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Onion smut

Onion smut

Crop: Onion
Disease: Fungal
Pathogen: Urocystis colchici and U. cepulae
  • Mature lesions contain a black, powdery mass of spores. On older plants raised, blister-like lesions can occur near the base of the scales, and large lesions cause leaves to curve downward.
  • When the plant grows lesions form on the leaf and any bulbs that form will be covered in black spots. Most of the time infected seeds will die within 3–5 weeks of planting.
  • Infected seedlings often die within six weeks of emergence. Dark areas can be seen first on cotyledons soon after their emergence from soil. On older plants raised, blister-like lesions can occur near the base of the scales, and large lesions cause leaves to curve downward.

  • Affected leaves may bend or twist abnormally and usually are shed prematurely. Elongated, raised black blisters can also be found in the outer scales of the developing bulb. Affected plants are usually severely stunted.

  • Dark areas can be seen first on cotyledons soon after their emergence from soil. On older plants raised, blister-like lesions can occur near the base of the scales, and large lesions cause leaves to curve downward. Streaks may develop within the leaves, leaf sheaths and bulbs. Mature lesions contain a black, powdery mass of spores. 

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