Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Downy mildew on cucumber was confirmed July 7 on the border of Caroline and Dorchester counties in Maryland and in Sussex County Delaware. It also was found on cucumber in Burks County, Pennsylvania this week. Downy mildew does not overwinter here in the MidAtlantic and must be reintroduced each year. The map here is from http://cdm.ipmpipe.org/ site, which tracks movement of the pathogen throughout the US. The counties shaded red indicate new reports in the last 7 days. Downy mildew is spreading rapidly to new areas. Even though it has only been reported in two Maryland counties and in Sussex Co., I believe it is likely present, but not yet detected in additional counties. Preventative applications are more effective that applications made after disease is detected. Effective products such as Ranman and Previcur Flex should be tank mixed with a protectant and alternated with other efficacious materials such as Zampro, Tanos, Forum or Curzate. Organic cucumber can be protected with copper and Serenade or other biorationals.
Map of reported cucurbit downy mildew distribution on July 9, 2015.
Early symptoms of downy mildew on cucumber.