With this year’s growing season done, many of us are storing root crops, bulbs, and everything in between. There’s a lot to be said about pulling an onion out of storage to add flavor to those warm inviting winter comfort foods such as seafood chowder, or the stuffing for the long-anticipated Thanksgiving meal - especially if you spent all summer watching them grow. On the other hand, it’s more than disappointing to pull an onion out of storage and have the neck slough off in your hands. Botrytis Neck Rot is a common disease found in bulbs, particularly in onions post-harvest. It is caused by B. allii, and is the culprit of slimy necks of onions. As for rotten bottoms, that is caused by Fusarium Basal Rot or Fusarium oxysporum f. sp. Cepae.
|Botrytis Neck Rot|
|Fusarium Basal Rot|
Both Botrytis Neck Rot and Fusarium Basal Rot are caused by fungi that reside in soil or plant debris. Botrytis Neck Rot primarily occurs on bulbs in storage and infection is most often initiated at bulb harvest. Mechanical wounds provide entry to conidia on neck tissue. As the disease progresses, neck tissue looks water-soaked, and a yellow discoloration of the neck begins and moves down towards the scales. Soon after that, bulbs break down into a soft, wet mass. After a gray mold develops in between scales, black bodies or sclerotia form around the neck.
Fusarium Basal Rot shows itself as a red-brown rot where the roots of onion bulbs were attached to the basal plate. This rot and discoloration is apparent all around the base and up to the scales. When you cut the onion open, the affected tissue is brown and watery. A white moldy growth is associated with Fusarium Basal Rot, and can be found on the stem plate or diseased scales.
To prevent post-harvest losses and to ensure more produce that is marketable and edible, proper harvesting, curing, and storage is important. Harvest onions in cool, dry weather after the tops have been allowed to mature fully. At least half of the leaves should be brown. Letting the bulbs dry in the field for 6-10 days can help as well. Do not store onions that have any green growth on them. Botrytis Neck Rot can move through green tissue into the bulb. When harvesting, do your best to minimize bruising or other mechanical damage. Bulbs should be stored in well-ventilated areas that can be kept at 32°F/0°C with humidity below 75%.
UMass Amherst Vegetable Program
Shika Agblor and Doug Waterer, Department of Plant Sciences,
University of Saskatchewan
Onion Disease Photos courtesy of Ontario Minister of Agriculture, Food and Rural Affairs
Article by Sonya Reynolds, Greenhouse Coordinator, Johnny’s Selected Seeds