12 common apple tree diseases (and how to treat them)

Apple tree diseases can be tricky to navigate, especially for novice gardeners. From fire blight and apple scab to cedar apple rust and powdery mildew – it’s easy for even experienced gardeners to be overwhelmed by all the potential issues that could affect their apples. In this article, we’ll take a look at some of the most common apple tree diseases so you can better protect your trees from harm.

The basics of apple tree diseases

Apple trees are, unfortunately, vulnerable to several illnesses. Common apple tree diseases include fire blight, apple scab, cedar apple rust, powdery mildew, and several viruses. Knowing how to identify and treat these diseases can help you keep your apple trees healthy and productive for years to come.

Fire blight is a bacterial disease that affects apples as well as other plants, such as pears and crabapples. It causes leaves and twigs on infected branches to turn black or brown suddenly, giving them an appearance similar to being burned by fire – hence its name. Fire blight can be treated with antibiotics if caught early enough; however it’s best avoided altogether by planting resistant cultivars of apples like ‘Liberty’ or ‘Empire’, which are known for their resistance against this disease.

Apple scab is another common fungal disease that affects both leaves and fruits of susceptible varieties. Symptoms include discolored spots on the surface of the fruit or leaf, which may eventually crack open, leading to premature dropping from the tree before harvest time arrives. Good sanitation practices like removing fallen leaves from around the base of your tree will help reduce infection rates since spores overwinter in debris left behind after harvesting season has ended.

As humidity levels rise in the springtime, cedar apple rust can cause orange-yellow lesions to form on young foliage, resulting in reduced photosynthesis efficiency and stunted growth potentials if left untreated. To mitigate this issue, fungicides containing active ingredients such as myclobutanil or thiophanate methyl should be applied at regular intervals from just prior bud break until petal fall. By using the right timing and application of these preventative measures, you can increase your odds of keeping your apple trees strong and productive during their growing period.

Other common apple tree diseases include fungal pathogens like powdery mildew, anthracnose, and perennial canker, as well as viruses like apple mosaic virus, apple russet ring virus, and apple green crinkle-associated virus. Apple tree diseases can be a complex topic, but understanding the basics is essential for properly caring for and maintaining your apple trees.

1. Fire blight

Fire blight is a serious bacterial disease that affects apple trees, as well as other hosts such as pear, crabapple, and mountain ash. It is caused by the bacteria Erwinia amylovora, which can infect fruit, flowers, twigs, and leaves of infected plants.

Symptoms of fire blight include wilting of new shoots, dieback of branches or entire limbs, and dark brown to black lesions on bark or stem. The bacteria are spread by wind-borne rain splashes carrying the spores from fallen leaves or infected tissue to healthy wood in springtime. And it really can spread almost as fast as wildfire!

Some cultivars are more prone to fire blight infection than others. Highly-susceptible varieties include Gala, Fuji, Braeburn, Golden Delicious, Red Delicious, Granny Smith, Jonathan, Jonagold, Mutsu, and Rome. Varieties with some natural resistance to fireblight include Melrose, Priscilla, Redfree, and Winesap.

The best way to prevent infection is to plant resistant cultivars when possible. Pruning out any affected areas during dry weather may also help reduce the spread of fire blight but should be done carefully so as not to spread airborne spores further into healthy parts of the tree. Applying copper-based fungicides at bud break will help protect against fungal infections like honey fungus but won’t do anything for bacterial diseases like fire blight.

If your apple tree has already been infected with fire blight, you need to take immediate action; prune off all dead leaves and branches well past the point where they become discolored (at least 8 inches). Disinfect pruning tools between cuts with a solution containing 10% bleach/water mix or 70% rubbing alcohol/water mix before moving onto another part of the tree so you don’t risk spreading it further throughout your yard or even worse – an entire apple orchard. Remove all prunings from the area.

To treat existing infections, use antibacterial sprays during bloom time, followed up with additional applications every seven days until harvest time if needed. This should stop any reinfection from occurring and keep your delicious apples safe from harm. Additionally, remove any fallen fruits from around your trees that may have been affected by brown rot (a common fungal infection) so that it does not spread throughout your garden either.

2. Apple scab

Apple scab is a common fungal disease that affects apple trees and other related species. It is caused by the fungus Venturia inaequalis, which overwinters in fallen leaves and produces airborne spores during wet spring weather. The infection can cause spots on infected plants’ leaves, fruit, and twigs.

