominal film thickness in a constant flow mode of 2.0 mLmin -1, an average

velocity of 41 cmsec -1 and a nominal initial pressure of 19.41 psi. Oven initial

temperature was 40°C and final temperature was 250°C. Initial temperature of inlet was

250°C. The NPD detector temperature was 325°C.

Carrier gas was He (64.9 mL min -1). Detector gases were air (60.0 mL min -1) and

H (3 mLmin -1). Inlet was in splitless mode with initial temperature of 250°C and a pressure of 19.4 psi. Residues were quantified by peak area measurement in comparison with Benfluralin (N-butyl-N-ethyl-2, 6-dinitro-4-(trifluoromethyl) aniline) as an internal standard peak area following calculations detailed by Agilent (1998).

One injection of 1 uL was made for each extract. Calibration standards were included every sixth extract. Control samples fortified at 1000 ppm and 100 ppm, plus a method blank was included with each batch of 50 samples. Recovery calculations were made using EPA (2007) formulas. Bensulide recovery from verdure and thatch, 0 to 5 cm

and 5 to 10 cm soil averaged 92% on day 0 with a coefficient of variation of 14%.

Concentrations of the herbicide were calculated on a basis of grams per kilogram

of dry soil section, using an equation built using a response ratio and an amount ratio,

described by (Agilent, 1998). In addition, calibration standards were made following

EPA (2007) protocols. Active ingredients to prepare calibration standards (Chem Service,

West Chester, PA) were included after every six samples.

Analysis of variance (ANOVA) was conducted on the data using SAS © (SAS ©

Institute Inc., Cary, NC, 2002) GLM procedure. Treatment means were compared to the

control using t tests lsd (least significance difference) with α=0.05.

RESULTS

Dissipation

Bensulide dissipated faster at the beginning of autumn (0 to 16 DAT) with half

lives of 12.8 ( R2=0.56, P=0.25), 25 ( R2=0.50, P=0.02), and 22 (R2=0.42, P=0.34) days for full following full dose, single full dose and half plus half dose, respectively. However from 32 DAT to 128 DAT bensulide dissipated slower than before with calculated half lives of 70 (R2=0.60, P=0.07), and 128 (R2=0.30, P=0.26), days for full following full

dose and half plus half dose, respectively. During the first days of spring (0 to 16 DAT)

bensulide had half lives of 14 ( R2=0.50, P=0.29), 11( R2=0.31, P=0.09),and 86 (R2=0.87,

P=0.06), days for full following full dose, single full dose and half plus half dose,

respectively. For the period of 32 to 128 DAT half lives were shorter than before with

computed half lives of 11 ( R2=0.65, P=0.05), and 33 ( R2=0.44, P=0.15), days for full

following full dose and half plus half dose, respectively.

Season of application was a significant factor; more bensulide was detected in

autumn than spring (Tables 7 and 8). The amount of herbicide detected on Day 0 in

autumn was higher than in spring for all doses (Figures 11 and 12).In spring the amount

of herbicide detected in full dose treatments (full following full and single full) (Figure

12). At the end of the season (128 DAT) more herbicide was detected on autumn

treatments. Soil section was a significant factor (Table 7); verdure-thatch section showed

more bensulide concentration on time, indicating a limited movement of the herbicide

through the profile (Figure 10).

Dose was a significant factor through all dates but 4, 16 and 48 DAT, demonstrating that more herbicide was detected on treatments with full dose. Interactions of soil section (SS) by dose, SS by season, dose by season and SS by dose by season were detected at 0 DAT after that the level of significance of the interactions was higher than

0.05 except for SS by season (Table 7).Showing more herbicide on thatch layer during spring. Bensulide dissipation was quicker in spring than autumn, with more herbicide detected at 0 and 128 DAT in autumn treatments (Figures 11 and 12).

Efficacy

Better crabgrass control was achieved when herbicide was applied in spring

(Table 8), even though the amount of bensulide in the soil was lower in spring than in

autumn, however the amount of herbicide at the date of crabgrass seed emergence

(starting on May 15) was higher for spring treatments. Comparing with the control

bensulide doses applied controlled crabgrass (Table 8). At the end of the season

treatments applied in spring showed no crabgrass coverage regardless dose.

