Pulse Industry

Project Abstract: Managing Herbicide Resistant Weeds in Pulses with Alternative Modes of Action

Field surveys on the Canadian Prairies have indicated that 37% of annually-cropped land is affected by herbicide-resistant weeds, totaling 9.9 million ha. Pulse crops are highly reliant on Group 2 (ALS inhibitor) herbicides; and resistance to this mode of action is prevalent in broadleaf weeds such as kochia, wild mustard, and cleavers. Alternative modes of action for controlling wild oat are also required.

Experiments conducted at the Scott Research Farm (Dark Brown Soil Zone) in 2016 evaluated herbicides and herbicide combinations with alternative modes of action (eg. Group 3, 6, 14, and 15) in lentil and field pea. Pyroxasulfone is a Group 15 soil applied herbicide that requires moisture for activation. Contrary to 2014 and 2015 results, pyroxasulfone caused injury in lentil, particularly with spring application. In addition, spring applied pyroxasulfone generally resulted in higher levels of weed control compared to fall application, which also is contrary to 2014 and 2015 results. The spring of 2015 was extremely dry; thus, spring applied pyroxasulfone likely did not activate. Rains in late May of 2016 at Scott enabled the pyroxasulfone to activate resulting in higher levels of injury and better weed control with spring application. Pyroxasulfone provided suppression to control of wild mustard, which was rate and timing dependent. Fluthiacet-methyl is a Group 14 post-emergence herbicide that is registered in soybean in the United States.

In previous studies, it has been shown to be quite effective in controlling Group 2 resistant kochia, and may be a potential tank-mix partner with Solo (imazamox) in Clearfield lentil. Visual tolerance of lentil to fluthiacet-methyl is marginal, and current research is investigating ways to reduce injury. Injury to Maxim lentil from fluthiacet-methyl application was not affected by timing or adjuvant choice, which is contrary to 2015 results, where injury was reduced by applying at the 3-node stage of lentil, compared to the 6- or 9- node stage. As with previous years, initial injury from fluthiacet-methyl was transient and did not result in reduced yields. Fall applied flumioxazin (Group 14 soil applied herbicide) resulted in excellent control of early spring germinated kochia and wild buckwheat in lentil. Contrary to previous years, lentil injury was unacceptable at rates > 70 g ai ha-1. Combining ethafluralin with 450 g ai ha-1 of propyzamide resulted in better control of wild oat than either product applied alone. There was little injury to lentil from propyzamide or propyzamide + ethafluralin applications, which is consistent with 2015 results. After 3 site-years of study, pre-emergence applications of sulfentrazone or clomazone followed by post-emergence applications of Viper (imazamox + bentazon) were effective in suppressing or controlling cleavers in field peas in the Black Soil Zone. Pre-seed burnoff treatments including carfentrazone, carfentrazone + sulfentrazone, carfentrazone + pyroxasulfone, carfentrazone + bromoxynil, flumioxazin, and pyraflufen-ethyl + MCPA provided greater than 80% control of kochia for up to 30 days after application. Bromoxynil applied alone only resulted in suppression (60 to 70% control) of kochia. Most experiments will be repeated in 2017, the final year of this project.

For more information, contact Dr. Hugh Beckie (306) 385-9350 hugh.beckie@agr.gc.ca


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