Lloyd M. Southwick

Methyl parathion and EPN washoff from cotton plants by simulated rainfall

Modeling the amount of pesticides that will be transported in runoff and sediment from agricultural lands to aquatic environments requires ability to predict amounts washed from plant canopy to soil by rainfall. Methyl parathion (MP) [ 0,O-dimethyl 0-(p-nitrophenyl) phosphorothioate] and EPN [ 0-ethyl 0-(p-nitrophenyl) phenylphosphonothioate] are used extensively for cotton (Gossypium hirsutum L.) insect control in the South during July, August, and September-months of high intensity thunderstorms. The MP and EPN washed from mature cotton were measured by the use of a multipleintensity rainfall simulator. Concentrations and amounts of MP and EPN washed from plants were independent of rain intensity when 24 mm of simulated rain was applied at 11,26,52, and 111 mm h-l just 2 h after MP and EPN were applied at 0.64 + 0.64 kg hab1. About 88 f 32% of the MP load and 62 f 18% of the EPN load on the plants were washed off. MP and EPN concentrations in storm runoff decreased with runoff volume as hyperbolic functions. Only rainfall amount affected MP and EPN washoff. This information greatly simplifies modeling the movement of MP and EPN from plant canopy to soil during natural storms when intensities vary greatly within storms and from storm to storm.

Carbaryl washoff from soybean plants

Both the efficacy and fate of most foliar-applied pesticides may be affected by weather variables, especially rain. A multiple-intensity rainfall simulator was used to determine the effects of rainfall intensity and amount on concentrations of carbaryl (Sevin® XLS Plus) washed from soybean plants. Two hours after carbaryl was applied at 1.12 kg/ha, 25 mm of rain was applied at intensities of 13.0, 27.4, 53.8, or 105.1 mm/h. About 67% of the carbaryl on the plants was washed off by 25 mm of rain. Rainfall intensity affected carbaryl concentrations in washoff; higher concentrations occurred at lower intensities. Even though the experimental conditions were designed for “worst-case” conditions, washoff patterns suggested improved carbaryl rainfastness when compared to carbaryl (formulated as a wettable powder) washoff from cotton plants in earlier studies. Rainfall amount had a greater effect on carbaryl concentrations in washoff than rainfall intensity.

Azinphosmethyl and fenvalerate washoff from cotton plants as a function of time between application and initial rainfall

Understanding pesticide foliar washoff is important in pest management, in development of integrated management systems, and in environmental modeling. This study was conducted to determine the effect of elapsed time between spray application and initial rainfall on insecticide washoff from foliage. Azinphosmethyl and fenvalerate were applied to mature cotton plants as tank-mixed emulsifiable concentrates with a water carrier. DT50s (50% disappearance time) for azinphosmethyl and fenvalerate were 3.9 and 237 h, respectively. Simulated rain (51 mm in 1 h) was applied to the cotton plants at times ranging from 2 to 146 h after insecticide application to determine washoff characteristics for both compounds. Residues of both insecticides became increasingly resistant to wash-off with increasing time interval between insecticide application and initial rainfall, e.g., about 95% of the plant Xload washed off 2 h after application, whereas at 146 h <50% washed off. The mean amounts of both insecticides washed from the plants decreased with time and were related to the mean plant loads. The results of this study show that foliar pesticide application should be delayed when rain is imminent.

The polarographic reduction of some dinitroaniline herbicides

Polarography of 2,6-dinitroaniline herbicides in aqueous ethanol revealed a marked pH dependence of the reduction potentials. The study included the herbicides trifluralin (I), benefin (II), isopropalin (III), dinitramine (IV), nitralin (V), and oryzalin (VI), for which E12 values (mV vs. SCE) for the first polarographic wave, at pH 1.5, 5.1, 7.4, and 9.2, respectively, were (I) −190, −430, −540, −640; (II) −190, −430, −540, −640; (III) −170, −360, −560, −650; (IV) −230, −510, −720, −810; (V) −160, −330, −540, −650; (VI) −160, −370, −540, −680.

