DELTA CENTER WEED SCIENCE
Pesticide Residue Samples for Drift Incidents
When a drift incident occurs persons frequently wish to have injured plants analyzed for residues of the suspected herbicides. We generally do not recommend this type of testing for several reasons:
Pesticide residue testing can usually detect when a herbicide has been applied directly to plants; however, in cases of drift, the quantity is very small. Most pesticides break down fairly quickly- and often drift complaints are discovered over a week after the drift actually occurred. The low rate added to the time for the herbicide to break down means that herbicides are rarely detected even when drift damage is clear. When widespread whitening of vegetation (especially pecan trees) occurred after Command became available for cotton growers, Command could not be detected in white pecan leaves. During the summer of 2001, several thousand acres of cotton showed typical 2,4-D-type symptoms; however, residue testing did not detect 2,4-D, or any other hormone-type herbicide. Although chemical detection methods are sensitive, they are often unable to detect herbicides in older drift samples.
Residue tests are expensive- typically over $100.
Pesticide residue testing does not determine WHICH herbicides are present. Instead, the process is more of a confirmation- If you suspect that 2,4-D has damaged a plant, you may have that plant tested for 2,4-D residues, and will learn if 2,4-D was detected. If you do not have a good idea of which herbicide caused the damage, then you would have to request that the laboratory test for all chemicals that might have caused the damage, and pay a separate analysis fee for each chemical. The testing for each chemical is an independent step.
If there is a clear case of drift, if there is a great amount of certainty as to the offending herbicide, if the drift is fairly recent, and there are unfortunate circumstances that require that residue samples be taken- THEN, a testing may be worthwhile.
We typically suggest that persons contact A & L Laboratories in Memphis for analysis. Below are two links- one for the A & L website and the other which is a copy of a pamphlet describing residue analysis procedures. Other appropriate labs exist and the mention of this one does not constitute a recommendation of one laboratory over other appropriate pesticide residue labs.
A & L Residue Analysis Pamphlet (Adobe Acrobat PDF)