Cucurbit powdery mildew is caused worldwide by the fungal pathogens Podosphaera xanthii and Golovinomyces cichoracearum. Podosphaera xanthii is more common¹ and, apparently, may be the only one on cucurbits in North America². Early symptoms of powdery mildew include small, circular, yellow lesions on leaves and petioles. Lesions quickly become covered in white spores and may appear also on the underside of the leaf. The pathogen may be entirely restricted to the undersides of leaves in areas with intense sunshine, e.g., Imperial Valley, California. As disease progresses the entire leaf and petiole surface may become covered in the characteristic white powdery powdery spores that may also be found on peduncles (stems) and fruit. Powdery mildew affects all cucurbit crops such as cucumber, melon, squash, and watermelon.
- Cucurbit Downy Mildew, Cornell University, 2020
- Managing Cucurbit Powdery Mildew Successfully in the Northeastern USA in 2017,
Managing Cucurbit Powdery Mildew Successfully in NY in 2017, Cornell University, 2017
- UC Pest Management guidelines, State of California IPM program, 2016
- Vegetable Pathology Factsheets: Cucurbit Powdery Mildew, NC State University, 2015
- Watch for powdery mildew on vine crops, Michigan State University, 2014
¹Jahn, M., H.M. Munger, and J.D. McCreight. 2002. Breeding cucurbit crops for powdery mildew resistance, p. 239–248. In: R.R. Bélanger, W.R. Bushnell, A.J. Dik, and T.L.W. Carver (eds.). The powdery mildews: a comprehensive treatise. APS Press, St. Paul, Minnesota, USA.
²McCreight, J.D. 2004. Notes on the change of the causal species of cucurbit powdery mildew in the U.S. Cucurbit Genet. Coop. Rpt. 27:8–23.