The apricot tree, an easy-care, attractive tree, is one of the earliest spring-blooming fruit trees. It provides spring beauty, summer shade, fall color and small, delicious fruit. Apricots are a small stone fruit (fruit with one pit rather than a lot of seeds) like cherries. In fact, apricot trees and cherry trees both suffer from many of the same diseases.
Coryneum blight is caused by a fungus. The fungus covers the apricots with small brown spots, which are unsightly but do not prevent the fruit from being edible. For this reason, coryneum blight is often called "shot-hole" disease. Cankers (sunken, cracked areas of wood) can also appear on trees affected with this disease.
Prevention of coryneum blight involves spraying the tree with a fungicide in the spring, after the flowers have dropped, and in the fall after the leaves have dropped.
Bacterial canker disease is caused by a bacteria called Pseudomonas syringae and is spread by water--often by splashing rain or rainwater blown about by the wind. In the spring, the tree will start to die back from the tips of the twigs inward, and develop cankers, which may ooze yellow sap. Leaf spot may also occur.
The bacteria can live on healthy trees without harming them, and usually will infect only apricot trees that are weak or sick for other reasons. Fumigating soil that has previously hosted stone fruit trees before planting a new apricot tree is the best way to prevent the disease. Once bacterial canker infects a tree, it cannot be cured.
Black knot disease is so named for the distinctive hard, black knots on apricot trees. These are galls created by a fungus, and the fungal spores develop inside the swellings. The galls can encircle a branch, cutting off the flow of nutrients to that branch. In some cases, they can even girdle the entire trunk.
Galls should be pruned off 4 to 5 inches below the knot. In early spring, a preventative application of lime sulfur should be used on the tree. Or, use a fungicide that includes the ingredients captan plus benomyl after the buds begin to open.