R.D. Wauchope

College of Coastal Georgia, Georgia, United States

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Publications (36)53.72 Total impact

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    ABSTRACT: When synthetic, xenobiotic compounds such as agrochemicals and industrial chemicals are utilized, they eventually reach the soil environment where they are subject to degradation, leaching, volatilization, sorption, and uptake by organisms. The simplest assumption is that such chemicals in soil are totally available to microorganisms, plant roots, and soil fauna via direct, contact exposure; subsequently these organisms are consumed as part of food web processes and bioaccumulation may occur, increasing exposures to higher organisms up the food chain. However, studies in the last two decades have revealed that chemical residues in the environment are not completely bioavailable, so that their uptake by biota is less than the total amount present in soil (Alexander 1995; Gevao et al. 2003; Paine et al. 1996). Therefore, the toxicity, biodegradability, and efficacy of xenobiotics are dependent on their soil bioavailability, rendering this concept profoundly important to chemical risk assessment and pesticide registration.
    No preview · Article · Jan 2010 · Reviews of environmental contamination and toxicology
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    Full-text · Article · Jan 2008
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    ABSTRACT: The large-scale commercial cultivation of transgenic crops has undergone a steady increase since their introduction 10 years ago. Most of these crops bear introduced traits that are of agronomic importance, such as herbicide or insect resistance. These traits are likely to impact upon the use of pesticides on these crops, as well as the pesticide market as a whole. Organizations like USDA-ERS and NCFAP monitor the changes in crop pest management associated with the adoption of transgenic crops. As part of an IUPAC project on this topic, recent data are reviewed regarding the alterations in pesticide use that have been observed in practice. Most results indicate a decrease in the amounts of active ingredients applied to transgenic crops compared with conventional crops. In addition, a generic environmental indicator -- the environmental impact quotient (EIQ) -- has been applied by these authors and others to estimate the environmental consequences of the altered pesticide use on transgenic crops. The results show that the predicted environmental impact decreases in transgenic crops. With the advent of new types of agronomic trait and crops that have been genetically modified, it is useful to take also their potential environmental impacts into account.
    Full-text · Article · Nov 2007 · Pest Management Science
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    R W Malone · M J Shipitalo · R D Wauchope · H Sumner
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    ABSTRACT: Usage of glyphosate [N-(phosphonomethyl)-glycine] and glufosinate [2-amino-4-(hydroxy-methylphosphinyl)butanoic acid] may reduce the environmental impact of agriculture because they are more strongly sorbed to soil and may be less toxic than many of the residual herbicides they replace. Preferential flow complicates the picture, because due to this process, even strongly sorbed chemicals can move quickly to ground water. Therefore, four monolith lysimeters (8.1 m(2) by 2.4 m deep) were used to investigate leaching of contact and residual herbicides under a worst-case scenario. Glufosinate, atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diamine), alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide], and linuron (3-3,4-dichlorophenyl-1-methoxy-1-methylurea) were applied in 1999 before corn (Zea mays L.) planting and glyphosate, alachlor, and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were applied in 2000 before soybean [Glycine max (L.) Merr.] planting. A high-intensity rainfall was applied shortly after herbicide application both years. Most alachlor, metribuzin, atrazine, and linuron losses occurred within 1.1 d of rainfall initiation and the peak concentration of the herbicides coincided (within 0.1 d of rainfall initiation in 2000). More of the applied metribuzin leached compared with alachlor during the first 1.1 d after rainfall initiation (2.2% vs. 0.035%, P < 0.05). In 1999, 10 of 24 discrete samples contained atrazine above the maximum contaminant level (atrazine maximum contaminant level [MCL] = 3 mug L(-1)) while only one discrete sample contained glufosinate (19 mug L(-1), estimated MCL = 150 mug L(-1)). The results indicate that because of preferential flow, the breakthrough time of herbicides was independent of their sorptive properties but the transport amount was dependent on the herbicide properties. Even with preferential flow, glyphosate and glufosinate were not transported to 2.4 m at concentrations approaching environmental concern.
