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Crop Science 40:1333-1339 (2000)
© 2000 Crop Science Society of America

TURFGRASS SCIENCE

Effect of Turfgrass on Soil Mobility and Dissipation of Cyproconazole

D.S. Gardner, B.E. Branham and D.W. Lickfeldt

Dep. of Natural Resources and Environmental Sciences, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61802-4798 USA

bbranham{at}uiuc.edu


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Previous studies of pesticide fate in turfgrass have found less mobility and more rapid dissipation compared with studies using the same pesticide applied to bare soil. Few direct comparisons of pesticide mobility and dissipation in turfgrass vs. bare soil have been conducted. The mobility and persistence of cyproconazole [{alpha}-(4-chlorophenyl)-{alpha}-(1-cyclopropylethyl)-1H-1,2,4-triazole-1-ethanol] on bare soil (Flanagan silt loam; fine, smectitic, mesic Aquertic, Argiudoll) and turf containing varying levels of organic matter was examined under field conditions. Twenty-centimeter-diameter polyvinyl chloride (PVC) cylinders were installed in either creeping bentgrass turf (Agrostis palustris Huds.), or in turf in where either 33, 67, or 100% of the thatch and plant material had been removed. Cyproconazole was applied at 403 g a.i. ha-1 on 15 July 1996 and 8 July 1997. Replicate sampling cylinders were removed 2 h after treatment (HAT) and 4, 8, 16, 32, 64, and 128 d after treatment (DAT). Cylinder cores were sectioned into depths and assayed for cyproconazole by gas chromatography. On all sampling days, increasing the amount of surface organic matter decreased the amount of cyproconazole in the 0- to 1-, 1- to 3-, 3- to 5-, and 5- to 15-cm core sections. The amount of cyproconazole detected in the soil under a full stand of turf at 4 and 32 DAT was 1 and 11%, respectively, of that detected in bare soil. Cyproconazole residues never exceeded 20 µg kg-1 in the 15- to 30-cm core section of any treatment. The half-life of cyproconazole decreased from 129 d in bare soil to 12 d in a full bentgrass turf. Cyproconazole movement below 5 cm in the soil was reduced with increasing amounts of turfgrass thatch, and as little as one-third of a full stand of turf greatly decreased the half-life of cyproconazole. Application of cyproconazole to turfgrass results in less mobility and more rapid dissipation than is typically reported in other agronomic crops.

Abbreviations: DAT, days after treatment • HAT, hours after treatment • LOI, loss on ignition • PVC, polyvinyl chloride


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results
 Discussion
 REFERENCES
 
THERE ARE MANY ADVANTAGES to the environment of maintaining a stand of turfgrass (Beard and Green, 1994), but serious questions have been posed in recent years concerning the use of synthetic fertilizers and pesticides that have been implicated as potentially harmful to the environment. Turfgrass management accounts for a very small percentage of total pesticide usage; however, turfgrass is one of the most intensely managed biotic systems (Balogh et al., 1992).

A turfgrass system differs from many types of row crop agriculture in that turfgrass is a fixed layer of organic matter on top of the soil. Except at establishment, pesticides are applied directly to plant material. Pesticide not intercepted by plants is instead deposited in thatch or mat (Branham, 1994). Turfgrass has the ability to attenuate pesticide movement into the soil because of the high organic C content associated with turfgrass thatch (Branham and Wehner, 1985; Dell et al., 1994). Furthermore, even without thatch, the organic matter content of the 0- to 2.5-cm soil layer in established turf is usually higher than in agricultural soils due to senescence of plant parts, lack of tillage, and high root density (Niemczyk and Krause, 1994).

Laboratory studies show that turfgrass leaves and thatch strongly sorb organic compounds and thus should have a significant impact on the fate of pesticides applied to turfgrass (Lickfeldt and Branham, 1995; Dell et al., 1994). Similar results have also been reported with no-till corn residues (Boyd et al., 1990).

