Missed pre-seed? In-crop must be early

Wild oats and other weeds are coming up thick this week. Source: Anastasia Kubinec, MAFRD
Wild oats and other weeds are coming up thick this week. Source: Anastasia Kubinec, MAFRD

More growers may have skipped the pre-seed burnoff this year — given that weed emergence was delayed with the cool start to spring and because growers wanted to get seeding.

But the weeds are coming. Warmer temperatures and good moisture have inspired emergence of “carpets” of weeds in some fields. These weeds will have a tremendous impact on canola yield potential and have to be controlled within the first week of emergence. If the risk that weather will prevent you from spraying right after emergence gives you shivers, you’ll want to spray now then seed.

Seeding can begin fairly soon after a burnoff. For annuals and winter annuals, glyphosate needs only 24 hours to get to the growing point. After a day, the crop can be seeded. For perennial weeds, 3 days should be enough in sunny and warm conditions but 5 days is recommended before seeding if weather is cloudy or cool. (Post-seed, pre-emergence is another option.)

If the crop is seeded without spraying, in-crop weed control should occur as early as possible. Canola is much more vulnerable to weed competition prior to reaching complete ground cover. Smaller weeds are also much easier to kill than weeds at their 4-leaf stage or later.

Past research has demonstrated an advantage of 3 bu./ac. for controlling weeds at the 1-2 leaf stage of canola versus the 3-4 leaf stage, and a 7 bu./ac. advantage versus 6-7 leaf. At $12 per bushel, that’s $36 to $84 per acre more profit with no added cost. These numbers will be even higher if a preseed burnoff was not completed.

Scout fields to determine the number, size and species of that are present in each field before choosing a rate and tank mix. Here are the options for each herbicide tolerance system:

Roundup Ready (glyphosate tolerant): The window is from seeding to the 6-leaf stage of the canola crop. Applying after the 6-leaf stage or above label rates is known to cause yield loss. Maximum use rates are 270 g ae per acre on one application or two applications of 180 g ae/acre each. When going after thistles, buckwheat, and large dandelions, a tank mix of glyphosate and Lontrel 360 (co-packaged as Eclipse) at the 112 ml/acre rate can be applied after the 2-leaf stage.

Liberty Link (glufosinate tolerant): The window is from emergence to early bolting. Set the rate based on weed species and pressure. Split application is an option, but the maximum allowable rate per season is 2.97 litres per acre. Liberty may be tank mixed with clethodim at 25.5 mL/acre or up to 50 mL/acre for Centurion specifically for additional control of grassy weeds. The mixing order is unique when tank mixing clethodim with Liberty. Add the surfactant first, then Liberty, then clethodim. This is one of the only times when surfactant goes in the tank first. Click here for more on pesticide mixing rules.

No Lontrel tank mix for Liberty. If using Lontrel for thistle control in Liberty Link canola, it should be applied on its own, either before the Liberty application or after the thistles recover following the Liberty application. For acceptable control, Canada thistle should have ample leaf area in a living condition for contact and uptake. Canada thistle is 3 to 4 times more competitive per plant than wild oats. Research from AAFC in Lacombe, Alta., shows it only takes 10 Canada thistle shoots per square metre to cause 10% yield loss in canola.

Clearfield (IMI tolerant): The window is from the 2-leaf to the 6-leaf stages. You have a few different products to choose from with several different tank mix partners. Click the link below to see your provincial guide to crop protection. Odyssey Ultra, Ares or Tensile can be applied only once per season (no split or sequential applications), but Odyssey and Ares have some residual soil activity. If thistles are a target, Odyssey can be mixed with Lontrel at 0.17 to 0.23 L/acre. Tensile is a co-pack of Solo and the dry Lontrel formulation.

Note that nearly all kochia populations are resistant to Group 2 herbicides and there are no mixes with herbicides for Clearfield canola that will control kochia. There may also be rotational crop restrictions following the use of Clearfield herbicides.

Consult the guide to crop protection and/or product labels for recommended rates, staging, and tank mix partners. Click a province for a link to its guide to crop protection: Alberta Saskatchewan Manitoba.

No Dandelions Please. Manitoba Canola Growers Association wants to draw attention to a campaign to fight a pesticide ban on Manitoba lawns. Click here for more.