Weed management in safflower (Carthamus tinctorious L.) is a major challenge for growers due to very limited herbicide options available, particularly for broadleaf weed control. Field experiments were conducted at the Montana State University Southern Agricultural Research Center (MSU-SARC) near Huntley, MT in 2015 and 2016 to evaluate preemergence (PRE) soil-residual herbicides for crop safety and season-long broadleaf weed control in safflower. Among all herbicide programs tested, only sulfentrazone (105 g·ai·ha-1) alone or with pendimethalin (1064 g·ai·ha-1) caused 4% to 12% early-season visible injury to safflower, although the injury was not evident beyond 30 DAT. Sulfentrazone alone or with pendimethalin and pyroxasulfone (59 g·ai·ha-1) with pendimethalin had a season-long residual activity on kochia [Kochia scoparia (L.) Schrad] and Russian-thistle (Salsola tragus L), with 89% to 99% control at 60 DAT, and up to 98% reduction in weed density compared with dimethenamid-P (213 g·ai·ha-1) and S-metolachlor (433 g·ai·ha-1) at 65 DAT. Pyroxasulfone (59 or 118 g·ai·ha-1) alone or dimethenamid-P with pendimethalin provided a moderate to good control (65% to 79% at 60 DAT) of kochia and Russian-thistle. However, the end-season control of kochia or Russian-thistle was inadequate ( S-metolachlor alone program. Safflower grain yield with sulfentrazone alone or with pendimethalin, pyroxasulfone alone or with pendimethalin, and dimethenamid-P with pendimethalin averaged 3559 kg·ha-1, which was 195% higher compared with the nontreated check. In conclusion, sulfentrazone and pyroxasulfone or dimethenamid-P in combination with pendimethalin will be effective PRE herbicide programs for kochia and Russian-thistle control in safflower.
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