The following article was submitted by Chris Hicks, Smith County Extension Agent:
“That plant has been here for years and never caused a problem!” This is a common reaction when folks find out they have a toxic weed in their pasture. But are you sure it has never caused a problem? Just because you don’t see a dead animal doesn’t mean toxic weeds aren’t costing you through lower conception rates, decreased weight gain, sick animals, etc.
Yes, there are several weeds in Tennessee pastures that livestock producers need to be aware of and able to identify. Plants such as Perilla Mint, White Snakeroot, Poison Hemlock, and Hemp Dogbane are just a few of the many plants that can cause harm to livestock.
Of course, with any poison the old saying “the dose makes the poison” is applicable. One or two of these plants in a field isn’t cause to overreact and Roundup the entire farm, and in most cases animals will leave toxic plants alone, provided they have enough good quality forage to eat. However, as summer rolls along and fescue pastures basically go dormant, animals may eat plants they normally wouldn’t prefer.
Being able to recognize these plants and control them before they become a significant problem is important. We have some weed identification guides available free of charge at the UT Extension office, and are also available to identify suspicious plants on site.
An important thing to keep in mind when trying to control poisonous plants in your pastures is that some of these weeds become more palatable to livestock as they die down following an herbicide application. That means removing cattle from treated fields is highly suggested.
When thinking about potential toxins in your pasture, don’t forget about trees. Cattle can also be exposed to certain toxic compounds through ingesting the wilting leaves of trees in and around pastures. For example, hungry animals can be poisoned by eating as little as 2 ounces of cherry leaves from a limb blown down during a storm.
A final thing to keep in mind is that “good plants can go bad.” Plants that are commonly used in Tennessee forage production can poison cattle under the right circumstances. Johnsongrass and Sudex can release cyanide after the first few frosts in the fall, and in drought conditions or after heavy nitrogen fertilization some warm season grasses are prone to nitrate toxicity.
Animals becoming agitated, trembling, or staggering, as well as changes in eating and drinking patterns are signs to look for. Animals that have eaten toxic plants may also have difficulty breathing, dilated pupils, and diarrhea.
If you suspect you might have some poisonous plants in your pasture, we can come out and help with identification, or you are welcome to bring samples of plants to the UT Extension office at 125 Gordonsville Hwy. in Carthage.