    Full-text · Article · Nov 2004 · Journal of Environmental Quality
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    ABSTRACT: The purpose of this study was to compare two commonly used runoff experimental methods, which have different scales, on measurements of runoff and associated fenamiphos and metabolite losses over a 2-year period. Methods used were 15 m wide by 43 m long (645 m2) mesoplots and 1.8 m wide by 3 m long (5.4 m2) microplots, under simulated rainfall (25 mm h-1 for 2 h) at 1, 14, and 28 d after fenamiphos application. Mesoplots and microplots were established parallel to a 3% slope on a Tifton loamy sand (Plinthic Kandiudult). All plots were planted to corn (Zea mays L.). Target application rate for fenamiphos was 6.7 kg ha-1. Runoff totals and maximum rates for meso- and microplots were similar, with approximately 25% of the rainfall running off mesoplots and approximately 28% running off microplots. Runoff totals and maximum rates from meso- and microplots were each positively correlated (R2 = 0.89). In both years, fenamiphos lost in runoff decreased with each rainfall event (1, 14, and 28 d after application). The majority of fenamiphos lost in runoff was in the fenamiphos sulfoxide form. Fenamiphos sulfoxide lost over both years from mesoplots ranged from 51% to 93% of the total fenamiphos lost, and loss from microplots ranged from 47% to 100% of the total fenamiphos lost. Runoff from meso- and microplots 1 d after fenamiphos application, a "reasonable worst-case" event, had the greatest fenamiphos losses among events. Total losses of fenamiphos for this event averaged 1.2% (CV = 26%) of applied amount for mesoplots and 1.3% (CV = 47%) of applied amount for microplots. Maximum (seasonal) fenamiphos losses for meso- and microplots were 1.4% of applied for mesoplots and 2.6% of applied for microplots. A positive correlation was obtained between microplots and mesoplots for total losses of fenamiphos + metabolites (R2 = 0.88), fenamiphos parent (R2 = 0.89), and fenamiphos sulfoxide (R2 = 0.81). Relatively poor agreement was found for relatively small losses of fenamiphos sulfone between plot types (R2 = 0.34). Microplots and mesoplots yielded statistically similar results in terms of runoff and fenamiphos losses; thus, microplot results can be extrapolated up to larger mesoplot areas under these conditions. This has implications for field-scale management and watershed assessment in the Coastal Plain region of the southeast U.S. in that microplot and rainfall simulation results could be useful as statistically valid input datasets to estimate runoff and associated fenamiphos losses from larger areas.
    Preview · Article · May 2004
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    ABSTRACT: National governments introduced residue limits and guideline levels for pesticide residues in water when policies were implemented to minimize the contamination of ground and surface waters. Initially, the main attention was given to drinking water. Regulatory limits for pesticide residues in waters should have the following characteristics: definition of the type of water, definition of the residue, a suitable analytical method for the residues, and explanation for the basis for each limit. Limits may be derived by applying a safety factor to a no-effect-level, or from levels occurring when good practices are followed and also passing a safety assessment, or from the detection limit of an analytical method, or directly by legislative decision. The basis for limits and guideline values issued by WHO, Australia, the United States, New Zealand, Japan, Canada, European Union, and Taiwan is described, and examples of the limits are provided. Limits have been most commonly developed for drinking water, but values have also been proposed for environmental waters, effluent waters, irrigation waters, and livestock drinking waters. The contamination of ground water is of concern because it may be used as drinking water and act as a source of contamination for surface waters. Most commonly, drinking water standards have been applied to ground water. The same terminology may have different meanings in different systems. For example, guideline value (GV) in WHO means a value calculated from a toxicology parameter, whereas in Australia, a GV is at or about the analytical limit of determination or a maximum level that might occur if good practices are followed. In New Zealand, the GV is the concentration where aesthetic significance is influenced. The Australian health value (HV) is conceptually the same as the WHO GV. The New Zealand maximum acceptable value (MAV) and the Canadian maximum acceptable concentration (MAC) are also conceptually the same as the WHO GV. Each of the possible ways of defining the residues has its merits. A residue limit in water expressed as the sum of parent and toxicologically relevant transformation products makes sense where it is derived from the acceptable daily intake (ADI). For monitoring purposes, where it is best to keep the residue definition as simple as possible for the sake of practical enforcement and economy, the parent or a marker residue is preferable. It is also possible for parent and degradation products (hydrolysis and photolysis products and metabolites) to become physically separated as the water moves through soil strata, which suggests that separate limits should be set for parent and important degradation products. The Commission has made 12 recommendations for regulatory limits for pesticide residues in water. The recommendations will act as a checklist for authorities introducing or revising limits or guidelines for pesticide residues in water.
