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Onion > Leaves > Leaves Flattened or Distorted

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  • Image: Aster Yellows
    Credit: Whitney Cranshaw, Colorado State University, Bugwood.org
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green arrowAster Yellows
Aster Yellows Phytoplasma

  • Leaves become flattened and streaked yellow and green, and may become twisted
  • Youngest leaves yellow from the base upwards
  • Bulbs may be small
  • Infected plants are randomly scattered through field
  • More information on Aster Yellows ...
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  • Image: Onion Yellow Dwarf Virus 1
    Credit: R. Michael Davis, University of California Statewide IPM Program
  • Image: Onion Yellow Dwarf Virus 2
    Credit: R. Michael
    Davis, University of
    California Statewide
    IPM Program
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green arrowOnion Yellow Dwarf Virus

  • Leaves are crinkled, flattened and fall over
  • First see yellow streaks at the base of young leaves
  • Eventually all leaves show yellow streaking to complete yellowing
  • Bulbs fail to form if plants are infected when young or are firm but small when infected later in the season
  • Disease comes in on infected cloves or with the green peach aphid
  • More information on Onion Yellow Dwarf Virus ...
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  • Image: Onion Thrips 1
    Credit: Whitney Cranshaw, Colorado State University, Bugwood.org
  • Image: Onion Thrips 2
    Credit: Whitney
    Cranshaw,     Colorado
    State University,
    Bugwood.org
  • Image: Onion Thrips 3
    Credit: Howard F.
    Schwartz, Colorado State
    University, Bugwood.org
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green arrowOnion Thrips
Thrips tabaci

  • Leaves may become distorted
  • Thrips feed on the interior of the onion neck, on developing leaves
  • Feeding causes whitish spots and streaks on the leaves
  • Eventually results in a silvery-white stippled appearance sometimes referred to as white blast or silver top
  • Severe feeding can cause the bulb to become distorted or undersized
  • Thrips are very small (<1/20 inch) and a pale yellow color
  • More information on Onion Thrips(pdf) ...
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  • Image: Stem and Bulb Nematode 1
    Credit: Central Science Laboratory, Harpenden Archive, British Crown, Bugwood.org
  • Image: Stem and Bulb Nematode 2
    Credit: Howard F.
    Schwartz, Colorado
    State University,
    Bugwood.org
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green arrowStem and Bulb Nematode
Ditylenchus dipsaci

  • Leaves are twisted and stunted
  • In severe infestations, plant may wilt and die
  • Bulbs are often desiccated and light weight, secondary rot organisms like soft rot may invade and rot the bulb
  • Outer layer of bulb is split or has cracks
  • More information on Stem and Bulb Nematode ...

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