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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Vegetable > Onion > Flecks, spots, streaks or blotches on leaves

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Root Crops > Onion> Flecks, spots, streaks or blotches on leaves

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  • Image: Purple Blotch 1
  • Image: Purple Blotch 2

Purple blotch
Alternaria porri

  • Leaves develop target like purple to brown spots with many concentric rings and white margins
  • Leaf spots become covered with a brownish-black powdery growth in wet weather
  • When severe, leaves will turn yellow and wilt from the leaf spot to the leaf tip
  • Commonly infects leaves damaged by other pathogens, insects or abiotic problems like hail or sunscald
  • Older leaves are often more severely infected than younger leaves
  • More information on Purple Blotch ...
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  • Image: Botrytis Leaf Blight 1
  • Image: Botrytis Leaf Blight 2

Botrytis leaf blight
Botrytis squamosa

  • 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
  • Bulbs are not directly infected but may be smaller on plants with severe leaf damage
  • 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: Onion Yellow Dwarf Virus 1
  • Image: Onion Yellow Dwarf Virus 2

Onion yellow dwarf virus

  • 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
  • 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 Thripsr 1
  • Image: Onion Thripsr 2
  • Image: Onion Thripsr 3

Onion thrips
Thrips tabaci

  • Whitish spots and streaks are present on leaves
  • Leaves may become distorted
  • Thrips feed on the interior of the onion neck, on developing 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: Downy Mildew 1
  • Image: Downy Mildew 2
  • Image: Downy Mildew 3

Downy mildew
Peronospora destructor

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

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