    No preview · Article · Aug 2003
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    ABSTRACT: Lab studies provide an opportunity to isolate processes influencing water, sediment, and agrichemical transport under standard conditions. However, extending this information to field or watershed scales is often difficult. We compared runoff (R) and sediment (E) losses from a lab study with field data from a Tifton loamy sand (3% slope). Three plot scales/length-rainfall simulator methodologies were used: 1.) 0.32 m2 lab pan (L = 0.6 m) under an oscillating nozzle rainfall simulator; 2.) 5.5 m2 field plor (L = 3 m) under a Wobbler nozzle rainulator, and 3.) 600 m2 field plors (L = 43 m) under the same rainulator used in method 2. For field plors (methods 2 and 3), R and E losses were measured from six simulated rainfall events (I = 25.4 mm hr-1, 2 hr duration) during two corn growing seasons (five days before agrichemical application and 1, 14, 29, 49, and 108 days after agrichemical application). Similar rainfall intensity and duration were used in the lab study. R and E losses from lab pan (method 1) and 5.5 m2 field plors (method 2) were measured at 5 minute intervals, whereas R and E delivery for 600 m2 plots (method 3) were measured continuously and at selected times, respectively. R and E rates from all methods generally increased during each event with similar maximum rates. Total R and E for method 2 was at least an order of magnitude greater than those for method 1, and total R and E for method 3 were at least 1 order of magnitude greater than those for method 2. R and E were related to slope length (R2 = 0. 94-0. 99). Exponents (b) for R and E were 0.50-1.63. Detachment and transport processes varied spatially. Once a critical slope length was exceeded, rilling occurred. Rilling was non existent in method 1 and was present but nor dominant in method 2. For method 3, slope length was sufficient to cause rilling, therefore E was greater than that for methods 1 and 2.
    No preview · Article · Jan 2001 · Journal of Soil and Water Conservation
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    ABSTRACT: Accurate simulation of water transport (percolate, runoff, soil water content) under various management practices is important to accurately simulate water quality. Furthermore, simulation of macropore flow can be important to accurately simulate chemical transport to shallow groundwater. Therefore, we compared RZWQM simulated water transport to eighty days of data from two macroporous field plots (a short term no-till plot and a rototilled plot). The only calibrated parameters were the average macropore radius and the surface crust saturated hydraulic conductivity. The other parameters were determined from the literature or measured. The results indicate that RZWQM reasonably simulated runoff, percolate, and soil water content compared to daily observations with minimal calibration and reasonable input parameters.
    No preview · Conference Paper · Jan 2001
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    J. B. Unsworth · R.D. Wauchope · AW Klein · E. Dorn · B. Zeeh · S. M. Yeh · K.D. Racke
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    ABSTRACT: : Since the 1960s there has been a growing body of data regarding the presence of pesticides in the atmosphere. The monitoring results obtained show that traces of pesticides may undergo long range transport and be deposited considerable distances away from the treatment areas, including remote areas such as the Arctic and Antarctic regions. Pesticides have been found in air, rain, cloud water, fog and snow. The appearance and subsequent behaviour of pesticides in the atmosphere are complex processes and the concentrations found depend on several variables such as their volatility, photostability, method of application and extent of use. Whilst volatility of pesticides can be linked to their Henry's Law constant this is very much a simplification since it is also influenced by the surfaces treated, e.g. soil or leaves, and by the extent to which aerosols are formed during the application. The disappearance of pesticides from the atmosphere is due to hydrolysis, indirect photolysis via ...
