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Occurrence of 2,4,5-T and Picloram in Surface Runoff Water in the Blacklands of Texas¹

ABSTRACT

This investigation was conducted to determine the concentration of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid)] and picloram (4-amino-3,5,6-trichloropicolinic acid) in surface runoff water that may move from herbicide sprayed pastures and rangeland to untreated areas as a result of each major rainfall following treatment.

A 1:1 mixture of the triethylamine salts of 2,4,5-T + picloram was sprayed 5 times at 1.12 kg/ha every 6 months on a native-grass pasture watershed. Soil, grasses and runoff water were analyzed periodically following herbicide treatment. Herbicide content in the Houston Black clay from May 1970 to May 1972 remained low (0 to 238 ppb). Herbicide content on grass was high (50 to 70 ppm) immediately after treatment, but degraded rapidly thereafter. Plant "washoff" was the main source of herbicide detected in runoff water. Concentration of herbicide was moderately high (400 to 800 ppb) if heavy rainfall occurred immediately after treatment, but low (<5 ppb) if major storms occurred 1 month or longer after treatment. No damage occurred to cotton (Gossypium hirsutum L.) or sorghum (Sorghum bicolor (L.) Moench) from either spray drift or subsequent runoff water in fields adjacent and below several herbicide-treated watersheds.

Key Words: herbicides • watershed • residue

¹ Cooperative investigations of the Blackland Conservation Research Center, Temple and Riesel, Texas, USDA-ARS and the Texas Agr. Exp. Sta.

² Agronomist, Soil Scientist, Agricultural Engineer, Plant Physiologist, and Hydraulic Engineer, USDA-ARS, College Station, Temple, Riesel, and College Station, Texas, and Athens, Georgia, respectively.

³ Professor, Dept. Soil & Crop Sciences, Texas A&M University, College Station, Texas.

Received for publication March 30, 1973.