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