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Beef Column: Mowing is an option for controlling winter annuals and some biennial weeds.

January 22, 2019

3 Min Read
Black Angus grazing
IMPROVING PASTURES: Killing weeds is just one part of weed management in pastures. If you don’t encourage desirable species to grow after killing weeds in problem areas, then most likely, a new crop of weeds will grow. ablokhin/Getty Images

By Bill Halfman

Last fall’s weather in parts of Wisconsin did not lend itself to favorable conditions for fall weed control in pastures and grass hay fields. Some pastures and hay fields that were flooded may have new weeds this year to deal with.

Following are options for weed management this spring. The window for some options is not very long, and timing is critical for many species — it can be the difference between success and a waste of time and money.

Controlling weeds
Once weeds begin “setting seed,” a herbicide application will not be effective, and the seeds will most likely continue to develop and be viable. Winter annuals including yellow rocket and many of the other mustard species, common chickweed, marestail and fleabane are or soon will be growing rapidly, and will begin to flower and set seed very soon, if they haven’t already.

Biennials including bull, musk and plumeless thistle; burdock; wild parsnip; and wild carrot should be treated before they begin to bolt — and the smaller, the better. Early spring or late fall is really the best time to treat these species.

Some common herbicides used for control of many broadleaf weeds in grass hay fields and pastures this time of year are the plant growth regulator herbicides such as 2,4-D, dicamba, triclopyr and clopyralid. In addition, products containing metsulfuron can provide good control of many broadleaf weeds in the spring.

Follow the label directions any time you are using herbicides, and if the pasture or hay field was recently seeded, pay particular attention to restrictions on use after seeding. Some products that are safe on established forage species may cause injury to recently established forage species.

Mowing or clipping is also an option for controlling winter annuals and some biennials. Timing is critical for mowing, too. Mowing after weeds bolt (grow the taller stalk) but before they flower and produce seed is recommended for winter annuals, summer annuals and biennials.

If weeds are not too dense or too numerous, digging is also a method for controlling them. Biennial thistles are an example of a weed that, if not too thick once they bolt, can be dug or snapped off below ground before they flower to prevent seed production.

Encourage desirable species
Killing weeds is just one part of weed management in pastures. If you do not do anything to encourage desirable species to grow after killing the weeds in those problem areas, then you will most likely just get a new crop of weeds.

One common reason why some areas in a pasture are more prone to weeds than desirable species is soil fertility problems, maybe with pH or a deficit in one or more of the nutrients needed for plant growth. Overgrazing or hardpans from livestock traffic may also contribute to conditions not favorable for desired species. Soil testing to determine any corrective nutrient management needs and evaluating past management for problems that can be corrected will help encourage desirable species to grow. 

In summary, there are opportunities for spring pasture weed management, but timing is critical to their success. It is also important to follow up weed control by implementing a plant to encourage desirable species to grow in those areas after the weeds are controlled, or the weeds will return.

Halfman is the Extension agriculture agent in Monroe County, Wis.

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