The Q&A Archives: spots on leaves

Question: I have a crabapple (don't remember the name) that the leaves turn yellow and dark spots appear. It flowered this spring and was green, but now has this condition. What can I do?

Answer: Several diseases attack apples and crabapples in this area. The most common as well as the most destructive is fireblight. It causes the blossoms and young shoots to wilt suddenly and turn brown. The shoots curve over like a shepherd's crook. The dead leaves are brown to black and hang on all through the year.

During cool wet weather especially in late spring or early summer, apple scab will make its appearance. Young leaves develop brown spots and may pucker. Later on these spots will turn black. Similar spots develop on the young fruit, and cause the fruits to become distorted. If scab shows up, begin a spray program as soon as possible. The disease causes leaves to fall off the tree by mid-summer and causes the fruits to be gnarled and worthless. In the fall, rake up and destroy all fallen apple leaves. This will reduce the amount of scab next year.

Cedar apple rust is another disease which appears shortly after tree flowering. The leaves develop pale yellow spots on the tops of the leaves and later orange areas on the underside of the leaves. Severe infection causes the leaves to drop off the tree early in the year. Similar orange spots develop on the upper part of the apple. Rust is a disease that spends half of its life cycle on apples and the other half on junipers or cedars. Control of this disease requires a combination of practices. In early spring, check nearby cedars for red-brown galls. Remove and destroy these as early as possible. The second thing to do is spray your apple trees before they become infected. Fungicides are available at local garden centers and nurseries.

One other disease that may develop some years in Powdery Mildew. It produces a whitish dust on leaves and buds. The dust will rub off. Powdery Mildew causes apple leaves to be narrow and somewhat twisted. It develops at high humidity and normal temperatures. As soon as you see the symptoms, control with as fungicide.

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