Controlling Volunteer Roundup Ready Canola in Soybeans

When it comes to volunteer canola, as the saying goes, "once a canola grower, always a canola grower". This is because canola seed is not only prone to considerable harvesting losses, but can remain viable and dormant in the soil for variable periods of time, making this volunteer crop a very persistent weed. If this volunteer crop is also glyphosate resistant (i.e. Roundup Ready or "RR") then a producer will have to manage this weed with non glyphosate herbicides.

Figure 1- Volunteer canola seedling.
(Photo courtesy of Clive Schaupmeyer, Brooks, AB

Impact on Soybean Yield

Uncontrolled volunteer canola has reduced soybean yields by as much as 70% in field trials conducted at the University of Guelph.

Control in "Roundup Ready" Soybeans

Pre-plant applications: The most consistent control of volunteer "RR" canola in soybeans has been achieved with pre-plant treatments of Sencor applied at 200 g/acre. FirstRate and reduced rates of Pursuit have also proven effective.

* DAA = Days after application.
** Pricing for comparative purposes only and will vary across the province.
*** Rating based on only 1 year of data therefore level of consistency is unknown.

Post-emergent applications:

If unable to apply a pre-plant treatment, post emergent control of "RR" canola has been achieved with Classic and FirstRate (Table 2). Reduced rates of Pursuit can be effective but the volunteer canola must be small (cotyledon to 4 leaf stage).

Why such poor control with Pursuit in 2002?

In general the active ingredient in Pursuit (imazethapyr) is quite effective at controlling species in the mustard family provided they are at small growth stages. In 2002, post-emergent applications were made to volunteer canola that was flowering and around 10-15 cm in height. In 2003, post-emergent applications of Pursuit were made to volunteer canola at the 2-4 leaf stage of growth and therefore control was considerably better (Table 2).

*DAA = Days after application.
** Pricing for comparative purposes only and will vary across the province.
*** Rating based on only 1 year of data

Would "Guardian" control volunteer "RR" canola if applied pre-plant?

Good question. Unfortunately, pre-plant treatments of glyphosate + Classic (i.e. Guardian) have not been tested in field trials at the University of Guelph. Therefore we have not seen whether or not the Classic portion of that tank-mix would offer any residual control of volunteer "RR" canola. Representatives from DuPont feel that a pre-plant application of Guardian should provide effective control of volunteer "RR" canola, however there is no field work to support this hypothesis.

Figure 5 - Mature volunteer Canola

Summary:

Keys to successful management of volunteer "Roundup Ready" canola in soybeans can be achieved by:

• Selecting an effective non-glyphosate herbicide (See table 1 & Table 2).
• Applying the appropriate herbicide to volunteer canola when at the 2-4 leaf stage of growth.
• Minimize harvesting losses through proper combine setup.

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