Drift or volatilization of chlorophenoxy herbicides with resultant damage to non-target plants is an increasing problem in the Willamette Valley. The number of damage claims is increasing each year despite growing regulation and training of growers and applicators. The effects of lethal doses of the chlorophenoxy 2,4-D on broadleaf plants are well-known, but except for a few crops such as tomatoes and grapes, the effects of sublethal doses have not been well documented. The objectives of these experiments were to document the effects of trace amounts of 2,4-D on the growth, quality, and yield of several fresh market vegetable crops and determine 2,4-D residues as a function of the amount applied to the crop. The number of crops involved in these experiments was reduced from 12 in 1977 to five in 1978 and the number of rates of herbicide applied was reduced from 10 to two. Leaf samples were collected for residue analysis but the results are not yet available.
Methods
Crops and varieties for 1978 were Nantes carrot, Blue Lake 274 bush bean, Early Girl tomato, Victory cucumber, and Russet Burbank potato. All crops but tomato were exposed to single run-off sprays of 2,4-D dimethylamine at rates of 0, 5, and 50 ppm. Rates for tomato were 0, 1, and 10 ppm. Treatments were replicated three times in a randomized block design. Tomatoes, cucumbers, and potatoes were sprayed at first bloom, beans after expansion of the second trifoliate, and carrots after formation of the fleshy taproot. All leaf samples were taken 24 hours after spray application. Plants were observed daily following treatment and weighed and graded at harvest. No chemical pest control was used in the plots and fertilizer was applied according to standard practice for each crop.
Results
The tomato crop was severely infected with curly top shortly before bloom and yield data were not obtained. Carrot gross yields were increased nearly 25 percent over control by application of 5 ppm 2,4-D. However, 5 ppm reduced net fresh market yield nearly to zero since the roots were rough, scaley, misshapen and covered with prominent root primordia. Foliar symptoms were nearly indiscernible at this rate. Gross yields were reduced to about 65 percent of controls by 50 ppm 2,4-D and marketable yield was zero. Pronounced and lasting foliar symptoms were present at this rate.
Potato yields and tuber shape were not affected by 5 or 50 ppm 2,4-D although foliar symptoms of vein-clearing, and leaf margin distortion were evident at 50 ppm. Cucumber yields were unaffected at 5 ppm but reduced by 25 percent at 50 ppm. Foliar symptoms and fruit shape distortions were evident at both rates of 2,4-D. Bean yields appeared to be depressed slightly by both rates of 2,4-D but the differences were not statistically significant. Foliar symptoms were readily apparent at 50 ppm.
These results agree nicely with results from the 1977 trials. Crop damage can occur at low exposures and root crops are particularly sensitive. The ability to predict yield reductions after accidental exposure of non-target crops will depend upon correlation of residues with known amounts of 2,4-D applied.