Efeito de herbicidas sobre a ferrugem asiática da soja (Phakopsora pachyrhizi Sid. & P. Sid.)

Abstract

The influence of herbicides commonly used for weed control were evaluated on asian soybean rust. Field and laboratory experiments were conducted in the Centro Universitário da Grande Dourados and Universidade Federal da Grande Dourados. Initially we tested some commonly used herbicides for weed control in nontransgenic soybeans. The herbicides were chlorimuron-ethyl fomesafen + mineral oil, clethodin + fenoxaprop-P-ethyl, lactofen with and without application of picoxystrobin + cyproconazole applied on cultivars M-Soy 8001 and BRS 133. Trials were carried out with the herbicide glyphosate using the genetically modified soybean cultivars, M-SOY 7908 RR and BRS 245 RR. Different rates of glyphosate on BRS 245 RR cv. were studied as well. Herbicides were also tested on Phakopsora pachyrhizi urediniospores germination under 1, 2, 4, 8 and 24 h exposition times. The cv. M-SOY 8001 became more susceptible to asian soybean rust after application of clethodin + fenoxaprop-Pethyl, lactofen and fomesafen. A reduction in uredinia counts on M-SOY 8001 was detected after exposition to fomesafen and lactofen. This effect was limited only to the first evaluation, at the Vn stage. Glyphosate, applied on field rates, had an effect on the severity of asian soybean rust, but the effect was limited to initial disease establishment. All glyphosate levels had a short-term protection effect aganst desease severity. The herbicides had no effect on the soybean yield. All herbicides affected the urediniospores germination, however, fomesafen, and lactofen chlorimuron-ethyl showed limited inhibition. Urediniospores germ tubes length were negatively affected by glyphosate, clethodim + fenoxaprop-P-etílico, lactofen and chlorimuron-ethyl.