Abstract
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.
Highlights
Safflower is an annual oilseed crop well adapted to the semiarid regions of the US Great Plains and Canada
The treatment by year interaction was not significant on safflower visual injury, weed density, percent weed control, or safflower grain yield; data were pooled over years
The injury was less than 5% with those herbicides at 30 days after treatment (DAT)
Summary
Safflower is an annual oilseed crop well adapted to the semiarid regions of the US Great Plains and Canada. Safflower possesses a deep taproot system, which can extend to a depth of 2 to 3 m into the soil, and is more tolerant to drought stress compared to other oilseed and small grain crops [1] [2]. Safflower would be a potential fit as a second crop in the dryland winter wheat-fallow rotations in this region [3] [4]. In the absence of weed interference, safflower grain yields can exceed 2000 kg∙ha−1 when grown after winter wheat [2]. A season-long weed interference in safflower can reduce grain yields by 93% [4] [6]
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