Influence of herbicides on root rot of French beans (Phaseolus vulgaris L.), caused by Rhizoctonia solani.

The effects of four herbicides, namely bromacil, diuron, nitrofen, and alachlor, at 0.04 and 0.02% concentrations in vitro and nitrofen and alachlor at two concentrations under field conditions, were studied against root rot of French beans, caused by Rhizoctonia solani. Diuron at 0.04% concentration completely checked the growth of R. solani in in vitro incubation up to 72 hours. Alachlor was highly effective at both the concentrations, followed by nitrofen and bromacil. In field trials in 1977 and 1978, pre-inoculation application of both the herbicides was less effective than post-inoculation application. Pre-emergence mortality, following post-inoculation application of nitrofen and alachlor, varied in the two trials from 5.7 to 11.4% and 5.3 to 7.6%. respectively, as compared to 16.6 to 19.3% in untreated plots. Post-emergence mortality in post-inoculation application of nitrofen and alachlor varied from 3.9 to 9.5 and 5.3 to 12.2, respectively, whereas in untreated plots it was 13.8 to 21.9%. Yield of green pods was also significantly higher in post-inoculation application than in untreated control.