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.
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.
These diseases are of serious concern to maize producers in several countries of Asia, Africa, and throughout the Americas.