However, the timing of herbicide application or mowing is critical and can make the difference between an effective tactic and a waste of time and money. Once the weeds are in the “setting seed” stage 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, fleabane, annual bluegrass, downy brome, etc. are growing rapidly and have already or will begin to flower and set seed very soon. Biennials including musk and plumless thistle, burdock, wild carrot, etc. should be treated before they begin to bolt (they are bolting now or very soon) and the smaller the better. (Late fall or early spring is really the best time to treat them.) And finally, control summer annual weeds as soon after they emerge as possible when they are most sensitive to chemical control.
The most common herbicides used for control of many broadleaf weeds in grass hay/pasture this time of year are the plant growth regulator herbicides such as 2,4-D, dicamba (Banvel, Clarity, etc.), triclopyr products (Crossbow, Garlon, etc.), and clopyralid (Stinger, PastureGard, etc.). In addition products containing metsulfuron (Cimarron, other generic formulations, etc.) can provide good control of many broadleaf weeds in the spring. (Be cautious, if forage grasses were recently seeded and are not yet established many of these herbicides can cause severe crop injury.) Contact your state extension weed specialist for herbicide recommendations specific to your region (In the mid-Atlantic, refer to the 2017 Mid-Atlantic Field Crop Weed Management Guide for additional details. Below are some guidelines to provide a quick management summary for some common weeds of pasture.
Management guidelines for some problem weeds of pastures:
Winter annuals
(Mustard species, common chickweed, etc.)
- Mow after bolting to prevent seed production.
- Apply an effective herbicide in fall or spring prior to bolting.
- Most winter annuals emerge by late fall – a smaller percentage will emerge in early spring
- Prevent seed production to prevent spread.
Summer annuals
(Pigweed species, common lambsquarters, common ragweed, etc.)
- Keep pasture full and competitive.
- Mow after bolting to prevent seed production.
- Apply an effective herbicide in early summer.
- Prevent seed production to prevent spread.
Biennials
(common burdock, bull and musk thistle, poison hemlock, etc.)
- Mow after plants have bolted but before seed set to prevent seed production.
- Remove or dig individual plants by hand.
- Apply an effective herbicide to rosettes in the spring or fall.
- Prevent seed production to prevent spread.
