LOGAN — You may not realize it, but we are in the midst of an invasion. All you need to do is take a drive along U.S. 33 and you will notice (especially in northern Hocking County and into Fairfield County), along the fence rows and untilled areas, a sea of tall white flowering plants (some now starting to brown and go to seed). You may even think they are pretty until you realize that this plant is poison hemlock (Conium maculatum), an extremely deadly invasive species.
If you think that this is of no concern of yours, you are wrong. Poison hemlock is very toxic and sheep, cattle, swine, horses, and other domestic animals can be poisoned by eating small amounts of green or dried plant. It is also extremely poisonous to humans. This makes the invasion an extremely important issue for both farmers and homeowners alike.
According to the United States Department of Agriculture Agricultural Research Service, all parts of poison hemlock (leaves, stem, fruit, and root) are poisonous. Leaves are especially poisonous in the spring, up to the time the plant flowers.
Fresh leaves are unpalatable, so livestock seldom eat hemlock when other feed is available, however animals may be induced to eat this disagreeable plant because it is often one of few plants remaining green in winter and among the first to resume growth in the spring.
To stress its danger, cattle can be poisoned from eating as little as 300-500 grams and sheep as little as 100 to 500 grams of green leaves, and may die within a few hours after consumption.
An article in the Montana Stage University Extention’s MontGuide states that poison hemlock can invade perennial crops like alfalfa as well as contaminate harvested grain seed in grain fields. However, it is more common for poison hemlock to invade grazing areas than crop fields. It tends to grow in moist pastures and meadows where it has the potential to out-compete more desirable native species.
The article stresses that the largest impact of poison hemlock is its toxicity to humans and livestock, noting that serious livestock losses can occur when animals graze on fresh forage, harvested silage, or hay contaminated with poison hemlock.
Unfortunately, even if you are diligent about keeping your pastures free of poison hemlock, and the plant’s toxicity changes little if plants are fermented with silage or dried in hay. This means that poisoning can occur when animals consume the dried plant that has been baled in their hay. Likewise, since the seeds are highly toxic, they can be a source of poisoning when they contaminate cereal grains fed to livestock.
“The toxic compounds are coniine, g-coniceine, and related piperidine alkaloids. People may be poisoned by eating any part of a hemlock plant. Often, poisoning occurs after the victim confuses hemlock root with wild parsnips, hemlock leaves with parsley, or hemlock seed with anise. Whistles made from hollow stems of poison-hemlock have caused death in children” the USDA reports.
“Public health is a concern when dealing with poisoned animals because of the possibility of alkaloid residues in meat. Elimination of plant toxicants through the milk is a minor route of excretion but may be important when consumed by a calf or a human,” states the University of Kentucky, Department of Forestry and Natural Resources website.
The Ohio Perennial and Weed Guide, reports that this noxious plant typically grows in pastures, roadsides, ditches, waste areas, marshy areas, stream banks, and it has begun to appear as a weed in no-tillage fields. The species prefers rich soils and frequently grows in low or poorly drained areas. In other words, it will invade practically any space it can find. Plus, if all of this isn’t enough to send you out pulling and spraying, this weed also hosts many common diseases of alfalfa, celery, and carrot.
Now, don’t confuse this nasty little invader with all of our beautiful Canadian hemlock (Tsuga canadensis) that abound in the rocky hollows of the Hocking Hills region! While this graceful evergreen tree’s bark was one of the primary tree sources of tannins traditionally used for tanning hides for clothing during the 19th and early 20th centuries, poison hemlock is deadly poison to forest animals, pets, livestock and humans.
If you remember your Greek history and philosophy, you might recall that ancient the Greek philosopher Socrates, was probably the most famous individual to succumb to hemlock poisoning. In 399 BC, the 70-year-old was found guilty of heresy in Athens, and was sentence to death by hemlock, and was forced to drink the deadly poison. A famous 1787 painting, The Death of Socrates by Jacques-Louis David, depicts the philosopher surrounded by his students and adherents as he died.
