August 20, 2020 Posted by: Justin Miller
AUBURN UNIVERSITY, Ala. – In some areas of the state, the hot, dry weather may have limited the availability of some forages. These conditions often tempt livestock to consume anything that is green. Some poisonous plants have become masters at surviving these conditions. Perilla mint is one of the most dangerous.
An escaped ornamental, the leaves of perilla mint may look more attractive to grazing livestock. David Russell, an Alabama Extension weed scientist, said perilla mint has a bold color and aroma.
“Plants have serrated leaves, opposite each other along a square stem. They are often purplish in color on the undersides,” Russell said. “Perilla is a true mint in the Lamiaceae family, and the leaves give off a minty aroma when crushed.”
The toxic element in perilla mint is perilla ketone. The entire plant is poisonous but the flowering structures are the most toxic. Perilla mint usually grows in semi-shaded areas, such as wooded understories and in low-lying swales and stream zones.
“These are areas where livestock often congregate during the heat of the day,” Russell said. “Plant populations are also often found in disturbed areas of fertile soil such as feedlots, barns and around hay rings. Plants may reach 4 to 6 feet high in these areas.”
Poisonous to Livestock
When consumed, the toxin in perilla mint causes fluids to collect in and around the lungs in a variety of animals. Most cases of poisoning happen in cattle, horses and sometimes goats and sheep.
Soren Rodning, an Alabama Extension veterinarian, said that perilla mint is usually not an animal’s first choice for grazing.
“Normally, animals won’t graze perilla mint unless there is no other available forage,” Rodning said.
Cases of poisoning happen sporadically in the late summer or fall. When livestock ingest the plant, the effects can be deadly. Producers should note that birth defects in calves can occur when hay containing perilla mint is fed to cows early in pregnancy.
Signs of Perilla Mint Poisoning
Producers should check their livestock regularly for symptoms of poisoning. Animals will exhibit signs of major respiratory distress. They may also grunt while exhaling or have a nasal discharge and an elevated temperature.
“Treatment is usually ineffective once symptoms become severe. So, contact your veterinarian immediately if you suspect perilla mint poisoning,” Rodning said. “Producers should handle poisoned livestock gently and quietly. This can reduce further respiratory complication and subsequent death.”
Scouting for perilla mint is best done between April and June, before the reproductive stage of their growth. However, producers should continue to look for these plants throughout the summer and fall. Russell said currently, plants are starting their reproductive stage.
“Plants may be identified by their upright flower spike, usually 4 to 6 inches long,” Russell said. “These spikes will produce many white-to-purple flowers during late summer.”
Once a plant goes dormant, they usually remain intact over the winter. These dormant plants can help a producer identify areas where they may have to control the following season.
There are several physical and chemical options available to control perilla mint, including both postemergence (table 1) and preemergence herbicides (table 2).
“If using products listed with soil activity, avoid using the treated forage as compost or mulch,” Russell said. “Manure and urine from animals consuming grass or hay treated with these products could cause injury to sensitive broadleaf plants.”
As with any chemicals, Russell reminds growers to always read and follow the label recommendations.
Postemergence Herbicide Control Options for Perilla Mint
Each of these postemergence products require the addition of 0.25% v/v non-ionic surfactant.
|Herbicide||Trade Name||Rate (amount product/A)|
|2,4-D||2,4-D Amine 4||32 fl oz|
|Aminopyralid + 2,4-D||GrazonNext HL||19 fl oz|
|picloram + 2,4-D||Grazon P+D||16 fl oz|
|Glyphosate||RoundUp (41% a.i.)||24 fl oz|
|dicamba + 2,4-D||Weedmaster or Brash||16 fl oz|
“Each of these postemergence herbicides (those applied to above-ground plant foliage) are generally safe on established grass species except for Roundup,” Russell said. “Roundup is non-selective, meaning it will likely damage vegetation that it comes in contact with.”
Russell only recommends Roundup as an option if spot-spraying small areas or spraying in areas where no other desirable vegetation is near.
Preemergence Herbicide Control Options for Perilla Mint
Rainfall is required to activate the chemical into the soil.
|Herbicide||Trade Name||Rate (amount product/A)|
|aminopyralid + 2,4-D||GrazonNext HL||19 fl oz|
|picloram + 2,4-D||Grazon P+D||32 fl oz|
|dicamba + 2,4-D||Weedmaster or Brash||32 fl oz|
“If a known population exists from previous years, there are several forage-labeled herbicides that can be applied preemergence (prior to weed seed emergence),” Russell said. “You’ll notice these are also recommended for postemergence, but a portion of these products have soil residual activity.”
Physical Control Options
In addition to chemical options, producers can remove perilla mint by hand or by mowing. However, Russell said in order to use these options, producers must be timely.
“Hand pulling or mowing are physical control measures that are also effective,” Russell said. “However, these must be done prior to flowering in late summer to avoid seed production and new plants the following year.”
Livestock After Treatment
After an area with perilla mint receives treatment, producers may want to limit or stop grazing in that area. According to Russell, there is little known information about toxicity levels and how much it takes to be detrimental to grazing livestock.
“If treating large populations, I would recommend removing livestock until the plants have completely died, especially if desirable forage is limited.” Russell said. “This will help avoid the risk of ingestion and poisoning.”