Evaluation of seed coating treatment on maize (Zea mays L.) stand establishment and seed rot caused by Pythium species at early planting season
The effects of polymers and captan fungicide treatment of maize seed on rate of field emergence, final stand, and control of seed decay caused by Pythium spp. are reported. The polymer, Certop, in combination with captan was as effective as captan alone in increasing emergence. Compared to the untreated control, the emergence rate index (ERI) of a low vigor seed lot was increased from 2.70 to 6.06 and 6.28 for captan and captan plus Certop, respectively. For a high vigor seed lot, the ERI was increased from 5.82 in untreated control to 7.02 and 7.54, for captan and captan plus Certop, respectively. For both high and low quality seeds, treatments that increased ERI also significantly increased the final emergence and maize seedling height. The incidence of Pythium spp. in the embryo and coat of ungerminated maize seeds was negatively correlated with emergence rate and final stand, particularly for the low vigor seed lot. Polymers alone had no significant influence on increasing emergence rate or on preventing seed infection by Pythium spp. for either high or low vigor, treated seeds. Polymers in combination with captan were as effective as captan alone in increasing the rate of emergence and improving seedling height at early planting, but were inconsistent in the control of Pythium. Pythium ultimum and P. irregulare were the species most frequently isolated from both seed coats and embryos. Also in this study, the potential of two polymers, Daran°ler 8600-C and Chitosan (Nutri-Save°ler), applied to maize seeds alone or in combination with captan at three different rates for control of seed decay by Pythium spp., was evaluated. All dosages of captan improved the rate of emergence compared to the untreated control. Captan alone at 200 ppm seemed to be equally effective in improving final stand in both field and laboratory tests as captan at the commercial rate. Captan at 600 ppm, captan at 200 ppm, and Chitosan plus captan at 600 ppm reduced coat infection by Pythium spp. at 4 days after planting (DAP). Seed embryo infection was significantly less for seeds treated with captan at 600 ppm at 4 DAP compared to the untreated control. Under in vitro conditions Chitosan showed a fungistatic effect on Pythium spp., but this effect was not expressed under field conditions. In conclusion, the commercial rate of captan application to ensure acceptable emergence rate and final stand could be reduced. Seed treatment polymers, used in this study, in combination with reduced rates of captan were ineffective against infection of ungerminated maize seeds by Pythium spp.