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Common Apple Tree Diseases

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Apple trees and other plants in the rose family, like hawthorns, are susceptible to many diseases. These can affect the tree's ability to produce fruit or even kill it completely.

Luckily, these diseases are often preventable, and even when they aren't, they often cause damage mainly on an aesthetic level. Here are some of the most common apple tree diseases and how you can recognize and treat them:

Cedar Apple Rust

Cedar apple rust is common in many parts of the United States. It gets its name from the fact that it needs two hosts to reproduce, cedar tree and apple tree. Cedar apple is a fungus that uses two hosts to reproduce. It's caused by the pathogen called Gymnosporangium juniperi vinginianae.

Cedar Apple Rust
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You can identify cedar apple rust by the lesions it causes on branches and fruit. These usually affect young branches and enlarge every growing season. To prevent the spread of disease, apply fungicides containing fenarimol or myclobutanil. Avoid planting host trees near one another.

Prune remove all dead branches and affected fruit and clear the debris to prevent reinfection from remaining spores. Plus, plant resistant varieties, including red-free, William's pride, and freedom.

Powdery Mildew

Powdery mildew, caused by Podosphaera pannosa var. macropustulata, is considered an indigenous disease around the world. It's very common in apple trees and starts off as small white spots that resemble powder on leaves, flowers, and fruit. Powdery mildew is unlikely to kill your plants, but it will sap their strength.

The fungus causes gray white powdery patches to form on leaves. Tree growth often appears stunted or distorted, and flowers produce no fruit. Leaves and shoots may turn brown in mid summer. The fungus overwinters inside infected buds.

As these buds open in spring, they become covered with powdery spores. The wind carries the spores to infect new leaves, fruit, and shoots. To prevent this disease, prune infected branches and twigs early in the season. If the disease is severe, use fungicides for treatment. You can also consider how to get rid of mold and use the same method to control powdery mildew in your apple tree.

Fire Blight

Fire blight is a bacterial disease that affects fruit trees, including apples and pears. It causes small, water soaked lesions to form on the twigs, leaves, flowers, and fruit of apple trees. When cut open, these lesions develop into brown or black cankers that may bleed a sticky gum-like fluid.

Fire Blight
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Fire blight thrives in hot, humid climates, usually appearing strong in the spring and reducing as dryer summer temperatures occur. The bacteria infects trees undetectably in the fall or winter, hiding in branches and unopened buds. It begins to emerge through openings in the branches and foliage in the spring and becomes apparent.

The infection can be spread through gardening tools. Fire blight manifests as lesions on the branches and leaves of the tree, known as shepherd's crooks. Treating this type of apple tree disease can be a daunting task since overusing certain bacterial sprays can cause the tree to develop resistance to treatment.

The best way to fight fire blight is prompt pruning and sanitizing tools. As soon as you notice symptoms of infection, prune away the affected branches 8-12 inches from the lesion. Sanitize all gardening tools in a ten percent bleach solution mixed with a few drops of dish liquid to avoid spreading the bacteria between trees and branches.

Sooty Blotch and Flyspeck

Sooty blotch flyspeck tends to attack apple trees in the late summer and early autumn. The good news is that sooty blotch flyspeck is superficial, only affecting the appearance of the apple trees. These tree diseases look like matte black or gray blotches and tiny black specks.

Sooty Blotch and Flyspeck
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You can spot sooty blotch and flyspeck by the characteristics of small black blotches or speckles on the fruit. This makes apples look much less palatable, though it doesn't affect the taste or safety of the fruit. You can prevent the risk of sooty blotch and flyspeck by keeping your apple tree pruned.

This increases air circulation to healthy fruit and branches and reduces the risk of bacteria forming. Make sure not to let your apple tree get too wet, as this fungus thrives in high humidity. If you notice any signs of sooty blotch and flyspeck, mix one ounce of bleach and one gallon of water, then rub the fruit gently with the solution and a wet cloth to remove the fungus.

Apple Scab

You'll see the first sign of apple scab in the form of a lesion on the tree's new leaves in early or mid spring. The lesion will be darker than the leaf color, on the leaf's underside, which is light green, lesions will be olive colored, and on top of the leaf, which is darker green, lesions will be black.

Apple Scab
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Infected leaves may fall off altogether in summer. If the tree still manages to produce fruit, the apples will also have dark, scabby lesions. But the apples are usually edible. It's easy for the small scale grower to prevent apple scab because the cause is simply lack of observation and poor hygiene.

An infestation starts small, even going unnoticed. The real problem begins when you allow the infected leaves that fall to the ground at the end of the growing season to remain there all winter. Rainy weather provides ideal conditions for fungal spores to grow, and the following spring, they will find new leaves on which to land.

The presence of these spores can be detected, even if you missed seeing them land. They look like small patches of grayish white mold. To prevent the disease from spreading, rake up all fallen leaves in autumn before winter sets in so that there is no chance of spores landing and growing on them. The resistant cultivars include crimson crisp, gold rush, and Mac free.

Bitter Rot

Light colored apples such as Empire, Honeycrisp, Mclntosh, Sunrise, Paulared, and Jonagold are most susceptible to bitter rot. Lesions with concentric rings extend to the core of the fruit. These lesions often appear on the side of the apple with the most direct sun.

