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Poison Hemlock:
A toxic, noxious weed, often found in Ada County forage plots.
Poison Hemlock is a noxious weed that contains toxic alkaloids in all parts of the plant, including the roots.
Poison Hemlock typically grows on ditch-banks and poorly drained soils, and becomes a threat to grazing animals if they have access to it. Poison Hemlock is a biennial plant that spends the first portion of its life cycle as a low growing, fern like, rosette. There will be purple splotches on the stems, and the leaves are dark green, and have a wet or oily look. Poison Hemlock has a strong, musty, disagreeable odor as well. Mature stalks can grow to be as tall as 12 feet! The white flowers, and eventually the seeds, are arrayed in an “umbrella like” pattern at the ends of the stalks.
While most grazing animals will avoid this plant due to its unpleasant odor and taste, they can accidently ingest the plant while grazing. In the early spring, Poison Hemlock is one of the first plants to begin growth, and can be consumed with forage grasses, as they are not yet very tall. The toxic alkaloids in this plant are damaging to animals, and pose a health risk to them. The toxins cause nervous stimulation, and progresses to respiratory paralysis. Poison Hemlock is an unnecessary risk to your grazing animals.
There are several herbicides labeled for general weed control in grass pastures, and the most common ingredient in them is 2,4-D. Poison Hemlock is very susceptible to herbicides that contain 2,4-D,. Common, general use herbicides labeled for use on grass pastures are readily available at most farm and ranch stores. There are many herbicides to select from for pasture weed control, so unless you understand these products, contact a licensed applicator or professional consultant for specific recommendations before use. Please pay attention to any grazing restrictions discussed on the herbicide label, and it is a good idea to observe grazing animals that have access to treated Poison Hemlock. Herbicides that contain 2, 4-D, often leave a “salty” taste on the plant, and can make treated plants more attractive to grazing animals for a few days. Until the treated plants dry, and degrade, they are still poisonous. Make certain your animals are not feeding on any Poison Hemlock.
An excellent strategy is to treat a portion of your pasture or pastures for Poison Hemlock, and keep animals away from these areas for several days. Rotating animals out of treated pastures for two to three weeks is a good pasture management practice anyway. Pastures produce more feed when allowed to recover between grazing episodes, and will produce more feed per year than pastures that are constantly grazed. Cross fencing, or rotating livestock from pasture to pasture, will let you treat for weeds when animals are not present, and won’t be for a couple of weeks. This will allow treated Poison Hemlock plants to dry out and degrade, before grazing resumes. As always, do not allow herbicides to drift into water ways when treating this plant.
If you have questions regarding the identification and control of Poison Hemlock, or need specific herbicide recommendations or information about herbicide treatments, we encourage you to contact us. Ada County Weed Control has extensive experience controlling this plant, and will provide the information you need to do so as well.
Ada County Noxious Weed Control
975 E Pine Ave.
Meridian ID 83642
(208) 577-4646
M - F 7:30 a.m. - 5:00 p.m.
21 New Weeds.
Idaho has added 21 weeds to our list of Noxious Weeds.
Most of these plants are in a new classification called Early Detection/ Rapid Response (EDRR). Early Detection/Rapid response plants, are plants that cannot be placed in a containment plan. Containment is for plant species that we have no expectation of eradicating, but cause serious problems to Ada County residents, and that need to be addressed.
The plan behind the control of these new invasive plants is to destroy them as soon as they are discovered in Ada County; however, the exact mechanism we use to do this is still to be debated in a public forum. Ada County Noxious Weed Control is planning to public meetings to allow for comment on how the public would like us to accomplish these goals.
At the present time it is important to know what these plants look like, and if we have any of them in the county that we were not aware of. To this end, we wish to show you what these plants look like and discuss in which habitats they might be found.
The following is a link to the University of Idaho’s Interim Guide to Idaho’s Noxious Weeds. This document is not yet available as a finished booklet, but it may be printed from the link.
2007UI-ISDAweedbook
Aquatic Noxious Weeds:
We have several new aquatic plants that are infesting the waterways and ponds in Ada County. In most instances, these plants are in people’s ornamental ponds. These problem plants make for unsightly water features, and in waters used for swimming, they represent a safety hazard from entanglement, and drowning. Typically these problem plants are very long stemmed, and are very numerous in the water. It is easy to see how they are a hazard to swimmers, and can interfere with boating, irrigation, and other water uses.
It is our responsibility, to make every effort to keep them from spreading into our rivers and streams. Eurasian watermilfoil is a plant that has been on the Noxious Weed List since 2005. Ada County Noxious Weed Control has made numerous treatments to this plant, as well as participating in a program supported by the Idaho State Department of Agriculture. We have had some successes in our treatments, but are finding complete control in a few waterways elusive. By continuing these projects and programs, we feel that our results will improve over time.
New plants to the Noxious Weed list are the following:
Aquatic plants:
1. Parrotfeather Myriophyllum aquaticum Category: Control
2. Brazilian Elodea (Egeria Densa) Category: EDRR
3.Hydrilla Hydrillaverticillata Hydrocharitaceae, Category: EDRR
4. Water hyacinth Eichhornia crassipes Pontederiaceae, Category: EDRR
The following are new plants to the Noxious Weed List, and are categorized by the recognized management principles:
5. Giant hogweed Heracleum mantegazzianum, Category: EDRR
6. Yellow devil hawkweed Hieracium glomeratum, Category: EDRR
7. Squarrose knapweed Centaurea virgata var.squarrosa, Category: EDRR
8. Policeman’s Helmet Impatiens glandulifera, Category: EDRR
9. Tall hawkweed Hieracium piloselloides, Category: EDRR
10. Giant knotweed Polygonum sachalinense, Category: Control
11. Bohemian knotweed, Polygonum bohemicum, Category: Control
12. Japanese knotweed, Polygonum cuspidatum, Category: Control
13. Mediterranean sage Salvia aethiopis, Category: Control
14. Small bugloss Anchusa arvensis, Category: Control
15. Vipers bugloss or Blueweed Echium vulgare, Category: Control
16. Hoary alyssum Berteroa incana, Category: Containment
17. Oxeye Daisy Chrysanthemum leucanthemum , Category: Containment
18. Houndstongue or Beggar’s ticks Cynoglossum officinale, Category: Containment
19. Plumeless thistle Carduus acanthoides, Category: Containment
20. Salt cedar Tamarix sp. Category: Containment
21. White Bryony Bryonia alba, Category: Containment
Most of these plants are not known to be in Ada County, at the present time. The exceptions to this are the Parrots-feather milfoil, Houndstongue, Salt Cedar, and Bohemian and Japanese knotweed.
Ada County has made treatments to these varieties of noxious weeds, with the exception of the Houndstongue. The treatments have been made at the request of either private landowners, or for public agencies, such as the Bureau of Land Management. We will continue these treatments and find new ways to treat these less familiar plants. We attend training and informational seminars on a regular basis, to learn how others are controlling these plants, and how Ada County can adopt and implement Integrated Pest Management principles needed to control these plants. It is this way we provide effective and environmentally conscientious weed control to the residents of Ada County.
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