The effect of foliar-applicated (+/-)-2-(2,4-dichlorophenoxy)
propanoic acid (2,4-DP) under simultaneous influence of simulated
acid rain at pH levels of 3.3, 4.3, and 5.6 was examined for young plants of white mustard, rape, cress, lettuce, radish, carrot, oat, and barley grown in climate chambers. After 1-2 weeks with daily showers plants received a single foliar application of 2,4-DP in aqueous
solution (500 microliter; 0.25-50.0 mg X liter-1). After a post-treatment period of 2-3 weeks with daily showers the plants were sampled. 2,4-DP at 5 mg X liter-1 or higher concentrations caused various symptoms for the dicotyledons. Monocotyledons and carrot remained unaffected. The application of
acid rain at pH 3.3 produced morphological changes, increased the symptoms from 2,4-DP, and reduced the dry weight and the leaf to stem ratio. Cress exposed only to
acid rain showed necrotic spots and
chlorosis at pH 3.3. By decreasing pH taller plants with smaller leaves were observed. The combined effect of
acid rain and 2,4-DP was additive rather than synergistic.