Diseases of watermelon (Citrullus lanatus) in Arizona
Gummy stem blight
Gummy stem blight of watermelon is caused by the fungus Didymella bryoniae. It has occurred on watermelon in Arizona only as a seedling disease on infected transplants. The fungus causes lesions on the stems of seedlings weakening the stem. The seedling may be girdled by lesions if disease progresses or simply be so weakened by initial infection that it does not recover fully and is never productive. Gummy stem blight is a serious problem in regions of high rainfall, and since the fungus requires prolonged moisture to become established, it is doubtful that it would become a problem in mature vines in Arizona.
It is very important for growers to inspect seedlings before transplanting.
Infected seedlings should not be accepted. The fungus is seed borne,
and greenhouse operators should make sure that seed to be used in transplant
production has been assayed or inspected for gummy stem blight. Once
a greenhouse is infested with the fungus, it must be cleaned thoroughly
before using as a watermelon transplant facility again.
August 1, 2003