    Full-text · Article · Oct 2000 · Pest Management Science
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    ABSTRACT: High-intensity storms that occur shortly after chemical application have the greatest potential to cause chemical runoff. We examined how effectively current chemical transport models GLEAMS, Opus, PRZM2β, and PRZM3 could predict water runoff and runoff losses of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-l,3,5-triazine-2,4-dia mine] under such conditions, as compared with observations from a controlled field runoff experiment. The experiment was conducted for 2 yr using simulated rainfall on two 14.6- by 42.7-m plots within a corn (Zea mays L.) field on Tifton loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) under conventional tillage practices. For each plot-year, atrazine was applied as surface spray immediately after planting and followed by a 50-mm, 2-h simulated rainfall 24 h later. A similar preapplication rainfall and four subsequent rainfalls during the growing season were also applied. Observed water runoff averaged 20% of the applied rainfall. Less runoff occurred from freshly tilled soil or under full canopy cover; more runoff occurred when nearly bare soil had crusted. Observed total seasonal atrazine runoff averaged 2.7% of that applied, with the first posttreatment event runoff averaging 89% of the total. GLEAMS, Opus, PRZM2β and PRZM3 adequately predicted water runoff amounts, with normalized root mean square errors of 29, 29, 31, and 31%, respectively. GLEAMS and PRZM3 predicted atrazine concentrations in runoff within a factor of two of observed concentrations. PRZM2β overpredicted atrazine concentrations. Opus adequately predicted atrazine concentrations in runoff when it was run with an equilibrium adsorption submodel, but significantly underestimated atrazine concentrations when it was run with a kinetic sorpton submodel.
    No preview · Article · Jan 2000 · Soil Science Society of America Journal
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    ABSTRACT: A rainfall simulator was used to apply 5 cm of rainfall in 2 hours to two replicate 624 m2 plots at six times during each of the growing seasons of 1992 and 1993. Because the simulator generated reproducible and time-invariant rainfall intensities, the resulting 24 hydrographs reproducibly reveal the effects of tractor wheel compaction, tillage, soil reconsolidation, surface sealing, and corn canopy development. A time series data set including weather, crop development, soils properties, evapotranspiration, and antecedent soil water is available. These data should provide hydrologie modelers, particularly those interested in modeling runoff with time resolutions of <1 day, with a useful validation data set.
    No preview · Article · Sep 1999 · Water Resources Research
  • Q.L. Ma · J.E. Hook · R.D. Wauchope
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    ABSTRACT: Environmental fate models are increasingly used to evaluate potential impacts of agrochemicals on water quality to aid in decision making. However, errors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predictions of chemical fate and transport. This study compared approaches and predictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow-corn growing seasons under sprinkler irrigation. The comparison included annual cumulative daily potential ET (ET(p)), actual ET, and partitioning of total ET between soil evaporation (E(s)) and crop transpiration (E(t)). When measured pan evaporation was used for calculating ET(p) (the pan evaporation method), Opus, PRZM-2, and RZWQM predicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculating ET(p) (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicted 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporation method predicted a similar amount of ET to the combination methods for bare soil, but predicted less ET when both E(s) and E(t) occurred. RZWQM reasonably predicted partitioning of ET to E(s), while GLEAMS and Opus over-predicted this partitioning. A close correlation between soil water storage in the root zone and ET suggests that accurate soil water content predictions were fundamental to ET predictions.
