Leaves of coca are the primary source of cocaine. There is interest in using Fusarium oxysporum as a mycoherbicide in addition to other measures to control coca production, but information on coca physiology, including the stress responses of coca leaves, is limited. Deleafing coca plants stimulates rapid production of new leaves, and young expanding leaves readily abscise if treated with ethylene. Commercial preparations of cell wall degrading enzymes, as well as a 24-kDa elicitor from Fusarium oxysporum, induced significant levels of ethylene production by coca leaves. Ethylene pretreatment of coca leaves enhanced the production of ethylene by coca leaves in response to the cell wall degrading enzyme preparation, Driselase, and the 24-kDa elicitor. However, ethylene pretreatment did not enhance the rate of necrosis induced in response to either Driselase or purified 24-kDa elicitor. Driselase failed to elicit levels of necrosis comparable to the 24-kDa elicitor even at 30-fold higher protein concentrations. The response of coca leaves to the 24-kDa elicitor saturated at 6.7 μg ml−1. Age of coca leaves influenced both the level of resulting necrosis and the amount of ethylene produced in response to protein. Very young leaves produced the highest levels of ethylene and necrosis in response to Driselase and the 24-kDa elicitor. The data suggest that responsiveness of coca leaves to control measures may be synchronized over the first few weeks following defoliation.

Imazaquin movement in a field site that had Karnak silty clay soil was evaluated during a 2-yr study to determine if leaching was a significant dissipation mode for imazaquin. Imazaquin in water samples collected from subsurface tile drainage was measured by immunoassay. Total imazaquin losses due to leaching in 1993 were 0.8% of the total applied and in 1994, practically zero. Imazaquin concentrations as high as 80 μg L−1 were observed in drain water when rainfall occurred shortly after herbicide application. Imazaquin concentrations were lower with each successive drain flow event. Higher concentrations of imazaquin were associated with higher drainage flow, shortly after application. However, 40 d after application, the levels of imazaquin were low (<7 μg L−1) even when high tile flow occurred. The time between application and the first rainfall is an important factor in imazaquin leaching. In the dry growing season of 1994, imazaquin concentration in drain water did not exceed 5 μg L−1.

The hydrolytic and dealkylation products of cyanazine have been detected in soils, but the sorption of these products in soil has not been well studied. We examined sorption characteristics of five cyanazine degradation products in relation to cyanazine in Norfolk loamy sand, Tunica silty clay, and Dundee silt loam soils. Sorption was determined using a batch equilibrium method. Air-dried soil (3 g) was shaken in 6 ml of solution containing cyanazine or one of its degradation products for 48 h at 4 C. Five concentrations (2.04 to 54.67 μmol L−1) of each chemical were evaluated. The cyanazine Freundlich coefficient (Kf) ranged from 0.64 in Norfolk soil to 4.75 in Dundee no-tillage (NT) soil, and was higher in Dundee NT than in Dundee conventional-tillage (CT) soil. The Freundlich exponent (N) values for cyanazine were less than 0.85 in all soils, indicating nonlinearity of the sorption isotherm. In general, cyanazine sorption among the soils increased in the order of Norfolk << Dundee CT < Tunica < Dundee NT. Cyanazine sorption among the soils was correlated with fine texture and higher organic carbon content. Sorption of cyanazine degradation products was less than cyanazine sorption in all soils. Isotherms were nonlinear, with sorption decreasing in the order of cyanazine > desmethylpropanenitrile cyanazine > hydroxyacid cyanazine > desethyl cyanazine > cyanazine amide >> chloroacid cyanazine. The Kf for chloroacid cyanazine ranged from 0.21 in Norfolk soil to 0.42 in Dundee NT soil. Sorption patterns of five degradation products among the soils were generally similar to that of cyanazine. Our data indicate that under field conditions, cyanazine degradation products (especially cyanazine amide and chloroacid cyanazine) are more likely to remain in the aqueous phase and thus have a greater potential to move with water compared to cyanazine.

Laboratory experiments were conducted to evaluate soil adsorption and mobility of sulfentrazone. Sulfentrazone is a new phenyl triazolinone herbicide intended for use in soybean. Adsorption was evaluated through a soil solution technique, and mobility was evaluated with soil thin-layer chromatography. Experimental variables included soil, sulfentrazone concentration (adsorption study only), and pH. Adsorption was influenced by all experimental variables; however, pH had the greatest effect. Adsorption generally decreased in response to increasing pH. However, the greatest decrease occurred above the pKa of sulfentrazone (i.e., 6.56). Mobility generally reflected adsorption.

Greenhouse studies were conducted to determine the following: if treating henbit or downy brome with glyphosate increased populations of Fusarium solani f. sp. pisi and Pythium ultimum in soil and rhizosphere soil; if treating henbit or downy brome with glyphosate increased root colonization and infection by F. solani f. sp. pisi or P. ultimum; and, if henbit and downy brome are hosts of F. sohni f. sp. pisi or P. ultimum. Pythium ultimum populations increased only in soil containing glyphosate-treated henbit. Fusarium solani f. sp. pisi and P. ultimum populations increased in rhizosphere soil from glyphosate-treated henbit, while only P. ultimum populations increased in rhizosphere soil from glyphosate-treated downy brome. These results suggest that peas planted in soil where either downy brome or henbit had been treated with glyphosate could be exposed to higher populations of F. solani f. sp. pisi and P. ultimum. Root colonization and infection, plant height, and root weight data indicated that henbit and downy brome are alternate hosts of P. ultimum. F. sohni f. sp. pisi colonized, but did not readily infect roots of downy brome and henbit.