The mild winter in much of Nebraska has provided an early start for some weeds. On southern exposures and sheltered ditch banks poison hemlock (Conium maculatum) is already starting to grow and could pose a threat to cattle and humans due to poisonous alkaloids in its plant tissue.
Poison hemlock in a wooded, rural area of Lancaster County March 9, 2012. (Photos by Lowell Sandell)
While the plant is often not considered very palatable, livestock may be attracted to it at this time of year because it may be one of the few green, growing plants in the landscape. Efforts should be made to keep livestock from having access to it.
The poisonous alkaloids are present in all plant parts; however, leaves, flowers, and seeds tend to have the highest concentrations. Cattle are more sensitive to the effects of poison hemlock alkaloids relative to other livestock. Consuming just 5 lb of foliage can be potentially lethal for cows.
A number of poison hemlock plant samples have been submitted to the UNL Diagnostic Clinic for identification in the last four years. Poison hemlock, a member of the parsley family that flourishes in both rural and urban landscapes, also has health risks for humans. The lacy appearance of hemlock leaves can be confused with edible parsleys when plants are young. Ingesting even small amounts can sicken humans as well.
Description
Poison hemlock is a taprooted biennial broadleaf plant. A distinguishing identification characteristic is the purple to red spots or irregular blotches on the hollow stems. The leaves are finely divided, hairless, and may have a glossy green color. Leaves are alternate on the stem, but this may be difficult to determine in its first year of growth, since it may have a very basal rosette appearance until it produces a stalk in its second year of growth. Flowers are small, white, and arranged in relatively large compound umbels. When mature, plants can reach 10 feet in height. It is often described as thriving in moist soils and is commonly found in pastures, ditchbanks, and roadsides.
Controlling Poison Hemlock
A mixture of 2,4-D + dicamba or Grazon P&D can effectively control poison hemlock when applied in the fall or early spring. It is difficult to recommend treatment in early March due to potential variability in the weather; however spot treatments may be effective if three to four warm, sunny days, with nighttime temperatures above freezing, are expected to follow application. Keep livestock out of treated areas, as the poisonous alkaloids can still be present in dead leaf tissue. Dead plant tissues also tends to be more palatable to livestock than green, growing plants. To achieve adequate control, repeated herbicide applications may be necessary over many years in heavily infested areas. Repeated mowings also can provide effective control, but herbicides tend to provide faster results.
Lowell Sandell
Extension Educator – Weed Science
