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Ministry of Agriculture, Food and Rural Affairs

Neck Rot

Neck Rot Neck Rot
Click to enlarge.

Beginner

Scientific Name: caused by various Botrytis species including Botrytis aclada, B. byssoideaand B. squamosa.

Identification

  • First sign is the softening of the neck scale tissue which takes on a sunken, cooked appearance
  • As the disease progresses, the tissue becomes greyish and a grey mould may develop
  • Black sclerotia eventually appear in the affected tissue.

Often Confused with
Soft Rot

Period of Activity
Neck rot symptoms usually appear in storage; however, some necks may become soft and rotten immediately before harvest.  The fungi of the disease can survive in the soil for several years.  Symptoms usually occur during cool, wet conditions. 

Scouting Notes
Regular field scouting methods is best measure to assess disease levels.  There is a distinct margin between the diseased and healthy tissue even when the rot is advancing down towards the base of the bulb.   

Thresholds
None established.

 

Advanced

Scientific Name: caused by various species of Botrytis fungi including B. aclada, B. byssoidea and B. squamosa.

Most cultivars grown in Ontario are susceptible to neck rot, especially white and Spanish onions. 

Identification

  • First signs are softening of the affected neck scale tissue which takes on a sunken, cooked appearance
  • As the disease progresses, the tissue becomes grey and a grey mold may also develop
  • Black sclerotia eventually appear in the affected tissue.

Often Confused with
Soft Rot

Biology
As the lesions gets older, the tissue becomes gray in colour and later a dense, grayish, cottony growth of the fungus appears on the surface of the scales.  This growth gives rise to a gray-brown powdery mass of spores which serve to spread the fungus through the air.  Still later, small, whitish, kernel-like bodies that soon turn black and hard (sclerotia) appear.  In some soils and cull piles, sclerotia may survive for several years, germinating in suitable moist conditions to produce crop after crop of spores.  Eventually, the whole bulb may become mummified, but the fungus is still active and is a potential hazard in growing and stored crops.

The spores can infect young plants long before neck-rot symptoms appear.  There are usually no symptoms although the fungus can be there, growing down inside the leaf to the neck for much of the growing season.  The fungus can also be seed-borne.     

Period of Activity
Neck rot symptoms usually appear in storage; however, some necks may become soft and rotten immediately before harvest.  The fungi of the disease can survive in the soil for several years.  Symptoms usually occur during cool, wet conditions ranging from 15 -20°C (59- 68°F). 

Scouting Notes
Regular field scouting is the best way to monitor disease levels.  There is a destinct margin between the diseased and healthy tissue, which remains apparent as the rot advances down towards the base of the bulb.   

Tolerances
None established.

Management Notes

  • Select less-susceptible types of onion for situations with a history of neck rot
  • All onions should be grown away from cull piles and on land free of diseased crop remnants
  • Avoid planting onions and related crops (shallots, leeks, garlic and chives) for at least two years on soils where neck rot has been an issue
  • Plant spacings should be generous to help avoid humid conditions and promote rapid leaf drying
  • Proper curing is essential, either in the windrow or by artificial heat immediately after lifting
  • If sets are used for onion production, they should have been properly stored to reduce incidence of thick-necks in the crop, which often don’t cure properly