Days After Treatment (DAT) Source DF 0 4 8 16 32 36 40 48 64 128 ______p>F ______Season 1 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.0013 0.0003 0.0001 <0.0001 <0.0001 Replication*Season 4 0.4183 0.1344 0.8303 0.8466 0.2290 0.1269 0.1503 0.9441 0.3505 0.0886 Soil Section (SS) 2 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.0005 <0.0001 0.0010 0.0004 0.0739 Dose 2 <0.0001 0.7110 0.0331 0.3509 0.0241 0.0506 0.0022 0.1517 0.0463 0.0800 SS*Dose 4 <0.0001 0.2755 0.7370 0.5883 0.2710 0.3494 0.0026 0.5362 0.1904 0.3342 SS*Season 2 <0.0001 0.0002 <0.0001 <0.0001 0.0114 0.0512 0.3488 0.1346 0.0116 0.0789 Dose*Season 2 0.0270 0.7160 0.1755 0.2746 0.0807 0.0506 0.8400 0.4849 0.0755 0.0829 SS*Dose*Season 4 0.0075 0.4039 0.6850 0.8023 0.2147 0.3679 0.9800 0.9642 0.3042 0.3241

Table 7. Analysis of Variance (ANOVA) on bensulide concentration in 3 soil section (SS) verdure and thatch, 0 to 5

70 cm and 5 to 10 cm at different sampling dates (DAT).

6.00000

5.00000 a

verdure -thatch 4.00000

0-5 cm

3.00000 a 5-10 cm a

2.00000 a a a a mg of/kgdry soil of bensulide mg b a a 1.00000 a b b b b b b b aab c c b b b b b b b c 0.00000 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 10. Distribution of bensulide residues (mg kg dry soil -1) among verdure-thatch, 0 to 5 cm and 5 to 10 cm Autumn 07 and Spring 2008. Columns followed by different letters are significantly different at p=0.05.Columns without letters were not significantly different.

Season Days After treatment DAT 0 4 8 16 32 36 40 48 64 128 ______Bensulide detected mg kg -1 dry soil ______AU 07 2.55a 1.66a 1.22a 1.39a 2.05a 1.61a 1.16a 1.03a 0.79a 0.65a SP 08 0.95b 0.55b 0.14b 0.18b 0.47b 0.49b 0.40b 0.17b 0.07b 0.00b

Table 8. Mean concentration of bensulide (mg kg -1 dry soil) residues over time in different seasons of applications. 72

4.5 11.3 kg a.i ha-1 +11.3 kg a.i ha- 1(2x)AU 4 11.3 kg a.i ha -1(1x)AU 3.5 5.7 kg a. i ha -1+ 5.7 kg a. i ha - 3 1(1x)AU

2.5

1.5

1 mg bensulide/kg dry soil bensulide/kgmg 0.5

0 0 4 8 16 32 36 40 48 64 128

Days After Treatment

Figure 11 .Dissipation curve for bensulide applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2007.Dates of application for autumn were 8 October 2007 and 12 November 2007

2.5

11.3 kg a.i ha-1 +11.3 kg a.i ha-1(2x)SP 2 11.3 kg a.i ha-1(1x)SP

1.5 5.7 kg a. i ha -1+ 5.7 kg a. i ha-1(1x)SP

1 mg bensulide/kg dry soil bensulide/kgmg 0.5

0 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 12 .Dissipation curve for bensulide applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008. Dates of application for spring were 15 April 2008 and 15 May 2008.

Factor 30 Jul 2008 15 Aug 2008 30 Aug 2008 15 Sep 2008 30 Sep 2008

Treatment Dose Season Number % Number % Number % Number % Number % crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass coverage coverage coverage coverage coverage Bensumec 11.3 kg a.i ha- Au 3b 1.88 7b 3.75 14b 8.12 33c 18.75 44b 25 4LF 1 Bensumec 11.3 kg a.i ha- Au 14b 8.12 22b 12.50 33b 18.75 48c 27 59b 33 4LF 1 +11.3 kg a.i ha-1 Bensumec 5.7 kg a. i ha- Au 59b 33.12 40b 22.50 51b 28.75 70b 39.37 51b 28.75 4LF 1+ 5.7 kg a. i ha-1 Control Au 86a 48.12 119a 67 89a 50.00 167a 93.75 133a 75

Bensumec 11.3 kg a.i ha- Sp 0b 0 0b 0 0b 0 0c 0 0b 0 4LF 1 Bensumec 11.3 kg a.i ha- Sp 0b 0 0b 0 0b 0 0c 0 0b 0 4LF 1 +11.3 kg a.i ha-1 Bensumec 5.7 kg a. i ha- Sp 0b 0 3b 1.88 3b 1.88 0c 0 0b 0 4LF 1+ 5.7 kg a. i ha-1 Control Sp 111a 62.50 130a 73.12 178a 100 178a 100 167a 93.75 75 Analysis of Variance

