Common Apple Tree Diseases & How To Treat Them

Usually, when we hear “apple tree,” we think of a thriving orchard. The sun is shining through the trees, the fruit are heavy and beautiful on the branches, and there are a few apples on the ground. The image is idyllic, and many of us cling to this thought when we buy our first cluster of apple trees (or our first orchard). And while many orchards and backyard apple trees are healthy, there are diseases that can pop up and hurt your trees. As with human diseases, some are more concerning than others. But if you’re the proud parent of an apple tree, or two, or two hundred, you should know about the common apple tree diseases and how to treat them. Let’s get started!

Fire Blight

This apple tree disease is one of the most common. Fire blight is a bacterial disease that, if left untreated, can damage entire trees, and ruin your orchard. Fortunately, fire blight is easy to identify, so if you see these signs, act immediately!

Infected trees will begin to show symptoms of fire blight in the spring and summer. Symptoms include:

• Browning of leaves or blossoms, with or without open cankers
• Damage on branches

To treat fire blight, you will want to get rid of any infected tissue on the tree. Prune a few inches below the visible infection and be sure to sanitize your shears after pruning each tree. This way, you’ll avoid spreading the disease to other healthy trees.

Powdery Mildew

Next up on our list of common apple tree diseases and how to treat them is powdery mildew. This disease is common to just about any plant or tree. While it won’t necessarily cause significant damage to your apple trees, it can weaken them. You can spot powdery mildew by its fluffy white presence on leaves and branches.

To treat powdery mildew, spray your apple trees with lime sulfur and prune away any mildew-infested shoots. Prevent the mildew from returning in the spring by cleaning up leaves in the fall.

Apple Scab

This disease is caused by a fungus, making it difficult to control. It’s especially common after periods of rainy weather. To identify apple scab, look for darker lesions on tops of leaves and lighter lesions on the bottom of leaves. In milder cases, your apple trees will still be able to produce fruit. However, you’ll notice lesions on the apples, too.

If your trees have apple scab, be sure to get rid of any leaves in the fall as they can re-infect trees in the spring.

Phytophthora Rot

Another disease caused by fungi, phytophthora rot is very common in apple trees. This disease can stunt your tree’s growth and weaken them significantly. Unlike other diseases, this one is tricky to spot. You need to peel back a layer of bark and look for an orange or brown color. The presence of these colors will tell you if your tree has been struck by this disease. Trees in the advanced stages of this disease will have yellowish leaves that turn purple in the fall.

Treatment can be difficult for this particular disease, so you want to try to prevent it as much as possible. Ensure good drainage for your trees, as this fungus thrives in wet soil.

Apple Rust

This disease is known for its rusty, orangish-yellow stains on an apple tree’s leaves, branches, and fruit. The fungus uses one tree as a host and spreads out to other trees around it. If you know which tree is serving as the host, it’s important to get rid of it as quickly as possible. You can also spray your trees with lime sulfur, which helps fight the fungal spores.

Black Rot

This disease affects apples directly. If your apple tree is infected with black rot, you will notice brown spots on the end of each apple. The spots grow larger and larger and turn black. At this point, your precious apples will begin to rot. You may also notice holes in an infected tree’s leaves. If treatment isn’t administered, the disease can kill the tree completely.

As with all apple tree diseases, your best bet is to catch the disease early. If you notice signs of black rot, prune or burn the infected part of the tree. Then, spray them with sulfur or Captan to prevent the disease from spreading.

Sooty Blotch

While this one sounds scary, it’s not as dangerous as other apple tree diseases. You’ll recognize trees infected with sooty blotch if apples have black or gray spots. The good news is that the disease doesn’t make the apples inedible, they just don’t look as gorgeous as the perfect apples in the supermarket.

To treat trees infected with sooty blotch, you’ll want to treat them with a chemical spray. It’s also a good idea to prune back trees for better air flow, as sooty blotch thrives in areas with poor air circulation.

Apple Mosaic Virus

While this disease doesn’t seem to be very harmful in its beginning stages, it can cause leaves to die prematurely. In turn, overall tree growth and fruit production are stunted. Apple mosaic virus can be very damaging to apple orchards that rely on picking and production to make a living.

You can spot the beginning stages of apple mosaic virus by checking the leaves in the spring. You’ll notice small, yellowish spots that grow larger as the disease advances.

White Rot

White rot is very common in southern regions. You will know if your apple trees are infected with this disease when you see small spots and blisters on the trees’ branches. You may also notice branches turning an unhealthy shade of orange. If apples are produced, you will notice that they are covered with brown or white spots.

To treat a tree impacted by white rot, you can consider using fungicide. Also, be sure to prune the infected tree thoroughly and get rid of any and all infected wood.

If concerned about your apple tree, always reach out to your local Agricultural Extension office who will come out and diagnose your tree for you. This will eliminate unnecessary chemical usage and reassure you on what you may be dealing with on your apple tree. If you take the appropriate preventative measures, remain vigilant, and take action at the first sign of infection, your apple trees (and you) won’t have anything to worry about. If you’re ready to get started on your apple tree adventure, find healthy potted apple trees for sale at Plant Me Green.