Damage Symptoms

The disease is most severe on cucumber and cantaloupe, but it attacks and can be damaging to all cucurbit crops. Symptoms occur mainly on the leaves where they begin as yellow angular spots becoming tan to brown with age. During periods of high moisture, sporulation may be evident to the naked eye on the lower surface of leaf lesions where the sporangiophores protrude through stomata and produce pigmented sporangia abundantly.


Conditions for Development

The pathogen is an obligate parasite that may exist on crop plants, volunteer crop plants, or wild cucurbits year-round in tropical and subtropical regions. Sporangia carried by air currents or rain splash are the main means of disease dissemination. Disease development can occur over a wide temperature range under conditions of high humidity resulting from dew, fogs, or rainfall.

Control

Use resistant cultivars when available. Fungicidal sprays are important in the absence of resistant cultivars when the crop is grown under conditions conducive for disease development.