Source p>F

Treatment ** ** ** ** **

Dose NS NS NS * NS

Season NS NS NS ** **

Season*Dose NS NS NS * NS

Treatment * Dose NS NS NS NS NS

Treatment * Season NS NS ** ** **

Table 9. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different bensulide doses applied on Autumn 2007 and Spring 2008. Significance taken at P=0.05, NS† indicates no significance, ** indicates significance at 0.005,* indicates significance at 0.05. Numbers in the same column followed by different letters are significantly different at p=0.05

DISCUSSION

The amount of bensulide detected in autumn was higher, in all sampling dates, than in spring. This indicates a quick degradation of the herbicide under high soil temperatures (between 15 to 25°C) and low soil moisture (200cbar) (Figures 1 and 2), as reported in the literature. Bensulide degradation increases with increasing soil temperature (U.S. Public Health Service, 1995; McCarty and Colvin, 1993). Approximate

half life for bensulide was between 8 to 16 days. Reported half lives for bensulide varies

with minimum values of 8 days (EPA, 2002) and maximum of 363 days (Pest

Management Regulatory Agency, Health Canada. 2004). The decrease of half-life in

pesticides applied over turf has been reported in the literature by Gardner et al. (2000).

Better crabgrass control was achieved with spring applications. This fact was

observed by Reicher and Throssell (1993) even though the amount of herbicide detected

in spring was lower than in autumn. Nevertheless the amount of herbicide in spring when

crabgrass seeds were emerging (starting on May 15) was higher than for autumn. Autumn

treatments controlled crabgrass, as reported in literature, bensulide persists in soil to

control large crabgrass a year after treatment (Callahan et al, 1983). However bensulide

applied in autumn does not provide 0 % crabgrass coverage as spring application does,

mainly because the timing of herbicide application was better in spring than autumn for

crabgrass control. This fact was different from the one reported by Agnew and Christians

(1989), they tested six different application dates in autumn and spring in Iowa starting

on November and finishing on May. They observed that bensulide provided 90% or

better crabgrass control on all application dates, the difference with the present study was, the autumn date of application, bensulide was applied on October 8, thus the herbicide was exposed to the high temperatures at the beginning of October (Figure 1).

Even though bensulide has been reported to be persistent (Niemczyk and Krause,1994),

an October application was early to control crabgrass the following spring.

BIBLIOGRAPHY

Agilent. 1998.Understanding your Agilent ChemStation. Available at http://www.chem.agilent.com/Library/usermanuals/Public/G2070- 91125_understanding_e-book.pdf (verified 15 April 2009)

Agnew, M., L. and Christians,N.E.1989. Influence of application dates on the effectiveness of four premergence herbicides for crabgrass control. The 6 th International Turfgrass Research Conference, Tokyo, July 31-August 5.

Bingham, S., W. and Schmidt, R., E. 1967. Residue of bensulide in turfgrass soil following annual treatments for crabgrass control. Agronomy Journal 59:327-329. Breeden,G and Brosnan J.,T. 2009. Crabgrass Species Control in Turfgrass. The University of Tennessee Extension. Available at http://www.utextension.utk.edu/publications/wfiles/W146.pdf (verified 20 June 2007)

Callahan, L., M., Overton, J., R., Sanders, W., L. 1983. Initial and Residual Herbicide Control of Crabgrass (Digitaria spp.) in Bermudagrass (Cynodon dactylon) Turf. Weed Science, 31:619-622

EPA. Environmental Field Branch Office of Pesticide Programs. 2002. Bensulide Analysis of Risks to Endangered and Threatened Salmon and Steelhead. Available at http://www.epa.gov/espp/litstatus/effects/bensulide_analysis_final.pdf (verified 20 June 2007)

EPA. 2006. Interim Reregistration Eligibility Decision (IRED) Bensulide. Available at http://www.epa.gov/oppsrrd1/REDs/2035ired.pdf (verified 20 June 2007)

EPA. Environmental Fate and Effects Division Office of Pesticide Programs. 2007. Risks of Bensulide Use to Federally Listed California Red Legged Frog (Rana aurora draytonii ). Pesticide Effects Determination. Available at

http://www.epa.gov/espp/litstatus/effects/redleg-frog/bensulide/determination.pdf (verified 20 June 2007)

Hall, J. R., Deal, E., E. and Powell, A., J. 1974. Seven years of smooth crabgrass control in turfgrass with registered and experimental herbicides. Proc. Northeast Weed Sci. Soc. 28:399-405. Pest Management Regulatory Agency Health Canada. 2004. Re-evaluation Decision Document. RRD2004-22. Available at http://dsp-psd.pwgsc.gc.ca/Collection/H113-12- 2004-22E.pdf (verified 20 June 2007) Hart, S. 2000.Crabgrass and Goosegrass control in cool season turfgrass. Rutgers Cooperative Extension Bulletin. Available at njaes.rutgers.edu/pubs/download- free.asp?strPubID=E233 (verified 20 June 2007)

Niemczyk H.D. and Krause A.A.1994.Behaviour and mobility of premergent herbicides in turfgrass: a field study.J.Environ.Sci.Health, B29(3), 507-539.

