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Alternaria leaf blight (Alternaria cucumerina) is found primarily on watermelon and muskmelon but may occur on cucurbits. Symptoms first appear at the time of fruit set on older leaves, beginning as small, necrotic spots that may be surrounded by a yellow halo. Lesions expand to form brown spots ranging from 1/2" to 3/4" in size; a concentric ring pattern may be present if conditions are wet. As lesions expand, they merge to form large, blighted areas, followed by leaf curling and eventual leaf drop.

Alternaria leaf blight on muskmelon foliage.

(Photo: Kenny Seebold, University of Kentucky)

Close-up of Alternaria leaf blight lesions.

(Photo: Kenny Seebold, University of Kentucky)

Management:

• Space plants for air circulation and rapid drying.
• Apply protectant fungicides beginning at fruit set.
• Promptly remove and destroy diseased plant material during the growing season.
• Manage weeds and potential alternative hosts.
• Promptly destroy crop residues after harvest.
• Deep plow to bury residual inoculum.
• Rotate with nonhost crops for at least 2 years. 

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