Like many carrot family weeds, spotted water hemlock populations in Manitoba have been spreading, likely due to wet conditions over the last several years. Managing populations in hayland and pasture is recommended since hemlock species are extremely poisonous to humans and livestock.
Identifying Spotted Water Hemlock
Proper identification is important since spotted water hemlock looks similar to water parsnip, another carrot family weed commonly found growing in wet areas across the province.
All parts of the hemlock plant are poisonous. Young leaves and re-growth after treatment may attract livestock, especially if other food sources are limited or less palatable. Access to water hemlock by livestock should be restricted while populations are being managed.
The following methods can be used to control or suppress spotted water hemlock in hayland and pastures:
- Hand pulling (wear gloves!). Pulled plants can be left in the sun to dry. Once dry, plants can be disposed of in an area away from people and livestock.
- Repeated cutting or mowing.
- Herbicide spot treatment or foliar application. Glyphosate, 2,4-D and picloram have activity on water hemlock. Refer to the label for grazing and haying restrictions.
Feeding Hay and Greenfeed with Water Hemlock to Livestock
Feeding hay with some water hemlock in it to livestock is okay, according to research from the US, as long as the hay (and hemlock) is thoroughly dried. The curing process allows the toxins in water hemlock to dissipate, reducing the risk of livestock poisoning. Hay with water hemlock should either be fed last to allow for maximum dissipation of the toxins or occasionally interspersed with hay not contaminated with water hemlock. If possible, contaminated hay should not be fed continuously to pregnant livestock, as there is evidence that chronic exposure to water hemlock toxins can result in birth defects.
Unlike hay, greenfeed contaminated with water hemlock should not be fed to livestock or used for silage or baleage. Testing done in Oregon found that ensiling causes certain toxins to accumulate rather than dissipate and remain at levels that are unsafe for livestock consumption.
Need help with plant identification?
Pictures can be emailed to [email protected] or samples can be submitted to your local Manitoba Agriculture office (www.gov.mb.ca/agriculture/crops/crop-diagnostic-services/).