Controlling weeds is probably one of the most important decisions to think about when managing horse pastures. Weeds are generally less palatable, less nutritious, and are less dependable as a forage supply to horses than the desirable pasture species they replace. Some pasture weeds are poisonous to horses. From a control standpoint, grouping weeds into categories based on life span is most practical. Annual, biennial and perennial are the main life spans of weeds.
Lifespan of Weeds
An annual germinates from seed, grows, matures, and dies in less than one year. Chemical control of annuals works best when applied in the spring to actively growing, young weeds. Mechanical control, such as mowing, is very effective against annuals.
Biennials require two years to complete their life cycles. They form a rosette (group of leaves at ground level) and store food in their roots the first year and flower the second year. Control measures, chemical or mechanical, are most effective when applied during the first year’s growth. If treatment is delayed until the second year, early season application of a herbicide before bloom is important.
Perennials live more than two years, and grow back from the same roots year after year. Perennials move nutrients into their roots during fall to prepare for winter. Because of this, chemical control of perennials works best when applied in the fall to actively growing and well-developed foliage. As the nutrients move into the roots, the chemical will too. Application of herbicides in spring, or frequent moving during the summer is also effective in controlling growth until fall. However, mowing alone may take a several growing seasons to effectively control the perennial weeds.
Herbicides and Minimizing Weeds in Pastures
When using herbicides, always read and follow labels carefully. Always follow grazing recommendations after herbicide application. Herbicide may make toxic weeds more palatable to horses. Horses should be excluded from the sprayed area for seven to ten days after treatment if poisonous plants are present. Herbicides alone will not result in a weed-free pasture.
Most herbicides control either grasses or broadleaves (i.e. alfalfa and clover). If you have a mixed pasture (both grasses and legumes like alfalfa and clovers), there are no herbicide options that will control unwanted weeds and leave BOTH legumes and grasses.
Steps To Minimize Weeds in Pastures
- Proper grazing management is a must. Overgrazing easily damages pastures. Overgrazing pastures tends to pull out roots of desirable plant species, giving weeds space to take hold.
- Protect new seedlings from grazing until they are well established and graze moderately thereafter.
- Allow established pastures a recovery period after grazing. This will reduce weeds and increase pasture yield and nutrition value.
- If possible, mow after each grazing period to control many pasture weeds and encourage new pasture growth. However, do not mow the pasture closer than four inches above the soil.
- During excessive dry or wet conditions, remove horses from pastures.
- In pastures with excessive weeds, where pasture forages are thin, reseeding may be the best practice.
- High yielding, well-managed pastures will choke out weeds.
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Krishona Martinson, Equine Extension Specialist, University of Minnesota