To prevent disease dissemination chemical treatment of maize (Zea mays) seeds becomes indispensable. However, the efficacy of this treatment may be influenced by a number of factors, such as seed size. Thus, the objective of this work was to evaluate the efficacy of the fungicide thiabendazole in treatment of maize seed to control S. maydis, taking into account different seed sizes. The seeds classified according to sieves 19, 22 and 24 were inoculated with S. maydis and treated with the fungicide thiabendazole in three doses. To evaluate the effect of seed treatment, test of germination on paper roll substrate, health test, (blotter method), and the dry weight of seedlings were considered. Seed treatment with fungicide provided conditions for increased germination and weight of seedlings, and reduced damping-off, caused by S. maydis. The efficacy of the fungicide seed treatment varied according to seed size and doses of the fungicide used.
