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.

Unexpected Side Effects of Herbicides: Modulation of Plant-Pathogen Interactions

“…The authors demonstrated that an application of glyphosate prior to Myrothecium verrucaria provided better weed control in kudzu (Pueraria lobata), redvine (Brunnichia ovata), and trumpetcreeper (Campis radicans). This was also the case for green foxtail, which was sufficiently controlled when treated with glyphosate prior to Pyricularia setariae inoculation (Peng & Byer, 2005). These results suggest that timing of glyphosate application in relation to combined treatment with a bioherbicide is important.…”

“…Wyss et al (2004) reported that certain pesticides and their adjuvants affected spore germination and growth of Phomopsis amaranthicola, an effective bioherbicides against Amaranthus species. Several herbicides such as glyphosate had also negative effects on spore germination of P. setariae (Peng & Byer, 2005). Thus, one strategy to overcome direct toxic effects of herbicides is a sequential rather than simultaneous application of the synthetic herbicide and the bioherbicides.…”

Interaction of a bioherbicide and glyphosate for controlling hemp sesbania in glyphosate‐resistant soybean

“…Recently, several herbicides, including glyphosate, were tested at reduced rates for possible interactions with the fungal pathogen, Pyriculoria setariae Niskoda, for the control of green foxtail ( Setoria viridis [L.] Beauv.) (Peng & Byer 2005). Propanil ( N‐ [3,4‐dichlorophenyl] propanamide), quinclorac (3,7‐dichloro‐8‐quinolinecarboxylic acid), and sethoxydim {2‐(1‐[ethoxyimino]butyl)‐5‐(2‐[ethylthio]propyl)‐3‐hydroxy‐2‐cyclohexen‐1‐one} applied 6 h prior to the pathogen generally resulted in greater efficacy.…”

Transcriptome analysis identified the mechanism of synergy between sethoxydim herbicide and a mycoherbicide on green foxtail

“…In a previous study, a host-specific fungal pathogen, Pyricularia setariae Nisikado, was efficacious against GFT seedlings, including the resistant biotype 7 . Applying sethoxydim at sub-lethal doses prior to or with P. setariae substantially improved its efficacy against GFT, extending the efficacy to older GFT plants and additional weedy foxtail species 8 . However, the key connections between the physiological and pathological events in this synergistic interaction were not understood.…”