Weeds like poison hemlock have had an ideal environment in southwest Missouri to flourish during the last three years. Dry weather in 2011 and 2012 weakened established grass and ample moisture during the 2013 spring has allowed weed seeds to come on like gangbusters.
The most opportunistic weed at this point in southwest Missouri appears to be poison hemlock according to Eldon Cole, a livestock specialist with University of Missouri Extension.
"Poison hemlock is not on Missouri's noxious weed list but many farmers feel it's more of a headache than some plants that are on the list," said Cole. "The biennial plant can be controlled with herbicides in the late fall or very early spring. Normally the toxicity is reduced, but not totally eliminated when dried, as in hay."
Poison hemlock is a highly visible plant since it reaches usually 5-to 7-feet tall this time of year.
"It's in full bloom now with an abundance of white blossom clusters. The favored location is along streams, ditches and old barn lots although it can be found about anywhere," said Cole.
Poison hemlock has a big, hollow stem with purple spots on it. Many refer to it incorrectly as wild carrot. Cole says there is an odor to the plant sometimes described as "mousy."
Impact on livestock
True to its name, the plant is moderately to highly poisonous to cattle, horses, swine and sheep. The most toxic parts of the plant are roots and seed. Affected animals show signs within two hours of eating it.