Are weeds in my pasture really a problem?

This is a question that Jennifer and I have been getting more and more frequently these days. Weeds in a pasture, especially weeds such as buttercup and horsetail, are a serious concern and should be dealt with as soon as possible!

Creeping buttercup (or Ranunculus repens for those science people out there) grows in acidic, boggy conditions such as what we experience on a daily basis here in the Fraser Valley. Buttercup contains toxins that will cause serious inflammation in the digestive tract. Sap from the stems can also cause blistering on the skin or mucous membranes and even around the hooves of horses. In addition, some of the other symptoms that result from the ingestion of buttercup include: mouth blisters, colic, bloody urine or diarrhea, twitching of the eyelids, loud breathing and a weak pulse. Horses have been known to consume buttercup when grass density and height are too low.

Another common weed in this region is field horsetail (Equisetum arvense), which is also found in poorly drained and acidic soils. Horsetail is especially poisonous for young horses and can cause symptoms such as: jaundice, loss of appetite, weakness, staggering gait, excitability and paralysis. Horses will also consume this when grass is in short supply and when fields have been overgrazed.

Finally, Tansy ragwort (Senecio jacobeae) is another weed that is highly prevalent in the lower mainland and southern Vancouver Island. Tansy ragwort contains liver-damaging alkaloids that can cause cells in the liver to expand and then eventually die. The symptoms of poisoning include: weakness, liver failure, high temperature, incoordination, and yellow mucous membranes.

Since there are no effective treatments for any of these plant poisonings the best mode of defense is preventative pasture management. If the pasture happens to be quite acidic (which you can determine through a simple soil test) then you should lime your fields to make them more alkaline. Also, spreading finished horse manure compost and overseeding with a good grass mixture tailored to your region will go a long way to outcompeting these nasty weeds. The more dense the grass, the less dense the weeds will be. Horses only graze weeds when there is not enough grass available in the field for them. Therefore, we need to ensure that the fields are not overgrazed and are left to rest when necessary.

See the news and events section of the website for more information on a new workshop addressing pasture management concerns. This workshop will be held on May 17th, 2007 in the Langley Firehall 6 from 7pm to 9pm.

More information on poisonous plants can be found through the British Columbia Ministry of Agriculture and Lands or the Ontario Ministry of Agriculture, Food and Rural Affairs (MAFRA). All pictures are courtesy of the Ontario MAFRA (http://www.omafra.gov.on.ca/english/livestock/horses/facts/poison.htm).