- Worldwide distribution. On members of the cucumber family (cucurbits): important on cucumber, rockmelon and zucchini, but also on gourd, melon, pumpkin, squash, watermelon, zucchini.
- Not a fungus, a water mould, or oomycete. Spots yellow, then brown, merge; leaves dry and die.
- Spread is by wind and water splash, and long distance in air currents when humidity is high. Survival is on volunteer plants and weeds.
- Cultural control: avoid overhead irrigation; space plants to allow air movement; avoid planting in warm and wet times of the year; tolerant varieties available (melon, cucumber, watermelon); weed.
- Chemical control: copper, chlorothalonil, mancozeb (protectants); metalaxyl, phosphorus acid (systemics).
Pacific Pests, Pathogens, Weeds & Pesticides
Cucumber downy mildew (143)
Photo 1. Yellow spots of downy mildew, Pseudoperonospora cubensis, on the upper surface of a leaf; they are often angular and restricted by the leaf veins.
Photo 4. Yellow irregular patches caused by downy mildew, Pseudoperonospora cubensis, on the upper surface of a melon leaf.
Cucumber downy mildew
AUTHOR Grahame Jackson
Information from Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany; and (including Photos 1&5) Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, et al. CSIRO Publishing; and from Quesada-Ocampo L (2018) Cucurbit downy mildew. Vegetable pathology factsheets. NC Extension. (https://content.ces.ncsu.edu/cucurbit-downy-mildew). Photos 2&3 Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org. Photo 4 Jacquie (Wright) Kami, formerly Plant Pathologist, Secretariat of the Pacific Community, Suva, Fiji.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.