THE EFFECT OF SEED-APPLIED PESTICIDES ON GROWTH AND N₂ FIXATION IN PEA, LENTIL, AND FABABEAN

Abstract

Conflicting recommendations exist on the effect of seed-applied pesticides on nodulation and N 2 fixation by Rhizobium leguminosarum. This paper reports the effects of captan, thiram, metalaxyl, Evershield, DL-PLUS ® and B-3 in a 2-yr field experiment on emergence, nodulation, acetylene-reducing activity, and shoot yield of pea (Pisum sativum L.), lentil (Lens culinaris L.), and fababean (Vicia faba L.) inoculated with seed-applied R. leguminosarum multi-strain inoculum. Seedling emergence was not detrimentally affected by pesticide application. While most of the pesticides had either stimulatory or minimally detrimental effects on nodulation and nitrogenase activity, captan reduced both in all three legumes. Captan-containing compounds such as B-3 (33.5% captan) and Evershield (29.5% captan) also reduced nodulation or nitrogenase activity in some of these legumes. DL-PLUS (15% captan) was not harmful, which suggests that compounds containing over 29.5% captan may not be compatible with seed-applied R. leguminosarum. Captan, which was consistently harmful, is considered the best wide-spectrum pesticide for use with these legumes. Thus, it will be necessary to select superior N 2 -fixing strains of R. leguminosarum that are tolerant of, if not resistant to, recommended rates of captan or to identify alternate pesticides that are more compatible with rhizobia.Key words: Captan, thiram, metalaxyl, Evershield, DL-PLUS, B-3