Melon
Symptom Cause  
Water-soaked spots on leaves
Angular Leaf Spots
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Small, dark spots on leaves; eventually leaves turn black; fruits may blacken/drop
Anthracnose (on plants)
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Leaves curled and discolored; honeydew on undersides of leaves, sooty mold forms
Aphids
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Small ragged holes in leaves
Cabbage Loopers
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Holes in leaves; stalks; and stems
Cucumber Beetles
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White powder on leaf undersides; foliage wilts
Downy Mildew
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Tiny holes in leaves
Flea Beetles
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Yellowing of the leaf margins (chlorosis) is an early symptom on the plant, and light- to dark-brown spots (necrosis) can appear, plus water-soaked regions on the stem.
Gummy Stem Blight (black rot)
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Tip of leaves brown, internal larvae trails visible. Leaves skeletonized and rolled up.
Leaf Miners
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Leaves curl, yellow or brown, brittle
Leafhoppers
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Flowers and new fruits damaged
Melonworms
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Flowers and new fruits damaged
Pickleworms
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White spots on leaves; eventually entire leaf is covered with powder; fruits ripen prematurely/poor flavor and texture
Powdery Mildew
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Sunken green spots on cucumbers
Scab
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Large ragged holes in leaves, often in middle
Slugs
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Leaves stippled, yellowing or bronze; dry out and drop may be webbing visible; sometimes galls form on leaves
Spider Mites
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Wilted; dried-up leaves
Squash Bugs
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