CENTRE COUNTY, Pa. (WTAJ) — An invasive plant species is once again popping up along Pennsylvania highways, waterways, and pastures. Poison hemlock is recognized for its white flowers that pack a toxic punch.

“Poison hemlock is what’s considered a biennial weed,” said Dwight Lingenfelter, an associate of weed science for Penn State Extension. “Its life cycle is typically over a two-year period.” 

The plant can grow up to six feet tall and has a purple spotted stem. It has a musty smell, or a parsley smell when crushed.

During the summer months, some poison hemlock plants are at the end of their lifecycle and are dropping seeds to start the process over again. Penn State Extension said now’s not the time, however, to drop your guard.

“The whole plant is toxic, even the seeds have some toxicity to them,” said Lingenfelter.

Mature seeds are the most poisonous. Significant poisoning can cause muscle paralysis and suffocation.

“It can cause some toxicity if it is ingested,” said Lingenfelter.

Its sap can cause dermatitis.

“A lot of times when homeowners or people in the lawn care industry, they’re out, say weed-whacking for example, and they have maybe a pair of shorts on and it gets on their legs or shins or wrists and so forth, that can cause some problems there,” said Lingenfelter.

If on your property, you can remove it with a shovel, but wear long clothing, gloves and keep your animals and livestock away.

Lingenfelter said the best time to control poison hemlock is with a chemical spray in the fall, including diquat, pelargonic acid, glyphosate, and 2,4-D.

He said there is no major economic threat and residents are simply advised to be aware of the plant, not consume it, and not touch it.