Weed control strategies for each HT system

Here are strategies to improve weed control for each herbicide-tolerant (HT) canola system. See the graph and table at the bottom for comparisons and extra details.


Group 2 products for the Clearfield system perform well with coarse sprays. Treat crops during warm weather when weeds are actively growing and soil moisture is adequate for rapid growth. Under cool or dry conditions, control for some weeds may be severely reduced and the risk of crop injury increases. Do not spray Group 2s if temperatures of 5°C or lower are forecast within 3 days of application.

Crop staging

The application window is 2- to 7-leaf stage of the crop for Ares (imazamox and imazapyr), and 2- to 6-leaf stage for other IMI products. Growers have various product choices, with several different tank mix partners. Only one application per season (no split applications) of Ares or any related product. Note that imazapyr in Ares has some flushing weed control from residual soil activity.

If thistles are a target: Add Lontrel at 84 mL/acre.


This is the Group-2 sulfonyl-urea-resistance system from FBN. The partner herbicide, called Draft, controls a wide variety of broadleaf weeds.

Crop staging

Apply from the 2- to 5-leaf stage. If necessary, apply grassy-weed herbicide from the 3- to 5-leaf stage.

Liberty Link

Apply Liberty as medium to slightly coarse droplets (approximately 200 – 350 microns) with water volumes of at least 10 gallons per acre. Liberty works best in bright sunshine when temperatures are hot and weeds are actively growing.

Most control issues for Liberty and other herbicides that rely heavily on contact activity are related to poor coverage from insufficient water carrier volumes, combined with a coarse or very course spray pattern and/or late stage at application.

Crop staging

The application window for Liberty is from emergence to early bolting. Set the rate based on weed species and pressure. Label changes for Liberty 150SN now allow for up to three applications with a maximum of 1.62 L/ac. for each application.

Tank mix Liberty with clethodim for additional control of grassy weeds or Facet to enhance cleaver control. 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. This tank mix goes into solution easily; excessive agitation is not recommended or required. The tech sheet from BASF has mixing rules for various tank mixes.

Thistles. Clopyralid-based herbicides (Lontrel brands, Pyralid, MPower Clobber) cannot be tank mixed with glufosinate-based herbicides (Liberty 150SN, MPower Vigor). If using Clopyralid for thistle control in Liberty Link canola, it should have its own separate application according to label rates and staging, either before the glufosinate application or after the thistles recover following the glufosinate application. For acceptable control, Canada thistle should have ample leaf area in a living condition for contact and uptake. For this reason, if thistles are the major problem weed, clopyralid should perhaps go before the glufosinate.

Roundup Ready

Use low drift (coarse droplet) sprays. Note however that coarse sprays at low water volumes may not provide enough droplets per square inch. A combination of coarse spray and 5 gal./ac. (20 L/ac.) water volume is best to get droplets on even the smallest weeds. Larger droplets from higher water volumes also reduce the drift risk.

Key steps to get the most out of glyphosate:

  • Sunny and warm are optimum conditions for top performance. This includes warm temperatures through the night.
  • Weeds should be actively growing. Plant growth stops below 5°C. Delay applications for at least 24 hours, preferably 48 hours, after temperatures near 0°C to allow plants to recover and begin growing again.
  • Use water volumes of 5-10 gal./ac. when water quality is good. For hard water: Use water volumes at the lower end of the range. Add ammonium sulphate to tie up cations in hard water. Find another water source for spraying glyphosate if hardness exceeds 40 grains/US gallon total hardness (700 ppm CaCO3 equivalent). For more specific tips, including ammonium sulphate rates, read Water quality and herbicides at Saskatchewan.ca.
  • Smaller weeds are easier to control. Growers want to make every effort to control species such as buckwheat and winter annual weeds at the 1-3 leaf stage.
  • Avoid travel speeds during spraying that will create large amounts of dust. Clark Brenzil, provincial specialist in weed management with Saskatchewan Ministry of Agriculture, says that if operators cannot avoid dusty conditions, spray perpendicular to the wind. Work from the downwind end of the field to the upwind end to minimize the dust deposition on unsprayed leaves. Front-mounted booms will also help this to some degree.

Crop staging – TruFlex trait

TruFlex expands the in-crop spray window to first flower. That is 10 to 14 days past the 6-leaf stage cut off for the Genuity system. TruFlex also allows for higher rates. Approved in-crop rates for Roundup WeatherMAX are 1.33 L/ac for a single application or 0.67 L/ac for two applications, up from 0.5 L/ac for a single or 0.33 L/ac for two applications in standard Roundup Ready canola. Bayer says that being able to apply Roundup WeatherMAX herbicide in-crop at these rates allows for the control of 24 additional weed species compared to the standard Roundup Ready canola system. This weeds list includes yellow foxtail, biennial wormwood and common milkweed.

Crop staging – Genuity trait

The window for glyphosate on original Genuity Roundup Ready canola is from emergence to the 6-leaf stage of the canola crop. Yield loss can occur with applications after the 6-leaf stage or above label rates. Maximum use rates are 270 grams of acid equivalant (ae) per acre on one application or two applications of 180 g ae/ac. 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.

Stacked RR and LL traits

Canola with both Roundup Ready and Liberty Link traits are available. Glyphosate and glufosinate, the actives in Roundup and Liberty, are both effective on most weeds in Western Canada (the only current exception is glyphosate-resistant kochia). Note that tank mixes of glyphosate and glufosinate are not recommended due to weed antagonism. They have to be applied in separate passes.

In-crop herbicides for use in canola

Click to enlarge


For the final word on herbicide rates and timing, check the product label and consult the guide to crop protection for your province: Alberta Saskatchewan Manitoba