Perilla mint, also known as beefsteak plant or rattlesnake weed, is an annual plant in the mint family which is toxic to livestock. Although livestock usually will not eat perilla mint if other forages are available, the chances of consumption increase when baled in hay or harvested in green chop. It also becomes more dangerous in late summer and fall when other forages may be declining in availability especially in overgrazed pastures or when drought limits forage supply.
Perilla mint can be identified by the distinctive purple-green leaves and stem. The plants also emit a distinctive minty odor. Leaves are oval shaped and have toothed margins. The plant will grow to be ½ to 2 feet tall and has a square stem. Flowers occur in terminal clusters giving a ‘bottle-brush’ appearance.
Individual flowers are small and white. Most often perilla mint occurs in shaded areas of pastures and along fence rows and on the edge of timber, rather than in full sunlight.
This plant is extremely toxic to all kinds of cattle, sheep, and horses. Perilla mint is considered one of the most poisonous plants in the multi-state region. The toxin remains viable even in dry hay, but most poisonings occur from consuming green plants. Livestock usually avoid this plant, but poisoning does occur when forage supply becomes limited from a drought or overgrazing.
To avoid toxicity problems, avoid harvesting forages in areas contaminated with perilla mint. Mow perilla mint plants before seeds are produced to avoid livestock grazing and to prevent weed population growth. Mowing has limited effectiveness because clipped plants are able to resprout and still produce seed, and mowing when seed has set can spread it to new areas.
Several of the broadleaf pasture herbicides, such as Weedmaster (active ingredient (a.i.) 2,4-D and dicamba), Grazon P+D (a.i. 2,4-D and picloram), Remedy (a.i. triclopyr), Crossbow (a.i. 2,4-D and triclopyr) 2,4-D, and others should provide excellent control if applied timely and at the correct rate. The best time for control is April thru June before plants begin to set seed.
For more information please call the MU Howell County extension office at 417-256-2391.