Tips for Controlling Weeds in Horse Pastures

Weed management in horse pastures is a constant process. It requires time, dedication, and ongoing effort from farm owners, but it’s crucial for promoting healthy forage for horses to eat.

To help property managers combat pasture weeds, Andy Kness, MS, agriculture educator for Harford County, Maryland, provided weed control tips during the University of Maryland Extension’s healthy horse-keeping webinar series.

The No. 1 rule to remember, he said, is a dense, healthy forage stand will naturally outcompete weeds. Your weed management program, however, “requires a comprehensive integrated approach,” he said. “No one single tool is going to do it for you.”

Kness then described the tools you’ll need in your pasture weed control toolbox.

It Starts With Soil

Soil is the base of a healthy pasture. “Think about it like the foundation on your house,” said Kness. “You can spend all the money and resources to build an extravagant house, but if it doesn’t have a good foundation, it’s going to crumble, and you’ve wasted all that time, effort, and money to have it fall apart.”

As such, he highly encourages property owners to run soil tests every one to three years. “This is going to be the benchmark for making management decisions in your pastures,” he said.

Those management decisions revolve primarily around soil pHs level and fertility. Soil pH is particularly important, Kness said, because it influences nutrient availability for the plants. “If we fall above or below the optimal pH range of 6-7, nutrient availability goes down,” he explained. “Monitor your pH and adjust accordingly (apply lime, for instance, to raise a low pH to a sufficient level) to keep it in that range.”

Also pay attention to the fertility levels on your soil test and amend as needed. “Plants need food,” said Kness. “You often have to supplement by spreading manure or other fertilizer sources to build (fertility) levels up to promote healthy plant growth. That healthy plant growth is going to work to choke out weeds.”

The local lab that processes your soil test can provide you with soil management recommendations, he said, as can your local extension office or county nutrient management advisor.

Forage Selection

Choose the right forage for your pasture, soil type, and goals and needs, because different plant species are adapted for different conditions. Consider appropriate drought resistance; sun, and shade tolerance; and cold hardiness.

“Don’t try to put a forage that’s not going to perform well in a site,” said Kness. “You’re just going to be asking for problems.”

Again, your local ag agent can help you determine the appropriate species for your specific pasture.

Pasture Management

Maintain adequate leaf material in your pasture plants to not stress them to the point they die, which is when opportunistic weeds will take their place. In other words, don’t overgraze, said Kness.

“Your pasture should not look like a putting green,” he explained. “Plants need leaf material to function and be healthy. When you remove leaf material (via grazing, mowing), you’re also clipping the amount of roots that plant has. It takes root reserves and stores to push up new shoots.”

To avoid stressing your pasture grasses, never graze or mow them below 4 inches. “When you get to that 4-inch mark, that’s your signal to move or rotate your horses to a new pasture or paddock,” said Kness.

Allow that paddock to regrow to at least 8 inches before returning horses to it.

Kness recommended owners manage grazing height using rotational grazing and adjusting stocking rates (if possible) to one horse per 1.5 to 2 acres. “Don’t set yourself up for failure by putting too many animals on that pasture at once,” he said.

You might also set up a sacrifice lot, where you can house horses during certain times (post-heavy rain, for instance, to prevent horses from tearing the grass up and making a muddy mess, he added) until ground conditions improve.

Grazing Management

Don’t assume grazing is bad for your pastures, though. It actually acts as a type of mechanical weed control.

“Having animals graze paddocks properly helps clip weeds and keeps them from producing seeds,” said Kness. “A lot of the weeds we have do provide decent forage. It’s just that when they get to producing seeds, they get to be very unpalatable to livestock and become reproductive nightmares, producing seed and making the problem worse. Just grazing properly will help keep weeds at bay.”

Mowing

“The mower is your friend,” said Kness. “It provides a lot of benefits as far as weed control and forage quality.”

These benefits include keeping grasses in a vegetative growth stage, weeds from going to seed, and pastures uniform.

“What we want to do is always keep plants in a vegetative growth state,” he explained. “When you start to see flowers, it’s no longer in a vegetative growth stage, it’s going into a reproductive stage.”

When pasture grasses reach the reproductive stage (characterized by seedheads), they become stemmy and unpalatable and provide less energy for the horse. “This is undesirable from a forage quality standpoint,” said Kness.

If you see plants start to set seedheads out, mow (again, no lower than 4 inches) to keep them in that vegetative state.

Kness debunked the idea that letting pastures go to seed will lead to thicker future stands: “These forage species we have are domesticated plants,” he explained. “We’ve bred them over several hundreds of years to provide desirable forage quality and not necessarily self-seed themselves. Our forage species generally don’t self-sow very well.”

Chemical Control

When it comes to selecting effective herbicides for your fields, Kness said chemistry (e.g., the active ingredient) and timing of application are important. Look at active ingredients on product labels—these are the chemicals doing the weed control, and they only work on certain weed types.

Herbicides fall under several categories; select the best one for your needs. These include:

• Systemic Apply systemic products, said Kness, to actively growing plants. They absorb the chemical through their leaves, and it translocates (moves down) through the plants to the roots. Once in the roots, the chemical binds to specific receptors, disrupting biological processes and ultimately killing the plant. Systemic herbicides such as Roundup are usually effective at managing perennial weeds, he said.
• Contact These herbicides (e.g., Paraquat) only kill the plant parts (leaves, shoots) they contact. If the weeds are annuals, the plants will die. Otherwise, they might be able to sprout new shoots.
• Selective vs. nonselective Selective herbicides (e.g., 2,4-D, dicamba) have the ability to target certain types of plants. They might kill all broadleaf weeds, for instance, but not your grasses.
• Pre-emergent vs. post-emergent You must apply pre-emergent products, which are useful for annual species, said Kness, before weed seeds germinate. Apply post-emergent herbicides to plants that are actively growing.

When it doesn’t make sense to apply herbicides to an entire pasture, simply spot-treat your problem areas, he added.

If you’re confused about which product to use and when, consult with your local extension agent for recommendations. Always read and follow the label’s directions when applying any type of herbicide.

Overseeding

“Perennial pastures will decline over the years—it’s just their nature,” said Kness.

If your pastures is getting thin areas in places, fill them in with desirable plants before weeds have the chance to fill them in for you. Overseed with the appropriate grass or clover species to try to keep ground cover on those thin areas and combat weed problems, he said.

Take-Home Message

Be proactive and constant in your weed management program.

“Scout your pastures, and pay attention to how they’re performing,” said Kness. “Do it multiple times a year, because you’ll see different things appear in your pasture depending on the time of year.”

Identify the weeds you have, and take appropriate control measures depending on their life cycle, he added.

“Plants are not static beings; they are living just like horses,” he said. “They require maintenance and upkeep. So we need to be sure we are promoting the health of our forages, and that will in turn suppress weeds.”