Perilla mint [Perilla frutescens (L.) Britt.] is an annual plant in the mint family that is toxic to livestock. Although cattle, horses and other livestock usually will not eat perilla mint if other plants (forage grasses, for example) are available, the chances of consumption increase if this toxic plant is baled in hay or harvested in green chop or other similar forages. Most often perilla mint occurs in shaded areas of the pasture, rather than in full sunlight. According to "Poisonous Plants of the Southeastern United States," seeds of perilla mint are often found in stomachs of deceased animals.
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 prevent weed population growth. Several of the broadleaf pasture herbicides, such as Weedmaster, Grazon P+D, 2,4-D, Banvel, Remedy, Crossbow, etc. should provide excellent control if applied timely and according to the label rate. Sometimes spraying makes a plant more palatable so management may dictate removing livestock from problem areas for a sufficient time frame to allow plants to decompose.