Herbicides in Irrigation Water Following Canal-Bank Treatment for Weed Control

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Abstract
Concentrations of 2,2-dichloropropionic acid (dalapon), trichloroacetic acid (TCA), and (2,4-dichlorophenoxy) acetic acid (2,4-D) were determined in irrigation water following bank applications for weed control. Maximum concentrations of dalapon in the water varied from 23 to 365 ppb from application rates of 6.7 to 20 lb/A. The highest levels of TCA ranged from 31 to 128 ppb following applications of 3.8 to 5.9 lb/A. Applications of 1.9 to 3 lb/A of 2,4-D produced maximum concentrations of 25 to 61 ppb. Reduction of herbicide levels appeared to be due to dilution as the water flowed downstream. Rates of reduction in herbicide levels showed that negligible concentrations would remain after the water traveled a distance of 20 to 25 miles. The low concentrations of herbicides observed in the irrigation water likely would not be hazardous to crops or animals.