purple mint weed

Perilla Mint

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Did You Know?

A few facts:

  • Can be toxic to livestock
  • Can be used for medicinal and culinary purposes

How to get rid of perilla mint:

  • Remove manually
  • Treat with herbicides

Information by Rakesh Chandran, Ph.D., WVU Extension Service Weed Science Specialist

A Pasture Plant of Concern

Can you think of a plant with medicinal and culinary attributes, yet it’s often toxic to livestock? The weed in question is perilla mint ( Perilla frutescens). Perilla mint is becoming more and more common in pastures across West Virginia, causing concern for some.

Sometimes known as beefsteak plant, Chinese basil or purple mint, perilla mint was introduced from East Asia for its ornamental and culinary values. Usually, animals do not consume this plant, but poisoning can occur when more desirable plants are in short supply. After consumption, livestock can develop symptoms related to respiratory distress such as acute inflammation of the lungs, causing fatality in some.

Perilla Mint Identification

Perilla mint is an annual weed prevalent in pastures, periphery of woodlots and occasionally, in gardens and other disturbed fields. It can be easily identified by its ribbed, square stems and broad leaves, arranged oppositely with a toothed margin. The leaves vary in color from green to purple, especially when found growing in the shade, and boast a minty aroma when crushed.

It produces a spindly, hairy spike (raceme) bearing purple or white flowers in pairs. It comes to bloom from July to October and is especially toxic to animals when in bloom. Although not all varieties of perilla mint are considered toxic to animals, and its toxicity can vary due to environmental conditions, this plant must be controlled in pastures or other areas frequented by animals.

Perilla Mint Control

Perilla mint is most susceptible to control during the spring months when the plants are young and actively growing. Once they come to bloom, the plants become hardy and more difficult to control. As an annual, it can be removed mechanically by taking advantage of its shallow root system. Herbicides, such as 2,4-D (low-volatile ester formulations) or tank-mixtures containing both 2,4-D and dicamba (several formulations) along with a surfactant, provide good control when applied in early spring. Herbicides containing aminopyrlid (Milestone, Grazon Next) also provide effective control, but may persist in treated hay and in manure derived from animals that were fed with treated forage or hay.

Perilla Mint and Livestock

Perilla mint continues to be a problem weed in West Virginia pastures. Multiple animal fatalities were attributed to this weed in 2019 and 2018.

In fall 2018, a request was made by a veterinarian in the eastern panhandle region to help identify poisonous weeds in three different pastures where there were 35 cow fatalities. At all three locations, perilla mint was noted in large quantities where animals grazed actively.

Abnormal breathing is manifested in affected animals referred to as atypical interstitial pneumonia syndrome (AIP).

In 2018, excess moisture in the region caused in suboptimal growing conditions, which resulted in poor forage stand. Whereas in 2019, drought-like conditions in late summer and early fall resulted in similar conditions. Producers involved did not realize that until it was too late.

Such events require producers to monitor pastures for good stands of desirable plant species prior to grazing events and proper management of poisonous weeds at the same time. Other factors, such as high amounts of certain toxic metabolites like tryptophan/3-methylindole present in lush forages, nitrous oxides present especially around silos and allergens from moldy feed, also can cause varying levels of toxicity to animals.

The volatile oils present in perilla mint contain several compounds in varying amounts. Among these, the perilla ketones are considered to me most toxic to animals and are present in high quantities during later stages (August to October) of the growing season, especially in seeds.

Animal feeding studies have revealed that perilla mint in the seed stage was most lethal. Animal fatality occurred within three days when a 174-pound calf was fed with 5 pounds of perilla mint hay in the seed stage along with 5 pounds of regular hay. A 291-pound calf fed for a period of 15 days with similar amounts of perilla mint hay in the green stage collected in July, failed to demonstrate any clinical signs. A third calf weighing 398 pounds fed for three days with 14.5 pounds per day of dry hay collected in January of the previous year also failed to demonstrate any clinical signs.

Author: Rakesh Chandran, WVU Extension Weed Science Specialist
Last Reviewed: April 2020

Recommendations for the use of agricultural chemicals are included as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services does not imply endorsement by West Virginia University Extension Service nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

Perilla Mint Share this Did You Know? A few facts: Can be toxic to livestock Can be used for medicinal and culinary purposes How to get rid of perilla mint:

Perilla Mint

Trifoliate Orange

There are a number of weeds that can be found in lawns, turf, and landscapes that may be coveted for their culinary uses. Wild herbs are often at the top of the list. For example, wild sage grows high up in the Rocky Mountains and adds a delicious taste and aroma to many culinary experiences. Wild strawberries and wild garlic are prevalent in many parts of the country, and although they are not usually desired growths in landscapes, they are edible and have many culinary uses. Perilla mint, however, is not an edible herb. In fact, when perilla mint is found in pastures, it endangers cattle and other livestock as it is highly toxic to ruminants.

Perilla mint belongs to the same family as cultivated mint. Its scientific name is Perilla frutescens and is easily identified by the aroma and appearance. Like cultivated mint, perilla mint has a strong minty aroma. Plants can grow as tall as four feet, and leaves are almost heart-shaped and toothed at the edges. The undersides of leaves may be purplish in color, and stems are square in shape and hairy. Flowers may occur in clusters, which can give a mature plant a bottle-brush appearance. Individual flowers are small and white to whitish purple in color and hairy, perilla mint is often referred to as beefsteak plant, common perilla, purple perilla, purple mint, and Chinese basil, just to name a few.

This variety of weedy mint originated in southeast Asia. It is often cultivated and considered an ornamental plant in gardens because of its purple and green foliage. However, it is an escaped ornamental, which is what caused its spread and become a weedy pest mostly in the southeastern United States. It can be found in pastures, edges of woods, along farm structures, and along fence rows.

Plants are spread through seeds, and roots are a shallow and fibrous taproot. They emerge between late April and early June. This is also the best time to scout for perilla mint in pastures, farm structures, and fence rows. By late summer, plants are often too large to remove mechanically or with an approved weed killer.

All parts of the perilla mint plant are toxic to cattle, livestock, sheep, and horses. When ingested by livestock, the leaves contain ketones that cause respiratory distress. It is one of the most toxic weeds in the southeastern United States for cattle and livestock and so checking pastures and grazing areas for the distinctive-looking weed are critical. In most cases, grazing animals are not prone to eat perilla mint plants. However, in late fall and early winter when cattle and livestock are hungry, and there isn’t enough grass or greenery to eat, they will often consume this toxic plant.

Even though it is highly toxic for livestock, there have been some human uses for perilla mint. Their seeds have been used to make cooking oil and fuel. Native Americans used to use parts of the plant medicinally, although it is not currently recommended.

Because it is the most toxic known plant to cattle and livestock, eliminating the plant is very important. The best time to scout areas for these weeds are in late spring and early summer. Mowing them down before they produce seeds will prevent the spread of perilla mint. If it is not managed before late summer, it is crucial to provide an adequate food source to grazing animals to avoid them from consuming them. Once they begin flowering in late summer, they are considerably more deadly to farm animals. Broadleaf herbicides specific to pastures are also a reasonably effective means of controlling perilla mint.

Perilla mint (Perilla frutescens) research and weed control advice in the Broadleaf Lawn Weeds Directory at the WinLAWN Lawn Care Guide. ]]>