Black rot and White rot: Black rot is a fungal disease that can cause serious losses in apple orchards, especially in warm, humid areas. Three forms of the disease can occur: a fruit rot, a leaf spot known as frogeye leaf spot, and a limb canker. Infected fruit become unmarketable, severe leaf spotting can result in defoliation which weakens the tree, and limb cankers can girdle and eventually kill entire branches. The fungus causing white rot is ubiquitous in nature, occurring on a wide variety of woody plants including birch, chestnut, peach, and blueberry. White rot is often referred to as Botryosphaeria rot or Bot rot and is a serious pathogen of apple fruit and wood. Fruit rot infection is most common in areas of the southeastern U.S. where losses of up to 50 percent have been reported. The canker phase of the pathogen can also cause considerable loss in many regions of the south, midwest, and northeast. Drought stress and winter injury have also been associated with an increase in infection and canker expansion.
Management: Black rot is managed by removal of inoculum sources (dead wood and mummies) and application of fungicides. Fungicide applications from silver tip through harvest may be necessary where the disease is a recurrent problem. The differences in varietal susceptibility to fruit rot are small, although Cortland and Empire may be slightly more susceptible. White rot is managed by removal of inoculum sources (dead wood and mummies) and application of fungicides. Prompt removal of fire blighted twigs also helps reduce inoculum since the fungus rapidly colonizes and reproduces on dead woody tissues. Fungicide applications from bloom through harvest may be necessary where the disease is a recurrent problem. The differences in varietal susceptibility to fruit rot are small, although Golden Delicious, Empire, and Jersey Mac may be slightly more susceptible. Irrigation during hot, dry weather may help prevent occurrence of twig and branch infections, although irrigation is not a practical alternative for most growers.