Miller, J., H; Keeley P., E.; Thullen, R. J. and Carter C. H. 1978. Persistence and Movement of Ten Herbicides in Soil. Weed Science 26: 20-27.

Menges, R., M. and Tamez, S. 1974. Movement and persistence of bensulide and trifluralin in irrigated soil. Weed Science 22: 67-71.

U.S. Public Health Service. 1995. Hazardous Substance Data Bank. Washington, DC. Pages 5-9

Watschke, T.L., Duich,J.M. and Waddington,D.V.1974.Evaluation of premergence herbicides for crabgrass control in 1973.Proceedings of the annual meeting of the Northeastern Weed Science Society.28:395-398.

CHAPTER 4

DISSIPATION AND EFFICACY OF DITHIOPYR

ABSTRACT

Dithiopyr [ S,S -dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-

(trifluoromethyl)-3,5-pyridinedicarbothioate] was the first herbicide released from the new pyridine class and it was particularly developed for control of annual grasses and annual broadleaf weeds in established turfgrasses. This study was conducted to determine the efficacy and dissipation dynamics of the herbicide dithiopyr, under different dose and timings of application (autumn and spring). Dithiopyr was applied at three rates

(maximum label rate applied twice at 30 days interval, half label rate applied twice at 30 days interval and maximum label rate applied once) and application timing (autumn and spring).The design of the experiment was completely randomized with three replicates per treatment. The whole experimental area was reseeded with crabgrass ( Digitaria sp) before herbicide application. Soil temperature and moisture were measured during the experiment. Soil samples were taken from each individual plot: 0, 4, 8, 16, 32, 36, 40, 48,

64 and 128 days after treatment. Each soil sample was divided in to three sections: verdure-thatch, 0 to 5 cm and 5 to 10 cm and assayed for dithiopyr. More herbicide was detected on the verdure and thatch layer; dissipation curves showed a quick loss between

4 and 16 DAT. After the second application 32 DAT, the rate of loss for autumn treatments was lower than for spring treatments due to differences in soil temperature and moisture between seasons. Dithiopyr offered excellent crabgrass control throughout the season regardless of application timing.

INTRODUCTION

Dithiopyr [ S,S -dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-

(trifluoromethyl)-3,5-pyridinedicarbothioate] is a preemergence and early postemergence

herbicide. Dithiopyr was specifically developed for control of annual grasses and annual

broadleaf weeds in established lawns and ornamental turf (Kackley at al.,1990;

Kaufman,1991; EPA, 1991).

Dithiopyr has chemical characteristics such as low water solubility (1.38 mg/kg),

high octanol-water partition coefficient [(Kow ) 56 250)], and organic carbon partition

coefficient[ (Koc ) 1920)] that suggest a high capacity for retention within the thatch, mat, and surface soil as reported in the literature (Schleicher et al.,1995; Hong and

Smith,2001). As reported by Hong and Smith (2001) dithiopyr is not mobile in golf course greens rooting medium and has minimal potential for movement into surface water drainage or ground water.

The half-life for dithiopyr reported by Hong and Smith (1999) under laboratory conditions ranges from 68.8 days (sterile, dark, 20°C) to 39.2 days (nonsterile, dark,

35°C). In field studies with turfgrass the reported half-lives were from 4 to 49 days for dithiopyr (Adams and Cowell, 1990). This was also reported by Saikia and Kulshrestha

(2002) who calculated a half-life of dithiopyr in soil that ranged between 17.3 and 25.0 days. Bacterial and fungal population effects dithiopyr dissipation as shown by Saikia and Kulshrestha (2002).

Enache and Ilnicki (1991) working with dithiopyr applied preemergence with doses ranging from 0.43 to 0.56 kg ai ha -1 and found excellent crabgrass control.

Schleicher et al. (1995), in a two year study, observed that dithiopyr applied in spring at 0.6 kg ai ha -1 reduced large crabgrass infestation by 90% up to 87 days after

treatment. Dithiopyr produced season long control of crabgrass when applied at the high

rate in late fall and early spring (Reicher and Throssell, 1993).

