An Evaluation of Dimethyl Sulfoxide as a Possible Adjuvant for Several Herbicides

Dimethyl sulfoxide DMSO and Tween 20 were compared as adjuvants for foliar applications of 1,1-ethylene-2,2-dipyridylium dibromide diquat dibromide, 2-methoxy-3,6-dichlorobenzoic acid dicamba, and 4-amino-3,5,6- trichloropicolinic acid picloram to bean plants growing under greenhouse or growth-chamber conditions. Inhibition of growth was the criterion of injury employed in evaluating these data. The effect of a commercial formulation of diquat alone and diquat plus 0.5 or 1.0 DMSO on growth of Red Kidney beans was not significantly different from the control because of the sublethal dose of herbicide applied. However, the addition of 5 or 10 DMSO caused an increase in phytotoxicity that was significantly different from either the control or diquat alone. Diquat plus 50 DMSO the highest level employed was the most phytotoxic treatment but it was not significantly different from the 20 and 30 rates of DMSO. Various combinations of 0.5 Tween 20, 30 DMSO, and technical grade picloram 12 micro g per plant applied to Black Valentine beans showed that both adjuvants significantly increased the effectiveness of picloram. DMSO, however, offered no advantage over Tween 20.