An apple tree might look perfectly healthy and disease-free to the untrained eye. However, apple trees are actually susceptible to many diseases that can be difficult to detect and even more difficult to manage effectively. 

Here are six of the most common Apple Tree Diseases and how you can prevent them from harming your precious tree and its tasty fruit harvest.

1. Apple Scab Disease

Apple scab is caused by a fungus that lives on spores that are too small for us to see with our eyes. When they rain down onto leaves, they cause black or brown spots that can eventually turn into blight. 

This disease mainly affects trees growing in damp or humid areas; if you live in an area like this, there are a few simple ways to prevent it. First of all, plant your tree in well-drained soil; then prune and thin out branches so air can circulate freely around your apple tree.

Prevention & Control

Chemical control effectively reduces infections, but it is challenging to apply at the right time. In order to prevent apple scab infestations, cultivars that are resistant to the disease are the best option. Fall is a good time to rake and remove leaves around trees to reduce infection sources.   

2. SOOTY BLOTCH & Flyspeck

Sooty blotch and flyspeck can be devastating for your apple trees, reducing their yield by as much as 40%. This fungus causes characteristic lesions on leaves. In order to prevent sooty blotch, you must plant resistant varieties, prune infected branches and remove nearby host trees.

Flyspeck is another similar common summer disease. You may also want to consider using a copper-based fungicide spray every spring if there are a lot of fungal spores in the air. Make sure that if you use this type of chemical spray, it is applied when the wind isn’t blowing directly at your apple tree or other fruit trees.

Prevention & Control

The surface of fruit infected with flyspeck and sooty blotch is not infected with any harmful bacteria, which means they are perfectly safe to consume. The best way to prevent both diseases is to prune trees to promote good air circulation and thin out developing fruit. Both cultivars ‘Pristine’ and ‘Enterprise’ are resistant to these diseases.  

3. Fire blight

This bacterial disease is caused by Erwinia amylovora. These bacteria produce an exotoxin that enters through an opening in the bark and causes lesions on twigs, branches, leaves, and fruit. The bacterium also spreads from tree to tree by airborne spores. In late summer, droplets of bacterial ooze containing these spores will drip from fire blighted fruit onto adjacent trees, infecting them as well.

Prevention & Control

Pruning and sanitizing tools are the best ways to combat fire blight. Pruning away the affected branches 8-12 inches from the lesion should be done as soon as you notice symptoms of infection. Cultivars resistant to the disease would be another solution to prevent fire blight. 

4. Black Rot & Spots

The disease directly affects apples. A black rot-infected apple tree will have brown spots on each apple. Spots become larger and blacker as they grow. By this time, your precious apples will start to rot. 

Black rot is caused by a bacterium that invades an apple tree through wounds, open blossom ends or other entry points. This is a common problem in wet weather; black rot can become fatal if not treated immediately. 

Prevention & Control

As soon as you notice diseased fruit, remove it. It reduces the growth of fungi that cause black rots and spots.

5) Powdery Mildew

Powdery mildew, caused by a fungus, thrives during hot, dry periods and infects apples by attacking their leaves. The powdery mildew is evident when gray-white patches appear on new shoots and leaves. The growth of infected plants is typically stunted, curled, or distorted.

Prevention & Control

Whenever you see infected branches or twigs, remove them and discard them immediately. A number of cultivars are resistant to powdery mildew. Therefore, the use of a sterol inhibitor fungicide may be necessary for severe infections.

6) Cedar Apple Rust

Cedar apple rust causes lesions on branches and fruit. Usually, these are found on young branches, and they enlarge with every growing season. It is easy to identify cedar-apple rust by its bright orange-yellow spots on leaves. Leaves and fruit often drop when the spots appear in mid-to-late spring. Fruits that do hang from the tree are often small and malformed. 

Prevention & Control

Treatment for cedar-apple rust is limited to extensive pruning. To prevent re-infection, remove all dead branches and affected fruit and remove any debris. You should also remove any lesions found on cedar trees in the area. In this way, the fungal life cycle will be disrupted and the risk of recurrence will be reduced.