Take these steps to control fall weeds and avoid herbicide carryover damage in fields planned for canola next spring:
Step 1: Assess fields for weed presence. If you find narrow-leaved hawk’s beard, stork’s bill, sow thistle, other tough winter annuals, or perennials like dandelion or Canada thistle, they are best sprayed this fall. You may not get good control next spring when these weeds have less leaf area to target early on, have a more established root system, and are moving energy out of (instead of into) root systems.
Step 2: Once problem weeds are identified, determine whether they are winter annuals or perennials and likely to be still present next spring. If they are, then you should spray. If they are mainly annuals and significant further seed set is unlikely before freeze up, leaving them untreated to die through the winter is probably the most economical choice.
Step 3: If you decide to spray, the list of fall-applied products is fairly short for fields that will be in canola next year. (See the Further Reading link below.) Glyphosate is one choice but there are a few others. Talk to your retailer or agronomist about the best products for specific target weeds and their sizes, and be sure to specify that you intend to seed canola on those acres next year.
Step 4: Warmer temperatures and bright sunshine improve herbicide activity. Apply glyphosate and other systemic herbicides during the heat of day when perennial weeds are actively growing and putting energy into their roots.
Step 5: Before spraying, make sure weeds are actively growing with new supple leaf area to target. Weeds cut off at harvest need time to accumulate new leaf tissues that will act as suitable surfaces for absorption of herbicides applied post-harvest. Even with the recommended to wait for 4 to 6 weeks of regrowth, leaf surface area is still only a fraction of what it was prior to harvest. Therefore glyphosate rates may need to increase by 2 to 3 times to get the same concentration of glyphosate in the plant. If frost is predicted or has occurred, avoid application until leaf condition of the target weeds can be evaluated.
Herbicides for fall application on fields planned for 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.|