Peronosclerospora sorghi is a plant pathogen. It is the causal agent of sorghum downy mildew. The pathogen is a fungal-like protist in the oomycota, or water mold, class. Peronosclerospora sorghi infects susceptible plants though sexual oospores, which survive in the soil, and asexual sporangia which are disseminated by wind. Symptoms of sorghum downy mildew include chlorosis, shredding of leaves, and death. Peronosclerospora sorghi infects maize and sorghum around the world, but causes the most severe yield reductions in Africa. The disease is controlled mainly through genetic resistance, chemical control, crop rotation, and strategic timing of planting.
A combination of chemical, genetic, and cultural methods are used to control sorghum downy mildew. A number of single-gene sources of resistance have been found, and many resistant varieties are commercially available. However, new pathotypes of the fungus continue to evolve to overcome different sources of host plant resistance. Seed treatments with the systemic fungicides metalaxyl and mefenoxam have been widely used to prevent systemic infections of Sorghum Downy Mildew. Metalaxyl, which inhibits protein synthesis in the pathogen, can also be applied as a foliar spray. In Texas, use of these two fungicides, in conjunction with the use of resistant hybrids, made the disease a minor problem until one of the pathotypes endemic in the region evolved resistance to both chemicals