Efficacy and Antagonism of Pinoxaden Alone and in Combination with Other Pesticides for Annual Grass Control

Abstract

Pinoxaden is an acetyl coenzyme A carboxylase (ACCase) inhibiting herbicide in the phenylpyrazoline chemical family. Recently, pinoxaden was labelled for turfgrass use with a limited number of labelled susceptible weeds. Variable susceptibility to ACCase inhibiting herbicides between grassy weeds is common. For this reason, greenhouse trials were conducted in order to better understand grassy weed susceptibility to pinoxaden. A rate response screen was carried out using ten rates of pinoxaden on nine grassy weed species. Plant visual injury and above-ground biomass data were taken. Nonlinear regressions were run to estimate the rates of pinoxaden that injury and reduce the biomass of each species 50 and 90% (I50 and I90). According to the data, the nine species tested can be ranked from most to least susceptible as such, perennial ryegrass (Lolium perenne L.) > yellow foxtail (Setaria pumila Poir.) > dallisgrass (Paspalum dilatatum Poir.) > southern sandbur (Cenchrus echinatus L.) > large crabgrass (Digitaria sanguinalis L.) > roughstalk bluegrass (Poa trivialis L.) > bahiagrass (Paspalum notatum Fleugg.) > goosegrass (Eleusine indica L. Gaertn.) > annual bluegrass (Poa annua L.). ACCase inhibiting herbicides are often called graminicides because they are active on grasses only. Because of this limited selectivity, graminicides are often tank mixed with herbicides targeting broadleaf weed species. Many of these tank mixtures have an antagonistic response on the ACCase inhibitor. Experiments were conducted in order to test different tank-mix combinations for antagonistic responses. According to the data, metsulfuron, halosulfuron, chlorothalonil and propiconazole antagonize pinoxaden injury of St. Augustinegrass (Stenotaphrum secundatum (Walter) Kuntze). Metsulfuron, halosulfuron and chlorothalonil antagonize pinoxaden control of smooth crabgrass (Digitaria ischaemum Schreb.). The data indicate that metsulfuron antagonizes pinoxaden to a greater extent than the other chemicals tested. Mixtures with chlorothalonil were also observed to induce unexpected injury similar to a contact herbicide.