Snow and fall weeds. When freezing temperatures stop fall weed control plans, snow is likely more of a help than a hindrance with respect to overall weed condition. The snow layer is likely to insulate the weed leaf material from the colder conditions that follow it. That could mean you’re back spraying earlier than you would be with frost alone. Spray decisions — when to spray or whether to spray at all — will depend on leaf condition after the snow is gone. Note that it could take a couple of days to properly assess frost damage, as green leaf material can appear quite healthy immediately after a frost. Read more.
Frost and fall weeds. When scouting to determine the value of post harvest weed control, consider…
- Are there enough weeds to warrant a spray?
- Are they winter annuals or perennials? Fall is a good time to hit perennials, biennials and winter annuals. On annuals: Spraying annuals in the fall can be worthwhile if it looks like they’ll produce mature seeds before freeze up. If annuals have already set seed, it may be better to save the burnoff for next spring when those seeds emerge. (NOTE: Research out of southern Alberta suggests that kochia regrowing after a mid-August harvest will not produce seed before a killing frost in most years. If using glyphosate to control those annual weeds, you may simply be adding additional selection pressure for the development of glyphosate resistance.)
- Are weeds actively growing?
- Is frost damage less than 40% of the leaf tissue?
If these conditions exist, then a fall herbicide treatment may be of benefit. But this is important: You still want to apply glyphosate and Group 2 herbicides on sunny and warm days for best results. Read more.
Best timing depends on the weeds present. Fall is a good time to control perennial and winter annual weeds, but spraying immediately after harvest may not provide the best results. Before spraying, identify the weeds present. Are they perennials? Winter annuals? Annuals? Clubroot hosts? This article has tips for each.
Herbicides for fall application ahead of canola
|wdt_ID||Herbicides registered for use in the fall on land planned for canola.||Notes and recommendations|
|1||Glyphosate||Apply at least 1,040 GAE (grams of glyphosate acid) per acre to get effective perennial control, given that leaf area will be smaller than pre-harvest. Monsanto does not recommend any tank-mixes with Roundup for use in fall.|
|16||Distinct||Distinct combines Group 4 dicamba and Group 19 diflufenzapyr. BASF recommends it as a tank mix partner with glyphosate for enhanced control of broadleaf weeds. Apply prior to October 1 at 58 g/acre when planning a canola crop the following year.|
|3||Tribenuron (Express SG, Spike, Nuance, MPowerX)||DuPont recommends an application of its Express SG before October 1 on fields planned for canola. Express SG must be tank mixed with at least 0.5 litre/acre glyphosate equivalent for fall application prior to seeding canola in spring.|
|4||Heat LQ||Heat LQ (Group 14 saflufenacil) can be applied in fall to prep land for canola the following spring. Applications can be made any time during the fall on actively growing weeds.|
|19||2,4-D||Use caution. Phenoxies (2,4-D, MCPA) should not be used in the fall on fields planned for canola next spring. The most effective timing is just prior to freeze-up, which does not allow enough breakdown until after the soils warm up in spring.|
|6||MCPA||MCPA has no recropping restrictions listed, but it does present a re-cropping risk for canola – especially when conditions at application are extremely dry. Growers are advised to avoid using MCPA on land intended for canola next spring.|
|7||KoAct||KoAct has both 5 oz of 2,4-D and 4 g of tribenuron. NuFarm is comfortable with an October 15 cutoff with this product.|
|8||Lontrel||You need higher rates and generally get poorer control in the fall than the early in-crop stage.|
|9||Soil-active herbicides approved for fall application on fields planned for canola||These products are applied in the fall but are designed to control weeds emerging early in the spring. The act of incorporation will provide some management of existing fall weeds. Notes and restrictions:|
|10||Avadex (triallate)||It controls wild oats and wild millet as they emergence through the herbicide layer in the spring. Fall activity is not really needed or desired for these annual weeds anyway.|
|11||Bonanza, Rival, Treflan (trifluralin)||Trifluralin becomes active at soil temperatures typically above 5°C, so apply it in the fall at cooler temperatures before soil freeze up so it doesn’t dissipate before the spring.|
|12||Edge (ethalfluralin)||This Group-3 herbicide goes on dry and must be worked to a depth of 1/4" to 1/2" into the soil. Light harrow is often enough. Apply after September 1 for conventional till, after October 1 for no-till/min-till.|
|13||Fortress (triallate, trifluralin)||This is applied in the fall but stays dormant all winter. It controls wild oats and wild millet as they emerge through the herbicide layer in the spring. Fall activity is not really needed or desired for these annual weeds.|