Each spring I get calls concerning apple tree problems. The trees leafed out to some degree and may or may not have flowered before disaster strikes. The leaves just start shriveling up and falling off. Many of the trees have black rot in some stage of development.

Black rot is a canker disease which gets under the tree bark through wounds or damaged areas. Unprotected fireblight or sunscald wounds are especially good entry points for black rot. Clean up and treat all pruning wounds and sunscalded areas with pruning paint (wound dressing). Once established, black rot cankers may girdle large branches or even the main trunk on your trees. The killed bark turns a dark color and when cut is brown underneath rather than the green or white of healthy bark. On last years dead areas, you'll notice tiny raised black pimples on the bark. These are the fruiting bodies of the black rot fungus.

Prevention is the main method of control. If you are pruning or cleaning up damaged areas on apple, crabapple or mountain ash trees, seal up the open areas with a pruning paint. This will help keep the black rot organism out. Once black rot has gotten under the bark of your trees, the cankers can be excised and cankered branches removed as you would remove fireblight cankers. After making each cut, sterilize your pruning tools and the cut surface with a 10:1 mixture of water and household bleach. Dip your shears, knife or saw into the disinfectant or pour over the cutting edge. Be sure to rinse and oil your tools after use to prevent corrosion.

This page was last updated May 2003

Go to Information Page

Go to Horticulture Page