Recent research suggests that pesticide mobility in turfgrass may be lower than in agronomic soils (Petrovic et al., 1996). The reduced mobility of pesticides in turf is likely due to retention by thatch (Niemczyk and Kruger, 1987; Sears and Chapman, 1979). Several studies have found that the majority of pesticide residues are contained in the thatch (Cisar and Snyder, 1996; Horst et al., 1996; Stahnke et al., 1991) and that pesticide leaching decreases as turf density and organic matter increases (Petrovic et al., 1996). Turfgrass thatch creates an aerobic zone that is high in microbial activity and can result in enhanced dissipation in the turfgrass root zone (Gold et al., 1988; Horst et al., 1996).

Cyproconazole, a triazole fungicide, is a relatively new product used for the control of several pathogens. Cyproconazole has a water solubility of 140 mg L-1 and an octanol/water partition coefficient (Kow) of 819, indicating the potential for some leaching through the turfgrass–soil profile. Cyproconazole is highly persistent, with a half-life of {approx}90 d in agricultural soils (Royal Society of Chemistry, 1991).

Our objective was to quantify the effect of surface organic matter on the mobility and persistence of cyproconazole. The relationship between the quantity of verdure and thatch present and the distribution of cyproconazole among the verdure, thatch, and soil was also investigated.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results
 Discussion
 REFERENCES
 
Field Procedures
Field experiments were conducted in `Pennlinks' creeping bentgrass turf in 1996 and `Penneagle' creeping bentgrass turf in 1997 at the University of Illinois Landscape Horticulture Research Center in Urbana, IL. Plots with either 33 or 67% thatch were prepared by making 8 or 16 passes over the turf with a vertical mower (Ransomes, Lincoln, NE).1

The amount of thatch removed from the plots was determined by collecting soil cores, isolating the thatch from the core, and drying the thatch. The dried thatch was weighed, placed in a muffle furnace at 500°C for 24 h, and weighed again to determine mass by loss on ignition (LOI). Bare soil plots were prepared by stripping the sod from the plot with a sod-cutter. The soil was a Flanagan silt loam (fine, smectitic, mesic Aquertic, Argiudoll), 52 g kg-1 organic matter (LOI), 1.38 g cm-3 bulk density, and pH 6.5 in water). Thatch was 10 to 14 mm thick, with a bulk density of 0.53 g cm-3, 241 g kg-1 organic matter (LOI), and pH 6.7 in water.

Sampling cylinders were constructed of 20-cm-diam. schedule 40 PVC pipe cut into 30-cm lengths and beveled at one end to ease insertion into the soil. Sampling cylinders were inserted into each plot on 12 July 1996 and 5 July 1997 using a hydraulic press (Alden Enterprises, Okemos, MI) attached to a tractor.

Cyproconazole (Sentinel 40 WG, Novartis, Greensboro, NC) was applied to the plots on 15 July 1996 and 8 July 1997 at 403 g a.i. ha-1 with a backpack sprayer equipped with a TEEJET 8006E (Spraying Systems Co., Wheaton, IL) nozzle at a height of 35.5 cm, with an effective spray width of 30.5 cm. Cyproconazole was applied in 1120 L water ha-1 at 276 kPa with irrigation (0.4 cm) immediately following treatment.

The experimental area was mowed three times per week at 1.8 cm with a reel mower with clippings collected beginning 2 DAT. The site was irrigated as necessary to avoid wilt, and natural precipitation was measured (Fig. 1) .



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  		Fig. 1 Rainfall and irrigation from date of pesticide application to last sample collection date. Pesticide application dates were 15 July 1996 and 8 July 1997

 
Sampling and Analysis of Pesticides
Sampling cylinders were removed with a spade and hand tools from three replicate blocks of each level of turf organic matter 2 HAT and 4, 8, 16, 32, 64, and 128 DAT. Sampling dates in 1996 were 15 July, 19 July, 23 July, 31 July, 16 August, and 17 September. The 128-d samples were not collected in 1996. Sampling dates in 1997 were 8 July, 12 July, 16 July, 24 July, 9 August, 10 September, and 13 November. Verdure and thatch were separated from the cores that had 67 and 100% organic matter; however, only thatch remained on the cores that had 33% organic matter. The soil cores were partitioned into 0- to 1-, 1- to 3-, 3- to 5-, 5- to 15-, and 15- to 30-cm soil depth sections. Samples were weighed, placed in glass mason jars with aluminum foil-capped lids, and stored at -20°C until residue analysis.

