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Gummy stem blight is caused by the fungus Didymella bryoniae (anamorph: Phoma cucurbitacearum). Leaf lesions initially appear as dark, greasy-appearing spots that dry with age. Conidia, which are produced within fruiting bodies (called pycnidia) formed in the lesions, are spread primarily by splashing rain.
Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum, may cause wilting of individual runners or collapse of the whole plant.
Anthracnose lesions, caused by Colletotrichum orbiculare, can occur on all aboveground parts of the watermelon, including the fruit. Lesions on leaves are typically irregular in shape and are often associated with the leaf veins.
Gummy stem blight lesions occurring on the runner vines may cause them to wilt and die, but lesions on the crown may kill the whole plant.
Characteristic browning of the vascular tissues associated with Fusarium wilt.
Cucurbit downy mildew is Pseudoperonospora cubensis, an Oomycete or water mold that attacks the foliage. Typical symptoms include the appearance of small chlorotic spots that quickly become necrotic as well as upward curling of the leaves. When disease is severe, loss of the leaf canopy exposes the fruit to the sun, and they may burn.
Bacterial rind necrosis is reported to be caused by a variety of bacteria, including Erwinia sp., that normally reside within healthy tissues. Symptoms are rarely evident until the watermelon is cut open.
The LSU AgCenter and the LSU College of Agriculture
