Poisonous Weeds to Horses

This is a listing of the most commonly found poisonous weeds in horse pastures and is not all inclusive. For example, Carolina jessamine, one of the most dangerous plants in North Carolina.

In most cases the weeds are unpalatable and will not be grazed unless desirable forages are unavailable. The notable exceptions are black cherry and red maple leaves. These leaves are toxic in even small amounts. Horse will sometimes eat the wilted leaves from a blown down black cherry and a few fallen red maple leaves can easily be picked up when grazing. A few years ago three horses died in Burke County when their owner fed their hay under a red maple during leaf drop.

Some of these plants may surprise you and you will probably despair of ever learning them all. But learning them all is not the point. Your stock are living in a dangerous environment and the best way to protect them from toxic weeds is to develop and utilize a comprehensive weed control program. Such a program with involve both mowing and herbicides. Depending on mowing alone will result in a prevalence of perennial weeds while reliance on herbicides alone will develop an annual weed problem. A dual approach is best.

Associated Toxicities of Some Pasture Plants

Red Clover

Black patch fungus on leaves causes slobbers. In horses it can cause dehydration to a life threatening degree. This fungus is also found quite often on white clover types and should be suspected anytime excessive slobbering is observed in the horse.

Sudangrass or Sorghum

Can cause cystitis syndrome when grazed after a prolonged drought or heavy frost. While these compounds break down in hay in a matter of a few weeks these forages are still not recommended for horse hay due to the difficulty in drying down the thick stems and the attendant risk of the hay molding in the bales.

Nitrates

Can cause poisoning and death in heavily fertilized grass pastures
 and hay fields especially in drought conditions.

German Millet

When fed as a major forage can cause kidney, joint and bone problems, especially when plants are mature.

Lush pastures

Horses unaccustomed to lush pasture can colic or founder
 if suddenly changed to them.

 

Tall fescue

Tall fescue is our most common pasture grass and hay species primarily because of its resiliency and low maintenance. A large measure of these benefits can be attributed to the presence of an endophyte fungus living in a symbiotic relationship within the plant. The fungus also produces an alkaloid which causes a number of problems for cattle and bred mares.

Information from the University of North Carolina
Cooperative Extension