By Bev Johnson

Master Gardener

There are two diseases of ornamental and fruit trees that can leave homeowners tearing their hair out. The first is fire blight. This attacks apple, pear and mountain ash trees. Your tree will look as though it has been scorched. The affected branch will have blackened leaves and blossoms and the tip of the branch will turn down like a shepherd’s crook. Infected fruit turns dark, shrivels, mummifies, and may cling to the tree for several months. If not caught quickly, it may kill the tree. 

Bacteria which cause fire blight overwinter at the edge of cankers (diseased areas on woody tissue). They become active in spring. In warm, humid weather, a gummy substance called bacterial ooze is pushed out through cracks in the bark. This attracts insects that become contaminated with the ooze. The insect then visits your apple blossoms leaving some of the bacteria in the flower nectar. Aphids and leafhoppers spread it as do birds, rain and wind.

Remove any infected branches as soon as you see them. Cut back at least a foot behind the infected branch. Sterilize your tools with Listerine mouth wash between cuts. This works well and doesn’t damage the cutting edges of tools like alcohol does. Bag and burn infected branches to stop or at least slow down the infection. If the tree develops cankers on the stem, the tree is toast. Summer pruning is bad, more apt to spread the disease. 

Some do’s and don’ts. Heavy pruning promotes excessive new growth that is especially susceptible to fire blight. Instead, prune every year in late winter, February or March. Fertilize only in early spring and then sparingly. Too much nitrogen stimulates excessive new growth. Actually, when you fertilize the grass around the tree, that is enough. Plant on an area with good drainage. Do a soil test. Apples like our alkaline soil. As acid soil will stunt the tree and make it more susceptible to diseases. 

Apple scab attacks mostly crab apples but Cortland and McIntosh are very susceptible. Liberty and Freedom are more resistant. Probably some of the newer varieties are too. 

Apple scab is a fungus found mostly on the leaves and fruit. It causes the leaves to fall prematurely. Infections start in spring on the leaves and flower parts. The infections look like green to gray velvet. Leaves turn yellow and fall off. Fruit develops brown, corky spots with cracks in the fruit. The apple matures unevenly and is deformed. This disease will not kill the tree unless it is defoliated three vears in a row.

The fungus overwinters in leaf litter and cracks and crevices in the bark. Black pimple-like reproductive structures develop in late fall and early spring. Spores from these structures produce infections in the spring. We must have a wet spring for the infection to take. If summer continues to be wetter than usual, there will be continuing infections. 

The best way to prevent this fungus from attacking your apple trees is to religiously rake up and bag leaves as soon as they fall and either bag or burn them. 

If you have fruit trees, take a stroll through them at least twice a week checking for broken branches, unhealthy looking leaves, or anything out of the ordinary. Catch the problem early and prevent the tears when you lose a favorite tree.