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Residual herbicide and crop injury

When the worst happens: what questions to ask and how to soil test for a bioassay

Your cereal, oil seed or legume crop clearly shows that it has been significantly damaged by herbicide application or residual herbicide that was applied to cropland one or more years previously. You are considering possible legal action. What do you do next?

First of all, you just don’t take a few photographs, complain about significantly reduced yield and expect a financial settlement. You have got to come up with a plan of action. You need data, and proof of crop injury and crop loss. You will be pitted against chemical company crop representatives who have dealt with claim issues like yours dozens of times.

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Gathering information

First, find out if you really have clear cut crop damage. For ease of understanding here is a list of 17 questions you should ask and the procedures you should adopt:

  1. Is there clear and obvious crop damage in treated and untreated areas of the field where you have suspected herbicide injury residues from this year or from previous years?
  2. Does the crop in the sprayed miss areas look good and those in sprayed areas look poor? Determine this by walking along the edges of damaged fields.
  3. Did you spray only part of a field this year or the previous year? If only 80 acres of a quarter were sprayed and the same crop occupies the whole quarter then you have a relatively easy crop yield comparison.
  4. Did you spray at the recommended rate and time, and follow the crop rotational guidelines?
  5. Did you spray the same or a closely related weed control chemical, more than recommended on the product label?
  6. Do you understand the factors affecting soil persistence and breakdown for the herbicide in question?
  7. Do you know your soil pH and percentage organic matter? This is very important with respect to soil persistence of many herbicides.
  8. Did you know that the chemical or chemicals used were known to be persistent in the soil?
  9. Was this land farmed exclusively by you or was it rented out sometime in the last 10 years?
  10. Do you have records over the last five or so years of pesticide use, fertilizer inputs, previous crop yields, planting times and yearly moisture levels?
  11. Did you do a bioassay of the soil as perhaps recommended by the manufacturer or did someone else do the soil herbicide bioassay test?
  12. Is your crop choice known to be unusually sensitive to one or more soil-persistent herbicides?
  13. Are you familiar with the injury symptoms specific for the crop, crop growth stage and herbicide in question?
  14. Since your crop looks significantly damaged this year from a persistent, previous season herbicide and you have ruled out damage from this year’s herbicide(s) application, what do you do now?
  15. Do you want to proceed with a claim against the manufacturer of the herbicide? Are you sure that only one particular herbicide is the cause of the problem and not a combination of one or more herbicides?
  16. Are you reasonably confident that the crop damage resulted from an herbicide applied this year or any time in the past 10 years?
  17. If you suspect a specific herbicide applied this year or in previous years, are you going to do a chemical assay or a plant bioassay? Chemical assays are very expensive and only tell you if the herbicide is present or absent. It does not say if the herbicide is active or inactive. Bioassays will tell you if the chemical is active and how active by growing selective crop species identical to the damaged crop. It may also indicate the type of herbicide.

Soil samples for a bioassay

If you are contemplating litigation, you’ll need to take soil samples for a bioassay.

Most soil-persistent crop-damaging herbicides are very immobile in the soil and will be usually confined to the top two to three inches of soil.

Take six to seven pounds of topsoil (two to three inches in depth) from three areas of the crop:

1. areas of significant crop injury — stunting or distortion;
2. areas with little or no injury; and,
3. spray miss areas in the field, i.e. near utility poles or on headlands where the crop looks normal.

Take three lots of samples at each location, for a total of nine samples. Air dry these samples in paper bags and freeze two of the sample lots (you’ll have six samples for future reference). Forward the air dried or drier samples from each of the three sites immediately for bioassay. Store the other six samples dry and cool or frozen.

At crop harvest in the field, take square metre yield samples of the grain (cereals, canola, peas, and flax) from each of the three sampled areas, i.e. the significant injury, little injury and sprayer misses. Based on your square metre plot results, estimate the actual crop yield loss.

In each step that you take, from soil sampling, photographs of the crop damage, to actual yield analysis, have at least one other person (a witness) with you. Include that person in the photographs. Have your witness hold the damaged and healthy crop samples. Involving one or more witnesses at each stage gives credence to your potential damage claim.

Litigation claims initiated for crop loss from residual herbicide injury can drag on for many years. If you can eliminate any possible mistakes that could be responsible for crop damage contact your chemical company representative. If the crop damage is clearly not your fault, your chemical company representative will generally arrange for one way or another for crop loss compensation.

Avoid contacting members of the legal profession unless you are looking at significant or major crop losses and your chemical representative is uncooperative. Legal litigation can cost lots of money for little or no gain and more likely a further loss of money.

In conclusion the best way to deal with soil-persistent herbicides is to understand their biology and mode of action, soil persistence and crop sensitivity and avoid, or at least minimize situations that could lead to crop loss in terms of yield and quality.

About the author


Dr. Ieuan Evans is a forensic plant pathologist based in Edmonton, Alta. He can be reached at [email protected]



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