tomato damageMSU Schutter Diagnostic Laboratory received over 112 garden samples in 2009 and 2010 which showed symptoms consistent with pesticide exposure from a class of chemicals known as 'growth regulator herbicides'. Growth regulator (auxinic) herbicides target broadleaf plants, but typically don't injure grasses at recommended rates. Symptoms of injury include cupping of leaves, stunting of plant, and twisting of growing tips (see photos). The source of contamination is often herbicide contaminated compost or manure added to the garden as a soil amendment.

Applicators and homeowners should be aware that many growth regulator herbicide active ingredients aren't inactivated by livestock digestion, thus resulting manure is a source of pesticide contamination towards susceptible broadleaf plants. Contaminated grass clippings shouldn't be added to compost or directly to gardens as mulch. Users must be sure that grass clippings haven't been sprayed with growth regulator herbicides prior to cutting. Special precautions should be taken when using these growth regulator herbicide active ingredients to avoid contamination to manure or grass clippings which may be distributed to homeowners.

  • BENZOIC ACID HERBICIDES (soil 1/2 life of around 14 days)
    • dicamba: Banvel, Clarity, Dicamba, Fallow Star, Vision, Outlaw, etc...
  • PHENOXY ACETIC HERBICIDES (short soil 1/2 life)
    • 2,4-D, 2,4-DB, MCPP, MCPA: Hardball, Latigo, Unison, etc...
  • PYRIDINE CARBOXYLIC ACID HERBICIDES (highest concern -- high soil 1/2 life)
    • picloram: Tordon, Outpost 22K, Terva 22K, Grazon, etc...
    • clopyralid: Curtail M, Cutback M, Redeem R & P, Transline, Stinger, etc...
    • aminopyralid: Forefront, Milestone and Chapparal
    • aminocyclopyrachlor: Imprelis, Method 240 SL, Viewpoint, Streamline, etc...

Drift may also cause non-target symptoms towards desirable trees and vegetables. Any pesticide may drift if misused, thus causing non-target toxicity. Some of the pyridine carboxylic acid (PCA) chemistries may persist for longer periods of time, while others may cause sublethal symptoms at extremely low concentrations. The use of the PCA herbicide named 'Imprelis' has resulted in non-target symptoms to certain species of evergreen trees in 22 states at 5 - 6,000 sites across the United States (Revocation of Imprelis).  The active ingredient in this product – ‘aminocyclopyrachlor’ provides selective broadleaf weed control in turf-grasses on lawns, golf courses, parks, cemeteries, athletic fields, right of ways, wildlife management areas and sod farms. This product was available and used in Montana by applicators since fall 2010 until revocation in August 2011.  The use of grass-clippings or damaged trees contaminanted with 'aminocyclopyrachlor' as compost has also resulted in non-target plant damage.

Applicators

If distributing Grass-Clippings or Manure collected from Livestock. Always read and follow all precautionary statements upon the pesticide product label. If using growth regulator herbicides (as listed above) don't distribute manure if it was collected from livestock which have immediately (see your pesticide product label for exact time interval requirements) grazed upon treated forage. Contaminated manure or grass clippings should only be used on grasses. Follow pesticide product label interval requirements regarding the grazing and further distribution of manure collected from livestock. See the 'aminopyralid stewardship factsheet' for more information regarding the proper stewardship of aminopyralid.

Always be aware of Drift. Don't spray when temperatures exceed 80 degree's F or wind velocity exceeds 8 - 10 mph. Many pesticide formulations become volatile at high temperatures, causing pesticide droplets to break down into a gas prior to drifting offsite. Always be aware of sensitive areas adjacent to spray zone and create buffer zones to minimize drift potential. More information on pesticide drift can be found on the MSU Pesticide Education website at 'DRIFT'.

Always be aware of your Pesticides Characteristics. Pesticides have inherent characteristics that enable it to: 1) bind to soil particulates and be rendered inert (Soil Adsorption; Sorption Potential, KOC), 2) dissolve into water and be easily transported off-site (Solubility), and 3) persist for certains periods of time before breaking down into an in-active residual (persistence). Your pesticide characteristics can be looked up online at the National Pesticide Information Center (NPIC) or contact the chemical manufacturer. If you have further questions regarding solubilty, persistence and/or adsorption see the MontGuide titled 'Pesticides in the Environment'.

Homeowners

Do you suspect pesticide contamination around your home and garden?

If you suspect pesticide injury around your home and garden it may be necessary to conduct your own mini-investigation to determine your best options. When conducting your own investigation it is necessary to get background details necessary to make an informed decision. You need to determine if: 1) a pesticide was misapplied directly to site, 2) a pesticide was carried from a nearby location to contaminated site through pesticide drift, or 3) if the timing of symptoms coincides with the addition of soil amendments.

  • Timing of symptoms coincides with the addition of grass clippings, manure or compost within the last 12 months. Growth regulator herbicides which target broadleaf plants are of primary concern due to the persistence of some of these chemistries under anaerobic (without oxygen) conditions present in manure, compost and some soils. In most cases broadleaf plants (tomatoes, potatoes, beans, peas) are impacted, not grasses (wheat or corn) if soil is contaminated with growth regulator herbicides. Growth regulator herbicides often cause cupping of leaves, veination and/or stunted growth (see symptomology / mode of action characteristics at: University of Arizona key). A soil bioassay should be conducted to verify the presence of pesticide contamination. See instructions at 'what to do if you suspect soil contamination'.
  • Timing coincides with the observation of pesticide drift from a neighboring area being sprayed or a misapplication directly to site. Pesticide drift may cause non-target toxicity towards beneficial plants. Drift is likely a candidate if applications were made when temperatures exceeded 80 degrees F or wind velocity exceeded 8 - 10 mph. Many pesticide formulations become volatile at high temperatures, causing pesticide droplets to break down into a gas prior to moving offsite. Symptoms may vary according to which chemical was used in the application. Contact the certified applicator and ask which pesticide product they were spraying on that day. Symptomology should match mode of action used by applicator. See symptomology / mode of action characteristics at (University of Arizona key) or contact the MSU Pesticide Education Program (406)994-5067.
    • Contact your local MSU county Extension Agent for more information regarding pesticide drift on your property. An MSU County Extension Agent with the support of MSU Schutter Diagnostics / MSU Pesticide Education Program can also diagnose other abiotic (pH, nutrient deficiencies, water stress) and biotic (insects, plant diseases) factors which may mimic pesticide drift.