According to the website, mentalfloss.com, poison hemlock is a flowering plant with fleshy, carrot-like roots that can grow up to 10 feet tall. All parts of the poison hemlock plant contain poison alkaloids. If ingested, conium will cause paralysis of various body systems. Paralysis of the respiratory system is the usual cause of death. Meanwhile, a victim can’t move but is aware of what is happening as the mind is unaffected until death is imminent.
The Ohio State University recently issued a poisonous plants warning that included poison hemlock as a headliner. Their website Buckeye Yard and Garden onLine (bygl.osu.edu) warns about the dangers of poison hemlock, noting that it is one of the nastiest non-native weeds found in Ohio.
Poison hemlock is a member of the carrot family, Apiaceae. They have umbel flowers. which are a key family feature. Apiacease have short flower stalks rising from a common point like the ribs on an umbrella.
Poison hemlock is a biennial weed, which means it takes two years for the plant to produce seed. First year plants that appear as low-growing basal rosettes, secretly producing a long, thick taproot to nourish its next stage of growth.
In its second year of life, the plant will “bolt” by producing erect, towering stalks and multi-branched stems topped with umbel flowers, which help to bolster their invasive powers. It can germinate at temperatures over 49 degrees and germinate in darkness as well as in light. In addition, poison hemlock is a prolific seed producers with a single plant responsible for over 38,000 seeds!
As mentioned earlier, poison hemlock contain highly toxic piperidine alkaloid compounds, including Connie and gamma-coniceine, which cause respiratory failure and death in mammals.
The roots are more toxic than the leaves and stems; however, all parts of the plant including the seeds should be considered dangerous, because the toxins really do not need to be ingested, they can also enter through the eyes or nasal passages to induce poisoning.
Even though the plant does not produce skin rashes, it should be handled with care because sap on the skin can be rubbed into the eyes or accidentally ingested during food handling.
According to the Ohio Perennial and Biennial Weed Guide, poison hemlock is native to Eurasia. It was, like many invasive species, introduced into North America as an ornamental but escaped cultivation and became naturalized throughout much of the United States and adjacent areas in Canada.
Currently, poison hemlock can be found all over Ohio and is especially prevalent in counties located in the central, south central, and southwestern portions of the state.
The Buckeye Yard Gardner onLine states that it is becoming too late to effectively manage this weed in southern Ohio, but there may still be time to reduce infestations in the central or north parts of the states.
However, the plants can be pulled, or chopped down, but the fallen plants must be removed and destroyed because once the flowers are mature, the seeds will still produce as the plant wilts on the ground. The guide also notes, that poison-hemlock is easily controlled with herbicides.
It is important to prevent the expansion of poison hemlock from small to large-scale infestations. If you discover poison hemlock on your property, MontGuide recommends that you map and monitor areas of current populations and scout for newly established plants. Eradicate infestations of one to a few plants immediately (preferably before the plant sets seed) by hoeing or spot-applying herbicide.
It recommends that the best way to contain large populations of poison hemlock is to spray the borders of the infested area with a herbicide, and points out that containment is a long-term management commitment since spraying does not eliminate or reduce the infestation level, it simply limits the weed spread.
Biological Control may be a consideration. The European palearctic moth, or hemlock moth (Agonopterix alstroemeriana [Clerck]), is the only approved biological control agent for poison hemlock in the United States. Although it is not known how the insect was introduced to the United States, the hemlock moth has become widely dispersed.
It’s only known host plant in Europe and the United States is poison hemlock. Moth’s larvae feed on foliage, buds, immature seeds, stems, and flowers in the spring and early summer. Unfortunately, the success of the hemlock moth in controlling poison hemlock populations is questionable, and decreases in poison hemlock density due to the moth have not been documented in the northwestern United States, the MontGuide observed.
If all of this is alarming to you, get out and help reverse the invasion, take back our roadsides and fields. If you see this plant growing in your pasture or hayfield your livestock could also be in danger. Remove it immediately!