Contamination of cotton fields by 2,4-D or hormone-type weed sprays

Indiscriminate use of 2, 4-D or hormone type weed sprays in the 1945 season in southern New Mexico resulted in very abnormal growth of cotton in adjacent areas, the amount of injury depending on degree and time of contamination. Materials used for the experiments presented herein were not absorbed from the ground surface or leached from dead weed tops to any extent by irrigation water. Observations on spray drift indicated that injury in commercial cotton fields extended over distances far too great to be explained by actual spray drift. Evaporation and distillation tests indicated that tested materials known to contain an "esterified" 2,4-dichlorophenoxyacetic acid were highly volatile when exposed directly to the sun in summer months, adjacent cotton plants being seriously injured by the vapor. It is concluded that highly volatile materials or other formulae prepared in any manner that are highly conducive to transportation by air currents cannot be used safely during the summer months in intensive cotton growing areas such as those in southern New Mexico. Materials containing unmodified 2,4-dichlorophenoxyacetic acid or a salt thereof were nonvolatile and could be used with safety very close to cotton plants when care was taken to control actual spray drift. The extreme sensitivity of the cotton plant is indicated by results showing that only 0.01 cc of solution containing 1,000 p.p.m.;. of ammonium salt of 2,4-dichlorophenoxyacetic acid caused development of abnormal foliage on rapidly growing cotton plants in midseason. Degree of injury varied with amount applied, and symptoms were more quickly evident when applied to top than to bottom or middle leaves. When applied as a spray to entire plants, 1 p.p.m. caused injury from which plants recovered, while 10 p.p.m. caused serious injury and prevented normal fruit set; however, growth of the plant in height was almost normal.