UACES Facebook Grape Downy Mildew
skip to main content

Grape Downy Mildew

Plant Health Clinic Disease Note Issue 31

Sherrie Smith and Jason Pavel

Grape leaf showing downy mildew symptoms, including yellowish lesions
Grape Downy Mildew-Plasmopara viticola. Photo by Sherrie Smith, University of Arkansas System Division of Agriculture 

Downy Mildew is a common disease of grapes in Arkansas. The causal agent, Plasmopara viticola, can attack all green parts of the plant, including leaves, petioles, stems, and fruit.

What are the symptoms of downy mildew in grapes? 

Leaf lesions are yellowish and oily, or angular, yellow to reddish brown, and limited by the veins. A dense, white, cottony growth of sporulation occurs on the underside of the leaf. Infected shoots curl into a shepherd’s crook, and become white with sporulation, eventually turning brown and dying. Leaves with numerous Downy Mildew lesions drop prematurely, reducing sugar content in the fruit and decreasing winter hardiness of the buds. Young berries are also highly susceptible. They appear grayish in color and covered with downy felt-like sporulation. Infected berries do not ripen normally, but remain firm, eventually dropping from the vine.

How do I control downy mildew in grapes? 

As with all downy mildews, good soil drainage is essential. The cleanup of fallen leaves and berries, and the removal of infected shoots helps limit inoculum, but rarely are these measures sufficient in themselves to control Downy mildew in areas with high disease pressure. Fungicides must be applied, starting at 3-6” shoot growth. Captan, Mancozeb, Ziram, Abound, Sovran, Pristine, Aliette, Scala, Reason, and Gavel are labeled for Downy mildew control among others.

Grape leaf with white, cottony growth of sporulation on its underside.
Grape Downy Mildew-Plasmopara viticola. Photo by Sherrie Smith, University of Arkansas System Division of Agriculture 
A grape cluster where half of the berries stopping forming, and died.
Grape Downy Mildew-Plasmopara viticola. Photo by Sherrie Smith, University of Arkansas System Division of Agriculture 

Take Aways:
• Clean up fallen leaves and berries and remove infected shoots.
• Begin fungicide applications at 3”-6” shoot growth.

 

Follow us on Facebook!

UAEX Plant Health Clinic

This work is supported by the Crop Protection and Pest Management Program [grant no. 2017-70006- 27279/project accession no. 1013890] from the USDA National Institute of Food and Agriculture.

 

Top