A sour smelling rot develops. As the infected fruit ripens, it continues to decay and dry up. Bitter rot doesn't need the fruit to have a wound to establish infection. The fungus can infect the fruit through direct penetration of the skin. These concentric rings begin to ooze a gelatinous, pink substance made up of spores.

This mass of spores is then spread by rainfall to other fruit. To treat this disease, remove diseased fruit, dead wood, and any cankers formed in the wood tissue.. Applying fungicides 10 -14 days through harvest and more frequently under bitter rot's preferred conditions can be beneficial.

At the first sign of infection, remove any fruit that shows signs of rot or physical damage. Don't let infected fruit stay on branch for extended periods because it will become “bitter rot” which is actually caused by a completely different fungus called bitter rot.

Black Rot

There are many different types of black rot, but most have similar economic impacts on apple production. Black rot is generally found near the branch unions of apple fruit.  Black rot causes frog eye leaf spot, fruit rot, and cankers on the fruit. Infected leaves form spots thought to look like frog eyes with reddish edges and tan middles.

Large, brown, rotten spots develop on the apple, most commonly on the blossom end. Although the apple's surface is brown, the flesh of the apple remains firm. Fruits shrivel up and dry out while remaining attached to the tree. The fungus can affect trunks, leaves, branches, and fruits.

Pycnidia, spore producing structures, develop on infected fruit. Pycnidia appear as small, black spots. When there is wet weather, the rainfall and wind carry the spores to other susceptible areas. The fungus infects leaves, wood, and fruit through openings or wounds. Trees are more vulnerable to black rot when infected with fire blight.

To treat this disease, remove dead or diseased branches and dried fruits. Burn or bury all infected materials. If you cut down the tree. remove the stump to ensure the spores do not spread. Fungicides are typically not used to manage black rot. Use captain or sulfur products labeled for black rot control. Perform protective measures for fire blight to ensure your trees do not become more susceptible to root rot.

White Rot

This fungus lives in the soil and enters trees through wounds. It is active when roots are wet such as after a rainstorm. White rot affects fruit, but will not kill the tree. Apples begin to develop a soft rot, unlike bitter rot and black rot which form firm rots.

Most damage occurs during early spring or late fall. Warm temperatures and rainfall can trigger white rot during these times. The fungus infects the root system and spreads up the trunk. Blackened areas may appear at aboveground cuts or wounds.

White rot can be prevented by planting in well-drained soils and pruning out diseased wood below ground level. This fungus thrives during moist conditions so avoid irrigation from dawn to early evening. To decrease stress, remove fire blighted wood and water stress during drought.

Cork Spot Disease

A Cork spot is a condition that causes pits or depressions in apples. Though it's often confused with apple diseases, it's actually caused by a reduced level l of calcium in the tree. The Cork spot appears like dimples, pits, or depressions on the surface of the apple. They're not significantly different in texture from the rest of the fruit but often look unappealing.

Once a cork spot appears, it's very difficult to treat it since it seems related to vitamin levels in developing, or it. However, there seems to be a correlation between low soil pH and fruit overgrowth, and a higher incidence of cork spots. Make sure you know how to test soil pH to enable you to control this disease.

Phytophthora Rots

This is a fungus-like disease that sap's a trees strength. It can attack various parts of the tree, including the trunk or roots. If you suspect your apple tree may be infested with a phytophthora disease, perform the same sort of test, you would do to see if an arborvitae shrub is alive or dead.

Take a sharp knife and remove a small strip of the outer bark of the trunk to check on the color underneath. Healthy wood is green,n while diseased wood will be orange or brown. The cause of this disease is often contamination, which can come from the soil you've brought onto your property, irrigation water, or even the plant itself.

For prevention, other than being careful to avoid contamination, take moisture-related precautions as you would for fungus prevention. For example, plant on landscape berms or raised beds instead of ground level to improve drainage. Also, when buying, ask for a tree with a Geneva series rootstock, it will have superior resistance.

FAQs on Common Apple Tree Diseases

What disease kills apple trees?

Southern blight is the most fatal and rapidly kills infected areas. Fortunately, apple trees become resistant to southern blight as they age, and those that are most severely affected are typically one to three years old.

Can a sick apple tree be saved?

Yes, cut back dead, broken, or diseased branches to sound wood. Also, remove stems that are overcrowded or weak. Such stems typically grew in shaded parts of the tree and drooped downwards. Either cut them off completely or shorten them to the point where they start their downward arc.

When should you call a professional?

If an inspection is widespread around your garden or isn't responding to treatment, contact a professional orchardist who will be able to diagnose the problem and suggest treatment options. The best way to prevent these diseases is by planting resistant varieties of apples. Control aphid infestations with

Final Thought on Common Apple Tree Diseases

The most effective way of protecting your apple trees from disease is through prevention, which you can do through proper watering, pruning, soil treatment, and sanitation. This will keep your apple trees completely healthy and productive.


Kristina Perrin

Kristina Perrin

Kristina is an expert DIY home remodeler and mom to three. When she's not cooking or experimenting with new recipes, you can find her working on new home improvement projects or writing about her favorite kitchen appliances or DIY projects on Kitchen Infinity blog.

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