Some data from over 15 years ago may help people better asses the damage from phenoxy herbicide drift in the San Joaquin Valley this year. This data is only for one trial in one year, but shows the range of damage which can occur in cotton. The yield losses were the greatest when the cotton plants show continued phenoxy symptoms on new growth all season long.
Thousands of acres of cotton in the Sacramento Valley were damaged by phenoxy herbicide drift in 1995. Cotton had not been planted on a large acreage in the Sacramento Valley since being planted in the 1920’s. This widespread damage continued in 1996 and 1997 and only stopped when the phenoxy herbicde manufactures severely restricted their products use for rice.
The attached “January 1997 Field Crops” newsletter article gives the results of a large scale replicated field trial showing the effects of phenoxy herbicides on cotton production. Because this injury was cause by a ground application by the cotton grower, the exact date of injury was known, June 18th, 1996. This injury occurred from a one-time application, about two weeks before the start of bloom. In this trial, a light phenoxy herbicide injury caused a 5 percent yield loss, a moderate injury a 20 percent yield loss, and very severe injury resulted in over 50 percent yield loss.
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