Powdery mildew affects all cucurbits, but most often damages cantaloupes, squash, and pumpkins. Two different fungi, Erysiphe cichoracearum and Sphaerotheca fuliginea, can cause powdery mildew on cucurbits. Both fungi grow as a white, powdery mass on leaves, petioles, and stems. The resulting decrease in photosynthesis may cause significant reductions in the quality and yield of fruit.
Powdery mildew appears on leaves, petioles, and young stems as a white powdery mass composed of mycelium and countless numbers of spores (Fig.1-2). Under favorable environmental conditions the entire top surface of the leaf may be covered with the powdery fungus and an entire field may appear to turn white within a few days. Infections may also occur on lower leaf surfaces. Badly infected leaves become yellow, turn brown, and shrivel.
Cucurbit fruits are not directly attacked by powdery mildew fungi; however, they may be malformed or sunburned due to loss of foliage cover. In severe infections both the size and number of fruit may be reduced.
|Table 1. Cucurbit cultivars with resistance to powdery mildew|
|Calypso-F11||Dasher II-F1||Burpless 26-F1|
|Carolina-F1||Daytona-F1||Green Dragon Burpless|
|Fancipak M-F1||Lightning-F1||Orient Express-F1|
|Lucky Strike-F1||Seneca Longbow-F1|
|Big Moon (R)2|
|Magic Lantern (MR)|
|1 Note: F1 refers to the hybrid generation produced by a cross of two inbred lines. Seed from these plants will not produce plants that are true to type and should not be saved for future plantings.|
|2 MR = moderately resistant; R = resistant|
|Refer to the current Virginia Pest Management Guide for Home Grounds and Animals (VCE Publication 456-018), http://pubs.ext.vt.edu/456/456-018/456-018.html, for details on the proper use of pesticides.|
Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products which also may be suitable.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Interim Administrator, 1890 Extension Program, Virginia State University, Petersburg.
May 1, 2009