Detection and Chemical Control of Cercospora Sojina Infecting Soybean Seed in Argentina

Frogeye leaf spot (FLS) of soybean caused by Cercospora sojina Hara is an important disease in the Argentine Pampas region. The primary inoculum sources of the disease are infected seeds and plant debris. Thus, use of pathogen-free or fungicide-treated seeds is crucial to prevent the introduction and further spread of the disease. The aims of this research were i) to quantify C. sojina incidence in harvested soybean seeds, ii) to compare media-based incubation methods for detection of the pathogen in seeds, and iii) to evaluate the effect of fungicide seed treatments in reducing FLS incidence. Among eight different detection methods evaluated, no difference in pathogen incidence was found, but the water restriction blotter method should be recommended as it is more time and cost-effective. Out of 13 different fungicide seed treatment combinations in three independent experiments, benzimidazole seed treatments resulted in zero FLS incidence. Any other of the tested fungicidal active ingredients either did not control the disease or did so poorly only when initial infection levels were low. Treating seeds with benzimidazole fungicides may help to reduce FLS incidence during initial soybean field stands when using infected seed lots.