Evaluation of Herbicides for Management of Weeds in Sweet Basil (Ocimum basilicum)

Sweet basil (Ocimum basilicum L.) is one of the world’s most popular herbs, with much of the U.S. fresh market basil being produced in Florida. In the field, weed control is a continual problem. With few registered herbicides, growers must rely on mechanical control or hand-weeding, which are frequently ineffective and/or expensive. During 2009, trials were initiated to select potential candidates for chemical control. On a commercial sand soil site during spring, eight herbicides were screened for crop tolerance and weed control. Candidates included linuron, S-metalochlor, napropamide, halosulfuron, and dimethenamid applied preemergence, and linuron, halosulfuron, and clopyralid applied postemergence. Of the preemergence treatments, all provided good weed control but linuron, dimethenamid, and metalochlor resulted in crop death at the rates tested. Napropamide (2.0 lb ai/acre) resulted in the highest crop vigor, followed by halosulfuron (0.375 oz ai/acre). Of the postemergence treatments, all gave some measure of weed control, with clopyralid producing the least crop damage, followed by halosulfuron, and then linuron. In a trial conducted on an organic soil site during winter, linuron was tested at three different rates preemergence, followed by linuron, imazethapyr, and prometryn, each at three different rates postemergence. Linuron as a preemergence treatment on muck provided significant weed control and acceptable crop vigor at all three rates tested (0.125, 0.25, and 0.375 lb ai/acre). Of the postemergence treatments, only linuron at 0.1 ai/acre provided significant weed control with minimal reductions in crop vigor. Prometryn resulted in crop death and imazethapyr significantly reduced crop vigor at the rates tested.