“Don’t Wait Too Late”
Last August I had several calls and folks in the office asking about perilla mint. Many were concerned because they heard it was poisonous, which it is, and were afraid it would spread if not controlled, which it will. Unfortunately, August was too late to do much with these weeds.
Perilla mint is a summer annual meaning it germinates in late spring and early summer as temperatures warm up. If you know what you’re looking for, you may have seen this weed for about the last month or two in pastures and hayfields. Waiting until the plant grows upright and goes to seed makes it easier to identify, but much more difficult to kill.
Perilla mint causes more cattle deaths in Tennessee than any other toxic plant. All plant parts are toxic, especially the flowering structures. Dried plants in hay can be toxic, but the greatest risk is associated with consumption of fresh plant material, especially if flowers and fruit are present. Cases of poisoning from these weeds are a concern during the late summer and early fall when other grasses and forages might be in short supply and the perilla mint is flowering.
Cattle will normally not feed on these toxic weeds unless there is a shortage of other feed. Therefore, it is crucial to have a ready supply of quality feed available for farm animals during this time of the year. Don’t wait until you already have problems with toxicity to manage this weed.
Cases of animal poisoning from consuming perilla mint are usually seen in late summer and early fall after grazing of the plant. Cattle, horses, and sheep are the most commonly affected animals. These animals will exhibit signs of respiratory distress. Clinical signs include labored breathing, a grunting sound when exhaling, and possible nasal discharge and elevated temperature.
Once these symptoms begin to appear, treatment is usually ineffective. Injections of antihistamines, steroids, and antibiotics may be given. Affected animals should be handled gently to prevent further respiratory complications.
The best time to scout for and control perilla mint is early summer when the plants are small. The distinctive minty odor and oval, green to purple leaves with toothed margins are all characteristics that help in the identification of perilla mint. It is very difficult to control perilla mint in late summer and early fall when it also becomes the most dangerous to livestock. Again, don’t wait until the plant is two feet tall to try and kill it with herbicide.
If control measures were not taken early, it becomes even more crucial in late summer to maintain an adequate supply of quality feed for cattle and other farm animals so they will not feed on these toxic weeds.
Several of the broadleaf pasture herbicides, such as Brash, 2,4-D, GrazonNext HL, and Banvel should provide excellent control if applied timely and at the correct rate. Don’t wait until you have a field overgrown with weeds to try and spray, or until you have dead animals to think about poisonous plants. If you have any questions regarding perilla mint or any other poisonous plant, feel free to call me at the University of Tennessee Extension office at 615-735-2900.
Article submitted by Chris Hicks – Smith County UT Extension Agent