Runoff and leaching of metolachlor from Mississippi River alluvial soil during seasons of average and below-average rainfall.

The movement of the herbicide metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] via runoff and leaching from 0.21 ha plots planted to corn on Mississippi River alluvial soil (Commerce silt loam) was measured for a 6-year period, 1995-2000. The first three years received normal rainfall (30 year average); the second three years experienced reduced rainfall. The 4-month periods prior to application plus the following 4 months after application were characterized by 1039 +/- 148 mm of rainfall for 1995-1997 and by 674 +/- 108 mm for 1998-2000. During the normal rainfall years 216 +/- 150 mm of runoff occurred during the study seasons (4 months following herbicide application), accompanied by 76.9 +/- 38.9 mm of leachate. For the low-rainfall years these amounts were 16.2 +/- 18.2 mm of runoff (92% less than the normal years) and 45.1 +/- 25.5 mm of leachate (41% less than the normal seasons). Runoff of metolachlor during the normal-rainfall seasons was 4.5-6.1% of application, whereas leaching was 0.10-0.18%. For the below-normal periods, these losses were 0.07-0.37% of application in runoff and 0.22-0.27% in leachate. When averages over the three normal and the three less-than-normal seasons were taken, a 35% reduction in rainfall was characterized by a 97% reduction in runoff loss and a 71% increase in leachate loss of metolachlor on a percent of application basis. The data indicate an increase in preferential flow in the leaching movement of metolachlor from the surface soil layer during the reduced rainfall periods. Even with increased preferential flow through the soil during the below-average rainfall seasons, leachate loss (percent of application) of the herbicide remained below 0.3%. Compared to the average rainfall seasons of 1995-1997, the below-normal seasons of 1998-2000 were characterized by a 79% reduction in total runoff and leachate flow and by a 93% reduction in corresponding metolachlor movement via these routes. An added observation in the study was that neither runoff of rainfall nor runoff loss of metolachlor was influenced by the presence of subsurface drains, compared to the results from plots without such drains that were described in an earlier paper.

Leaf residue compartmentalization and efficacy of permethrin applied to soybean.

Permethrin (EC, 0.084 kg AI/ha) was applied to soybean by backpack sprayer and eight determinations of leaf residue compartmentalization and insect mortality were made during the 27 days following ...

Impacts of Sugarcane Post-Harvest Residue Management on Runoff, Soil Erosion, and Nitrate Loss

Public concern over the burning of sugarcane residue has resulted in increased in-field residue management in Louisiana. However, this practice has been linked to increased soil water content and delayed spring growth. We established a soil-bed (< 0.2 % slope) experiment under simulated rainfall to evaluate residue management effects on runoff quantity, total solids (erosion) and nitrate loss, and on antecedent soil water content. Fertilizer (220 kg/ha applied as 32% N solution) was applied in an 8 cm deep knife cut prior to the first simulated rainfall, with soil immediately repacked over the cut. Three soil-beds were established for each treatment: Bare soil to mimic burning; a blanket of residue applied at 5 Mg/ha; and 5 Mg/ha of residue applied as a center strip to mimic brushing to the furrows (Swept). Rainfall (30 mm in 0.5 h) was applied twice weekly for four weeks. Bare soil resulted in 199 mm runoff, erosion of 1.9 Mg/ha, and nitrate loss of 9.0 kg/ha. Blanket residue reduced runoff by 85 %, erosion by 95 %, and nitrate loss by 90 % compared to bare soil. Swept residue reduced runoff by only 6 %, but did decrease erosion by 60 % and nitrate loss by 32 % compared to bare soil. Residue management did not affect soil water content; however these containers were well-drained. Leaving a residue blanket would provide the greatest benefit. However, at this slope, sweeping residue to the furrows would decrease erosion to an acceptable rate, without increasing soil water content.

Persistence of Diflubenzuron on Soybean Leaves

Diflubenzuron [Dimilin™, N-[{(4-chlorophenyl)amino}carbonyl]-2-6-difluorobenzamide] is an insect growth regulator that is highly effective and provides residual control (up to 54 days) against velv...