    No preview · Article · Feb 1999 · Agricultural Systems
  • Q. L. Ma · J. E. Hook · R. D. Wauchope
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    ABSTRACT: Environmental fate models are increasingly used to evaluate potential impacts of agrochemicals on water quality to aid in decision making. However, errors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predictions of chemical fate and transport. This study compared approaches and predictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow–corn growing seasons under sprinkler irrigation. The comparison included annual cumulative daily potential ET (ETp), actual ET, and partitioning of total ET between soil evaporation (Es) and crop transpiration (Et). When measured pan evaporation was used for calculating ETp (the pan evaporation method), Opus, PRZM-2, and RZWQM predicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculating ETp (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicted 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporation method predicted a similar amount of ET to the combination methods for bare soil, but predicted less ET when both Es and Et occurred. RZWQM reasonably predicted partitioning of ET to Es, while GLEAMS and Opus over-predicted this partitioning. A close correlation between soil water storage in the root zone and ET suggests that accurate soil water content predictions were fundamental to ET predictions. ©
    No preview · Article · Jan 1999
  • Q.L. Ma · J.E. Hook · R.D. Wauchope

    No preview · Article · Jan 1999 · Agricultural Systems
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    ABSTRACT: Runoff from crop land can enhance eutrophication of fresh water and hypoxia in sea water. We simulated rain at 25 mm hr -1 for 2 hr, 8 d prior and 1, 14, 29, 49 and 108 d after fertilization and planting of corn (Zea mays L.). Experimental sites received 50 kg N, 45 kg P, and 125 kg K ha -1 as granulated fertilizer broadcast and incorporated to a depth of 150 mm. An additional 118 kg N ha -1 was surface-banded as solution fertilizer at Day 28, which was 1 d prior to the Day 29 rain. The study was conducted for 2 yr on a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults) with a slope of 4.5%, on micro- (5.57 m 2) and meso-scale (622 m 2) plots. Runoff was equal for the two scales of plots. There were greater runoff losses of soluble-P from meso- (1.4 kg ha -1) than from micro-plots (1.0 kg ha -1). Nitrate-N losses averaged 2.7 kg ha -1 and bioavailable-P losses were 2.3 kg ha -1. Greatest NO 3-N and soluble-P losses occurred the day after application of the solid fertilizer, whereas bioavailable-P loss was greatest at Day 14 and 29. No increase in NO 3-N losses was found 1 d after the application of urea ammonium nitrate solution, possibly indicating that liquid fertilizers are not as susceptible to runoff losses as solid fertilizers. Results of this study should encourage the use of small plots, thereby saving research time and expense and provide data useful for estimating losses at similar sites.
    No preview · Article · Nov 1998 · Soil Science Society of America Journal
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    ABSTRACT: In simulations on the fate of agricultural chemicals applied to crops, accurate partitioning of rainfall between infiltration and runoff is fundamental to chemical runoff predictions. We evaluated the Root Zone Water Quality Model (RZWQM version 3.1) against measured runoff from two field plots (15×45 m with 3% slope) on a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult). Six simulated rainfall events, each 25 mm h−1 for 2 h, were applied to maize (Zea mays, L.) each year. In the uncalibrated mode, RZWQM under-predicted runoff by 40% on average, with the closest fit for events that occurred after full canopy. Saturated hydraulic conductivity (Ks) accounted for the majority of the uncertainty in predicted runoff. When Ks of the surface crust was back calibrated from the measured runoff, RZWQM predicted runoff closely for the remaining plots and events. Alternatively, using different Ks values for wheel track and crop beds, running the model for each and, then, proportionally assigning runoff also led to predictions that agreed with measured runoff. When spatial and temporal changes in Ks were calibrated to specific conditions at the site, RZWQM effectively predicted runoff.
