Research report to the Oregon Processed Vegetable Commission
OSU Department of Horticulture
Weed interference is a major, ongoing pest problem in sweet corn and a diverse community of weeds persists until harvest in most fields, with some weeds that are very resistant to triazine herbicides. HPPD herbicides are commonly used now in the PNW with great success in controlling wild proso millet, but resistance to this class of herbicides has begun to emerge in the southern US. The first objective of this research was to assess efficacy and cost of common weed control schemes in sweet corn, with and without cultivation. Treatments were commonly used herbicide programs supplemented with cultivation or as stand-alone treatments. Trials were conducted at two sites in the Willamette Valley in cooperation with Dr. Williams at USDA, Urbana Ill. At the Lebanon site, lambsquarters was not controlled by atrazine PRE or EPOST at nearly 2 lb ai/A, indicating triazine resistance in this population. The most economically efficient treatment at this site (that included wild-proso millet) was Outlook PRE fb + Laudis EPOST, a yield of 11.5 t/A at a cost of $41, and weed control at harvest of 100%. At Corvallis, competition was severe (primarily broadleaved weeds) in the unweeded check plot and yield was only 1.5 tons/A; the cultivation-only plots yielded 3.8 t/A. The most economically efficient treatment at this site (dominated by broadleaved weeds) was Outlook + Sharpen PRE with a yield of 10.0 t/A, a cost of $29/A, and weed control at harvest of 96%.
The second objective of this project evaluated weed control potential and sweet corn tolerance to fluthiacet-methyl (Cadet), a recently labeled herbicide pre-packaged with pyroxasulfone (Anthem, not registered). Crop injury varied significantly between treatments, but statistically there was no evidence that any of the four varieties tolerated one treatment better than another. Anthem only provided 60% control at 2 WAT, with very little injury to the crop. Following Anthem PRE with Solstice (fluthiacet + mesotrione) EPOST increased crop injury substantially, but also improved weed control.