Herbicide Treatments for Non-Thermal Grass-Seed Production

Legislation phasing down open-field burning in the Willamette Valley of Oregon is forcing grass seed growers to alter crop production piactices. Adoption of new mechanical means for straw removal has increased reliance on herbicides. Volunteer seedling control and crop tolerance for 15 herbicide treatment sequences were evaluated in established tall fcscue (Festuca arundinacea) and perennial ryegrass (Lolimn perenne) stands during 2 growing seasons using 5 methods of residue removal. Pre-emergence pendimethalin was extremely safe yet fairly effective on volunteer seedlings in both crops. For perennial ryegrass subsequently treated with post-emergence herbicides, pre-emergence metolachlor was slightly more effective than pendimethalin, but less safe. In tall fescue, pre-emergence oxyfluorfen also was effective, but reduced seed yield at least I 00 kg/ha. For adequate weed control, even the best pre­emergence herbicides must be followed by aggressive post-emergence treatments, e.g., tank-mixes of oxyfluorfen plus diuron. Seedling grasses can be controlled without field burning in established perennial grasses.