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In the Weeds

Weeds can be a problem in pastures, especially areas that are overgrazed or trampled—such as high traffic areas around water sources, shade, and gates. Weeds are opportunistic; whenever grass cover is diminished or weakened, weeds take over. Their seeds need only sunlight and a little moisture to germinate. That’s why bare spots are soon covered by annuals. The weeds serve as nature’s band-aid to cover the ground and help prevent erosion whenever the perennial grasses are gone.

The solution? Pasture management efforts must balance use with growth, so that bare spots are avoided or minimized and weeds have less chance to get started. A change in grazing pressure will change the dynamics of a plant population, for better or worse, especially during drought or other stresses.

Preventing Weeds

“If you can keep good vegetative cover—a thriving stand of desirable grasses—this helps keep weeds from getting started. Make sure you have proper fertility and soil pH to promote growth of desirable plants,” says Dr. Jonathan D. Green, weed science specialist at the University of Kentucky. Learn about the needs of grass plants—when to fertilize, when they need nitrogen, and when they don’t.

An important part of good pasture management is to rotate animals to different areas, to give each grazing area a chance to regrow before horses come back to it. “You may always have some sacrifice areas in certain pastures, however, where horses congregate and tromp out the grass. Even if you put a lot of energy into weed control or reseeding, you might still have trouble maintaining desirable plants in those areas. With rotational grazing, however, you can keep most of the pasture in good shape,” says Green. How much grazing or rotation is enough? You learn by trial and error. A lot of it. The length of time the horses can spend in each segment can vary each year, depending on weather conditions and/or availability of irrigation water.

A key tactic is keeping the weeds trimmed so that they never mature enough to go to seed. You can do this in two ways: mowing, and grazing. When young and tender, most weeds are good feed. If your horses eat the more palatable weeds, the weeds may never mature. If a pasture gets ahead of the horses, you may have to mow it. Keep enough pressure on weeds with grazing or clipping and with competition from desirable plants, and you generally won’t need to use herbicides.

If you buy hay or straw, check it closely for weeds. If there are any strange plants in it, don’t feed that bale or those flakes of hay, nor use that bale of straw for bedding. Even if the weeds are not toxic, they may spread seeds that end up in your pasture. If you feed hay in the pasture, the feeding area is where horses congregate and trample most—inhibiting grass plants or beating them out—making it easier for unwanted plants to grow. Plus, weed seeds in straw can be dispersed onto your pastures if you use composted bedding/manure as fertilizer.

To keep weeds in check, it’s a good idea to keep horses away from pasture during the non-growing season to prevent trampling. Instead, feed hay in a corral. If weeds get started there, however, wind may carry their seeds to pastures, or horses eating those weeds may spread seeds via manure. So destroy weeds that become established in drylots or barnyards, too.

Getting Rid of Weeds

“We can often use herbicides to kill problem plants, but if you kill them out and leave a bare spot, it will grow right back to weeds unless you reseed it to grass,” says Green. Herbicides are just a tool in the overall management program and not a cure-all. They may be just the first step in reclaiming part of your pasture.

If you want to banish a particular weed, learn as much about it as you can. If you know its life cycle you’ll know the best time of year to remove it by mowing, chopping, or spraying. “Mowing won’t totally prevent new seed production because you’ll get regrowth and new blooms on some plants, such as thistles, after they’ve been mowed,” says Green. “But the number of new seeds produced will be tremendously lower than if you didn’t mow, or if you waited too long and the plants are fully mature.”

Mowing can be quite effective in controlling weeds that spread mainly by seed (such as spotted knapweed, Scotch thistle, and musk thistle). They tend to die out after a few years because they are biennials rather than perennials. Canada thistle, however, will spread even if you mow to prevent a seed crop—because it can spread via its root system. You may have to use selective herbicide to kill some noxious plants, and then reseed that area with a good forage plant.

Timing is crucial for good weed control. If you mow too soon or spray at the wrong time of year, you won’t get a good kill on the plant. Frequent mowing, such as every two or three weeks, can adequately control biennial thistles, except those in the fenceline where they can’t be reached with a mower. These may have to be sprayed.

“There’s no one specific time of year that will take care of all weed problems,” says Green. “Some weeds are summer annuals, others are winter annuals or perennials that reproduce at different times of year.” Discuss control plans with a weed specialist in your area who can advise you on proper timing.

Sometimes there are effective options besides spraying or mowing. Goats can eat off some weed patches, especially if you confine them to an area with electric fencing. Goats readily eat forbs and brush that horses won’t, preferring weeds and bushes to grass. This works best if you can use large numbers of goats to quickly eat the weeds before they go to seed. Grazing won’t kill the plants, but grazing or mowing weed patches over time will allow grasses to come in and crowd out the weeds.

In some situations you can control weeds with fire. You might burn some areas selectively, with a weed burner—for instance, to get rid of weeds along a ditch bank or metal fence, instead of spraying.

Biological controls like insect predators are sometimes helpful. “In Kentucky we’re utilizing thistlehead weevil for musk thistle control, especially on large rough pastures that are not easily mowed,” says Green.

Some of the biggest weed problems in well-managed horse pastures are weeds that grow close to the ground and escape the effects of mowing. “Curly dock, plantain, chicory and dandelions are some of the common broadleaf weeds we find scattered throughout these horse pastures,” says Green. Many of our worst weed problems are not recognized until after they’re already going to seed.

Crabgrass, goosegrass and cheatgrass are summer annual “weed” grasses. Undesirable grasses are harder to get rid of than a broadleaf plant because they cannot be selectively controlled with herbicides. “Research is underway to look at newer herbicide options, but right now the only reliable way to get rid of an unwanted grass in a pasture is to do a total renovation, usually with a non-selective herbicide spray that kills everything. You get rid of the unwanted grasses, then replant with more desirable forage grasses. This may not be feasible if you don’t have other pastures for the horses, since it takes a renovated pasture out of production for six months or longer before a new stand is established,” says Green.

Many people are reluctant to use herbicides because of potential risk to other plants, neighbors’ gardens, animals, wetlands, etc. In that case, the best prevention against weeds is vigilant management.

Herbicides merely treat the symptom, not the problem, but they can get you started in the right direction. “This is where they fit best, as part of a total management program—to get rid of an existing weed problem. Then you have to diligently keep the weeds out with good pasture management,” Green says.

Before you decide to spray, check with your local extension agent regarding which herbicides to use for certain plants and how to use them.

With a little effort, your pastures can be greener without the weeds.


Unwanted plants usually come in two varieties: those that are toxic, and those that crowd out valuable forage plants. Toxic plants include poison hemlock, water hemlock, buttercup, hemp dogbane, some milkweeds, locoweed, Russian knapweed, yellow star thistle, and houndstongue.

Other plants are a nuisance or health issue. Burdock and cocklebur, for instance, produce prickly burrs that stick to manes, tails and hair. Ripe burrs from burdock plants contain microscopic sharp “slivers” that can float in the air and get caught under an eyelid, producing inflammation and infection. Unwanted grasses with sharp awns—such as downy brome (also called cheat grass) or foxtail—may puncture mouth tissues when the horse eats them, creating sores or abscesses.

Thistles or crabgrass may proliferate and crowd out more desirable forage plants. In arid regions, exotic plants like knapweed or leafy spurge may take over pastureland.

Each geographic region has its own problem plants. Become familiar with the toxic and nuisance weeds in your area, especially the ones that are health hazards for horses, so you can recognize and eliminate them. A good control program will help you eradicate unwanted plants before they become too numerous. Good pasture management is the best way to keep them from getting started in the first place.