    No preview · Article · Apr 1998 · Agricultural Systems

  • No preview · Article · Feb 1998 · Agricultural Systems
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    ABSTRACT: Comprehensive models for agrichemical transport necessarily include runoff predictions to partition rainfall between infiltration and runoff, as this ability is fundamental to predictions of chemical runoff and leaching. We compared GLEAMS, Opus, and PRZM-2 model runoff predictions with runoff measured in a precisely controlled field site used for chemical runoff studies. In 1992 and 1993, two 14.5 m x 42.9 m corn (Zea mays, L.) field plots with 3% slope on Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) received six severe, artificial rainfall events over the growing season with each event consisting of a 25 mm h-1 rainfall for 2 h. Runoff was monitored continuously using a collector and flume. Model performance criteria included sensitivity analysis, graphical comparison and statistical analysis including mean, ratio of means, root mean square error (RMSE), and a paired difference t-test. Observed runoff averaged 20% of added rainfall. Lowest values occurred with freshly plowed soil or full canopy cover, while 24 to 34% runoff occurred when nearly bare soils had crusted over. Using an initial moisture condition-II curve number (CN) of 85, GLEAMS and Opus predicted runoff within 10%, overall, and produced a pattern of high and low runoff that closely followed observed. PRZM-2 overpredicted runoff by 90%, overall, and predicted its highest runoff when observed runoff was lowest. Paired difference t-tests indicated a significant difference between measured and predicted runoff for PRZM-2 (p<0.001 at α = 0.05), but none for GLEAMS (p = 0.761) or Opus (p = 0.194). Mean, ratio of means, and RMSE showed that GLEAMS and Opus performed better than PRZM-2. All three models were very sensitive to CN values which were empirical and subjective, but less sensitive to measurable soil physical properties. With careful parameterization, GLEAMS and Opus could be used to simulate runoff from similar row-crop and soil conditions.
    No preview · Article · Jan 1998
  • R.D. Wauchope · H.R. Sumner · C.C. Dowler
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    ABSTRACT: A plant-weighing procedure was used to measure the total mass of spray mixture intercepted by small whole corn and cotton plants. Mixtures of water and water plus crop oil concentrate or spreader-sticker were applied at spray volumes of 280 to 28,000 L/ha. The plants were weighed before and after passing under the spray and leaf areas, and shoot fresh and dry weights for each plant were measured. Spray deposition increased with spray volumes but not proportionally. Corn plants were larger than cotton plants and retained more spray per plant; however, cotton retained more spray per unit leaf area. The two adjuvants had similar effects on deposition, tending to increase it in corn and decrease it in cotton.
    No preview · Article · Jul 1997
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    A W Johnson · R D Wauchope · D R Sumner
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    ABSTRACT: Recoverable fenamiphos in the soil and residue in squash following different simulated rainfall treatments after nematicide application were determined in a 2-year study. Efficacy of fenamiphos also was evaluated. Fenamiphos treatments (3 SC and 15 G) were broadcast (6.7 kg a.i./ha) over plots and incorporated into the top 15 cm of soil immediately before planting 'Dixie Hybrid' squash. Simulated rainfall treatments of 0, 2.5, and 5.0 cm water were applied 1 day after fenamiphos application. Soil samples from 0- to 8-cm, 8- to 15-cm, and 15- to 30-cm soil depths were collected 1 day after the simulated rainfall applications and analyzed for fenamiphos, fenamiphos sulfoxide (FSO), and fenamiphos sulfone (FSO). Squash was analyzed for total fenamiphos residue. Greater concentrations of fenamiphos were present in the 0- to 8-cm soil layer following application of 15 G than 3 SC formulation. Simulated rainfall treatments did not alter fenamiphos concentrations in any soil layer (except for the 0- to 8-cm depth in 1992) or concentration of FSO and total fenamiphos residue in the 15- to 30-cm soil layer. Root-gall indices were greater from untreated than most fenamiphos-treated plots, but were not affected by formulations of fenamiphos or simulated rainfall treatments. Concentrations of total residue in squash ranged from 1 to 4 mug FSO/g.
    Preview · Article · Oct 1996 · Journal of nematology

Publication Stats

1k Citations
53.72 Total Impact Points

Institutions

  • 1995
    • College of Coastal Georgia
      Georgia, United States
  • 1993
    • United States Department of Agriculture
      Washington, Washington, D.C., United States
  • 1992
    • Agricultural Research Service
      ERV, Texas, United States
  • 1990
    • University of Toronto
      Toronto, Ontario, Canada