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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Vegetable > Onion > Undersized or no bulb developed

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Onion > Bulb > Undersized or no bulb developed

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  • Image: Aster Yellows

Aster 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
  • Image: Botrytis Leaf Blight 2

Botrytis 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

Nitrogen deficiency

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  • Image: Yellow Dwarf Virus 1
  • Image: Yellow Dwarf Virus 2

Onion 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

Pink 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
  • Image: Downy Mildew 2
  • Image: Downy Mildew 3

Downy 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
  • Image: Onion Thrips 2
  • Image: Onion Thrips 3

Onion thrips
Thrips tabaci

  • Bulbs can become distorted or undersized
  • Whitish spots and streaks are present on leaves
  • Leaves may become distorted
  • Bulbs can become distorted or undersized
  • Thrips are very small (< 1/20 inch) and a pale yellow color
  • Thrips are found feeding on the interior of the onion neck and on developing leaves
  • More information on Onion Thrips ...
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  • Image: Northern Root Knot Nematode

Northern root knot nematode
Meloidogyne hapla

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