Spring is a Good Time to Scout Pastures for Toxic Weeds

Spring is a Good Time to Scout Pastures for Toxic Weeds

Perilla mint, a plant toxic to livestock, in a pasture. Photo Credit: Jennifer Bearden

Spring is a good time to walk your pastures to scout for toxic weeds. Summer pastures are just greening up, but are still short, and warm season weeds are just beginning to pop up out of the ground.  In almost every case, it is much easier to kill small weeds as young plants, than to wait until summer when they are more mature, established plants.

What makes a plant toxic to livestock?

Certain plants naturally contain chemical compounds that are poisonous to animals.  Certain conditions can also cause plants to accumulate toxins that can lead to illness or even death when consumed.  The degree of relative danger of toxic plants depends on plant prevalence, toxicity, and palatability.  Some toxic plants are acutely toxic, meaning symptoms occur immediately after consumption.  Other plants, cause chronic toxicity with prolonged exposure.  These symptoms occur as toxins slowly accumulate in the animal from ongoing consumption.   The symptoms of toxic plant poisoning in livestock can also vary greatly.  Some plants just make the animals uncomfortable or sick while others result in death.

Animals do not normally eat toxic weeds when adequate fresh forage is readily available, or is sufficiently supplied in the form of hay. Late fall and early spring, when both pastures and hay are in short supply, are the times of the year when livestock poisoning are more common.  Toxic weeds can also be baled in with hay, and be accidentally fed to livestock .  Overgrazing pastures can lead to the deadly combination of increased weed populations and hungry animals resulting in toxic plant consumption.  Introducing naive animals to new pastures that have toxic plants can also lead to poisoning, as these animals graze unfamiliar plants.

A few plants are palatable to livestock, such as red maple and cherry laurel trees, that become toxic when the leaves wilt.  While uncommon, there are situations such as after a storm or when cleaning out fence rows, when livestock gain access to large limbs or tree piles with wilting leaves. Some weeds can become toxic following fertilization, if they accumulate nitrates in the leaves. Also, during drought, toxins can concentrate in plant tissue causing them to become acutely toxic to livestock.  Even herbicide applications can cause plants to accumulate toxins and, at the same time, become more palatable to animals.

Examples of common toxic plants in the Northwest Florida area include:

  • Pokeweed or Pokeberry – results in gastrointestinal issues (cramping, diarrhea, and convulsions)
  • Oleander – extremely toxic plant that can poison both livestock and humans in just a few hours
  • Bracken fern – is a native plant that contains an enzyme which inactivates Vitamin B1 over time
  • Cherry Laurel – affects the blood of the animals when wilted leaves are consumed
  • Lantana – affects the skin by making animals hypersensitive to sunlight
  • Coffee Weed – affects skeletal muscles, kidney, and liver
  • Black nightshade – causes irritation of the mouth and intestines
  • Perilla mint – affects the respiratory system
  • Showy crotalaria – affects the liver
  • Creeping indigo – wide range of non-neurological to neurological symptoms

Creeping Indigo. Photo Credit: Jennifer Bearden

This is a relatively short list of common toxic weeds in the Panhandle. There are a number of resources available to learn to identify them, and how they affect livestock.

  1. Download:  Poisonous Plants of the Southeastern United States
  2. You can purchase the UF/IFAS pocket ID card deck that provides identifying characteristics for 35 common poisonous pasture weeds to carry with you out in the field to compare with plants you see:   Poisonous Pasture Plants of Florida
  3. Dr. Dennis Hancock, UGA Extension Forage Specialist developed a YouTube video series called Plants that are Poisonous to Livestock with excellent descriptions of common toxic pasture weeds:

 

Livestock poisonings from grazing toxic plants are relatively rare, but it is important for livestock owners to become unfamiliar these plants and the conditions that make them toxic.  For help identifying toxic weeds in your pastures, and for weed control recommendations, contact your local extension agent.

 

Scout Pastures for Toxic Perilla Mint this Fall

Perilla mint in a pasture in Jackson County.  Photo credit:  Doug Mayo

Perilla mint in a pasture in Jackson County. Photo credit: Doug Mayo

Documented distribution of perilla mint in Florida.  Source:  Atlas of Florida Vascular Plants.

Documented distribution of perilla mint in Florida. Source: Atlas of Florida Vascular Plants.

Perilla mint (perilla frutescnes) aka Beefstakeplant is a toxic weed that typically grows in shady, to partially shaded areas, damp spots, woodland edges, and  fence-lines of pastures in the Southeast. Positive identification of this weed has been made in a number of Panhandle Counties, as can be seen in the map developed by the Atlas of Florida Vascular Plants.  This does not mean that this weed is not present in the other counties, just that the herbarium has not received samples from those counties.

Livestock will typically avoid grazing perilla mint.  You may have some growing in your pastures, and still not have a problem.  Typically livestock poisonings occur in the fall and early winter, when livestock can become hungry from an inadequate feed supply.  The best way then to prevent livestock poisoning from perilla mint and other toxic weeds, is to make sure there is an ample supply of fresh grass or hay continuously available.  Even so, it is also advisable to scout for this and other toxic weeds and control them with herbicides labeled for pasture use.

The J.B. Taylor Diagnostic Laboratory in Elba, Alabama has recently received necropsy samples from cows that died from grazing perilla mint on two different farms.  Dr. Joel Cline, DMV, Director of the lab, reports that August through October is typically when they diagnose cases of perilla mint poisonings.  He said that “Livestock poisoned by perilla mint have respiratory problems from lung lesions,  with symptoms similar to pneumonia.”  He advises, “Handle cattle gently if you suspect they have grazed perilla mint.  Many times the stress of moving cattle too quickly to the cowpens for treatment is the ultimate cause of death.”

Identification of Perilla Mint

Undersid of a perilla mint leaf showing the reddish to purple color that is unique to this member of the mint family.  Photo credit:  Doug Mayo

Underside of a perilla mint leaf showing the reddish to purple color that is unique to this member of the mint family. Photo credit: Doug Mayo

As a member of the mint family of plants, it has the typical square stems.  Leaves are oval, pointed and somewhat heart shaped with serrated edges.  The stems and undersides of leaves have a purple to reddish hue.  Perilla mint typically grows to a height of three to four feet tall.  Flowers are pink to purple, and grow along terminal spikes up to six inches long.

Perilla mint has square stems with a reddish to purple tint.  Photo credit:  Doug Mayo

Perilla mint has square stems with a reddish to purple tint. Photo credit: Doug Mayo

Perilla mint  Photo Credit: Tennessee Vascular Plants Eugene Wofford

Periila mint flower.  Photo Credit:  Tennessee Vascular Plants Eugene Wofford.

Perilla mint flower. Photo Credit: Tennessee Vascular Plants Eugene Wofford.

Control of Perilla Mint

While livestock may not normally graze perilla mint, why not remove the risk?  Even one livestock death, or serious illness is too many.  Perilla mint can be controlled with several common herbicides, labeled for pasture use.  GrazonNext, Milestone, Weedmaster, and 2,4-D will provide good control of Perilla Mint .  (Source:  UT Extension Weed Management in Pasture and Hay CropsAt the very least these weeds should be mowed, or physically removed before or during flowering, to prevent seed production.

To learn more about perilla mint, download:

Poisonous Plants of the Southeast: Perilla Mint

Perilla Mint Toxicosis

Beefsteak-plant, Perilla Mint