Apple anthracnose

Asked April 25, 2014, 10:08 AM EDT

I have apple anthracnose pretty severely on my apple trees. I am considering cutting them all down and starting over. Can you tell me: Does the fungus live in the vicinity after I remove the trees and burn them? Does the fungus live on other fruit trees? Rick Smith

Thurston County Washington horticulture

1 Response

Apple anthracnose is severe in the wet areas west of the Cascades in Washington and BC. Anthracnose cankers are often called fiddle-string cankers because long, string-like fibers of the inner bark are left exposed in the center of the canker. These cankers usually occur on smaller twigs and branches and expand for only a single season. The cause of the disease is a fungus, currently called Cryptosporiopsis curvispora. The fungus produces asexual spores (conidia) in the cankers, and these conidia are washed and splashed to other branches and trees during rains or irrigation. Infection occurs most readily any time weather is cool and damp, especially in the fall. Any type of apple can be attacked. Other hosts include crabapples, most pome and stone fruit, Amelanchier, hawthorn, and mountain ash.

Infection occurs in the fall, but cankers will not appear until spring. Small injuries may facilitate penetration, but the fungus can penetrate uninjured bark. The canker grows actively only 1 year; however, the fungus continues to live 2 or 3 years in the dead canker tissue and produces large numbers of spores.

Cultural control

Aggressive scouting for and removal of cankers is the key to long term control. Whole tree removal is recommended in British Columbia when cankers are found.

  • Establish new plantings with clean stock free of visible cankers.
  • Locate new orchards as far as possible from older orchards that may have existing cankers.
  • Scout new orchards for the disease, because early detection will aid in overall control.
  • Prune out and burn affected twigs and branches, especially on highly susceptible cultivars. This is best done in dry weather before fall rains. On larger limbs and branches, use a sharp knife to remove cankers that are less than half the branch width. Cut out a pointed oval oriented along the axis of the branch.
Chemical control

Must be combined with canker removal to be effective. Relying on chemical control alone has not been successful in British Columbia.
  • Apply a dormant bordeaux 6-6-100. Spray may be combined with the oil emulsion (3.2% actual oil) recommended for insect control. Bordeaux is not compatible with lime sulfur or polysulfide.
  • Spray at petal fall and preharvest to control bull's-eye rot.
  • Bonide Captan 50 WP may be used in Oregon home gardens at 1 Tbsp/gal water.
  • Captan 80 WDG at 3.75 lb/A. May be applied up to the day of harvest. Group M4 fungicide. 24-hr reentry.
  • Mancozeb (such as Dithane , Manzate, or Penncozeb) 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. Group M3 fungicides. 24-hr reentry.
  • Topsin M WSB at 0.75 to 1 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. Group 1 fungicide. 2-day reentry.
  • Ziram 76 DF at 6 lb/A. Do not use within 14 days of harvest. Group M3 fungicide. 48-hr reentry.
  • Apply these materials before fall rains and again (about 1 month later) when leaves fall from trees. If used preharvest then they may control bull's-eye rot as well as canker development.
  • Basic copper sulfate (98%) at 1 lb/25 gal water. Thorough coverage is essential. 24-hr reentry.
  • Bordeaux 6-3-100. The presence of bordeaux spray on yellow-colored cultivars, when fall rains are early, may cause a reddish fruit-spotting around the lenticels.
  • Captan 80 WDG at 3.75 lb/A. May be applied up to the day of harvest. Group M4 fungicide. 24-hr reentry.
  • C-O-C-S WDG at 8 to 15.5 lb/A plus dormant spray oil. 48-hr reentry.
  • Copper-Count-N at 8 to 10 quarts/A. Post harvest only. 48-hr reentry.
  • Cueva at 0.5 to 1 gal/100 gal water/A. May be used on day of harvest. Group M1 fungicide. 4-hr reentry. O
  • Cuprofix Ultra 40 Disperss at 8 to 20 lb/A. Post harvest only. 48-hr reentry.
  • Kocide 3000 at 5.25 to 7 lb/A. Harvest yellow cultivars before use. 48-hr reentry.
  • Monterey Liqui-Cop at 3 to 4 teaspoons/gal water. Use after harvest only. H
  • Nordox 75 WG at 5 to 6.5 lb/A. Post harvest only. 12-hr reentry. O
  • Nu-Cop 50 DF at 12 to 16 lb/A. Do not use if soil pH is 5.5 or below. 48-hr reentry. O
  • Ziram 76 DF at 6 lb/A. Do not use within 14 days of harvest. Group M3 fungicide. 48-hr reentry.