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Protect Your Cucumber Plants from Cucurbit Diseases

April 15, 2020

University of Georgia Extension compiled a list of the most common pests and diseases impacting vegetables, particularly cucurbits, in the Southeast. Powdery mildew, gummy stem blight and leaf spot continue to be top of mind for growers as they plan for the season ahead.

Podosphaera xanthii and Erysiphe cichoracerarum, the 2 pathogens that cause cucurbit powdery mildew, attack cucurbits, particularly cucumbers, year-round. P. xanthii is a particularly aggressive pathogen that attacks during warmer months, while E. cichiracearum strikes during cool spring and early summer. The disease thrives in high humidity, making the Southeast a high-risk area for powdery mildew.

Powdery mildew causes white spots on leaf surfaces, which can expand and weaken the plant, reducing yield potential. You can monitor for the disease by looking for a white tint on all leaves, especially lower ones, throughout the season. Powdery mildew tends to appear in the middle of the season, so preventive treatments can help maximize yield potential while preventing plant damage.

Caused by the fungal pathogen Didymella bryoniae, gummy stem blight affects all parts of a cucurbit vegetable. Symptoms of gummy stem blight often begin as water-soaked spots on seedling cotyledons and stems and develop into dry brown lesions. Severely infected plants can develop small black fungal fruiting bodies called pycnidia that can be seen with a 10x hand lens. When left untreated, this blight can cause reduced yield and even plant death. Gummy stem blight carries on season-to-season in infected crops and weeds, causing damage year after year. Early intervention is the best tool to prevent and treat pre-season signs of gummy stem blight.

Miravis Prime provides control of gummy stem blight in cururbits.

Miravis® Prime provides control of gummy stem blight in cururbits.


Alternaria leaf spot and Cercospora leaf spot cause brown spots to appear on leaves, causing them to wither and die. Leaf spot particularly affects cucumber growers, though they can appear across any cucurbit plant. Alternaria leaf spot survives on crop residue even after a growing season, so you may consider a 2-year crop rotation if leaf spot is present. Regular field surveillance for leaf spot can help identify the disease immediately and prevent further crop damage, though early-season treatment is the best way to prevent and treat both powdery mildew and leaf spot.

This agronomic image shows Miravis Prime efficacy against powdery mildew


Miravis Prime fungicide contains 2 chemistries, fludioxonil and Adepidyn® fungicide, to help treat difficult-to-control diseases in cucurbit vegetables. The 2 powerful active ingredients offer strong disease control that evenly distributes on leaf surfaces to protect against powdery mildew, leaf spot, gummy stem blight and plenty of other diseases that threaten yield potential.

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