Reicher et al. (1991) working with sequential applications of unlike preemergence

herbicides to control crabgrass in Indiana, observed the highest large crabgrass control

ratings through September with pendimethalin plus dithiopyr (applied six weeks later),

and dithiopyr alone postemergence (applied in late spring).

The objective of this study was to associate crabgrass control with herbicide residue level following application of different rates of dithiopyr. The timing of the application (autumn and spring) was also studied to determine if differences in crabgrass control exist after an autumn application.

MATERIALS AND METHODS

Field Procedures

Field experiments were conducted in Kentucky bluegrass turf at the The Ohio

Turfgrass Foundation Research & Education Facility in Columbus, Ohio during autumn

2007 and spring 2008. The turfgrass area was prepared and dethatched with a Bluebird

dethatcher/Lawn Comb (BlueBird Beatrice, Nebraska) and seeded with smooth crabgrass

(Digitaria ischaemum ) at 1.2 kg ha-1 the third week of September 2007.

Adequate turfgrass recovery time was allowed before herbicide application. The soil was a Brookston silty-clay loam (fine, loamy, mixed, mesic Typic Argiaquoll) with

21% sand, 44% silt, 36% clay, 6.4% organic matter, pH 7.0 , cation exchange capacity

(CEC) of 11.7 meq/100g. Field plots were 1.7 m2 with a 0.9 m border and were arranged

in a randomized complete block design with treatments replicated three times.

Herbicide efficacy ratings were taken every two weeks from 1 May to 30

September, 2008 and were based on total crabgrass plant counts (number per m2, with a

minimum of 0 and a maximum of 16) and visual percentage of weeds coverage

(minimum of 0% and maximum of 100%).

Dithiopyr (Dimension 2EW, DowAgroSciences LLC, Indianapolis, IN 46268) was applied to the plots at either 421.88 g a.i ha -1 (full dose) or 211 g a. i ha -1 (half dose).

Treatments were, full dose followed 32 days later by a second full dose application, half dose followed by half dose and full dose applied once. Dates of application were 8

October 2007 and 12 November 2007 (autumn applications) and 15 April 2008 and 15

May 2008 (spring applications).

Applications were made with a CO 2-pressurized backpack sprayer at 40 psi (R&D

Sprayers, Opelousas, LA) equipped with two-6503 flat fan nozzles (Teejet, Wheaton, IL) nozzles height of 40 cm, with an effective spray width of 3 feet with water as carrier.

Herbicide was applied in 2 liters of water with irrigation of 1.3 cm immediately after treatment.

The experimental area was mowed once a week at 5 cm with a Walker mower

with catcher (Walker Manufacturing Co , Fort Collins, Co) and clippings collected .

The site was irrigated as necessary to avoid wilt and soil temperature (Figure 1) and soil moisture (Figure 2) were registered once per hour using four 250 Data Logger

Temp/RH (Spectrum Technologies, Inc. Plainfield, IL) installed on each side of the

experimental area. Each of them had one external soil temperature sensor and one

watermark soil. Data from sensors was processed using Spec 7 Basic Software (Spectrum

Technologies, Inc., Plainfield, IL). In addition natural precipitation was measured (Figure

3).

Sampling and analysis of pesticides

Soil samples were randomly taken 0 (2 hours after herbicide application), 4, 8, 16,

32, 36, 40, 48, 64 and 120 days after treatment (DAT), using a lever action hole cutter

(Par-Aide Products Co., Lino Lakes, Minnesota). Each soil sample was partitioned into

verdure and thatch, 0 to 5 cm, and 5 to 10 cm soil depth sections. Samples were weighed,

placed in 16 oz. glass jars and covered with aluminum foil, properly labeled and stored at

-20°C until residue analysis.

For herbicide analysis, each soil section was thawed and a representative 20 g

sample was placed in a 500 ml Erlenmeyer flask, herbicide was extracted from the soil by

shaking with 100 mL ethyl acetate for 3 hours on a platform shaker (Lab-line

Instruments, Inc. Melrose Park. IL. 60160) at 200 RPM.

The extract was vacuum filtered by passing through Whatman G6 glass fiber filter

paper. The flask was rinsed 3 times with 5 ml of ethyl acetate, swirling the flask and

pouring rinsate through the filter. Ethyl acetate was removed by rotary evaporation

(Rotavapor RE 121, Buchi, Switzerland) at 40° C, using a water bath (Buchi 461,

Switzerland). The evaporatory flask was rinsed 3 times with 3 mL of Dichloromethane each time; the rinsate was transferred to a 10 ml Reacti-Vial (Thermo-Fisher Scientific,

Rockford, IL). The Dichloromethane was evaporated to a final volume of 2 ml of the concentrate using a Reacti-Vap, Evaporating Unit (Pierce Model 18780, Rockford, IL).

