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.