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Cucurbits - Powdery Mildew


Powdery mildew is a fungal disease of cucurbits.

Most cucurbit crops including cucumber, squash, zucchini, pumpkin and watermelon, are susceptible to this disease. The impact of powdery mildew on crop production includes reduced photosynthesis, impaired growth, premature senescence and yield loss. Early leaf senescence lowers market quality because the fruit becomes sunburned, does not store well, or loses flavor.

Symptoms and Diagnostics

The disease usually starts on the older leaves. The first symptoms of powdery mildew are small, circular, white, powdery fungal colonies (mycelia and conidia) on upper leaf surfaces. White colonies can be seen occasionally on the lower surfaces of leaves and stems.

Cucurbit fruits are not directly attacked by the pathogen; however they may be malformed or become sunburned due to early loss of foliage. Severe epidemics of powdery mildew will reduce both the size and number of fruit.

Disease Development

Powdery mildew develops quickly under favorable conditions such as dense plant growth, low light intensity, warm temperatures and high relative humidity. However moisture on the leaf surface is not required for spore germination and infection.


Fungicide applications: a scouting program is helpful to detect disease infestation so that the fungicide program can be initiated. Alternate fungicide modes-of-action in the application program.