Cyproconazole was extracted from soil, verdure, and thatch according to procedures obtained from Sandoz, Inc. and modified for our use. Soil samples were thawed and a representative 20-g sample placed in 500-mL Erlenmeyer flasks. Cyproconazole was extracted from the soil by shaking with 1 M HCl (100 mL) for 30 min on a platform shaker. The samples were placed in a heated water bath (95°C) for 30 min. Ethanol (100 mL) was added and the samples were shaken for 30 min. The extract was vacuum filtered, first by passing through Whatman G6 glass fiber filter paper, then through a 5-µm nylon membrane filter (MSI Inc., Westboro, MA). The ethanol was removed by rotary evaporation at 40°C.

Twenty grams of thatch or 3 to 10 g of verdure were extracted by shaking with 1 M HCl (100 mL) on a platform shaker for 60 min. The samples were heated in a water bath (95°C) for 60 min. The extract was vacuum filtered by passing through Whatman G6 glass fiber filter paper.

Cyproconazole was separated from impurities using C-18 solid phase extraction tubes (Alltech, Deerfield, IL). Twenty milliliters of extract were passed through the tube followed by 10 mL methanol/water (10:90%, v/v) and 10 mL of hexane. The column was dried under vacuum, and cyproconazole was eluted from the tube by adding 6 mL of 2-propanol/toluene (25:75%, v/v) in 2-mL increments. Two milliliters of the extract were transferred to an autosampler vial for analysis by gas chromatography (Model 5890, Hewlett-Packard Corp., San Fernando, CA) with thermionic N–P detection. Cyproconazole was separated on a 30-m, 0.25-mm-i.d. capillary column with a bonded DB-5 phase (J & W Scientific, Folsum, CA). Typical operating temperatures were 230°C (column oven), and 250°C (injector and detector). Carrier gas was He (25 mL min-1). Detector gases were air (110 mL min-1) and H (4 mL min-1). Residues were quantified by peak area measurements in comparison with a 10 mg mL-1 external standard. The limit of detection was 20 mg kg-1.

Two injections were made for each extract. Calibration standards were included after every third extract. A control sample fortified at 1 mg kg-1 and a method blank were included with each batch of 22 samples. Cyproconazole recovery from soil, verdure, and thatch samples averaged 77% with a coefficient of variation of 12.5. In 1997 only, the amount of cyproconazole remaining in each soil profile was estimated from the concentration of cyproconazole in a soil core section and the mass of that core section.

The experiment was designed as a split-plot with organic matter as the whole-plot and turf-soil core as the subplot. On each sampling date, data were subjected to analysis of variance (SAS Institute, 1990). Concentration data were transformed to logarithmic values before analysis of variance to achieve more normally distributed data. Measured residues of cyproconazole 2 HAT were used to estimate half-life.


   Results
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
Discussion
 REFERENCES
 
The estimated amount of surface organic matter removed from the plots was 37 and 70% for the two thatch removal treatments. Due to the thatch removal technique, variation in the amount of organic matter remaining was observed not only within each plot, but also within each cylinder. Therefore, to simplify data presentation, the plots were designated as having 33% (or {approx}1/3) and 67% (or {approx}2/3) of the amount of thatch present in the full stand of turf.

Cyproconazole concentration in the different soil layers varied due to surface organic matter content. The distribution of cyproconazole by depth and amount of surface organic matter differed between the 2 yr until 16 DAT; however, there was no variation (P < 0.05) due to year at either 32 or 64 DAT (Table 1) .


