Minimizing periods of leaf wetness can lower the incidence and severity of downy mildew. Because the disease does not overwinter in many production areas but is blown in from areas to the south, the occurrence of the disease is not affected by crop rotation or post-harvest sanitation.5 2Īdequate management of downy mildew requires an integrated approach to reduce the periods of leaf wetness, avoiding the disease by planting early in the season, the use of disease-resistant varieties, and the application of fungicides. Symptoms usually develop three to twelve days after infection, depending on the temperature and moisture levels present, with new sporangia formed in a little as four days. Disease development is slowed by warm (>95☏) temperatures, while periods of fog, rain, and frequent dews are favorable for infection. Infection and disease development occurs most rapidly during periods with moderate temperatures (59-68☏) and cool nights. 4,5 Inoculum from infected, greenhouse-grown plants in the region may result in the disease showing up on field-grown plants earlier than would be expected. In these regions, the pathogen arrives first in the more southern locations and makes its way northward, usually arriving in the Midwest and New York in late July, August, or September. 3įor the Eastern and Midwestern production areas, inoculum typically comes from southern Florida and Texas. The pathogen is disseminated by windblown sporangia that can travel up to 600 miles in 48 hours on air currents. ![]() ![]() In the U.S., the pathogen overwinters on live cucurbit plants in areas with mild winter climates or plants growing in greenhouse/protected culture environments. ![]() It does not overwinter on plant debris in most areas. The downy mildew pathogen is an obligate parasite that needs living cucurbit plants in order to grow and survive. Downy mildew of cucumber is caused by Pseudoperonospora cubensis, a member of the water mold group (Oomycota) of fungal-like organisms.
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