Weed Control in Spring and Summer After Fall Application of Sulfometuron

This study tested the residual spring and summer efficacy of sulfometuron after fall applications in forest regeneration settings in coastal forests of Oregon. This is the first reporting of results from what is becoming a more widely used silvicultural treatment. Sulfometuron alone (S) and sulfometuron plus imazapyr and glyphosate (SIG) were applied to vegetation on mechanically scarified sites and unscarified sites. The applications were replicated each month through fall 1994. Vegetation cover was assessed in mid-June and mid-August 1995. The SIG treatment controlled the vegetation more than the S treatment did, although cover was significantly lower for both herbicide treatments (9% to 54%for summed cover) compared to the control (64% to I04% for summed cover). On scarified sites, the month of application, early or late fall, did not significantly influence the efficacy of S or SIG treatments. On unscarified sites, however, later applications of the SIG treatment were less effective than earlier treatments were. These results suggest that fall applications of sulfometuron are still effective in spring and may eliminate the need to retreat sites in the spring to achieve effective weed control. West. J. Appl. For. 14(2):80-85.