Gummy stem blight

Gummy stem blight produces a variety of symptoms which are referred to as leaf spot, stem canker, vine wilt and black fruit rot. Lesions on leaves and fruit usually begin as spreading water-soaked areas; in the former these may have a chlorotic halo, become light brown and irregular in outline; leaves can be destroyed. On fruit, dark cracked sunken lesions form, beneath which an extensive rot is found. In the field the first symptoms may be plant collapse where sunken, girdling cankers lead to total loss. Infection also occurs on seedlings. Spots on stems often elongate into streaks (usually starting at the joints) and have an amber exudate of gummy material. The size and colouring of spots vary according to crop. The main characteristic features are the gummy exudate on stem and fruit lesions, and the abundant pycnidia followed by perithecia. The pycnidia, whether on fruit, stem, or leaf, are closely spaced groups of the dark brown to black fruiting bodies, just large enough to be seen without a hand lens. Sometimes they are arranged in rings on the fruit or leaf surface.

During the rainy season lesions can become water soaked and can spread and lead to severe defoliation. Further development can lead to bark scaling and cracking in cucurbit vines and the collar region of watermelon. Gummy exudates may occur from cracks, especially in watermelon and pumpkin. Severe infection often results in death of the plant (University of Hawaii, 2012).