Dissipation of Pendimethalin in Organic Soils in Florida

Abstract

Understanding the persistence of PRE-applied pendimethalin is important in determining timing of subsequent weed management programs in sugarcane on organic soils in the Everglades Agricultural Area (EAA). Dissipation of oil- and water-based pendimethalin formulations applied PRE at 2, 4, and 8 kg ai ha−1were compared in 2011 and 2012 on organic soils in the EAA. The rate of dissipation of both formulations was very similar. Both formulations had an initial rapid rate of dissipation followed by a slower rate of dissipation. However, the initial amount of pendimethalin in the soil was higher with the water-based compared to the oil-based formulation, most likely because of the lower volatility of the water-based formulation. The half-lives (DT50s) of the oil-based formulation were 32, 18, and 10 d and 8, 8, and 12 d at 2, 4, and 8 kg ha−1, respectively, in 2011 and 2012, respectively. The DT50s of the water-based formulation were 20, 13, and 10 d and 12, 12, and 14 d at 2, 4, and 8 kg ha−1, respectively in 2011 and 2012, respectively. These DT50values were attributed to low soil water content as well as the absence of incorporation following application. Our results suggest that dissipation of pendimethalin is rapid on organic soils irrespective of the formulation when applied under dry soil conditions with no incorporation into the soil.