The Effect of Downy Mildew on Corn


"Downy mildew" may refer to one of 10 different fungal species in the genera Peronosclerospora, Scleropthora and Sclerospora. In regions favorable to downy mildew, a rapid disease cycle can lead to devastation of staple corn crops.


Leaves become mottled and may display chlorotic (chlorophyll-poor) streaking. White-striped, shredding leaves and a fuzzy growth on either side of the leaf are other indications. Infected plants may demonstrate narrow, erect leaves and malformed tassels and ears.

Infection Vector

Downy mildew spores may remain viable in the soil for up to 10 years. They may infect new plants via the roots. Fresh airborne spores may also infect young neighboring plants via the stoma.

Effects on Growth

In plants less than four weeks old, downy mildew infections cause stunted, chlorotic growth and premature plant death.

Risk Period

Spores germinate in soil temperatures above 20 degrees Celsius while the corn crop is in the seedling stage. Airborne infection, which requires humidity and wet leaves, occurs at a high rate at temperatures greater than 16 degrees C.

Regions Affected

Downy mildew presents its greatest threat in tropical regions of Africa and Asia. Optimal conditions for infection are cool, wet and humid.


  • MaizeDoctor: Downy Mildew
  • NAPPFAST: Pest Assessment: Peronsclerospora maydis, (Corn Downy Mildew)
  • Oregon State University: Philippine Downy Mildew of Corn

Who Can Help

  • Plant Industry Division, Department of Agriculture: Study on Downy Mildew of Corn and Sorghum
Keywords: downy mildew, corn disease, Peronosclerospora, Scleropthora, Sclerospora, chlorosis

About this Author

Nicole J. LeBoeuf-Little is a freelance writer, blogger, and web designer from New Orleans, Louisiana. She is a graduate of the professional SF/F workshop Viable Paradise (2006). Recent published work appears at and, with a short story forthcoming at (March 2010).