The concentrate was passed through a 0.45 um nylon membrane filter (Gelman Sciencies,

Ann Harbor, MI). Two millimeters of the extract were transferred to an autosampler vial for analysis by gas chromatography (Model 6890 Universal, Agilent Technologies,

Wilmington, DE) with a Nitrogen Phosphorus Detector (NPD).

Dithiopyr was separated on capillary column model Agilent 19091S-433, HP-5

MS (5%-Phenyl)-Methyl Siloxane, 30 m nominal length, 0.25 mm nominal diameter,

0.25 um nominal film thickness in a constant flow mode of 1.0 mLmin -1, an average

velocity of 30 cmsec -1 and a nominal initial pressure of 18.43 psi. Oven initial

temperature was 180°C and final temperature was 230°C. Initial temperature of inlet was

230°C. The NPD detector temperature was 300°C. Carrier gas was He (63.9 mL min -1).

Detector gases were air (60.0 mL min -1) and H (3 mL min -1). Inlet was in splitless mode with initial temperature of 230°C and a pressure of 18.42 psi. Residues were quantified by peak area measurement in comparison with Benfluralin (N-butyl-N-ethyl-2, 6-dinitro-

4-(trifluoromethyl) aniline) as an internal standard peak area following calculations detailed by Agilent (1998).

made using EPA (2007) formulas. Dithiopyr recovery from verdure and thatch, 0 to 5 cm and 5 to 10 cm soil averaged 78% on day 0 with a coefficient of variation of 14%.

Concentrations of the herbicide were calculated on a basis of milligrams per

kilograms of dry soil section, using an equation built using a response ratio and an

amount ratio, described by Agilent (1998). Calibration standards were made following

EPA (2007) protocols. Active ingredients to prepare calibration standards (Chem Service,

West Chester, PA) were included after every six samples.

Institute Inc., Cary, NC, 2002) GLM procedure. Treatment means were compared to the

control using t tests lsd (least significance difference) with α=0.05.

RESULTS

Dissipation

Dithiopyr half lives for the first part of autumn (0 to 16 DAT) were low. A calculated half life of 2 days ( R2=0.48 , P=0.30) for full following full and half following

half dose (R2=0.46 , P=0.31). However a longer half life, 250 days ( R2=0.07 , P=0.45)

was obtained when dithiopyr was sprayed once using the full recommended dose. For the

second part of a half lives were higher than those reported at the beginning of autumn,

108 ( R2=0.31, P=0.25) and 79 ( R2=0.26 , P=0.30) days for full following full and half following half dose, respectively, suggesting different rates of dithiopyr degradation on time. Calculated half lives for spring were lower regarding the amount of days after

application. Half lives of 2.7 ( R2=0.49, P=0.29) , 2.5 (R2=0.47, P=0.30) days were calculated for full following full and half following half dose, respectively, for the first part of spring (0 to 16 DAT).Only the full single dose reported a higher half life,57.5

(R2=0.22, P=0.16) days for spring application. The second half of the spring (32 to 128

DAT) reported half lives of 2.9 (R2=0.32, P=0.24) and 2.56 (R2=0.29, P=0.26) days for

full following full and half following half dose, respectively, suggesting a quick

dissipation rate for the whole spring season.

Soil section and dose were significant factors at 0 and 128 DAT (Table 9). More

herbicide was detected in the verdure and thatch layer (Figure 13). More herbicide was

detected at 128 days after application in autumn. However, no difference between

seasons was detected when the treatments were applied (0 DAT) (Table 10).

Dissipation curves showed a quick loss between 4 and 16 DAT and quick

recovery of herbicide concentration after the second application 32 DAT.

After the second application, the rate of loss for autumn treatments was lower

than for spring treatments (Figures 14 and 15).

None of the factors analyzed were significantly different through the whole

season. However, at the end (128 DAT) of the season, soil section and dose were

significant, indicating more herbicide was detected at the end of autumn, in the verdure

and thatch layer on the areas were full plus full dose of dithiopyr was applied.

