Onion smudge is caused by the fungus Colletotrichum circinans. It is a common disease of onions worldwide that occurs in temperate regions. The disease causes small dark spots on onion bulbs that can coalesce and reduce market value. Under moist conditions, spores are produced on the lesions that can spread the fungus. The fungus survives in soil and infected plant debris. Warm, moist conditions favor disease development. Management strategies include crop rotation, drainage, using disease-free seed and plant material, and fungicide applications before harvest.

1. COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore-3)
Kullapuram (Po),ViaVaigai Dam, Theni-625 562
Onion smudge
Student Course teacher
A. Sowbejan Dr. Parthasarathy. S
2015021122 Assistant Professor (Plant Pathology)

2. Name of disease
Common name: Onion smudge
Pathogen name: Colletotrichum circinans
Other name: Anthracnose of onions

3. kingdom Fungi
Phylum Ascomycota
Class Sordariomycetes
order Glomarales
Family Glomerellaceae
Genus Colletotrichum
Species C. circinans

4. Occurrence
• The disease is wide spread in temperate regions of the world and was first described
in England.
• Since than it has been reported from many countries of the world like USA, Japan,
Argentina and European countries.
• The disease is of common occurrence in India also.
Inventor: Colletotrichum circinans (Berk)
Host: Onion

5. Economic Importance
• The main damage is the infection of the outer scale leaves of the
bulb of onions this is unsightly and reduces market value.
• If bulbs are stored for a long time, smudge causes the scale leaves
to shrink, the bulbs to sprout prematurely and to become
susceptible to other storage rots.
• Leaf infections can be serious occasionally, although rare in
Pacific island countries.
• They are reported from Solomon Islands.
• Damping-off occurs on seedlings and can lead to total loss.

6. Symptoms
• The disease is characterized as small dark green to black
dots that appear on the outer scales.
• These small dotes are scattered over the surface of the bulbs
or grouped together in concentric rings giving a smudge
appearance to the white onions.
• During moist conditions, acervuli of the fungus develop on
the infected areas and spore masses and the setae can be
easily recognized fleshy scales resulting in yellow
depressions on the bulb

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8. Disease cycle
• The fungus survives in the soil on the remains of onion
leaves, producing spores to infect the next crop.
• Damp soil and soil temperatures above 20 ºC are best for
rapid development of the disease. Water is also needed
for spore germination.
• Spread of the fungus occurs when spores, either on the
outside surface of the bulbs or as infections of the scale
leaves, are moved in wind-blown rain.

9. • Temperature ranges from 10 to 32 ºC
• Excessive rainfall.
• Moist condition are essential for production of conidia.
Favourable condition

10. Management
• Cultural practices like as crop rotation, good drainage, use
of healthy seed materials.
• Protection of the harvested crop from rains, rapid and
through curing and provision of well- ventilated storage
also reduce the incidence of the disease.
• Pre-harvest sprays either of Carbendazim or Mancozeb
reduce the infection of this disease under storage
conditions.