Downy mildew is a fungal disease caused by Pseudoperonospora cubensis. It affects cucurbits (cucumber, melon, squash, pumpkin) and a few weeds. The disease is found worldwide in temperate and tropical areas and is one of the most important foliar diseases of cucurbits. It occurs sporadically in the northeast. It causes small fruit, due to lost leaf area, and the fruit may have a poor flavor. After the leaves die, fruit is exposed to the sun and may become sunscalded. This disease is favored by cool (61o-72o F), moist weather.
Powdery Mildew is caused by the fungi Erysiphe cichoracearum and Sphaerotheca fuliginea. This disease is a major production problem. It has been observed since the 1800s. Although there are powdery mildew fungi on many plants, these two infect only muskmelon, cucumber, squash, pumpkin, gourd, and watermelon. This disease can cause fruit to be smaller in size, fewer in number, less able to be successfully stored, sunscalded, incompletely ripe, and have a poor flavor. It may also predispose plants to black rot. It is favored by moderate temperatures. These fungi are unusual in that they do not require the leaves to be wet for them to infect the leaf, but rather the humidity must be high. They produce spores when the humidity is low.
By Pamela S. Mercure, IPM Program Assistant, University of Connecticut, 1998.
McGrath, M. T. 1997. Proceedings of the New England Vegetable and Berry Conference. Cooperative Extension System.
McGrath, M. T. and C. E. Thomas. 1996. Powdery Mildew in Compendium of Cucurbit Diseases. T.A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. APS Press, St. Paul, MN. pp. 28-30.
Reuveni, R., and M. Raviv. 1997. Control of Downy Mildew in greenhouse-grown cucumbers using blue photoselective polyethylene sheets. Plant Disease. 81:999-1004.
Sherf, A.F. and A. A. MacNab. 1986. Vegetable Diseases and Their Control. John Wiley and Sons, New York.
Thomas, C.E. 1996. Downy Mildew in Compendium of Cucurbit Diseases. T.A. Zitter, D. L. Hopkins, and C. E. Thomas, eds. APS Press, St. Paul, MN. pp. 25-27
This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
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