Days After Treatment (DAT) Source DF 0 4 8 16 32 36 40 48 64 128

______p>F ______Season 1 0.3919 0.0016 0.1171 <.0001 0.6132 0.6817 0.9336 0.0626 0.0021 0.0010 Replication*Season 4 0.7199 0.1299 0.5326 0.2556 0.2305 0.6363 0.3897 0.9009 0.9031 0.1567 Soil Section (SS) 2 <.0001 <.0001 0.4787 <.0001 0.1580 0.2102 0.1623 0.3537 0.0394 0.0148 Dose 2 0.0007 0.1176 0.5908 0.0228 0.0315 0.0179 0.0430 0.4009 0.4682 0.0604 SS*Dose 4 0.0770 0.1565 0.2892 0.0057 0.4608 0.7377 0.3362 0.2965 0.0082 0.1731 SS*Season 2 <.0001 <.0001 0.4850 <.0001 0.0801 0.4670 0.1232 0.5776 0.8632 0.0266 Dose*Season 2 0.0013 0.2389 0.5869 0.0322 0.8113 0.6678 0.8863 0.5070 0.5896 0.0839 SS*Dose*Season 4 0.0271 0.1237 0.2995 0.0143 0.2098 0.7344 0.4456 0.4006 0.0721 0.1419

Table 10. Analysis of Variance (ANOVA) on dithiopyr concentration in 3 soil section (SS) verdure and thatch, 0 to 5 cm and 5 to 10 cm at different sampling dates (DAT) 87

Season Days After Treatment (DAT) 0 4 8 16 32 36 40 48 64 128

------Dithiopyr detected mg kg -1 dry soil------

AU 07 0.08807a 0.001219b 0.00054a 0.000393b 0.13209a 0.03673a 0.03967a 0.06256a 0.014274a 0.019704a SP 08 0.10377a 0.014859a 0.04506a 0.010552a 0.09793a 0.03001a 0.03737a 0.00649a 0.003593b 0.000556b

Table 11. Mean concentration of dithiopyr (mg kg -1 dry soil) residues over time in different seasons of applications. 88

0.25000

0.20000 a verdure and thatch

0-5 cm

0.15000 5-10 cm a

0.10000 a b a

mg dithiopyr/kgdry soil mg a a 0.05000 a a a a a a a a a a a b b ab b b b b a b b b 0.00000 0 4 8 16 32 36 40 48 64 128 Days After Treatment

Figure 13. Distribution of dithiopyr residues (mg kg dry soil -1) among verdure-thatch, 0 to 5 cm and 5 to 10 cm soil layers Autumn 07 and Spring 2008. Columns followed by different letters are significantly different at p=0.05.Columns without letters were not significantly different.

0.3500 0.42 kg a.i ha -1 + 0.42 kg a.i ha -1 (2x)AU 0.3000 0.42 kg a.i ha-1 (1x) AU

0.2500 0.42 kg a. i ha -1 + 0.42 kg a. i ha - 1(1x)AU 0.2000

0.1500

0.1000 mg ofdry soil dithiopyr/kgmg

0.0500

0.0000 0 4 8 16 32 36 40 48 64 128

Days After Treatment Figure 14 .Dissipation curve for dithiopyr applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in autumn 2007. Dates of application for autumn were 8 October 2007 and 12 November 2007.

0.3500 0.42 kg a.i ha -1 + 0.42 kg a.i ha -1 0.3000 (2x)SP 0.42 kg a.i ha-1 (1x) SP 0.2500

0.42 kg a. i ha -1 + 0.42 kg a. i ha - 0.2000 1(1x)SP

0.1500

0.1000

mg dithiopyr/kgdry soil mg 0.0500

0.0000 0 4 8 16 32 36 40 48 64 128 Day After Treatment

Figure 15 .Dissipation curve for dithiopyr applied on a Kentucky bluegrass turf in Columbus, Ohio using three different doses in spring 2008.Dates of application for spring were 15 April 2008 and 15 May 2008 (spring applications).

Efficacy

Dimension offered excellent crabgrass control throughout the season (Table 11).

Autumn treatments did not show crabgrass counts and spring treatments only showed on treatments with either half plus half dose or single full dose, however this difference in control was not significant at the end of the season 128 DAT (Table 11).

Two applications at the full label rate resulted in a complete control of crabgrass regardless of season of application (Table 11). No significant difference in crabgrass count was detected between half-rate followed by a second application at half-rate or a

single full dose applied in spring (Table 11).Treatment was a significant factor throughout the season. Dose was a significant factor at 0 DAT and at 128 DAT was near to be significant p=0.06, indicating that higher doses were more effective in controlling crabgrass (Table 11).

