![]() ![]() Scout transplants for the presence of symptoms and rogue diseased plants and neighboring plants, even if neighboring plants do not yet have symptoms.ĭidymella bryoniae can survive in the soil or on infected plant debris. When transplants are used, it is critical to reduce the level of humidity in the greenhouse by increasing ventilation and managing irrigation. Michigan State University Extension recommends growers plant seed that has been treated with a fungicide to decrease the risk of introducing the pathogen into clean fields. The pathogen that causes gummy stem blight is seedborne, therefore infection can occur as early as the seedling stage. Photo credit: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Tactics to manage gummy stem blight ![]() Gummy stem blight symptoms on winter squash fruit. Butternut, Hubbard, buttercup, and acorn squashes are most susceptible to fruit symptoms. Black rot can occur in the field or in storage. Fruit lesions expand and eventually can turn the watermelon fruit black, often referred to as black rot. On fruit, symptoms start as water-soaked lesions with or without the gummy exudate on the blossom end of the fruit. A gummy exudate is generally associated with the stem lesions, thus the name “ gummy stem blight." Infections in older muskmelon vines result in abundant stem cankers and ultimately can result in vine wilting. Photo credit: Jason Brock, University of Georgia, Gummy stem blight symptoms on watermelon seedlings. In both leaf and stem lesions, small dots known as pycnidia, or fruiting bodies of the pathogen, can be observed using a magnifying hand lens. Canker symptoms are more common in muskmelons than cucumbers, pumpkins, squash and bottle gourds. Stem cankers and girdling can result in death of newly transplanted plants. Symptoms on the stems start as large, water-soaked lesions that expand and form a canker (tissue turns necrotic, brown and hardens). In watermelons and muskmelons, severe foliar symptoms can result in sunburned fruit and smaller fruit size. Melon and watermelon foliage is more susceptible to gummy stem blight than squash and pumpkin foliage. Lesions on leaves expand and coalesce and can cause leaf blighting. Circular, water-soaked lesions develop on seedlings, cotyledons, first true leaves and secondary leaves. Symptoms of gummy stem blight occur in leaves, stems, plant crowns and fruit. Wounding of the stem and fruit plays a role on initial infection and can increase disease severity. Field dispersal of the pathogen is aided by rain and wind. Disease development is highly influenced by humidity and free moisture on leaves caused by rain or extended dew periods. ![]() Gummy stem blight is caused by the fungal pathogen Didymella bryoniae. Gummy stem blight is a common disease of cucurbits worldwide, and in northern states has been prevalent on squashes and pumpkins. ![]()
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