Category Archives: Weed Control

Start looking now for Perilla Mint

Start Looking Now for Perilla Mint

Dr. Michelle Arnold, DVM (Ruminant Extension Veterinarian, UKVDL), JD Green, PhD (Extension Professor [Weed Scientist], UK Plant and Soil Sciences Department), Megan Romano, DVM (Clinical Veterinary Toxicologist, UKVDL)

Poisonous plants can be responsible for considerable losses in livestock although many cases go unrecognized and undiagnosed due to a lack of knowledge of which plants are dangerous and the wide range of signs that may be observed after consumption. The risk posed to animals by a particular plant depends on a variety of factors, including how much of the plant is consumed and over what time period; the stage or maturity of plant growth; which parts of the plant are eaten; whether the plant is green or dried; and the animal’s age, species, and in some cases breed. Most weeds are tough and unpalatable, and cattle will not consume them unless baled in hay or the pasture is limited due to drought or overgrazing and there is little else to consume.

If cattle on pasture suddenly develop symptoms such as diarrhea, salivation or slobbering, muscle weakness, trembling, incoordination, staggering, collapse, difficulty breathing, or rapid death, then poisoning due to plants or any number of other toxicants should be high on the list of possible causes.

Oftentimes poisonous plants affect just a few cattle in the herd. Cases occur more often shortly after animals are moved to a new field. The severity of signs primarily depends on how much of the plant or other toxicant is consumed over what time period (the rate of consumption). If plant poisoning in livestock is suspected, the first thing to do is call a veterinarian, since prompt treatment is critical to the animal’s chances of survival. Until the veterinarian arrives, keep the affected animal quiet and confined where a physical examination can be performed, and treatment given. Other animals should be moved as carefully as possible from the pasture where the suspected poisoning occurred until the cause of illness has been determined. Prevention involves learning to recognize poisonous plants, implementing effective weed control and pasture improvement, and offering supplemental forage or feed when pasture is limited so cattle are not forced to graze toxic weeds. A common summer weed in Kentucky that can cause problems in livestock is perilla mint (Perilla frutescens), also known as perilla, purple mint, mint weed, beefsteak plant, and wild coleus. Severe lung damage can result from ingestion of the leaves and seeds, resulting in “atypical interstitial pneumonia” or AIP. Perilla is a summer annual that thrives in late summer when pastures are frequently dry and dormant. The opposite ovate leaves attached to square stems can be dark green to purple with toothed leaf margins.

Perilla mint has a distinctive mint aroma, with opposite dark green to purplish leaves that have serrated leaf margins attached to square stems.  Mature plants reach 2-3 feet tall and produce small, white to purple flowers with abundant seeds.  Pictures courtesy JD Green

Perilla reaches 20 to 30 inches in height at maturity with opposite leaves. The white to whitish-purple flowers and subsequent seed which occur in late summer are attached to terminal spikes. The plant also has a distinct, minty odor, especially as it becomes more mature. The weed prefers shaded areas along creeks, in fence rows, and the edges of the woods and partially shaded pastures. Once it becomes established, perilla produces many seeds and large colonies can develop in succeeding years. The early pre-seed stage of the weed is of relatively low toxicity while the flowering and green seed stage plant is most toxic, especially the seeds themselves. The time of year when perilla reaches the seed stage often corresponds to periods when desirable pasture grasses are scarce and the weather is hot, enticing cattle to consume plants they normally avoid, especially those in shady areas. The flowering or seed parts of perilla mint contain the highest concentration of toxic agents, perilla ketones. Perilla ketones are toxic in both fresh plants and in hay. Once ingested, they are absorbed into the bloodstream and carried to the lungs. Within the lungs, perilla ketones and other similar compounds are then activated, damaging the cells lining the air sacs and severely impairing gas exchange and lung function. This lung damage causes the animal to develop acute respiratory distress syndrome (ARDS), a sudden and dramatic onset of severe breathing difficulty. Treatment is of limited value and severe cases seldom survive. 

Photo used with permission from Dr. Alan Doster, University of Nebraska-Lincoln

The clinical signs of acute respiratory distress syndrome include a sudden onset of open-mouth breathing with the head and neck extended, nostrils dilated, a sway-back appearance, tongue protruding with foam coming from the mouth, an open-shouldered stance, and sometimes aggression. Breathing is shallow and rapid (35-75 breaths per minute) and may have a loud expiratory grunt.  Temperature is typically normal but may be mildly elevated due to the severity of the condition. In extreme cases, air under the skin (subcutaneous crepitation) may be felt over the upper portions of the neck, shoulders and back. Mild exercise may cause the animal to collapse and die. Generally, there is an absence of coughing and no signs of infection such as fever or depression unless a secondary bacterial pneumonia develops. Severely affected animals usually die within 1-2 days but animals that survive may develop chronic lung damage or heart failure. The stress of handling can cause prompt death so treatment must be approached with caution. A dart gun may be necessary to avoid moving the animal to a treatment facility. Treatments administered or prescribed by a veterinarian may include diuretics, nonsteroidal anti-inflammatory medications and corticosteroids used in an extra-label manner.

