2017 ASHS Annual Conference

Land managers commonly utilize synthetic pesticides as part of comprehensive pest management plans. When using synthetic pesticides, it is imperative to manage pesticide inputs so as not to adversely affect off-target plants or species. Off-target herbicide movement and associated adverse effects are problematic, particularly in close proximity to sensitive species. Aminocyclopyrachlor, flumioxazin, fluroxypyr, indaziflam, and metsulfuron-methyl are commonly used herbicides that have been associated with select cases of off-target injury to desirable plants. Greenhouse research was conducted to elucidate the effect of varying soil organic matter content (OMC) and volumetric water content (VWC) on soil bioavailability of the aforementioned herbicides. Soil organic matter (sphagnum peat amendment) content levels included 0.5, 1.5, or 4.5% w/w, while VWC levels included 12, 25, or 40% v/v. Herbicides were syringed over the soil surface of pots containing the bioindicator: mustard (Brassica juncea) for indaziflam and flumioxazin, and sunflower (Helianthus annuus) for aminocyclopyrachlor, metsulfuron-methyl, and fluroxypyr. As VWC increased from 12% to 40%, injury caused by aminocyclopyrachlor, flumioxazin, fluroxypyr, indaziflam, and metsulfuron-methyl 21 days after treatment (DAT) increased 19%, 87% 15%, 84%, and 13%, respectively. Increasing OMC from 0.5% to 4.5% reduced injury from aminocyclopyrachlor, flumioxazin, fluroxypyr, indaziflam, and metsulfuron-methyl 76%, 49%, 62%, 29%, and 86%, respectively, at 21 DAT. Results from this research improve our understanding of edaphic factors as they influence herbicide transport and uptake, which allow us to create best management practices to reduce off-target injury.