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  		Table 1 Analysis of Variance (ANOVA) on cyproconazole concentration in verdure, thatch, and soil profile components at different sampling dates

 
In 1996, the concentration of cyproconazole decreased rapidly in verdure and decreased more slowly in thatch (Table 2) . On all sampling dates, cyproconazole concentration at 0 to 1 cm was higher in bare soil than in treatments containing surface organic matter, regardless of the amount. At 1 to 3 cm, more cyproconazole was present in bare soil than in turf covered plots at 4, 16, and 64 DAT. No cyproconazole applied to a full stand of turfgrass was detected below 3 to 5 cm on any sampling date. However, where there was less than a full stand of turf, cyproconazole was detected in the 5- to 15-cm soil layer 8, 32, and 64 DAT.


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  		Table 2 Concentration of cyproconazole residues over time in treatments containing different amounts of organic matter from creeping bentgrass in 1996

 
In 1997, the concentration of cyproconazole again decreased rapidly in verdure and decreased more slowly in thatch (Table 3) . As was observed in 1996, cyproconazole concentration at 0 to 1 cm was higher in bare soil than in treatments containing surface organic matter, regardless of the amount, on all sampling dates. At 1 to 3 cm, the concentration of cyproconazole was higher in bare soil on all sampling dates, but the differences were statistically nonsignificant. The maximum depth of cyproconazole movement detected in a full stand of turf was 1 to 3 cm. In contrast, cyproconazole was detected at 3 to 5 cm in treatments containing 33 or 67% organic matter and at 5 to 15 cm on bare soil.


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  		Table 3 Concentration of cyproconazole residues over time in treatments containing different amounts of organic matter from creeping bentgrass in 1997

 
There were differences in the distribution of the mass of cyproconazole residues due to surface organic matter content on all sampling dates in 1997 (Table 4) . Cyproconazole dissipated rapidly from the soil profile in treatments containing turfgrass, regardless of the amount of surface organic matter (Fig. 2) . The estimated half-life of cyproconazole on bare soil was 128 d. Where varying amounts of turf were present, the half-life was 8 to 12 d.


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  		Table 4 Analysis of Variance (ANOVA) on the mass of cyproconazole residues in verdure, thatch, and soil profile components on different sampling dates during 1997

 


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  		Fig. 2 Percentage of cyproconazole residues remaining in each soil treatment as a function of sampling time in 1997

 
When cyproconazole was applied to bare soil, the amount detected below 0 to 1 cm increased until 64 DAT (Fig. 3) . In treatments containing 33 and 67% surface organic matter, the amount of cyproconazole detected in verdure and thatch decreased rapidly over time, but the amount of cyproconazole detected in soil did not increase as rapidly, due to an increased dissipation rate where turf was present.



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  		Fig. 3 Distribution of cyproconazole residues among verdure, thatch, and different soil depths over time in 1997. Horizontal bars represent standard error of the means

 
On all sampling days, increasing the amount of surface organic matter decreased the amount of cyproconazole in the 0- to 1-, 1- to 3-, 3- to 5-, and 5- to 15-cm core sections. No cyproconazole was detected in the 15- to 30-cm core section. Cyproconazole applied to a full stand of turf degraded rapidly and was not detected below 0 to 1 cm at 0, 4, 16, or 32 DAT. At 128 DAT, there was still significantly more cyproconazole in the 0- to 1-cm core section in bare soil compared with treatments containing turf.

Where turf was present, cyproconazole was highly retained by thatch. The amount of cyproconazole detected in soil 4 DAT under a full stand of turf was only 1% of the amount detected in the bare soil treatment. This amount increased to 11 and 10% at 8 and 32 DAT, respectively. By 128 DAT, the amount of cyproconazole in the soil under a full stand of turf was 32% of that found in bare soil.


   Discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
 Discussion
REFERENCES
 
Differences in the measured concentration of cyproconazole in 1996 vs. 1997 were due to the variability in the verdure and thatch. By 32 DAT, the concentration of cyproconazole in the verdure and thatch had decreased and was no longer a source of variation between years.

