Interactions ofPyricularia setariaewith Herbicides for Control of Green Foxtail (Setaria viridis)

Abstract

Sethoxydim, tralkoxydim, imazethapyr, quinclorac, propanil, glyphosate, and glufosinate were tested at rates below those recommended by the manufacturers withPyricularia setariaeNiskada under greenhouse conditions for control of green foxtail. At one-tenth of the recommended rate in a 100 L/ha carrier volume, only the sethoxydim–P. setariaecombination achieved more effective green foxtail control when compared with the herbicide or pathogen alone. Selected herbicides at one-tenth, one-fourth, and one-half of the recommended rates showed variable interactions with the pathogen on plants with three and five leaves. Propanil (recommended rate 0.99 kg ai/ha) was more synergistic at higher rates, especially on larger plants, for which the combined treatment increased green foxtail mortality from zero in the herbicide alone to 100%. Quinclorac (recommended rate 0.10 kg ai/ha) acted similarly to propanil with slightly lower synergy effects. Sethoxydim (recommended rate 0.15 kg ai/ha) at one-tenth or one-quarter of the rate plusP. setariaeoften enhanced green foxtail control on larger plants. On smaller plants, the herbicide and pathogen alone were highly efficacious. Compared with tank mixes withP. setariae, propanil, quinclorac, or sethoxydim applied 6 h before the pathogen or earlier generally showed greater efficacy. Delaying a tank mix application for up to 2 h had little negative effect, but longer than 4 h often reduced efficacy. When combining the pathogen at different doses with propanil, quinclorac, or sethoxydim at one-tenth, one-quarter, and one-half of the rate, both fungal dose and herbicide rate affected the efficacy. Coapplying any of the herbicides at the one-quarter rate with the pathogen at the sublethal dose of 2 × 107spores/ml achieved complete control of green foxtail.