At necropsy, atypical interstitial pneumonia (AIP) is recognized when the chest cavity is opened, because the lungs remain fully expanded, sometimes with rib indentations on them, rather than collapsed as with a normal lung. AIP-affected lungs are heavy with a firm, rubbery texture instead of the expected light and spongy lung tissue. These necropsy findings are confirmed microscopically as a very distinct pattern of damage to the lung cells. In addition, the leaves and distinct square stems are sometimes identifiable in rumen contents.

The best time of the year to begin scouting for perilla mint is late spring (May and June). During the late summer months when plants are flowering and producing new seed, grazing infested fields should be limited. Mowing can be used for control but must be timely to reduce new seed production. Unfortunately, mowing or clipping fields may not be feasible in some areas since many plants grow near trees and in fence lines. Chemical control options include herbicides labeled for use in pastures and hay fields that consist of single or premixed active ingredients of 2,4-D, dicamba (e.g., Weedmaster®, Rifle-D®, Brash®, etc.), triclopyr (eg. Crossbow®, etc.) or aminopyralid (e.g., DuraCor®, GrazonNext®).  For best results, herbicide applications should be made to smaller, actively growing plants. Control is likely to be less effective when applied to taller, flowering plants. Grazing animals should be removed for a while after herbicide treatment since they may be more attracted to dying perilla mint plants. Furthermore, use good stewardship and observe label precautions when applying herbicides. 

Prevention begins with learning to recognize poisonous plants, where they grow, and when they cause problems. Toxic weeds may be found in fence rows, along creek or stream banks, near ponds and in the woods although some (such as cocklebur, horsenettle and pigweed) are found in pastures and hayfields. Scout summer pastures and offer supplemental forage or feed when pasture is limited so cattle are not forced to graze toxic weeds. Do not harvest toxic weeds in hay or silage since cattle do not sort through these feedstuffs and will readily ingest the weeds. Most importantly, implement effective weed control at the right time and use management practices to thicken the stand and improve the growth of desirable forages which can compete with the emergence and growth of annual weeds.

A newly revised UK Extension publication entitled “Guide to Plants of Kentucky Potentially Poisonous to Livestock” is available at the UK Extension Website or ask the county ag and natural resources (ANR) extension agent how to access this information. Pictures of many of the weeds and control options available for pasture weed control can be found at the following websites:

AGR-172:Weed Management in Grass Pastures, Hayfields, and Other Farmstead Sites, 2021

AGR-207:Broadleaf Weeds of Kentucky Pastures, 2021 

Control efforts for Poison Hemlock and Buttercups Begin in Late Winter | Kentucky Forage News

For further help identifying weeds, individuals can submit unknown weed samples through the local county extension office. When sampling plants, collect as much of the plant as possible (roots, leaves, stems, flowers, etc.) for submission to the county extension office. State the general structure or size of the plant and provide details about the specific site where it was collected, and other characteristics, such as color of flowers, that can be useful for proper identification. Pictures of the whole plant and close-up photos of distinctive features can also be helpful with identification. If plants cannot be sent in fresh condition, they should be pressed out flat and packaged between pieces of cardboard or paper before sending.

2021 Weed Control Options Come into Clearer View

The recent announcements of the EU approval of RR2XtendFlex (RoundupReady 2 XtendFlex) soybean and EPA approval of three dicamba products has brought a clearer view of soybean weed control options available to Kentucky farmers in 2021.   Prior to these two announcements the waters were murky with unknowns of if the flexibility of the RR2Xtendflex system would be available and if any dicamba formulations would be available to spray on any dicamba tolerant soybean acres.   With the recent announcement came answers and clarification, but also prompted a few more questions and restrictions.

Palmer amaranth

The most recent event to occur was the approval of Xtendimax (Bayer), Engenia (BASF), and Tavium (Syngenta) for applications to DT (dicamba tolerant) soybean.   The three labels stayed largely unchanged from previous versions although crops outside of DT soybean and DT cotton have been removed from the labels.  Restrictions of nozzles, tank mixes, sprayer speed, boom height, wind speed, and temperature inversions remain the same as previous labels.  The restrictions that have changed are rate changes for Xtendimax burndowns, application cutoff date/growth stages, increases in buffer requirements, and the new requirements of a volatility reduction agent or buffer agent.  Each change is described below:

