Pacific Northwest 1998 An Online Guide to Plant Disease Control

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Apple -- Perennial Canker (Bull's-eye Rot)
See Also: Apple -- Anthracnose (Bull's-eye Rot)
 
Cause: Cryptosporiopsis perennans (sexual: Neofabraea perennans), a fungus. The fungus is closely related to that causing anthracnose, and the diseases are somewhat similar. Perennial canker, however, is often associated with the presence of woolly apple aphids, low temperature injury, and pruning wounds.
Symptoms: On wood--cankers made up of overlapping concentric rings of woody tissue encircling the center wound are characteristic of the disease. Apple anthracnose does not have the concentric rings of woody tissue in the canker. Each ring indicates the disease's progress for 1 year. As the canker enlarges from year to year, it cuts off more of the sap-conducting tissue, reducing the growth and bearing capacity of the tree. Sometimes scaffold limbs are girdled and a large part of the tree killed.

On fruit--the symptoms of the fruit rot, "bull's-eye," phase of the disease are identical to that caused by anthracnose. "Bull's-eye rot" occurs at open lenticels or at breaks in the skin. The rot spots may be only specks, but most of them are 0.5 to 1 inch across by the time the fruit reaches the market. Spots may occur singly or be numerous. They may be pale yellowish cream or uniformly brown but are most often brown with a pale center that forms a bull's-eye. Spots are flat to sunken, and rotted tissues are relatively firm. The skin over the surface does not break easily under slight pressure. Rot may be shallow or nearly as deep as wide. In deeper rots, penetration is more or less U-shaped. Usually, decayed tissue is somewhat mealy and does not separate readily from healthy tissue. Spore-bearing tufts on the causal fungus may or may not be present on the surface of the rot but when present are short, wet, cream colored, and protrude through the skin.

Perennial canker on branches following winter injury. Sample from Hood River.

 
Cultural control:

  1. Prune out cankers when practical.
  2. Keep fruit dry after picking and remove from orchard as soon as possible.
  3. Avoid wounding trees. If wounds occur, induce rapid healing.
Chemical control: Not recommended for the canker phase of this disease.

  1. Spray at petal fall and preharvest to control bull's-eye rot.
    1. Captan 80 WDG at 3.75 lb/A. May be applied up to the day of harvest. 24-hr reentry.
    2. Mancozeb (such as Dithane M-45, Manzate 75 DF, or Penncozeb 75 DF) up to 6 lb/A prebloom or at 3 lb/A after bloom. Do not combine the 6 lb/A prebloom or the 3 lb/A all-season schedules or apply more than 21 lb/A/year. Do not apply within 77 days of harvest. See label restrictions. 24-hr reentry.
    3. Topsin M WSB at 1.5 lb/A for apples. Do not use more than 4 lb/A/season or within 1 day of harvest. Do not use at any time in the orchard if your packing house uses a benzimidazole (such as Mertect or Decco Salt 19) post harvest. 1 day reentry.
    4. Ziram 76 DF at 6 to 8 lb/A. Do not use within 14 days of harvest. 48-hr reentry.
  2. Control woolly apple aphids. See PNW Insect Control Handbook.
References:
Jones, A.L. and H.S. Aldwinkle. 1990. Compendium of Apple and Pear Diseases. 1990. St. Paul, MN: APS Press.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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