Influence of panicle fungicides and harvest schedules on sorghum seed quality under humid tropical conditions in Puerto Rico

Abstract

Fungicide applied directly to developing panicles of the sorghum cultivars TAM 428 and Pioneer 846 substantially reduced seed quality losses caused by fungal infections at harvest at physiological maturity (pm) and in delayed harvests under warm humid tropical conditions in Puerto Rico. With four sprays of benomyl plus captan, germination losses 2 weeks after pm were 30.3%; for nonsprayed plots 75.3%. Compared to a four spray schedule and no sprays, one spray 3 weeks after boot stage gave approximately 75% control of germination losses at 2 weeks after pm. Observed losses in seed appearance and germinability were strongly associated with decreases in seed density, increases in harvest delay, and reductions in fungicide applications. All seedlots except those from plants sprayed 2 or 4 times and which were harvested at either pm or 1 week later, produced unacceptable germination rates (less than 80%). Under warm humid tropical environment, local production of high quality sorghum seeds for planting depended on both timely harvesting and chemical control methods. Losses in seed density over delayed harvest were direct economic losse. Twenty percent loss was noted after 2 weeks and 10% after 1 week. The best fungicide control treatment yielded 5% denser seed at pm than nonprotected counterparts at the same harvest.