Methiozolin Soil Sorption and Influence On Herbicidal Activity.

Methiozolin is a herbicide currently being evaluated for annual bluegrass (Poa annua) control in golf course putting greens. Previous research indicates methiozolin is root- and foliar-absorbed, but translocation only occurs acropetally; root-exposure is necessary for maximum herbicide efficacy. Therefore, methiozolin must be available for root uptake in the soil for successful field application; methiozolin must not be excessively sorbed to soil and not readily leached from the root zone. Little is known about the soil sorption of methiozolin. Research was conducted to evaluate methiozolin sorption to various soil media. Soil solution batch-equilibrium methods were used with ¹⁴C-methiozolin at 1 mg L^-1 to determine Kd values for United States Golf Association (USGA) grade sand with 0 to 20% (w/w) peat, USGA grade sand-based root zones that were 0, 10, and >15 years old, and a Wickham sandy loam (locally collected field soil). Results indicate that organic matter content greatly influenced Kd values, while soil pH did not influence Kd values. Clay content was not included in the analysis due to its narrow range (1.3 to 2.5%) across the soil media evaluated. Kd values ranged from 1.43 for pure sand to 30.3 for sand with 20% peat. Native field soil had a Kd value of 6.59. Kd values observed are consistent with other soil-active herbicides. Soil media with 0.3 to 6.1% organic matter resulted 9.3 to 32% of applied methiozolin in solution after equilibrium. Across all soil media, 23.5% of methiozolin remained in soil solution after equilibrium, and therefore is immediately available for plant uptake via root absorption. Overall, results indicate that methiozolin is available for plant uptake but binds enough to soil to resist leaching from the root zone.