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Onion > Bulb > Undersized or no bulb developed

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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

  • Plants may produce small bulbs
  • Youngest leaves yellow from the base upwards
  • Leaves become flattened and streaked yellow and green, and may become twisted
  • Infected plants are randomly scattered through field
  • More information on Aster Yellows ...
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  • Image: Botrytis Leaf Blight 1
    Credit: Jack Kelly Clark, UC Statewide IPM Project
  • Image: Botrytis Leaf Blight 2
    Credit: David B.
    Langston, University
    of Georgia,
    Bugwood.org
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green arrowBotrytis Leaf Blight
Botrytis squamosa

  • Bulbs are not directly infected but may be smaller on plants with severe leaf damage
  • Leaves develop small white circular to elliptical spots surrounded by a light green to silvery white halo
  • Centers of the spots usually become sunken, straw colored, and may break apart in a lengthwise slit
  • In cool (54-75F) wet weather, disease develops rapidly, entire plants dieback starting with the oldest leaves first
  • More information on Botrytis Leaf Blight...
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  • Image: Nitrogen Deficiency
    Credit: Carl Rosen, University of Minnesota
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green arrowNitrogen Deficiency

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  • Image: Yellow Dwarf Virus 1
    Credit: R. Michael Davis, University of California Statewide IPM Program
  • Image: Yellow Dwarf Virus 2
    Credit: R. Michael
    Davis, University of
    California Statewide
    IPM Program
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green arrowOnion Yellow Dwarf Virus
Trichoplusia ni

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

  • Plants are stunted and may produce no to very small bulbs
  • Sunken dark pink to maroon areas on roots
  • Infected roots break off easily
  • Leaves turn yellow with a reddish tinge from the tip down due to root damage
  • Commonly occurs mid to late season, in areas with poor soil
  • More information on Pink Root ...
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  • Image: Downy Mildew 1
    Credit: Howard F. Schwartz, Colorado State University, Bugwood.org
  • Image: Downy Mildew 2
    Credit: Howard F.
    Schwartz, Colorado
    State University,
    Bugwood.org
  • Image: Downy Mildew 3
    Credit: Howard F.
    Schwartz, Colorado
    State University,
    Bugwood.org
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green arrowDowny Mildew
Peronospora destructor

  • Plants may produce small bulbs
  • Leaves develop elongated pale green to tan spots
  • Purplish gray fuzzy growth develops on leaves
  • Severely infected leaves collapse and die
  • Disease is most severe in cool wet weather
  • More information on Downy Mildew ...
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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

  • Severe feeding can cause the bulb to become distorted or undersized
  • Thrips feed on the interior of the onion neck, on developing leaves
  • Feeding causes whitish spots and streaks on the leaves
  • Leaves may become distorted
  • Eventually results in a silvery-white stippled appearance sometimes referred to as white blast or silver top
  • Thrips are very small (<1/20 inch) and a pale yellow color
  • More information on Onion Thrips ...
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  • Image: Northern Root Knot Nematode
    Credit: David B. Langston, University of Georgia, Bugwood.org
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green arrowNorthern Root Knot Nematode
Meloidogyne hapla

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