Downy Mildew
Plasmopara viticola  |
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Signs and Symptoms:
Downy mildew is caused by the fungus Plasmopara viticola.
- This fungus can grow and sporulate on all green vegetation and fruit of the grapevine.
- The sporulating fungus appears white, dense, and fluffy concentrated within lesions on the underside of leaves, and covering the surface of young berries and shoot tips.
- The shoot tips may become thick and curled - this symptom is called a "shepherd's crook"
- In the spring symptoms may appear as an "oil-spot" on the upper side of leaf, and in the fall as angular yellow to red lesions.
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Optimal Conditions for Disease:
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| Conditions which lead to increased moisture of the soil, air and host favor the development of downy mildew. Downy mildew infections are greatest when there is a wet winter followed by a wet spring and a warm summer with rain showers every 8-15 days. |
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Links:
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References:
Compendium of Grape Diseases. 1988. R.C. Pearson and A.C. Goheen. APS Press, St. Paul, Minnesota . 93 pp.
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