Pumpkin plants are part of the cucurbit group of vegetables, which also includes cucumbers, gourds, squashes and other plants in the genus Cucurbita. Many different varieties of pumpkins exist, some growing as vines, some as bushes or semi-bushes, and some as miniatures. In general, pumpkin plants are not plagued by many diseases, but sometimes they can suffer from a variety of fungi. You’ll need to identify and treat the fungal disease with the appropriate fungicide in order to get rid of the fungus.
Treat black rot, caused by the fungus Didymella bryoniae, by applying the fungicides chlorothalonil or thiophanate-methyl. Black rot commonly occurs in the field when pumpkins are growing, especially when there are high moisture levels. Black rot causes black decomposing lesions on the outside of the pumpkin and gummy stems.
Cure downy mildew, which causes the pumpkin plant leaves to turn yellow and then brown and fuzzy, by applying chlorothalonil mixed with dimethomorph. Alternate this mixture with a fungicide containing mefenoxam. Downy mildew is caused by the fungus Pseudoperonospora cubensis, causing spots on the tops of the leaves with purplish or grayish spores on the lower leaf surfaces, and often infects pumpkin plants during moist, cool conditions.
Treat anthracnose, caused by the fungus Colletotrichum orbiculare, by applying chlorothalonil and alternating with applications of azoxystrobin or pyraclostrobin. You can identify anthracnose fungus on your pumpkins by the brown or tan oval lesions on the leaf surfaces, with raised, salmon-colored bumps and lesions on the fruits.
Spot powdery mildew on your pumpkins by looking for white, powdery spots on the leaves and stems. Get rid of this fungus by spraying the pumpkins with chlorothalonil mixed with a strobilurin or thiophanate-methyl. You can alternate your fungicide sprayings with applications of paraffinic oil.
Treat phytophthora blight (Phytophthora capsici) on your pumpkins by spraying the plants with dimethomorph mixed with chlorothalonil. You can spot this blight on your pumpkins by looking for yeast-like growths on the undersides of the fruits and spreading to the topsides.
Look for tiny water-soaked spots turning white and rash-like on the pumpkin fruits, as well as black dots on the leaves and stems, to identify Septoria leaf spot, caused by the fungus Septoria cucurbitacearum. Treat this fungal disease by spraying the pumpkin plants with chlorothalonil.