Yield losses of over 50% can occur from bluegrass competition in winter wheat. Bluegrass species often head at the same time as winter wheat and could intercept and reduce the amount of fusarium head blight fungicide reaching the grain head. There are several species of bluegrass found in Ontario. Annual, roughstalk and Canada bluegrass are the most common species in field crops. These competitive grassy weeds will emerge in the fall or early spring. Plants smaller than 10 cm in height are more easily controlled by herbicides. Based on preliminary Ontario data in winter wheat, April herbicide applications made to bluegrass are more effective than May applications.
Testing herbicide effectiveness
An on-farm research trial evaluated 5 different herbicides, 3 of which are currently available in Ontario. The field site contained primarily roughstalk bluegrass. Herbicides were applied when bluegrass was 5-7.5 cm tall and the winter wheat crop was just at stem elongation. By contrast the rest of the field was sprayed one month later when bluegrass was between 20-30 cm tall.
Key Learnings
- Axial, Simplicity GoDRI and Varro provided excellent control of roughstalk bluegrass that was less than 10 cm tall at application.
- Delaying herbicide applications into May, when bluegrass was greater than 20 cm tall, reduced control but did keep bluegrass from heading above the wheat canopy (as of June). However, there was plenty of bluegrass under the wheat canopy that was beginning to flower. This will likely result in seed dispersal back into the field.
- Varro herbicide has labelled guidelines that restrict its use when temperatures are below 3 °C and/or winter wheat has reached the first node stage of growth. Both those restrictions were violated in this experiment. Significant yellowing and slight stunting occurred as a result. However, plants fully recovered within 14 days of application.
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