URBANA, Ill. - Apple trees are susceptible to a number of disease problems that can affect fruit quality and the tree’s health. Part of successful apple production includes continued good management practices even after the crop has been harvested, said University of Illinois Extension educator Elizabeth Wahle.
“Because some pests overwinter on fruit trees, one of the best times to manage these pests is during winter when the trees are dormant—after leaves fall but before visible growth in the spring,” Wahle said.
One key management practice during the dormant season is sanitation to remove and destroy mummified fruit on the tree and diseased fruit and leaves from the ground. Apple scab is a good example of a disease that overwinters in infected leaves and fruit on the ground and if left in place can serve as a source for tree reinfection the following spring. “By simply removing and destroying all fallen infected leaves and apples, early-season scab infection the following spring can be greatly reduced. Another component of sanitation is to prune out dead, diseased, and broken branches,” Wahle said.
Bitter rot, black rot, and white rot are all fungal diseases that can survive season to season on mummified apples just like apple scab but also in cankers on the tree. “By removing these over-wintering sources of inoculum, early season infection can be greatly reduced,” she said.
Fire blight is a bacterial disease that can result in significant injury in certain apple cultivars like Jonathan, Braeburn, Fuji, and Gala. The most obvious symptom of a fire blight “strike” is flagging or wilting of the shoot tip accompanied by black or brown discoloration of the twig and leaves.
Because the bacteria overwinter in living tissues at the margins of cankers, pruning cuts made at least 6 inches below the last visible point of infection during the dormant season will remove a significant amount of primary inoculum.