Alternative herbicide formulations may have the potential to reduce atrazine leaching. This study was conducted to determine if starch-encapsulation produced using an extrusion process or several acrylic polymer additives reduced atrazine leaching in soil columns packed with Plainfield sand (98% sand and 0.7% organic matter). Three watering regimes were evaluated to determine the effects of water volume and rate of application on atrazine movement When 7.6 cm of water (0.44-pore volumes) was applied over 2 h, polymer treatments reduced atrazine movement from the soil surface by 9 to 21% compared to atrazine without the additives. With increased water volume and time, the effectiveness of several polymer treatments diminished. Acrysol ASE-108 and G110 polymers (mixed with atrazine at a 1:1 ratio) most effectively reduced atrazine leaching over all watering regimes. Starch encapsulation was more effective than any polymer additive in retarding atrazine movement Increasing the water volume from 7.6 to 15.2 cm (0.88-pore volumes) did not increase leaching of starch-encapsulated atrazine. Ninety-nine percent of the starch-encapsulated atrazine was retained in the top 5 cm of the column compared to only 18 and 13% of the dry flowable formulation (DF) when 0.44- and 0.88-pore volumes of water were applied over 2 and 4 h, respectively. When 0.88-pore volumes of water were applied over 12 d, 81% of the starch-encapsulated atrazine was retained in the upper 5 cm of the column compared to only 5% of the DF formulation of atrazine. This study indicates that starch encapsulation reduces atrazine movement to a greater extent than polymer additives and suggests that starch encapsulation may be an effective method of reducing atrazine leaching.

The interaction of chloramben and paraquat on weed control and crop safety in peanuts was examined in a series of experiments. Greenhouse experiments revealed that chloramben was antagonistic toward paraquat on sicklepod and peanut, which are species tolerant to chloramben and sensitive to paraquat Control of Florida beggarweed, a species sensitive to both herbicides, was generally improved with tank mixtures. Similar results were obtained in field studies. Antagonism obtained with tank-mixing chloramben plus paraquat was also obtained by applying chloramben prior to paraquat Studies with 14C-labeled herbicides on Florida beggarweed revealed that chloramben inhibited foliar penetration of paraquat, but paraquat had no effect on foliar penetration of chloramben.

Optimum conditions for leafy spurge control with sulfometuron were determined. Absorption and translocation of 14C-sulfometuron to roots in leafy spurge averaged 11 and 0.1% of applied herbicide, respectively, and were not affected by growth stage. Absorption and translocation increased to 40 and 4%, respectively, of applied 14C-sulfometuron when the relative humidity remained at 90 and 95% for at least 72 h after treatment Absorption and translocation of 14C-sulfometuron to the roots were similar at 18/14 and 24/20 C and when 14C-sulfometuron was applied with picloram or 2,4-D. Absorption of 14C-picloram was greater but 14C-2,4-D absorption was less when applied with sulfometuron compared to picloram or 2,4-D applied alone. Sulfometuron plus picloram applied during the fall regrowth stage provided better leafy spurge control than either herbicide applied alone. The combination treatment would be useful especially in areas where grass injury was acceptable in order to extend the fall treatment season by 2 to 3 wk compared to present practices.

Effects of tillage and herbicide application method on the persistence and residual activity of clomazone, imazaquin, and imazethapyr were investigated in a 2-yr field study. Herbicides were applied preemergence and preplant incorporated to conventional- and reduced-tillage soybeans in 1987 and 1988. Herbicide dissipation was monitored using chromatographic and bioassay techniques. In 1987, dissipation rates for clomazone, imazaquin, and imazethapyr were similar, regardless of tillage system or application method. In 1988, all three herbicides applied preplant incorporated dissipated more slowly than in preemergence treatments. Corn planted in rotation in 1989 displayed greater levels of injury in the incorporated treatments for all three herbicides. Although herbicide concentrations were similar 322 d following application in both tillage treatments in 1989, corn injury was greater with imazaquin and imazethapyr and less with clomazone in the reduced-tillage plots than in the conventional-tillage treatments.

Laboratory and field studies were conducted in 1988 through 1990 to determine the effect of soil pH on imazaquin adsorption and persistence in a Crosby silt loam (1.6% organic matter) and a Hoytville clay (3.3% organic matter). Above a pH of 6, 6 to 7% of the total imazaquin present was adsorbed to both soils. Adsorption increased as pH decreased from about 7 to 4.5, with a maximum of 16.5 and 31% adsorbed on Crosby and Hoytville soils, respectively. Imazaquin was more persistent in the Hoytville clay than in the Crosby silt loam. Herbicide dissipated more slowly in both soils in 1988 than in 1989 due to dry soil conditions immediately prior to and following herbicide application in 1988. In both soils, imazaquin persistence increased as soil pH decreased, over a pH range from 6.5 to 4.5. Increased persistence with decreasing pH was attributed in part to increased adsorption and decreased availability for microbial degradation.

The effect of glyphosate on growth and reproduction of two pathogenic fungi of green peas was evaluated in laboratory studies. Liquid and agar media containing 0 to 50 mM glyphosate were inoculated with two isolates each of Fusarium solani f. sp. pisi and Pythium ultimum. Mycelial growth and spore production of the fungi were inhibited or stimulated by glyphosate, depending on concentration. Glyphosate did not affect pathogenicity of F. solani f. sp. pisi. The effect of glyphosate on pathogenicity of P. ultimum was not determined. Under field conditions, glyphosate probably would not affect pathogenicity or survival of either fungus.