Published September, 2013

Fall is a good time to evaluate the quality of horse pastures, because it is easy to see which weeds were most prevalent and uncontrolled during the summer. These weeds will now be large and seed-producing. It is also a good time to develop a pasture weed management plan for the coming year.

An effective weed management plan should consider the purpose of the pasture, weed species and abundance, which weeds should be controlled and how, and sources of information.

Purpose of the Pasture

If pasture is a significant portion of a horse's diet, it should be high-quality and nearly weed-free. Conversely, a “pasture” maintained as a drylot for feeding horses will contain many weeds. There is little reason to control these weeds since there are few, if any, desirable forages in the drylot. Kentucky horse pastures are usually maintained between these two extremes. Frequently asked questions from horse owners include, “Why are these weeds in my pasture?” and “What should I do about weeds in the pasture?” Ensuring pastures have adequate fertility and are not overgrazed will help limit weeds but will not prevent all weeds from growing.

Weed Species, Abundance, and Distribution

Plants we call weeds grow in ecological niches--environments that allow for germination, vegetative growth, and maturation. A horse pasture offers several of these ecological niches in which weeds thrive.

Kentucky is located in the temperate transition zone, which allows warm-season or cool-season plants to grow. Warm-season weeds germinate in spring or early summer, grow, and produce seeds before frost. Cool-season weeds germinate and produce some growth in the fall, and produce seeds the following spring or summer. The numerous weed species provides horse pasture managers with the challenge of determining what weeds, if any, they should be controlling in a pasture. The most abundant weeds in horse pastures are usually annual species that produce thousands of seeds.

For instance, spiny pigweed, also known as spiny amaranth, produces more than 100,000 seeds per plant. This weed is widespread and grows most often in compacted areas along fences and around feeding and watering areas of pastures. Spiny pigweed is also a "patchy" weed that grows only in certain portions of the pasture where its ecological niche occurs.

Which Weeds to Control and Methods to Use

Generally, property owner should remove from pastures poisonous weeds and those that inhibit grazing. Poison hemlock occurs widely across Kentucky and is toxic to horses and other animals. Although rarely eaten by horses, it should be removed from pastures. Musk thistle and bull thistle are found throughout Kentucky and inhibit grazing. Canada thistle occurs less frequently but also inhibits grazing and is more difficult to control. Large crabgrass and yellow foxtail are warm-season grasses of summer. Horses graze the large crabgrass but not yellow foxtail. Buckhorn plantain is a cool-season plant that horses consume when pasture grass is limiting. Many small, tender “weeds” are nutritious and readily consumed when small but rarely consumed as large plants.

Methods of removing weeds from horse pasture are limited to hand removal, mowing, and herbicides, and each have advantages and disadvantages. Hand weeding can be very effective and is particularly useful for removing poisonous plants such as poison hemlock. The downside of hand weeding is that the process is slow and inefficient for large areas.

Mowing is rarely effective for killing weeds in pastures. Mowing low enough to kill the weeds (2 inches or less) removes valuable forage. Mowing heights of about 6 inches will keep some large weeds from producing seeds but does not control smaller weeds.

Herbicides are efficient and provide excellent control, but in areas of the transition zone, such as Kentucky, there is not one herbicide that will control all the weeds with one treatment.

There are optimum times to control weeds with herbicides. The following months are preferred for herbicide treatment of several weedy species in Kentucky:

• October-November: common chickweed, henbit, purple deadnettle, dandelion, buckhorn plantain, buckhorn plantain, musk thistle, bull thistle, Canada thistle, and poison hemlock
• February-March: buttercups, curly dock, broadleaf dock, and chicory
• May-July: spiny pigweed, white clover, hemp dogbane, goldenrod, cocklebur, perilla mint, common ragweed, and jimsonweed

Consult your local Cooperative Extension Service agricultural agent for specific information on herbicides in your area. Remember, not all herbicides are registered for use in all states and countries, so read the label carefully and follow all directions. Many Cooperative Extension Services have publications regarding weed control in pastures; these include Broadleaf Weeds of Kentucky Pastures, AGR-207, and Weed Management in Grass Pastures, Hayfields, and Other Farmstead Site, AGR-172.

William W. Witt, Emeritus Professor, Weed Scientist, University of Kentucky, provided this information.