Weed Control in Perennial Forages - Frequently Asked Questions

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 When is the best time to control weeds in perennial forage fields?
A weed control program for perennial forage crops should start 1 to 2 years prior to seeding. The hard to control weed problems, (Canada thistle, quack grass, tansy, toadflax, ox-eye daisy, scentless chamomile) need to be controlled in annual crops prior to seeding the perennial forage. Using glyphosate for total vegetation pre-harvest control in annual crops, spot application of herbicide with residual activity for specific problems, or cutting and mowing bad weed areas are some options.

In a mixed grass - legume stand, what can be used for control of dandelion, thistle and scentless chamomile?
Unfortunately, any herbicide that will control these hard control weeds will also kill any legume in the stand. If problems are in small defined areas, it may be worth applying the herbicide and sacrificing the legume to prevent the spread of the problem weeds.

Are cover crops necessary to establish a forage stand and help reduce weed competition?
Cover crops compete with both the weeds and seedling forage crop. Light, nutrients and moisture are used by the cover crop. If a cover crop is used, seed at half the normal "crop" seeding rate (less than one bushel per acre), remove the cover crop as greenfeed or silage early to minimize competition. Cutting at the flowering to early milk stage is recommended. If possible, not using a cover crop creates a better environment for long-term forage production.

Are there any herbicides registered for use in mixed forage stands?
Yes, the only concern is that the window of application may be narrower than for normal cereal crops. The biggest advantage will be to apply herbicide in the year of establishment to reduce weed competition. Read the label and determine proper timing of application and which weeds will be controlled. Watch for the differences between seedling crops, established crops, and those grown for seed production. Each has specific use restrictions.

Are there any other methods of controlling the difficult weeds in a forage stand?
Cutting, mowing, or use of equipment other than a field sprayer to control weeds is possible. A weed wiper - or a wick applicator is effective in a new stand if the weeds are much taller than the crop. The herbicide applied is wiped onto the target plants and not onto the crop. This provides more options for weed control.

A balanced crop fertility program will increase competition and reduce weed populations.

Keep the forage stand healthy and productive by watching cutting height and not damaging the plant crowns. Do not cut in August to early September - perennial growth rates are slowing and the plant is preparing for winter. If you cut in this time period, root food reserves are sacrificed to increase plant growth rates and survival rates are compromised.

For more information please click on the following links:

Weed Control Act - Weed Regulation

Prepared by Barry Yaremcio, Ag-Info Centre, Alberta Agriculture and Rural Development

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For more information about the content of this document, contact Barry Yaremcio.
This document is maintained by Mary Ann Nelson.
This information published to the web on July 9, 2003.
Last Reviewed/Revised on November 27, 2013.