For an accessible format of this publication, visit The best information available indicates that the downy mildew of grape is endemic in North America, where it was for the first time reported by Schweinitz in 1837. Most severe epidemics have been noted when wet winters are followe… When humid nights are followed by rain events the next day, the risk is high for downy mildew infection. Figure 3. Symptoms       Management       Causes       More Info. Grape berries infected with downy mildew. 5. Once inside the plant, the fungus grows and spreads through tissues. Young shoots usually are stunted and become thickened and distorted. 2120 Fyffe Road | Room 3 Ag Admin Bldg. This site designed and maintained by CFAES Marketing and Communications. CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. 2015-41595-24254 from the USDA National Institute of Food and Agriculture. Downy mildew is an important disease of commercial and backyard grapes in Kentucky. Sanitation is important. At night during periods of high humidity and temperatures above 55 degrees F (13 degrees C), the fungus grows out through the stomates of infected tissue and produces microscopic, branched, tree-like structures (sporangiophores) on the lower leaf surface. Downy mildew, caused by the fungal-like organism Plasmopara viticola, typically occurs in excessively wet and warm, but not hot, years. Downy mildew on grapes is a serious fungal disease that wreaks havoc in vineyards around the world, especially when the weather is humid, rainy, and mild. ), vine-borne vegetables, and a variety of species of ornamental flowers. On the lower leaf surface, a cottony growth ( mycelium) is often readily apparent. On fruit, most infection occurs during the period from early bloom through three to four weeks after bloom. Practices such as shoot positioning and leaf removal that help to open the canopy for improved air circulation and spray coverage are also very important. The small sporangiophores and sporangia make up the cottony, downy mildew growth. ), roses (Rosa spp. This disease may also predispose grapevines to winter injury. This downy growth is directly under the pale-yellow spots on the upper surface. Rain events are considered the primary factor driving the disease. For more information, visit Phone: 614-292-6181, © 2020 | 2120 Fyffe Road | Room 3 Ag Admin Bldg. CFAES Diversity  |  Nondiscrimination notice  |  Site Map. Grape downy mildew occurs mainly in regions where it is warm and wet during the vegetative growth of the vine. For technical support please contact the CFAES Helpdesk. Young infections are very small, greenish-yellow, translucent spots that are difficult to see. and impatiens (Impatiens spp. Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildew is most damaging when factors exist that increase the moisture of soil, air, and the host plant. Cultivation also prevents overwintering spores from reaching developing vines in the spring. Downy mildew on upper side of grape leaf. The optimum temperature for disease development is 64 to 76 degrees F (18 to 25 degrees C). Temperature also plays a role, but downy mildew can grow in temperatures of 50ºF to 85ºF, with optimal temperatures from 65ºF to 72ºF. | Columbus, Ohio 43210 | 614-292-6181 When plant parts are covered with a film of moisture, the sporangia release small swimming spores, called zoospores. Columbus, Ohio 43210 The pathogen attacks all green parts of the vine. On the underside of the leaf, the fungus mycelium (the “downy mildew”) can be seen within the border of the lesion as a delicate, dense, white to grayish, cotton-like growth (Figure 2). The pathogen attacks all green parts of the vine and often causes significant premature defoliation. About Grapes with Downy Mildew… Figure 4. When it comes to battling powdery mildew and downy mildew on grapes, the following adage applies: “The early grower catches the fungus!” Early fruit set heralds a time of extra vigilance when it comes to disease control, as young fruit clusters are highly susceptible to all major diseases, including downy mildew and powdery mildew. For a long time it was almost the only remedy against mildew powdery mildew. New leaves infected by downy mildew often develop yellow lesions that look oily. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. The prime example is Peronospora farinosa featured in NCBI-Taxonomy and HYP3. It was taken from the Grape IPM Disease Identification Sheet No. Proper dormant pruning and sanitation are imperative to reduce the number of spores.