By Ed Lentz

Weather has prevented many crops from being planted, but it has not affected weed emergence and early growth.

A weed that is thriving this spring is poison hemlock. It continues to be a problem weed in the area for city dwellers and farmers.

It may be found along roadsides, at edges of fields, on stream banks, along fence rows, and in other non-mowed areas.

At flowering, the plants are quite visible since they may reach heights of 6 to 8 feet. Because of its height, many people mistake it for hogweed, another invasive toxic weed that fortunately has not been found in Hancock County.

All parts of the hemlock plant (leaves, stems, roots, and fruits) are poisonous and may harm animals and people if enough is consumed. Fortunately, most livestock will not eat the leaves of poison hemlock when other feed and plant sources are available in a pasture.

However, toxins will still be present if plants are harvested and dried in hay. Thus, farmers do not harvest portions of hayfields or other potential forage areas infested with poison hemlock.

Hay buyers need to be careful that hemlock is not in the forage this year since they may not be as selective with the current severe hay shortage.

People may be poisoned by ingesting any part of poison hemlock. Poisoning cases have often occurred when an individual confused poison hemlock roots for wild parsnip, the leaves for parsley, and the seed for anise.

Children have died from playing with whistles made from the hollow stems of poison hemlock. Illness may also occur from absorbing the toxin through the skin and breathing the plant dust, so wear protective clothing (gloves, goggles, masks) when handling this plant.

Poison hemlock is an exotic plant species native to Europe and Asia. It was introduced into our country as an ornamental plant, which has escaped and has become an invasive plant moving across northwestern Ohio.

Clusters of tiny white flowers are borne on structures called umbels (they look like upside-down umbrellas) on the upper part of the flowering stalks. Flowering season will last from now through August.

Poison hemlock (Conium maculatum) tends to have a biennial life cycle (lives for two years). It grows as a basal rosette the first year and the second year it will bolt and produce a towering flower stalk. However, it may act like a short-lived perennial under optimal conditions.

It is a member of the carrot family, so it shares many characteristics with other weeds found in Ohio including native wild carrot, also called Queen Anne’s Lace (Daucus carota), and wild parsnip (Pastinaca sativa), a non-native plant.

Wild parsnip has yellow flowers; poison hemlock and wild carrot have white flowers. Poison hemlock may be distinguished from wild carrot flowers by looking at the stem.

Poison hemlock has purple spots or blotches and no hairs along the flower stem. Wild carrot has no blotches and is usually covered with hairs. Wild carrot plants are generally much shorter, and the initial flowering period is later than poison hemlock.

Leaves look similar between poison hemlock and wild carrot. However, at all growth stages, leaves of poison hemlock tend to be bluish-green, strongly pinnately compound (fern-like), and the leaflet tips are sharp-pointed.

Wild carrot leaves tend to be green, less pinnately compound, and have more rounded tips.

Poison hemlock spreads by seed. The dried fruit is easily moved to new areas by wind, birds and rodents.

Control methods include manual removal, mowing, tilling, or by herbicides. It is best to control while in the rosette stage, particularly in the fall.

Manual removal (including the roots) is practical when only a few plants are present in an area. Do not compost removed plants but place in plastic trash bags and dispose with other trash.

Do not take plants to city yard waste disposal sites, and make sure to remove plants before seed dispersal. Also, wear protective clothing, gloves and dust mask while handling.

Mowing or cutting with a weed-trimmer before flowering can be effective. Wear a dust mask to avoid inhaling toxins while mowing or cutting.

If poison hemlock plants have already gone to seed, note the current location. Plants will be back in these areas because of the seed. Use mechanical or chemical control on these patches before plants bolt two years from now.

Look for the fern-like rosette of leaves this fall or early next spring.

For herbicide control, plants should be treated in the fall, but spring application will be effective prior to flowering. Triclopyr, 2,4-D plus dicamba, and metsulfuron are effective herbicides that will not kill grass around poison hemlock.

Glyphosate (Roundup) may be used as a non-selective herbicide. Herbicide applications may need to be repeated for full control.

Be careful when working around poison hemlock. Pictures and additional information on poison hemlock may found at the following addresses: https://bygl.osu.edu/index.php/node/1218 and https://ag.purdue.edu/btny/weedscience/Documents/Poison%20Hemlock.pdf

Lentz is extension educator for agriculture and natural resources for the Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at lentz.38@osu.edu.

Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.

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