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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Vegetable > Cucumber > Discolored leaves

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Cucumber > Leaves > Discolored leaves

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  • Image: Powdery Mildew 1
  • Image: Powdery Mildew 2
  • Image: Powdery Mildew 3

Powdery Mildew
Podosphaera xanthii

  • Initially pale yellow spots develop on the oldest leaves
  • White to gray powdery felt in spots, blotches or complete covering of leaves
  • Lesions develop on underside of leaves, or on shaded leaves first
  • Older leaves infected first
  • Severe infection can cause leaves and vines to wither and die
  • Fruit may be blotchy or have sunscald
  • More information on Powdery Mildew
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  • Image: Cold Temperature 1
  • Image: Cold Temperature 2

Cold Temperature

  • Weather has been cold (below 50°F) and wet
  • Soil is cold (below 62°F) and damp to the touch
  • Leaf edges turn olive green to brown
  • In severe cases entire leaves, young shoots or the entire plant may be completely discolored and wilted
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  • Image: Squash Bug 1
  • Image: Squash Bug 2
  • Image: Squash Bug 3

Squash Bug
Anasa tristis

  • Feeding can cause yellowing and wilting
  • More common on squash and pumpkins than cucumber
  • Adults are 5/8 inch long, somewhat flattened, and gray to dark brown with alternating orange and brown stripes on the edges of their abdomen
  • Nymphs are 1/10 to 1/2 inch and are a light to dark gray color
  • Active from May through September
  • More information on Squash Bug
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  • Image: Virus 1
  • Image: Virus 2
  • Image: Virus 3

Squash mosaic, cucumber mosaic, watermelon mosaic

  • Irregular, blotchy to wavy patterns of yellows and greens on leaves
  • Leaves may be distorted (sometimes fern-like), wrinkled, and curled
  • Plants may be stunted
  • Fruit may have unusual color patterns, blotches or rings but are not rotten
  • Fruit are often deformed and distorted
  • More information on Virus
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  • Image: Bacterial Wilt 1
  • Image: Bacterial Wilt 2
  • Image: Bacterial Wilt 3

Bacterial Wilt
Erwinia tracheiphila

  • Leaves first appear dull green, wilt during the day, and recover at night
  • Eventually wilted leaves die
  • Wilt progresses down the vine until entire vine is wilted or killed
  • Striped or spotted cucumber beetles will be present in the garden
  • Cucumbers and muskmelon most commonly affected (pumpkins and squash less affected)
  • More information on Bacterial Wilt
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  • Image: Spider Mites 1
  • Image: Spider Mites 2

Spider Mites
Tetranychus urticae

  • Feeding on the underside of leaves causes leaves to appear pale and stippled
  • Webbing can be found on underside of leaves when heavy infestations are present
  • Adult spider mites are very small (approximately 1/50 inch in length), and are yellow to dark crimson, with dark spots
  • Mites usually appear in late June and August, and are more prevalent in hot, dry weather
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  • Image: Downy Mildew 1
  • Image: Downy Mildew 2
  • Image: Downy Mildew 3

Downy Mildew
Pseudoperonospora cubensis

  • Pale green to yellow spots on upper surface of leaves, later turn brown
  • Angular spots bounded by leaf veins
  • Dark purplish grey fuzz on underside of leaf when high humidity
  • In wet or very humid conditions disease progresses rapidly, leaves turn brown and look like they were killed by frost
  • On watermelons, an exaggerated upward leaf curling is common
  • Cucumber and muskmelon most susceptible
  • More information on Downy Mildew
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  • Image: Aphids 1
  • Image: Aphids 2
  • Image: Aphids 3

Aphis gossypii, Myzus persicae

  • Aphids feed on leaves, resulting in yellowing
  • Leaves may wilt
  • Small (1/6” – 1/8”) soft bodied insects
  • Aphids can transmit viruses
  • Active from April through October
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  • Image: Squash Vine Borer 1
  • Image: Squash Vine Borer 2
  • Image: Squash Vine Borer 3

Squash Vine Borer
Melittia cucurbitae

  • Feeding by larvae causes yellowing of leaves and wilting
  • Holes filled with green to orange excrement near the base of the plant may be present
  • Less common on cucumbers
  • Adult borer resembles a wasp, is active mid-June through July
  • More information on Squash Vine Borer

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