Crown vetch, a member of the legume family, was originally planted as a ground cover and erosion barrier along road sides and other large areas. Originally from Europe, Asia and Africa, crown vetch is now present in most of the northern United States and southern Canada. Crown vetch is a large, low growing plant with green leaves and small pink flowers in the spring.
Crown vetch is classified as an invasive plant. Originally planted as a ground cover, it quickly overtakes nearby field and prairie land. It also invades grazing and farming land, quickly choking out other plants. Chemical control is done with foliar herbicides during the growth period in spring with limited success, though it must be applied over the course of several years. Controlled burns are successful in many areas to control the plant.
Crown vetch grows rapidly within one season. Its rhizomes reach sizes of 10 feet, then put out 6-foot long vines, quickly overtaking an area so nothing else grows. It produces seeds throughout summer and they are extremely viable. Seeds may germinate 15 years after being produced, so even a crown vetch problem that appears solved can reappear many years down the road. Frequent mowing before the seeds have a chance to form helps prevent seeding, though the vines and roots will still spread. Well tilled and maintained lands with good, native ground cover are resistant to vetch takeover, as crown vetch needs at least two summers before the plant is completely viable.
The stems, leaves and seeds of crown vetch all contain nitroglycoside, which is toxic to single-stomach mammals. Horses are most commonly affected by crown vetch poisoning. Poisoning slows down growth and causes paralysis. In extreme cases, it may lead to an animal's death. Cows and other rudiments, animals with complex stomachs, suffer no affect from the toxin. It takes consumption of large quantities before the horse feels the ill effects. Mow areas invaded by vetch often to make it less appealing to the horses and use a herbicide for extreme vetch problems in the pasture. A diet high in alfalfa helps counteract the effects of the crown vetch toxin.