Bacterial Disease on Pumpkin Fruit
Posted: September 10, 2014
Unfortunately, 2014 is going to be remembered as a bad year for bacterial diseases in vegetable crops including pumpkin for several regions of the state. As pumpkins are being harvested for market, growers are seeing small circular whitish lesions on the fruit. Depending on the cultivar, they can be surrounded by dark margin or sometimes a more orangish-yellow to tan margin if the cultivar has a white rind.
These could be the result of either bacterial leaf spot caused by Xanthomonas cucurbitae or angular leaf spot caused by Pseudomonas syringae pv. lachrymans however, the latter is more common on pumpkin. Both are foliar diseases and the fruit become infected when the bacteria are splash dispersed from the leaves onto the fruit or transferred during via passing equipment or people. The bacteria will colonize the lenticels on the fruit surface and under favorable conditions multiply and lead to the development of visible symptoms. The lesions can expand and exudates can ooze from the lesions and dry on the outside of the fruit. Secondary organisms can also infect and lead to soft rot.
Both pathogens are thought to be seedborne but the impact on disease development is not well understood. Efforts are being made at several universities to better understand the epidemiology of these bacterial diseases and to identify a potential seed treatment protocol since cucurbit seed is too sensitive to hot-water treat. A 2-year minimum crop rotation is recommended to allow the crop residue to thoroughly decompose. Applications of copper tank mixed with mancozeb beginning at fruit set through expansion will help reduce fruit symptoms, however thorough coverage of the leaves and fruit is necessary. Several university research trials have also demonstrated a reduction in fruit symptoms with the application of Actigard, a plant defense inducing product, in addition to copper prior to disease onset.