Several species of the genera Peronosclerospora, Sclerospora, and Sclerophthora are responsible for downy mildews:
- Crazy top downy mildew - Sclerophthora macrospora
- Brown stripe downy mildew - Sclerophthora rayssiae var. zeae
- Green ear disease- Sclerospora graminicola
- Java downy mildew - Peronosclerospora maydis
- Philippine downy mildew- Peronosclerospora philippinensis
- Sugarcane downy mildew- Peronosclerospora sacchari
- Sorghum downy mildew- Peronosclerospora sorghi
Nature of damage
- Some species causing downy mildew also induce tassel malformations, blocking pollen production and ear formation.
Signs
- Symptom expression is greatly affected by plant age, pathogen species, and environment. Usually, there is chlorotic striping or partial symptoms in leaves and leaf sheaths, along with dwarfing.
- Downy mildew becomes conspicuous after development of a downy growth on or under leaf surfaces.
- Leaves may be narrow, thick, and abnormally erect.
Factors favoring development
- The diseases are most prevalent in warm, humid regions.
- Cultivation of alternate hosts in rotation or simultaneously will build pathogen pressure.
- Moist soils favor oospore germination and therefore damp soil as a result of irrigation or reduced tillage techniques will encourage disease development.
Geographic development
- These diseases are of serious concern to maize producers in several countries of Asia, Africa, and throughout the Americas.
