Weeds: It’s go time

May 13, 2020 – Issue 9

With good moisture and warmer weather, weeds will be jumping out of the ground. Spraying before seeding will remove this competition for nutrients and moisture, and make the weeds easier to control – because they’re smaller. But in mid May, canola growers will want to achieve timely seeding as well. Whether weeds are targeted with pre-seed, pre-emergence or post-emergence herbicide (or a combination of timings), weeds are best controlled early. See Canola Encyclopedia for more on timing and options.

Our survey question included in last week’s quiz supported what weed specialists already know: That the top target weeds for pre-seed burnoff ahead of canola are cleavers, kochia and volunteer canola.

Cleavers. (Annual and winter annual) Removing the winter annuals now when they’re smaller means they won’t be around to affect canola quality later in the season. Two cleavers-focused actives are available to use in a pre-seed tank mix with glyphosate on fields planned for canola. They are Group-4 quinclorac and Group-13 clomazone. Clomazone is a pre-seed soil active herbicide that will provide residual flushing control of cleavers, but will not work on already germinated plants. Quinclorac provides foliar control of cleavers up to the three-whorl stage. Clomazone (Command/Command Charge) is not able to be used on fields with greater than 10 per cent organic matter or with heavy manure use because it will bind to the product. Quinclorac is not limited by these restrictions. Neither should be used on very sandy soils since both are lightly bound to soils and somewhat persistent. If using quinclorac in-crop, it should not be used prior to seeding. Carfentrazone (Group 14), pyraflufen (Group 14 active in Conquer II) and halauxifen (Group 4 in Prospect) also control cleavers. More on cleavers.

Cleavers seedling

Kochia. (Annual) Kochia tends to thrive in drier conditions and in more saline soils where competition from the crop is limited. Bromoxynil (Group 6), carfentrazone and pyraflufen will control kochia seedlings. Kochia is very susceptible to Group 14 herbicides, and given the presence of glyphosate-resistant kochia on the Prairies, using glyphosate alone is not recommended.

Kochia seedlings

Volunteer canola. (Annual) Apply carfentrazone and/or bromoxynil along with glyphosate to get glyphosate-tolerant volunteers. This tank mix is recommended even for growers who have never grown glyphosate-tolerant canola given that some volunteers will have both traits due to natural pollen transfer. Bromoxynil may have a slight edge over carfentrazone, and there will be an additive benefit to using both. Note that the tank mix will also reduce the risk of selecting for glyphosate-resistance among other weed species, especially kochia.

Concerned about other weeds, too? The Canola Encyclopedia has a table showing what pre-seed products control what weeds.

Dig deeper

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