Management of Apple Anthracnose Canker

Apple anthracnose (caused by Neofabraea malicorticis anamorph Cryptosporiopsis curvispora) is a fungal disease that causes cankers on trees and ‘Bull’s-eye rot’ on fruit. In western Washington, it is the canker phase of apple anthracnose that is considered most serious as it can result in death of newly planted trees and reduce the overall health and yield of established trees. A study was conducted at Mount Vernon, WA in 2014 and repeated in 2015 to evaluate 5 treatments to manage cankers in cider apple trees: 1) Carve out canker, spray carved area with 10% bleach solution; 2) Carve out canker, spray carved area with Nu-cop (copper fungicide); 3) Carve out canker, burn carved area with hand-held propane torch; 4) Carve out canker, burn carved area with hand-held propane torch and spray Nu-cop; 5) Completely cover canker and additional 1cm margin with Bordeaux paste; and 6) Carve out canker, apply Bordeaux paste on carved area (2015 only). These are all common practices used in the region to manage cankers, however their efficacy has not been tested. Treatments were applied once to new canker infections, on 16 Dec. 2014 and 11 Dec. 2015; different trees were included in the study each year. Prior to treatment application, the canker area was measured and there were no differences in canker size on trees assigned to treatments (average canker size 0.49 cm). Each year the treated area following canker removal was measured immediately after treatment application and every 2 weeks thereafter. Significant differences (P < 0.0001) were found due to treatments at each measurement time. The increase in removed canker area following each treatment was: treated with propane burning increased 86% in 2014 and 588% in 2015 as compared to the canker area immediately after treatment application. The removed canker area treated with propane burning + nu-cop increased 122% in 2014 and 1463% in 2015. The removed canker area treated with Nu-cop had a 2% increase in 2014 and a 28% increase in 2015. The removed canker area treated with bleach increased 25% in 2014 and 6% in 2015. The canker area treated with Bordeaux paste decreased 0.4% in 2014 and increased 10% in 2015. The removed canker area treated with Bordeaux mixture increased 5% by 9 wk in 2015. In follow-up assays, the fungus in all treatments appears to still be active.