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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Annuals and Perennials > Cosmos > Discolored leaves

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Cosmos > Leaves > Discolored leaves

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  • Aster yellows 1
  • Aster yellows 2
  • Aster yellows 3

Aster Yellows

  • Part or all of the leaves may turn yellow
  • Flowers fail to develop, remain small green and may be distorted
  • Clumps of weak shoots known as witches broom develop throughout the plant or on flower stalks
  • More information on aster yellows
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  • Spider mites 1
  • Spider mites 2
  • Spider mites 3

Spider Mites
Tetranychus urticae

  • Active during summer, particularly abundant during hot, dry weather
  • Pale stippling appears on the upper leaf surface
  • Leaves are discolored off green to whitish, yellowish, or bronze
  • Premature leaf drop can occur
  • Visible webbing occurs on infected leaves when populations are high
  • Adults are tiny (1/50th inch long) and oval, greenish or yellowish with a dark spot on either side of the body
  • More information on spider mites
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  • White mold 1
  • White mold 2
  • White mold 3

White Mold
Sclerotinia sclerotiorum

  • Entire plant or single branch wilts, leaves turn brown and die
  • Wilted stems are discolored, tan to off-white
  • Fluffy, white cotton-like fungal growth may been seen on infected plants when humidity is high
  • Black hard spheres ranging in size from 1/16 to 1/2 inch can be found clinging to the outside an infected stem or embedded inside the dead stem
  • Entire plant or single branch wilts, leaves turn brown and die
  • More information on white mold
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  • Gray mold 1
  • Gray mold 2
  • Gray mold 3

Gray Mold
Botrytis cinerea

  • Brown blossoms or petals; flowers drop off prematurely
  • Leaves may turn completely brown and rotted
  • Gray fuzzy mold develops on rotted tissue under humid conditions
  • Disease develops during cool, wet weather
  • More information on gray mold

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