Hemp Dogbane (Apocynum cannabinum) Toxicity

Sep 29, 2016

By Joel Hunter

A recent apparent hemp dogbane poisoning of some horses serves as a reminder for recognizing and managing this common perennial weed.

Most farmers can identify hemp dogbane. However, cases of livestock poisoning still pop up occasionally like it seems to have recently in Northwestern Pennsylvania. Hemp dogbane generally grows to about 3 feet high, has purplish to red stems, exudes milky sap when broken/damaged, and it’s rhizomatous (creeping). The convex flower clusters consist of very small, five-lobbed flowers are white to greenish- white and ultimately develop into bean-like seed pods.

Hemp Dogbane (Apocynum cannabinum) Toxicity

The type of poison in hemp dogbane is Cymarin (a glycoside), a potent compound that disrupts the heart function. The leaves are poisonous at all times, even when they are dry. Signs of poisoning include rapid pulse, vomiting, blue coloration of mucous membranes, progressive body weakness, convulsions, coma, and death. Sheep are most frequently affected, but cattle and horses can also be affected, particularly when other forages are scarce. Death from hemp dogbane poisoning may occur six to 12 hours after ingestion. A lethal dose for sheep is about one-half to 1 ounce per 100 pounds of body weight. A lethal dose for cattle and horses is slightly less at about one-half to three-fourths ounces per 100 pounds of body weight. Subsequently poisonings and death can occur rapidly after ingestion of moderate amounts of leaf material. Finally research results show that hemp dogbane control may be best achieved by systemic herbicide applications at flowering or after followed by clean-up broadleaf systemic post applications the following season (in corn or other some other grass crop.) Check the Penn State Agronomy Guide for details on herbicide options in a particular crop.

Source:psu.edu

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