Effect of temperature on the persistence of chlorimuron-ethyl, flumioxazin, and pyroxasulfone in Indiana field soils and under controlled conditions using a velvetleaf ( Abutilon theophrasti ) bioassay

Abstract

The increased adoption of early-planted soybean [ Glycine max (L.) Merr.] has required investigation of the persistence of commonly used residual herbicides under colder soil temperatures. Controlled environment and field studies evaluated the persistence of chlorimuron-ethyl, flumioxazin, and pyroxasulfone in Indiana soils (Wanatah [sandy loam, pH 6.2, 1.5% OM], Lafayette [silt loam, pH 6.6, 2.5% OM], and Butlerville [silt loam, pH 5.9, 1.6% OM]). A controlled environment bioassay assessed the effects of soil properties and incubation temperature on flumioxazin and pyroxasulfone persistence using velvetleaf ( Abutilon theophrasti Medik.) as the indicator species. Results indicated greater persistence of both herbicides under colder soil conditions. Flumioxazin persistence increased in soils with higher organic matter, while pyroxasulfone persistence was greater in soils with higher pH. Field studies conducted in 2024 and 2025 evaluated herbicide persistence following applications at soybean planting dates from late March to early June in Wanatah and Lafayette soils. Herbicide concentrations were quantified using chemical extraction and ultra-high performance liquid chromatography. In Wanatah soil in 2025, the early planting date, characterized by colder temperatures and lower precipitation, resulted in 45% higher flumioxazin and 25% higher pyroxasulfone concentrations at 30 d after planting (DAP) compared with the later planting date. However, in 2024, increased precipitation following early May planting reduced herbicide persistence relative to late May applications. In Lafayette soil, early May applications resulted in 77%, 35%, and 21% higher concentrations of chlorimuron-ethyl, flumioxazin, and pyroxasulfone, respectively, at 30 DAP compared with mid-June applications. These findings indicate that earlier planting dates can increase herbicide persistence under cooler and drier conditions, potentially extending the weed control window and increasing the risk of crop injury. However, extended residual weed control and the risk of crop injury under early planting conditions are limited by cumulative rainfall after application.