Phoma blight

Phoma blight (P. exigua var. exigua) is a plant pathogen of the genus Phoma whose hosts include beans and Cucurbits.

Cucurbits
The spots on cucurbit leaves produced by the Phoma blight are usually more irregular in shape and most often are on the margin of the leaves. The spots are light brown on cantaloupe and cucumber and dark brown on watermelon. Fewer lesions are produced on stems but symptoms also tend to spread from the crown of the plant, giving the plant a blighted appearance. Fruit are generally not affected.

Treatment
Spotted fruit, even though unsightly, is fit for food provided the diseased parts are cut away.

Chemical
A fungicide such as benomyl (Benlate), chlorothalonil (Bravo), copper, maneb (Manzate D or Dithane M-22 Special), mancozeb (Dithane M-45 or Manzate 200) or Dikar (Polyram) may be used to control the disease in the field. It is important to start the spray schedule as soon as the plants emerge and spray at 7-10 day intervals, covering all plant surfaces. High pressure (400 psi), high volume (100 gal/acre for a mature crop) spray equipment provides most effective coverage.

Prevention
Crop rotations with nonhost plants such as small grain, corn, of two or more years are effective in reducing the incidence if disease-free seed are used. Currently no varieties are resistant.

Similar conditions
Conditions which may be mistaken for phoma blight include :

Other fungi

 * Colletotrichum blight
 * Fusarium wilt
 * Botrytis cinerea
 * Sclerophoma
 * Sirococcus blight

Environmental

 * Chemical burn
 * Frost
 * Sun scald