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Diseases on an Apple Leaf

Dropped apple image by Ivana Lovic from

Apple trees require a great deal of care like mulching, pruning and watering in order to remain healthy and produce abundant crops. You must also make sure the soil has adequate nutrition so trees will produce higher yields. Taking proper care of your apple trees will reduce the instance of diseases that can ruin crops and cause devastating financial losses.

Apple Scab

Apple Scab is caused by a fungus that thrives in wet weather, or whenever moist conditions are present. The first signs of apple scab are light brown spots on the tree's leaves. These spots may grow in size and appear to have scabs. In advanced stages of the disease, leaves will yellow and then fall off the tree. Rake leaves of trees affected with apple scab and burn them to prevent the spread of this disease. Preventative measures include spraying orchards with a fungicide in the spring, or whenever signs of infection are present.

Cedar Apple Rust

Cedar apple rust is caused by a fungus, and is more common in wet weather. This disease also affects crab apples and juniper trees. When the disease is present in apple trees, yellowish-orange spots will develop on the top of the leaves. These spots sometimes appear to be tiny blisters. In the summer, apple trees affected with cedar apple rust will develop orange tubes on the underside of the leaves. The fruits of the trees will have spots similar to those found on the top of the tree's leaves. Look for a variety of apple that is known to have resistance to cedar apple rust in order to produce crops free of this disease

Powdery Mildew

This disease is caused by a fungus known as Podosphaera leucotricha. Powdery Mildew looks like white powder on the apple leaves. It sometimes has the appearance of white powdery spots, while other times the mildew will be splotchy. It thrives in humid conditions, especially when there is very little air flow. Trees that grow in little to moderate sunlight are more susceptible to this disease. Powdery mildew is noticeable on apple tree leaves as soon as they emerge from the buds. Many varieties of apples are resistant to this disease. If powdery mildew conditions are present, spray the tree with a sulfur compound.

Frogeye Leaf Spot

Frogeye leaf spot first appears as a purple spot on an apple leaf. These spots will grow over time, eventually becoming tan in the center with a purple ring around the outer rim. If late spring or early summer rains are especially heavy, frogeye leaf spot will be more common. To prevent this disease, prune properly in the winter, especially limbs with a black oozing rot. After trimming, cover the cuts with alcohol-based shellac. This may be followed with tree paint. Remove diseased limbs from the area and burn them. Remove fruit that has blackened and rotted as soon as you notice it to reduce the spread to healthy fruit.

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