Interaction of Methiozolin with Soil and Subsequent Influence on Poa annua Control
Type of Degreedissertation
Agronomy and Soils
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Annual bluegrass is a problematic turfgrass weed due to its ability to thrive at low mowing heights, disruption of aesthetics and utility, and few herbicidal control options. Methiozolin is a new, currently unregistered herbicide that selectively controls annual bluegrass in desirable turfgrasses. Studies were conducted to evaluate and compare annual bluegrass control from preemergence (PRE) applied methiozolin as influenced by rate and soil type and from postemergence (POST) applied methiozolin as influenced by rate, soil type, annual bluegrass growth stage, and treatment placement. Studies were also conducted to evaluate foliar and root absorption and subsequent translocation of methiozolin by annual bluegrass using radio-tracer techniques. PRE applied methiozolin controlled annual bluegrass > 99%. POST applied methiozolin resulted in < 80% control regardless of foliar versus root exposure. POST applications are more effective at higher rates and smaller growth stages. Foliar-plus-soil methiozolin application trended to result in the best control, compared to foliar-only or soil-only applications. Absorption and translocation data indicate that methiozolin is absorbed by both leaves and roots and moderately translocates upward in the plant toward the leaf tip with little to no basipetal translocation. Due to the fact that control is limited from a single methiozolin application (as observed in POST experiments), successful field application of methiozolin requires multiple, timely applications directed toward the roots and/or foliage of annual bluegrass. Previous research indicates that maximum weed control efficacy requires root exposure; however, soil sorption and mobility of methiozolin has not been established. Research was conducted to investigate soil sorption and subsequent desorption by dilution of methiozolin, as well as soil mobility using batch equilibrium experiments and thin-layer chromatography in nine root-zones. Evaluations focused on sand-based systems because they are used for construction of many golf course putting greens. Sorption coefficients (Kd values) ranged from 0.4 to 29.4 mL g-1 and averaged 13.8 mL g-1. Sorption was most influenced by organic matter content; conversely, soil pH had a negligible effect. Methiozolin desorption did not occur with 0.01 M CaCl2 dilution. Methiozolin mobility was low; retardation factors (Rf values) were < 0.05 for all media with ≥ 0.3 % organic matter. Sand (0.1% organic matter) resulted in an Rf value of 0.46. Overall, results indicated that ~24% of applied methiozolin was available for root uptake, and mobility was limited suggesting resistance to loss through leaching displacement. Golf course managers frequently tank-mix fertilizers with herbicides to reduce time and labor, but no information is available regarding such mixtures with methiozolin. Research was conducted to evaluate methiozolin for annual bluegrass control and creeping bentgrass safety when tank-mixed with ammonium sulfate and iron sulfate. Mixtures with ammonium sulfate did not influence annual bluegrass control while reducing creeping bentgrass injury in some instances. Mixtures with iron sulfate varied by experimental run but annual bluegrass control was either similar or increased while creeping bentgrass injury did not vary by experimental run and was not influenced. Paclobutrazol resulted in similar control and injury with and without iron sulfate, and injury and control were similar to methiozolin at appropriate rates. In a comparison study of methiozolin, amicarbazone, and ethofumesate applied alone, with ammonium sulfate, and with iron sulfate, respectively, treatments including methiozolin and ethofumesate generally resulted in greater annual bluegrass control than those with amicarbazone. However, ethofumesate resulted in unacceptable turfgrass quality and NDVI reductions. Therefore treatments including methiozolin were the best overall. While some differences were observed, generally annual bluegrass and creeping bentgrass response to these agrochemicals was not affected by tank-mix partner relative to that agrochemical applied alone.