Poison hemlock isn’t new to the Lebanon Valley – it’s been in the northeast United States since the 1800s when it was marketed as a decorative winter fern – but with its increase over the last decade, local residents are being strongly encouraged to take more active measures at preventing its growth, as this weed can be deadly.
You might know it from history class as the plant that tradition says Socrates, the ancient Greek philosopher, drank at the conclusion of his famous Athenian trial.
Lebanon County-based Del Voight, a senior educator with Penn State Extension’s field and forage crops team, says that poison hemlock has probably been around for his full 31-year career so far, but he didn’t start getting calls from people about it until about seven years ago.
Poison hemlock is the killer cousin of the carrot, and easily confused with wild carrots – both members of the carrot family, apiaceae.
It can be fatal to humans and animals when ingested and cause other health issues, such as rashes, even from contact exposure to the plant’s strong, alkaline oils.
Voight said that the plant is easy to control, but the hard part is recognizing it as a threat. He said land owners and managers had reached out to him with stories of trying to tackle its growth thinking it was an ordinary weed, and suffering the results after they pulled it by hand.
Poison hemlock has a biennial life cycle. Its first year, it comes out in rosette form, and then it bolts (or flowers) in its second year. The plant seems to prefer riparian areas and ditches right of ways where the soil is disturbed and shaded.
Dwight Lingenfelter, a Penn State Extension senior associate specializing in weed science, said that other weed scientists have described the growth of poison hemlock as “an explosion in slow motion.” The population of poison hemlock has been steadily increasing over the past few decades around the state, and it’s not some new invasion that has just happened recently, he said.
“As with many weeds, it may take many years before people start to notice them taking over an area,” said Lingenfelter.
The plant is more easily detected in its second-year life cycle when it has a large stature and show white flowers, but its best to control poison hemlock in the rosette stage, when it does not release seeds, he explained.
“Individual plants can be easily dug out with a shovel,” said Lingenfelter. “Larger infestations can be cut with a mower or string trimmer or may require the use of a herbicide.”
James Cessna, a roadside specialist for PennDOT District 8, said that poison hemlock was one of the first plants he ever learned about when beginning his 25-year career as a certified arborist. Cessna said that in the last 5-10 years, poison hemlock has really exploded, which he attributes to the warmer winters and warmer seasons. This year, for example, the plant had bloomed by mid-May when it usually doesn’t bloom until June, he said.
The major problem with controlling its spread is that each of the plants can produce thousands of seeds, which can fall into the soil below and create a seed bank which may be viable for years to come.
PennDOT District 8 has a contracted spray program that includes a special line item to deal with poison hemlock, along with thistle, with more than one thousand hours annually spent on tackling the problem. But resources are of course finite, and with PennDOT District 8 managing state roads in eight counties – Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, Perry, and York – and all the road surfaces, potholes, and improvement projects therein, only so much can be allocated for that particular program.
PennDOT District 8 spends about $156,000 annually on this line item – a good healthy chunk of change for one plant, said Cessna, but not enough to beat it back and control it anymore. Another complicating factor with PennDOT’s management practices: It can only spray its own right-of-ways, so if an adjacent property has unchecked spread of poison hemlock, those seeds can easily hop right back over the fence and come back the next year.
Cessna said that poison hemlock is all over the region, but Lancaster County is particularly susceptible to it.
“It just loves that soil down there, but it’s everywhere,” said Cessna. “It’s a big problem.”
Herbicides can be used on poison hemlock, and are most effective when the plant is in rosette stage or before it bolts. Options include 2,4-D + dicamba, Crossbow (2,4-D+triclopyr), or glyphosate as a spot treatment. A general herbicide such as Roundup can be used, but it will also kill other vegetation. So Voight highly encourages that anyone treating poison hemlock on their land makes sure to re-vegetate the area with a thick grass like rye, which can germinate quickly and provide a thick stand to help with weed supression.
If land owners or farmers have questions, Penn State Extension and the Master Gardeners are available to help – but maybe instead of tearing a plant off and bringing it into their office by the fairgrounds, just take a photo instead. Master Gardeners are available to help identify the plant – along with others in the lineup of undesirables such as poison ivy, poison oak, and wild parsnip – and share fact sheets or answer questions.
Voight says that as he’s been out and about Lebanon County, he’s seen the impact of treatment locally – although locals should still be vigilant, especially with children, when enjoying local waterways. He noted that he saw some treated poison hemlock at the Quittapahilla Creek & Nature Park when he was fishing there earlier this year.
Read More: Quittie Creek Nature Park reconnects humans with their natural habitat
How to recognize poison hemlock
Friends of Old Annville president Michael Schroeder, who also serves on the organization’s Quittie Creek Nature Park Committee, said that treatment there is collaborative with Les Powell and his crew at Annville Township Public Works, and two main methods are used to manage poison hemlock – the preferred being a “mechanical” intervention, a.k.a. taking a machete to it.
Each spring, Schroeder takes a machete out and “hacks to death every hemlock sprout he sees along the banks and main trails, roots and all.” He noted that poison hemlock does not grow in the woods or in the Quarry Pond. His prime hacking season goes from early February to late March. As a secondary method, volunteers also mark any remaining plants for Annville Township Public Works to spray with hand-targeted glyphosate (Roundup).
For anyone using a herbicide, Voight encourages the use of gloves, googles, and a respirator, and also to pay close attention to mixing ratios, which can vary dramatically based on the specific herbicide as well as the application method.
Cessna said that the best bet he sees for keeping poison hemlock off of PennDOT right of ways is encouraging the public and municipalities to adopt their own control mechanisms and seeing better public education on how to do that.
“If people know what to look for and are more aware of it during the fall or early spring when it can be better managed then using proper control tactics in a timely manner when the weed is most susceptible to control can lessen its impact the next year and beyond,” said Lingenfelter.
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