Noxious Species of the Month

Poison Hemlock 

This month’s invasive species is one that recently was added to the county declared list as we have seen an increase in infestations in recent years. It is a poisonous species that is not only a danger to animals consuming it, but can be deadly to humans. Its name, Poison Hemlock, is very fitting. We decided to put it on our county declared list after seeing a sharp increase in the summer of 2015 in and around Gillette city limits. Hopefully this article will help to identify this harmful weed and give you some ideas to combat this species.

Poison Hemlock is a biennial species that grows from a seedling plant the first year to a four to eight foot plant the second year with a large taproot. The stems are stout and are covered in small purple blotches. Leaves are pinnately divided into three or four segments, and are very distinctive. Lower leaves clasp the stem while upper leaves will have a short petiole. Flowers are small and white in an umbel shape at the top of the plant. The plant also has a unique musky odor. It is usually found in poor draining soil near drainages and waterways. Hopefully these characteristics along with the pictures provided will help you correctly ID this nasty weed species. If you happen to find this species, the next step is knowing what control methods are available, so you can implement one and prevent the spread of this noxious species.

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Poison Hemlock can be control using mechanical, chemical, or biological methods. The species is a biennial that doesn’t grow from root segments, so mechanically you can chop the plant off at the ground level to kill this weed. Chemically there are a few herbicides that would work 2, 4-D and Banvel (Dicamba) would work well in most situations. Also, other herbicides such as Tordon 22K (Picloram), Plateau (Imazapic), and Escort XP (methsulfuron-methyl) could be used depending on the site at which treatment is taking place. There is a biological option with an insect, call the Defoliating Hemlock Moth, which attacks and chews on the plants stem, leaves, and flowers preventing or drastically reducing the amount of seeds the plant produces. Remember implementing an integrated weed management plan is your best bet for overall control. This could be applying an herbicide early in the summer to an infestation, then returning later in and summer and chopping down any remaining plants. This should lead to the best results and the greatest chance for eradication.

This is an important species to keep an eye out for not just for the health of your animals, but the well-being of you, your family, and other people that are on your property. This species being a biennial can be vastly reduced with only one or two years of treatment, as long you do not let it get out of hand originally. If you have any questions about this or any other noxious species, please give us a call or stop by our office.
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