As summer wanes, weeds become more apparent than ever in many horse pastures. In late summer, forage growth tends to slow in many areas and it is easier to spot which weeds have established themselves in your pastures. Weeds are usually large and seed-producing in late summer. Therefore, this is an ideal time to evaluate your weed control strategies and any problem areas in your horse pastures.
 

Weeds tend to establish themselves and proliferate where grass is not well established or in bare patches due to overgrazing. When established, weeds will thrive and can eventually become the dominant plant species in a pasture. Not only can some weeds be poisonous to horses, they are usually non-palatable and low in nutritional value.

In a well-managed productive pasture, weeds tend not to grow well. It is only in pastures where grass stands are not well established or in thin areas of grass where weeds establish themselves. Regardless, even in the most productive and well managed pastures, weeds can become a nuisance.  Thus, as part of any pasture management strategy, weed control is a must.

A major concern for any horse owner is poisonous weeds, also called noxious weeds. Generally, as long as horses have sufficient forage available, they will not consume poisonous weeds since they are bitter tasting. Yet, a curious or hungry horse can consume lethal amounts of poisonous weeds. Some toxic weeds for horses are:

Poison or Water Hemlock - fernlike leaves with clusters of white flowers

Horsenettle (nightshade) - oblong irregular shaped leaves covered with fine hairs and has white or purple flowers

Ragwort - straight multi-stemmed plant with lobed leaves and small yellow flowers

Yellow Star Thistle - early stage has rosette of non-spiny leaves, followed by flowering stage with numerous yellow flowers surrounded by spines

Buttercup - short growing plant with glossy yellow flowers

Locoweed - short stems with multiple leaves, may or may not have hairs depending on plant species and can have either white or purple flowers

Bracken fern - typical fern with triangular shaped leaves

There are other toxic weeds and plants for horses. Owners are advised to become knowledgeable on the types of toxic/poisonous plants endemic to their area for better identification. If available, your local agriculture extension agent can help you identify weeds endemic to your area.

The most effective removal of any weed is by manually pulling the plant out of the ground, including its roots. While this is the most labor-intensive method, it is highly recommended for any identified poisonous weeds. Once pulled, these types of weeds also need to be completely removed from the pasture. Pulled weeds left in a pasture can become more palatable as they dry, which poses danger for any horses that consume them.

For most weeds and pastures, manual removal is not feasible. Thus, for these other types of weeds, there are other methods for removal. Herbicides can be one effective method of controlling weeds. It is important to always follow the directions from the manufacturer on how to use any particular herbicide.  Herbicides work best when applied to young and growing plants and can be effective in weed control and elimination. There are different times of year when best to apply herbicides.

  • Early Spring (March-April) to treat buttercup, thistles, poison hemlock and others
  • Early Summer (June) to treat common ragweed and others
  • Early Fall (October) to treat poison hemlock, common thistle and others

After spraying a pasture with an herbicide, the general rule of thumb is to keep horses off of it for a minimum of 7 days. Again, it is critical to follow the manufacturers recommendations when using herbicides.

Mowing is generally not the most effective method for treating a weed problem. However, mowing plants as part of any pasture management program is recommended and can be effective in controlling certain types of weeds. Pastures can be mowed down to 4 to 6 inches which will prevent tall weeds from producing seeds. Mowing, however, will miss affecting shorter weed types. Thus, mowing would not be recommended as the only weed control strategy.

The best weed prevention and control is proper pasture management. Properly managed pastures allow grass and legume plants to regrow and recover from grazing. This makes it more difficult for weeds to get established. Improper management, such as allowing pastures to be overgrazed, is a major reason weeds get established. Tips on how to best manage your pasture is highlighted in our Summer Pasture Management article.  

If weeds have overtaken a pasture, the last remaining recommended option would be to kill off all the vegetation in the pasture and reseed it. While not ideal, this would be the best and quickest method of establishing a productive pasture. It would normally take one growing season to get a pasture reestablished. However, this is the last resort and if the above-mentioned methods are utilized early and often, weeds will be a minimal nuisance to your operation.
 

Chris J. Mortensen, Ph.D.