OSU Extension warns beef cattle producers of toxic weed

The Osage County OSU Extension Office recently learned of several head of cows and calves dying from consuming a toxic weed called “Perilla Mint,” also commonly known as “Beefsteak Plant.” The cattle belonged to a beef cattle producer in eastern Osage County. Last known, there have been five cows and three spring-born calves that have died with many more showing symptoms and not expected to survive.

The plant is an escaped ornamental plant native to East Asia. Besides the minty smell, another plant identifier is the square stem, a characteristic of all mint plants. While the plant itself is toxic, the flower/seed head is most toxic and also more palatable than the rest of the plant, which is not palatable. Care should be taken if the weed is present in a pasture. This plant will most likely be found near creeks/rivers and other wetland type locations.

Normally, the plant does not lend itself to grazing because of palatability issues unless there is limited forage available to the cattle, according to officials with the Osage County Extension Office. In the known current cases, forage availability is not an issue. However, the cattle were recently relocated to the pasture with plants located in brush along a creek bank. The cattle had no previous experience with the plant and it was possibly more palatable than normal due to recent weather conditions, which may have led to its consumption.

The Area Agronomy Specialist recommends the following:

1. The best option would be to focus control strategies next year when the plant is young and actively growing.

2. If needing to take action now, it is recommended to finely shred and scatter plants with a brushhog. Depending on the stage of production, the plant may try to regrow before frost. It is advisable to spray with a herbicide and hold cattle off until brown-out. Plants can become more palatable immediately following phenoxy herbicide applications. This should likely be 5-10 days or slightly longer. It will be necessary to hold cattle off of plants until desiccation occurs following frost.

The plant is easily controlled with many herbicide options in May and early June, according to university literature from states in the southeast, like Tennessee. It will likely be more difficult to kill plants now that they have gone reproductive.

Regarding animal health, the plant is toxic to all grazing animals, not just beef cattle. It causes pneumonia-like systems and likely goes unrealized when one or maybe two acute cases are experienced. It can cause rapid death if enough of the plant is consumed at once.

Ranchers should not expect to find this plant in areas outside of wetlands and riparian areas. The plant has been reported in the area west of Burbank, so it appears not to be confined to the Crosstimbers of eastern Osage County. Neighbors east of Osage County should also be looking for the plant.