Poison hemlock is a non-native, invasive species that is spreading across Ohio at an alarming rate. It has a biennial life cycle wherein it spends the winter between its first and second year of its life cycle as a low growing rosette. It is in this rosette stage that the plant can be easily controlled before it bolts to produce the flowering stalk and eventual seeds in its second season. The newly greened rosettes are easy to spot scattered across the landscape mixed in with the tans and browns of last year’s dead herbaceous plant material. The parsley like leaves are a dark green color. Poison hemlock thrives in disturbed habitats and will be easily found along right of ways, ditch banks, fence lines, field edges, and soil pills. In recent years it has expanded out into grazed pasture lands and hay fields.

Poison hemlock is toxic to a wide variety of animals including man, birds, wildlife, cattle, sheep, goats, pigs, and horses. It contains several neurotoxic piperidine alkaloids; the two major ones are coniine (major alkaloid in the mature plant and seed) and the more toxic gamma-coniceine (predominate in green, vegetative growth). These alkaloids cause muscle paralysis by acting as a neuromuscular blocking agent, resulting in two major effects: 1) rapid, sometimes fatal effects on the nervous system and 2) they are teratogenic agents, meaning they are known to cause birth defects when consumed during certain times of gestation.

Fortunately, most animals avoid grazing poison hemlock if other forage is readily available. However, animals are more likely to consume green plants during the late winter and early spring when other forage species are limited or when dry lotted or starving animals gain access to an overgrown field. All parts of the plant, including the seeds, contain the toxic alkaloids coniine and gamma-coniceine. Gamma-coniceine is more toxic than coniine and is at its highest concentration in early growth.

Now is the time to search for established poison hemlock individual plants as well as stands of plants. Once they are found, it is a great time to control them. If there is but a few plants, they can be easily dug out of the ground to disposed of them. Large numbers and stands of poison hemlock plants are more efficiently managed with herbicides. It is best to control poison hemlock with an herbicide now before it gets a chance to begin growing more rapidly as the temperatures continue to increase and remain higher for longer periods. Another benefit to treating soon rather than waiting is that few other plants and especially desirable plants are currently not actively growing around the poison hemlocks. There will be less danger of harming the desirable plants.

A non-selective herbicide such as glyphosate (e.g., Roundup) is very effective against the poison hemlock rosette. If the poison hemlock is mixed in with grasses, it would be better to use a more selective herbicide that does not kill grasses such as 2,4-D, clopyralid (e.g., Transline), metsulfuron (e.g., Escort XP), or a combination product.

Unfortunately, it is not a one and done management project. More than likely at any site where poison hemlock has become established, there is already a build up of a seed bank. Seeds from one growing season remain viable for 4-6 years. Thus, one would have to keep checking for new poison hemlock plants for several years to be sure that the removal was complete. If possible, reseed areas where poison hemlock was removed with a desirable plant that is competitive for the space. Otherwise, the open space where the poison hemlock was removed is an invitation for poison hemlock to reestablish.

Poison hemlock has many lookalikes and if you ever need assistance with identifying this toxic weed, contact the extension office to schedule a visit or you can stop by the office with photos. You can always email photos as well at stoneking.24@osu.edu.

Upcoming Programs:

• March 29- Agriculture Fertilizer Certification Training- This meeting will fulfill the three-hour requirement for applicators who need the agricultural fertilizer applicator certification. By taking this training, you will not need to take the ODA test. The cost of this program is $30 and is located at the Brown County Extension Office from 9 a.m – noon. For any additional information, please contact Trevor at (937) 378-6716. This program is cohosted by Adams, Highland, and Clermont Counties.

• April 2- Prepping the Garden Site & Maintaining Healthy Plants Workshop from 6 – 8 p.m. at the Adams County Fairgrounds. Call the office at (937) 544-2339 to register for this free workshop or email me at stoneking.24@osu.edu

• April 4- Southern Ohio Women in Agriculture Conference- Join us at the Bell Manor in Chillicothe from 9 a.m. – 3:30 p.m, to learn and network with women working in agriculture. A catered lunch and Ohio wine tasting is included in the cost to register. Thanks to sponsors, registration is only $50. Register using the link http://go.osu.edu/womeninagconf

Session topics include:

– Cultivating Connections- Courageous Farm Family Communication

– How to Transfer the Farm Fairly

– Round Table Discussion with Agriculture Professionals

– Farm Service Agency Programs for Women

– Selling Farm-Based and Home-Produced Foods: Laws to Know