Downy Mildew (Plasmopara viticola)

DAMAGE AND SYMPTOMS

• Attacks any green tissue on the vine.

• Destroys tissue in a few days.

• Symptoms include large yellow spots on the tops of leaves, called “oil spots,” and white, cottony (“downy”) colonies on the undersides.

• Infections also attack shoots, shoot tips, petioles, berries, and rachises.

LIFE CYCLE

• Oospores overwinter in fruit and leaves on the vineyard floor.

• Oospores can be viable for several years.

• Primary infections begin in the spring at 52°F or higher and after a rain event of at least 0.1”.

• Secondary infections of sporangia form after humid nights followed by a rain event.

• Sporangia then release zoospores which move onto or around the vine via wind or rain (splashing).

• Zoospores enter the plant through the stomates.

• Downy mildew infections spread rapidly after this point.

• Under ideal conditions the time between generations is 4 to 5 days.

• Ideal conditions are night and morning temperatures between 65-77°F.

• Limiting temperatures are below 52°F and above 86°F. 

MANAGEMENT

• See “Downy Mildew” on UC Statewide IPM Website for specific recommendations.

• See Grape Disease Control for 2017 by Wayne Wilcox for recent research on the control of downy mildew with fungicides.

"Oil spot” on the surface of a leaf. (Mark D. Welch)	Colony of sporangia on underside of a leaf. (Mark D. Welch)

SOURCES:

Wilcox, Wayne. 2017. “Downy Mildew.” Grape Disease Control for 2017. Geneva, NY: Cornell University.

Gubler, W. Douglas, George M. Leavitt, and Larry J. Bettiga. 2013. “Downy Mildew.”  Pp. 117-119 in Grape Pest Management, 3rd. Edition. Larry J. Bettiga, Technical Editor. Oakland, CA: University of California Agriculture and Natural Resources: