Regular fungicide sprays may be necessary to control gummy stem blight during cool, rainy weather. Seed treatments should be routine practice for gummy stem blight control. Resistance to gummy stem blight is not available in commercially-acceptable watermelon, cucumber, or melon varieties. Orientating rows parallel to the prevailing wind direction can also help reduce periods of leaf wetness in semi-arid environments. Promote air movement within the plant canopy and rapid leaf drying by avoiding dense plantings, narrow row spacings, and excess and overhead irrigation. Practice a two-year or longer crop rotation to nonhosts. No biological control strategies have been developed for gummy stem blight. Gummy stem blight can reduce yield, quality, and marketability of fruit. Fruit lesions appear as small, water-soaked spots that enlarge gummy exudates are apparent on fruit. Lesions develop more slowly if infection occurs in older plants, and cankered vines wilt near mid-season. Seedlings can be killed from stem girdling. Small black specks, fruiting bodies of the fungus, are apparent on stem cankers. Stem cankers develop on cortical tissues and often produce brown, gummy exudates. Stem lesions are circular in shape, and tan to dark brown in color. Lesions often develop first at leaf margins, but eventually entire leaves become covered with lesions. ![]() Gummy stem blight symptoms first appear on leaves as circular, tan to dark brown spots, with or without water-soaking. The pathogen can be disseminated within and among fields by wind and splashing water, and survives between cucurbit crops in infested crop debris and diseased vines. Infection is favored by free moisture and cool to moderate (68 to 77✯) temperatures, but continuous leaf wetness is essential for disease to progress significantly. Fruit can be infected through wounds and flower scars at pollination. Young leaves of watermelon and melon are highly susceptible to infection, but cucumber and squash are resistant when young and become susceptible as they age. When these ascospores land on leaves and stems, they infect through natural openings, wounds, or by direct penetration. The disease cycle begins when spores (ascospores) are released from fungal fruiting bodes after rain or heavy dews. ![]() The pathogen can also attack fruit, causing a disease known as black rot. Gummy stem blight is caused by the fungus Didymella bryoniae (anamorph Phoma cucubitacearum).
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