Persistence of cyproconazole applied to turfgrass was much less than previously reported in bare soil (Royal Society of Chemistry, 1991). The rapid dissipation of cyproconazole where varying amounts of turf were present was consistent with previously published reports of rapid pesticide loss from turfgrass systems (Stahnke et al., 1991; Horst et al., 1996). Interestingly, the amount of turfgrass thatch present did not change the half-life of cyproconazole in this study. The half-life in soil was slightly longer than previously reported for agricultural crops.

Interception of the cyproconazole spray by the verdure resulted in high initial concentrations, but irrigation, rainfall, mowing activity, and dissipation caused a rapid decrease in concentration of the pesticide in the verdure. Cyproconazole was highly retained within thatch at all sampling dates. Increasing the amount of thatch increased the retention of cyproconazole (Tables 2 and 3). Several rainfall events exceeding 2 cm occurred between 32 and 64 DAT in 1997 (Fig. 1), resulting in movement of cyproconazole into the 5- to 15-cm soil section at 64 DAT in bare soil, but not where thatch was present.

Previous research has demonstrated that thatch and soil organic matter are similar in their ability to bind pesticides (Dell et al., 1994; Lickfeldt and Branham, 1995). Thatch is slightly less sorptive than soil, probably because it is less decomposed than soil organic matter. However, thatch has a significant effect on the capacity of the soil profile to sorb pesticides (Niemczyk and Krause, 1994; Dell et al., 1994).

The half-life of a pesticide in soil will vary according to conditions such as soil moisture, temperature, and microbial activity, and these conditions will vary according to location, season, weather, and soil depth (Primi et al., 1994). The rapid decrease in cyproconazole detected in turf compared with bare soil suggests more rapid microbial degradation within thatch. In this study, the amount of cyproconazole detected in thatch and soil under turf or turf with 67% of the organic matter decreased rapidly until 32 DAT and then decreased more slowly. Cyproconazole is applied at relatively low rates and the further decrease in concentration may have reduced the availability of cyproconazole for degradation by microbial populations. It is also possible that colder weather during the latter part of the study reduced the rate of microbial degradation.

Other factors that contribute to loss of pesticides in the field include runoff, photodegradation, and volatilization (Frederick et al., 1996). Our plots were flat and thus runoff losses were probably minimal, and cyproconazole does not possess characteristics that make it likely to volatilize (Royal Society of Chemistry, 1991).

Many authors have measured half-lives of pesticides applied to turfgrass and compared that data to previously published estimates of pesticide half-life in bare soil. Side-by-side plots containing variable amounts of turfgrass thatch have been used when measuring percentage of applied pesticide recovered in leachate (Petrovic et al., 1996). However, a thorough review of the literature indicates that this is the first study that directly compares pesticide dissipation and distribution in soil when applied to turf with different levels of thatch, but with the same soil, climate, and irrigation.

Turfgrass contains variable amounts of thatch and thus organic C and this, along with variability in soil characteristics and precipitation patterns, may affect the extent of leaching and the rate of degradation of applied pesticides at different locations. Nevertheless, this study indicates that cyproconazole movement through surface soil is reduced with increasing amounts of turfgrass thatch and as little as one-third of the turf organic matter found in a full stand of turf will greatly decrease the half-life of cyproconazole.


   ACKNOWLEDGMENTS
 
Financial support for this research was provided by the United States Golf Association, Far Hills, NJ.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
 Discussion
 REFERENCES
 
Part of a thesis by senior author in partial fulfillment of the requirements for the Ph.D. degree at Univ. of Illinois.

1 Mention of product and equipment trade names is for identification purposes only and does not imply a warranty or endorsement to the exclusion of other products that may be similar. Back

Received for publication September 5, 1999.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results
 Discussion
 REFERENCES
 




This article has been cited by other articles:


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D. S. Gardner and B. E. Branham
Effect of Turfgrass Cover and Irrigation on Soil Mobility and Dissipation of Mefenoxam and Propiconazole
J. Environ. Qual., September 1, 2001; 30(5): 1612 - 1618.
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