Pest Patrol: What have we learned in 2017 for managing glyphosate-resistant Canada fleabane?

#PestPatrol with Mike Cowbrough, OMAFRA, Dr. Clarence Swanton, Dr. François Tardif and Peter Smith, University of Guelph

Figure 1. Canada fleabane plants the following spring after surviving fall tillage. Note the plants have multiple branches at the base and were often 10 to15 cm taller than plants not exposed to fall tillage.

Multiple strategies are needed to control glyphosate-resistant Canada fleabane. Experience has taught agronomists and farmers that simply tank mixing another mode of action won’t be a good enough long-term approach.

Since 2016, we have evaluated different management tactics for Canada fleabane. The following are the results at our Oxford and Norfolk county field locations.

Tillage needs to be done multiple times (both fall and spring) to eliminate the majority of plants. Although a single tillage pass to a high population environment did result in fewer plants, the surviving plants were often 10 to 15 cm taller and branched (see Figure 1 at top), most likely because they didn’t have to compete with many other plants removed by the single tillage pass. These larger plants were more difficult to control with herbicides.

Figure 2. Canada fleabane control with Eragon LQ at 60 ml/ac. compared to the unsprayed control. The lower 30 ml/ac. rate failed to deliver acceptable control at the one field location. photo: Supplied

Fall-applied herbicides did not provide acceptable Canada fleabane control because a new flush of seedling plants germinated in the spring. Spring-applied herbicides were much more effective with both Eragon LQ (see Figure 2 above) and dicamba (see Figure 3 below) providing the best level of control. However, the lowest labelled rate of both herbicides failed to deliver acceptable control.

Figure 3. Canada fleabane control with the 400 ml/ac. rate of Engenia (dicamba) compared to the unsprayed control. The lower 200 ml/ac. rate failed to deliver acceptable control at the one field location. photo: Supplied

Notably, no Canada fleabane grew where cereal rye was planted in the fall (see Figure 4 below), regardless of herbicide or tillage treatment. This is an exciting observation that will require followup to understand how a cereal rye cover crop should be managed to optimize control of Canada fleabane.

Figure 4. Fall-planted cereal rye was very effective at inhibiting the germination of Canada fleabane seedlings (left) compared to where it wasn’t planted (right). photo: Supplied

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