Soil dissipation and efficacy on itchgrass of soil-applied residual herbicides pendimethalin and clomazone in Louisiana sugarcane

Authors: WAYMENT, DARCEY - Nicholls State University; Wright, Alice; Bergeron, Dallas; McCollam, Gerald; White, Paul

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2024
Publication Date: 9/29/2024
Citation: Wayment, D.G., Wright, A.A., Bergeron, D.R., Mccollam, G.A., White Jr, P.M. 2024. Soil dissipation and efficacy on itchgrass of soil-applied residual herbicides pendimethalin and clomazone in Louisiana sugarcane. Pest Management Science. https://doi.org/10.1002/ps.8432.
DOI: https://doi.org/10.1002/ps.8432

Interpretive Summary: Sugarcane (Saccharum sp.) growers in Louisiana report that a common chemical applied to sugarcane fields (Prowl) is no longer controlling itchgrass, one of the worst weedy plants. Because of this, growers started using a different chemical, Command. The objective of this project was to evaluate the degradation time of these two chemicals in a collection of soils commonly used to grow sugarcane in Louisiana, and to test how well these chemicals controlled itchgrass sprouted in each of the soils. Prowl decomposed rapidly, reaching 50% of the original chemical added between 7-59 days. Command was more persistent to degradation, with 50% remaining in all soils after 79 days. However, Prowl was more effective at controlling sprouted itchgrass when compared to Command.

Technical Abstract: Sugarcane (Saccharum sp.) growers in Louisiana report that the widely used soil residual herbicide, pendimethalin, is less effective at controlling itchgrass (Rottboellia chochinchinensis), possibly through accelerated dissipation from repeated applications. Some growers have started to use another herbicide, clomazone, in place of pendimethalin for itchgrass control when pendimethalin does not provide the necessary control. Little is known about the dissipation of these two herbicides, especially when applied together, in diverse sugarcane soils in Louisiana. Thus, the objective of the research was to measure the dissipation of pendimethalin and clomazone in soils having high itchgrass pressure. Soil samples from each field were fortified (4µg g-1) with clomazone and pendimethalin and monitored over the course of 163 days under laboratory conditions. Herbicide levels were determined by extracting the herbicides from soil with acetonitrile and analyzing the extracts with high performance liquid chromatography (HPLC). The results indicate that clomazone is persistent in the soils studied, with a half-life (DT50) of 79 d or higher. Pendimethalin dissipates more rapidly in soil with a DT50 ranging from 7 d - 59 d. However, when these soils were seeded with itchgrass, pendimethalin was more effective at controlling itchgrass than clomazone.