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Melanie Lewis Ivey, Hadziabdic, Denita, Hollier, Clayton A., Ferrin, Donald M., Overstreet, Charles
Anthracnose of cucumber caused by Colletotrichum orbiculare. Leaves initially show small, pale yellow or water-soaked areas that enlarge rapidly and turn tan to dark brown. These lesions may develop holes or cracks in the center.
Bacterial wilt of cucumbers caused by Erwinia tracheiphila. This bacterium is spread primarily by the striped cucumber beetle, Acalymma vittata, and the spotted cucumber beetle, Diabrotica undecimpunctata howardi.
Cucumber scab is caused by the fungus Cladosporium cucumerinum. Symptoms can occur on leaves, petioles and stems, but the most conspicuous symptoms occur on the fruit. Affected fruits are weakened and therefore often invaded by soft-rotting bacteria that produce a foul-smelling decay.
Downy mildew is a foliar disease of cucumbers and other cucurbits caused by Pseudoperonospora cubensis. Athough the pathogen does not attack the fruit, it can cause defoliation and yield loss. On cucumbers, symptoms are first evident as blocky, chlorotic spots that become necrotic. Grayish fungal sporulation may be observed on the underside of the lesions.
Alternaria leaf blight of cucumber, caused by Alternarai cucumerina. The pathogen rarely attacks the fruit but can cause defoliation, exposing the fruit to sunburn.
Belly rot is caused by soil-borne fungus Rhizoctonia solani. Symptoms occur on the underside and blossom end of the cucumber fruit and can be observed within as little as 24 hours after the pathogen invades cucumbers that are in contact with soil. As the disease progresses, lesions become sunken and irregular in shape. The entire fruit can rot in 72 hours.
Closer view of bacterial wilt of cucumbers. After infection occurs, dull green patches can appear on the damaged leaves, resulting in rapid wilting of the entire plant.
Root knot caused by the nematode Meloidogyne incognita. Note severe galling on cucumber roots. Parts above the ground appear stunted, unthrifty and yellowish, resulting in reduced overall quality and yield.
The LSU AgCenter and the LSU College of Agriculture
