Non-Target Plant Effects from Planting in Soil/Compost Media Containing Penoxsulam Herbicide.
David W. Roberts, Dow AgroSciences, 9330 Zionsville Rd, Indianapolis, IN 46268, William F. Brinton, Woods End Research Laboratory, Inc., 20 Old Rome Rd, Mt Vernon, ME 04352, and Timothy D. White, Crop Management Strategies, Inc., 6273 Mountain Rd, Germansville, PA 18053.
Public or private large-scale composting operations typically produce compost made from yard waste which potentially contain trace residues of xenobiotics (i.e., herbicides). This study investigated the effects of penoxsulam herbicide on non-target plants grown in media representative of compost/soil blends typical for garden, horticultural and agricultural use patterns. Compost was prepared from turfgrass which was treated at 0.022 and 0.067 lb ai/acre (25 and 75 g ai/ha) using SC and FG formulations. Turfgrass clippings from the two FG plots (25 and 75 g ai/ha plots) were collected at 5 days post treatment and each was separately combined with deciduous tree leaves at a C:N ratio of 30:1 and aerobically composted in replicated 120-L bench-scale vessels. The proportion of treated turfgrass in the total turfgrass feedstock contribution was 30%. At each of three compost periods, 90, 120 and 160 days after compost start, compost was blended with soil at 12% or 33% by volume, representing typical- or worst-case compost utilization rates, respectively, and used as growing media for bioassay testing using plant species with a known range of sensitivity to penoxsulam. The bioassay results indicated an absence of treatment related adverse effects at all three compost sampling dates, and among all species tested. Under maximum herbicide application rates, maximum green waste recycling capture rate (33%), normal composting regimes (> 90 days of composting), and under typical to extreme compost utilization regimes (12% and 33% by volume), penoxsulam produced no adverse effects on non-target plant species.