  • Xtendimax can only be applied at a rate of 22 fl oz/a per application, regardless of application timing.  Previous labels allowed up to 44 fl oz/a Xtendimax for preplant/burndown applications, but that rate is no longer labeled.
  • All three labels have a federal cutoff date of June 30th and no application can be made after that date.   The Xtendimax label also indicates a cutoff soybean growth stage of R1,  whereas the Tavium label has a soybean growth stage cutoff of V4.   In both cases whichever occurs first (date or growth stage) takes precedent.  The Engenia label does not include a cutoff growth stage, thus June 30th is the cutoff for this product. 
  • Down wind buffers have been extended from 110 ft in the previous labels to 240 ft in the new labels. Similar to previous labels these buffers can be included in directly adjacent roads, mowed grassy areas, corn fields, DT soybean fields, fields prepared for planting, and/or areas covered by a building.   THIS BUFFER IS NOT INTENDED FOR PROTECITON OF DICAMBA SENSITIVE CROPS,  THE LABELS REMAIN THE SAME IN THAT APPLICATIONS CANNOT BE MADE IF THE WIND IS BLOWING TOWARDS A SENSITIVE CROP SUCH AS NON-DT SOYBEAN, TOBACCO, VINEYARDS, AND TOMATOES.
    • These buffers can be reduced with the use of hooded/shielded sprayers or other approved drift reduction technologies (DRT), as outlined on each label website.
    • Areas in which endangered species are present may need a 310ft downwind buffer plus a 57 ft omnidirectional buffer.  A list of these areas can be found on the Bulletins Live 2 website. 
  • The addition of a volatility reduction agent (VRA) or buffer agent is also required for all three labels in addition to drift reduction agents (DRA) that were required by previous labels.   The list of approved VRA or buffers can be found on each respective products label website.

As in the past, dicamba specific training will still be required prior to application of Xtendimax, Engenia, and/or Tavium.  This training will be offed by the registrants and will largely be available online.

The additional restrictions bring some clarification to past issues of the previous dicamba labels, but the additional restrictions certainly do not make their application easier.  The extension of the downwind buffer to 240 ft may cause havoc as many Kentucky fields are surrounded by trees and thus the buffers will have to be placed within the production field being sprayed.   While the distance in necessary to protect our natural resources and endangered species,  240ft can add up to numerous acres very quickly.  In some cases, the area will be large enough for applicators/farmers to question the feasibility of applying the product to a given field.

The addition of the June 30th cutoff date places a hard deadline on applications, whereas past labels in which growth stages were used allowed many applications to continue to occur in the hot and humid months of July and August.  Weather conditions in Kentucky in July and August simply are not ideal for dicamba applications in any crops, not to mention the numerous sensitive crops that are out during those time of year including tobacco.  This cutoff date does however eliminate a lot of possible uses for double crop soybeans that likely will not be planted until late June and early July, so growers may need to seek an alternative herbicide programs for double crop soybean acres.

Despite the increase in restrictions of the new dicamba labels, the announcement of these labels comes on the heels of the approval of RoundupReady 2 XtendFlex soybean by the EU and thus full clearance for commercial production of those soybean varieties.   The availability of RR2XtendFlex soybean varieties brings versatility to the Xtend platform that can be compared to its closest competitors.   The XtendFlex soybean offers resistance to glyphosate and dicamba the same as RR2Xtend, but also offers glufosinate resistance.   The addition of glufosinate offers postemergence flexibility for farmers who are dealing with glyphosate resistant broadleaves such as Palmer amaranth or waterhemp.   The biggest fallacy, in my opinion, of the RR2Xtend soybean varieties was that farmers were largely married to dicamba for postemergence applications when dealing with waterhemp and Palmer amaranth, especially with the increasing incidence of PPO-resistance in these two weed species.   In many cases a farmer/applicator was stuck in between a rock and a hard place when deciding when to apply dicamba under restrictive conditions and a rapidly growing weed.   The addition of glufosinate offers a bit more flexibility and can allow a farmer to make an effective postemergence application of glufosinate if environmental conditions or surrounding crops do not allow for a timely application of dicamba.   It must be said, though, that glufosinate is very capable of drifting the same as any other herbicide and thus if the wind is blowing at high speeds towards a sensitive crop no herbicide application, glufosinate, dicamba, or other should be applied.

As has been the message from University of Kentucky Weed Science in the past, the specific dicamba formulation one wants to apply and/or when to apply glufosinate matters less than the residual herbicide applied.   Anybody choosing to raise RR2Xtendflex soybean who is dealing with Palmer amaranth or waterhemp must remain vigilant and apply robust preemergence herbicides.  Research supported by the Kentucky Soybean Board has shown that even with the flexibility of the RR2XtendFlex soybean platform the use of a residual herbicide with 2 to 3 effective sites of action is more influential on end of season waterhemp and Palmer control than the choice or sequence of postemergence herbicides.   This message applies to all herbicide tolerant soybean systems, and will continue to be the message for these two troublesome weeds.

Up to the recent two approvals of RR2XtendFlex soybean and Xtendimax, Engenia, and Tavium there was a lot of unknowns in weed control going into 2021.  These recent approvals have brought a lot clarification to what farmers will have available for weed control in 2021 and their options are now fairly large which is great for soybean farmers.

AGR-256, Identification of Palmer Amaranth, Waterhemp, and Other Pigweed Species:

Author: Travis Legleiter, Plant and Soil Sciences