Poison hemlock (Conium maculatum) has become more abundant over the past few years. I am seeing it all along the roadsides here in Centre County now.
It is a biennial, which means the first year of growth ends with a low growing (basal) rosette of foliage. During the second year, the stem, branches and flowers are produced. Poison hemlock can reach up to 6 feet in height. The white flowers are produced throughout the summer from June into August. Individual flowers are small but clustered in an umbrella-like grouping, which makes them noticeable. The plants overall appearance resembles carrot and parsley.
Poison hemlock has a long tap root (10 inches) and extensive fibrous roots. Hand removal is difficult because of the tough root system and the fact that the plant sap is, along with being toxic, a skin irritant. Even the use of weed trimmers needs to be conducted using precautions so that plant material doesn't come into contact with the body. There are no pre-emergent herbicides to use against poison hemlock in ornamental settings. Post-emergents include: diquat, pelargonic acid, glyphosate (all are non-selective), and 2,4-D. The most effective approach is to treat the 1st year rosettes and not the larger, mature plant.
State foresters warning about poisonous plant growing rampant in Pennsylvania
Fox 43 News
June 19, 2018
FERMANAGH TOWNSHIP, JUNIATA COUNTY, Pa. -- Foresters with the Department of Conservation and Natural Resources (DCNR) are warning about a poisonous plant growing throughout Pennsylvania. It’s called Poison Hemlock, and it can be dangerous.
According to the USDA, Poison hemlock contains eight known alkaloids, including coniine and coniceine that are extremely toxic to humans, livestock, and wildlife. Foresters say people have mistaken its roots for wild carrot; if ingested, it can cause death.
It's tall, it flowers, and bugs seem to like it, but if you touch Poison Hemlock, it won’t be pretty.
“Just by grabbing on it, pulling on it, you can have severe reactions, and we definitely don’t want people eating it, ingesting it… like livestock, animals, because it can cause death," said Lucas Book, a state forester, covering Juniata and Perry Counties.
Book says the plant is growing rampant throughout the state this year, colonizing along roadways and other ungroomed spots. FOX43 found a thick growth of plants off Route 35 in Fermanagh Township, Juniata County.
It’s commonly mistaken for other plants, and some people have never heard of it or its harmful effects. "This plant is in the carrot family; it actually looks similar to Queen Anne’s Lace," stated Book. It's different from Queen Anne's Lace, though, because of its hollow, purple spotted stems. People can recognize Poison Hemlock by its small, white flowers, developing into white umbrella shaped clusters.
If someone notices the plant growing, Book says its best to spray a herbicide, mow it down, or pull it out of the ground - just make sure you’re dressed appropriately. “I used to weed whack in shorts, and I only did that once or twice until I realized that was stupid; if you want to mow this, you’re going to want to wear long pants, long sleeves, and gloves," he laughed.
An employee at Spangler's Ace Hardware located at 4072 Carlisle Rd in Dover, York County recommends doing a bit of reading up on the plant. “This is not, you go to your local hardware store, you buy something and spray on it, you go home and go about your day. You have to do your research to find out what stage the hemlock is in before you can control it," said Jerry Frey, a salesman. The Plant's stage will determine which herbicide will work best.