Factor 30 Jul 2008 15 Aug 2008 30 Aug 2008 15 Sep 2008 30 Sep 2008

Treatment Dose Season Number % Number % Number % Number % Number % crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass crabgrass/m 2 crabgrass coverage coverage coverage coverage coverage Dimension Full Au 0b 0 0 0b 3.3b 1.8 14.4b 8.12 14.4b 8.12 2EW Dimension Fullnfull Au 0b 0 0 0b 0b 0 0b 0 0b 0 2EW Dimension Halfnhalf Au 0b 0 0 0b 0b 0 0b 0 0b 0 2EW Control Au 84.4a 47.5 117.7 66.25a 88.8a 50 166.6a 93.75 133.3a 75

Dimension Full Sp 0b 0 6.6 3.75b 11.1b 6.25 14.4b 8.12 17.7b 10 2EW Dimension Fullnfull Sp 0b 0 0 0b 0b 0 0b 0 0b 0 2EW Dimension Halfnhalf Sp 0b 0 0 0b 6.6b 3.75 17.7b 10 17.7b 10 2EW Control Sp 111.1a 62.5 128.8 72.5a 177.7a 100 173.3a 97.5 162.2a 91.25 93 Analysis of Variance

Source p>F

Treatment ** ** ** ** **

Dose NS * NS NS NS

Season NS * * NS NS

Season*Dose NS * NS NS NS

Treatment * Dose NS NS NS NS NS

Treatment * Season NS NS * NS NS

Table 12. Number of crabgrass plants per square meter and percentage of crabgrass coverage for three different dithiopyr doses applied on Autumn 2007 and Spring 2008 .Significance taken at p=0.05, NS† indicates no significance, ** indicates significance at 0.005,* indicates significance at 0.05. Numbers in the same column followed by different letters are significantly different at p=0.05

DISCUSSION

More dithiopyr was detected in the verdure and thatch layer as observed by

Schleicher et al.(1995) working in perenial ryegrass ( Lolium perenne ) turf and Hong and

Smith (2001) working with golf course greens rooting medium lysimiters, confirming

dithiopyr chemical characteristics and its relationship with its high potential of retention

in soil.

According to Magri and Haith (2009) strong pesticide retention in foliage and

thatch is arguably the most important factor governing pesticide dissipation in turf

systems. It makes the pesticides less susceptible to physical removal by runoff,

infiltration, and volatilization, but at the same time exposes them to microbial

populations, degradation on site by photolysis and/or hydrolysis and even removal of

clippings during mowing.

Quick dissipation of dithiopyr was observed from 0 to 4 DAT regardless of

season of application due to the high soil temperatures recorded during the first 4 days

after application in autumn and spring (Figure 1). Rapid dissipation of dithiopyr in the

field was reported by Mueth and Cowell (1990) and Saikia and Kulshrestha (2002).

Half life of dithiopyr was less than 4 days in both seasons, suggesting faster

pesticide degradation on vegetation surface than in bare soil as demonstrated by Gardner

and Branham, (2001) and Juraske et. al, (2008)

More herbicide was detected on autumn treatments at the end of the season (128

DAT), because the degradation after the second application (32 DAT) in autumn was

slower than in spring, due to differences in soil temperatures and moisture between seasons (Figure 1 and 2, respectively).

Temperature has been shown to significantly affect degradation kinetics of pesticides in soil; higher soil temperatures increase herbicide dissipation decreasing their half lives as observed by Choy et. Al (1988); Mervosh et.al (1995) and Taylor-Lovell et.al (2002) mainly due to an increasing soil microbial activity.

No crabgrass count was observed in sequential autumn treatments, even though dithiopyr dissipation was quick for the first application. Low temperatures in autumn kept rate of dithiopyr dissipation low for the second application, resulting in an adequate timing to control crabgrass seed germination. The efficacy of dithiopyr applied in autumn has been reported before by Reicher and Throssell (1993); they observed a season long control of crabgrass when dithiopyr was applied at the high rate late in fall in a Kentucky bluegrass turf in Indiana.

However, these authors did not observe significant differences in crabgrass control between late autumn and early spring dithiopyr applications. Spring applications

of dithiopyr have been frequently reported in the literature regarding crabgrass control.

Schleicher et al (1995) reported 90% of crabgrass control at 87 DAT in two years for

dithiopyr applied in spring in Nebraska. Bunnell (2001) reported excellent crabgrass

control when sequential applications of dithiopyr were made in spring in South Carolina.

This response suggests that herbicide efficacy is governed not only by the amount

of herbicide in the soil, but also by timing and environmental considerations, such as soil

temperature and moisture, at and after application.

According to the current results, dithiopyr applied at high rate (full following full dose) provides a 100% crabgrass control regardless of season of application.

The faster dithiopyr dissipation occurs in the first 4 days after first application due to high air and soil temperature. Amount of dithiopyr in soil was enough to control spring germination of crabgrass with autumn applications.

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