Even though the spring weather was wet, it will almost certainly be both hot and dry at some point. A hot, dry summer often means reduced pasture growth and overgrazing. Livestock on overgrazed pastures are more likely to graze on potentially poisonous plants.

There are many plants that have the potential to cause health problems for livestock, says Dennis Epplin, University of Illinois Extension crop systems educator. Some are toxic; others may cause photosensitization or mechanical irritation; or, they may contribute to undesirable odors in meat or milk. Identify and then remove or destroy poisonous plants from your pastures.

Signs of plant poisoning may differ considerably in intensity depending upon the kind of plant eaten, the stage of its growth, the amount eaten, the amount and kind of other feed eaten during the time that the poisonous plant was in the animal's digestive tract, and the tolerance of the individual animal to the poison.

Although many plants can cause problems, Epplin says only a few are responsible for most difficulties. Some of the plants that may affect animal health include black cherry, choke berry, cocklebur, hemp dogbane, jimsonweed, black locust, milkweed, nightshade, pigweed, poison hemlock and white snakeroot. Also, remember that yews, commonly planted in many landscapes, are considered among the most toxic plants to animals.

"A well-managed pasture minimizes problems associated with toxic plants," says Epplin. "Maintain adequate soil fertility to encourage desirable forage growth. Mow and/or utilize herbicide applications to control problem weeds."

For the most current weed management recommendations, consult the 2008 Illinois Agricultural Pest Management Handbook. The handbook can be purchased through local U of I Extension offices and is also available online at www.ipm.uiuc.edu/pubs/iapmh/index.html.

There are numerous electronic and print references on poisonous plants. One of the more recent books on the subject is A Guide to Plant Poisoning of Animals in North America by Knight and Walter.