RE-EVALUATION OF TCA FOR GREEN FOXTAIL CONTROL IN RELATION TO SEED YIELD AND OIL QUALITY OF FLAX

Abstract

The role of TCA (trichloroacetic acid) in green foxtail (Setaria viridis (L.) Beauv.) control and its effect on seed yield and oil composition of flax (Linum usitatissimum L.) cvs. Noralta, Raja, and Redwood were re-assessed under various weedy conditions from 1972 to 1975. When a mixture of weeds was present, TCA at 2.24 kg/ha controlled green foxtail but failed to control lamb’s-quarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.). However, TCA mixtures which included one or two broad-leaf herbicides gave good control of all weeds and a 40% increase in yield over the untreated check. Under natural infestation conditions where green foxtail was light but the predominant weed, TCA at 2.24–4.48 kg/ha gave partial weed control but did not increase the seed yield of flax. Cultivation consistently produced the highest yields and TCA alone generally produced the lowest yields. While the lower yields experienced with TCA were partially offset by cultivating before or after the application of TCA, in no cases were the yields from these combined treatments ever equal to that of cultivation alone. Plants treated with 3.36 and 4.48 kg/ha of TCA in the greenhouse showed leaf injury and a significant reduction in top weight. It is suggested that this type of injury is one of the factors contributing to the failure of TCA to significantly increase the yield of flax following suppression of green foxtail growth. TCA tended to increase protein content but has little effect on oil content, fatty acid composition, or iodine number.