Clomazone efficacy in snap beans and dissipation in soil

Studies were conducted from 1991 to 1993 to determine the effects of clomazone on snap bean (Phaseolus vulgaris) growth and yield. Field experiments were conducted on Etowah, Sequatchie, and Lily soils. Clomazone was applied preemergence at 0, 0.28, 0.56, 0.84, or 1.12 kg ai/ha in a randomized complete block with treatments replicated four times. Snap beans were evaluated for chlorosis, density and yield. Data were subjected to analysis of variance and means were separated utilizing Fisher's Least Significant Difference at the 0.05 probability level. Visual evaluations were made approximately 2, 4 and 6 wk after treatment in each experiment.

Preliminary studies in 1991 indicated an increase in snap bean yield as clomazone rates increased. In 1992 and 1993, snap beans were injured by clomazone at 1.12 kg ai/ha with chlorosis reaching 50%. However, injury was not observed in each planting. Yields were reduced 30% when significant injury occurred.

Clomazone dissipation under field conditions was also determined. Soil samples were obtained from field studies at approximately 0, 7, 14, 21, 28, 42 and 56 DAT. Clomazone was extracted and analyzed using high performance liquid chromatography.

Clomazone degradation in soil empirically fit pseudo-first order kinetics. Degradation was initially rapid and then degraded gradually resulting in a decrease in concentration. Half-life values ranged from 16 to 53 d. Clomazone adsorption was directly related to organic matter content. Kd values were 0.92, 0.85, and 1.12 for the Etowah, Sequatchie and Lily soil, respectively.

The effects of soil moisture (-1.5 and -0.033 mPa) and temperature (15 and 30 C) on clomazone degradation under controlled conditions were also evaluated. Clomazone degradation was slower under cool, dry conditions than warm conditions. Soil moisture had no influence on clomazone degradation except in the Sequatchie soil. After 84 d incubation, clomazone concentrations decreased 25% in the Sequatchie soil at 15 C compared with 75% in the Lily soil.