Apple varieties such as Delicious, Rome Beauty, Northern Spy, Jonathan, and Golden Delicious are particularly susceptible to this fungal disease. In contrast, scab-resistant varieties include Enterprise, Liberty, Pixie Crunch, Topaz, and CrimsonCrisp.

The first signs of apple scabs appear as small olive-green or yellowish spots on the upper surface of newly developing leaves or shoots. As the disease progresses, these spots may become larger with fringed margins. Infected fruits may also develop small brownish lesions surrounded by light green halos that eventually turn black if left untreated for long periods. Leaves may also curl up due to excessive moisture loss from transpiration caused by infection sites on leaf surfaces.

If you note signs of apple scab, start by cleaning up and removing all fallen leaves, fruit, and other plant debris from the area to maintain a “clean forest floor” in your orchard. You may also wish to apply a fungicide to the trees, especially in cool and wet weather. Lastly, keep up with annual pruning to make sure the tree canopies are open and allow for good airflow through the branches.

3. Cedar apple rust

Cedar apple rust is a common disease that affects many varieties of apple trees. It is caused by the fungus Gymnosporangium juniperi-virginianae, which alternates between its two host plants: cedars and apples. The fungal spores are spread by wind and rain from infected cedar trees to nearby apple trees. Signs of the disorder include yellow-orange patches on foliage, twigs, and fruit; brown spots on dropped leaves; early leaf shedding; and stunted or distorted growth in juvenile trees. Cultivars like McIntosh and Liberty may have some natural resistance, while varieties like Rome and Jonathan may be more susceptible than others.

Fungal infections can be difficult to treat once they’ve taken hold, so it’s important to take preventive measures if you want to keep your apple tree healthy. Plant resistant cultivars when possible – some varieties are more susceptible than others – and make sure your tree has adequate space for air circulation around it. Prune away dead branches regularly, rake up fallen leaves promptly, and water only at the soil around the tree’s drip line instead of overhead watering.

Inspecting your tree for signs of infection is also essential for prevention as well as early detection should an infection occur anyway. Look out for yellowish-orange spots on both sides of the leaf and deformed fruits with rough patches or lesions on them – these could indicate that something isn’t quite right with your beloved apple tree. If any symptoms are spotted, a certified arborist should be consulted without delay to identify the issue and recommend suitable solutions such as pruning or fungicide application that can rid the tree of infection while minimizing harm to other components.

4. Powdery mildew

Powdery mildew is a common disease of apple trees and many other plants that affects both the leaves and fruit. It is caused by a number of different fungi, which tend to thrive in warm, humid conditions. The fungus produces airborne spores that can spread to other plants and cause infection.

Symptoms include white or grayish-white powdery patches on the surface of infected leaves, stems, and fruits. In severe cases, these patches may cover most of the leaf surface. Infected fruits often have small brown spots on their skin and become distorted as they mature.

Different types of apples differ in their tolerance to powdery mildew; some are more resilient than others. Choosing resistant cultivars when planting an apple tree orchard or garden bed is important to reduce the risk of infection. Good air circulation around trees will also help prevent infection by keeping humidity levels low and allowing for rapid drying after rainfall or irrigation events.

5. Apple mosaic virus

Apple mosaic virus (ApMV) is a common disease of apple trees and can affect many varieties. The infection, brought about by a virus, is able to traverse through the foliage, blossoms, and apples of apple trees. Symptoms include yellow-green mottling on leaves, distorted or stunted growth of shoots and fruits, and reduced yield. ApMV can be spread from infected plants to healthy ones via contact with sap or airborne spores from infected tissue.

Infected trees may show signs of leaf spots or dead leaves in the springtime and white rot on their trunks during winter. If left untreated, ApMV can cause serious damage to an entire apple orchard over time by reducing yields significantly. To avoid recurrence, it is wise to implement good cleanliness practices such as collecting fallen foliage and trimming away any infected wood before the disease has a chance to spread. Apple mosaic virus is a highly contagious disease that can cause significant damage to apple trees.

6. Apple russet ring virus

Apple russet ring virus (ARRV) is a fungal disease that affects apple trees. It is caused by the fungus Diplocarpon mali, and can be identified by its characteristic yellow rings on leaves. ARRV causes leaf spots, browning of fruit, and premature defoliation of infected trees. The infection can spread quickly to nearby plants if not treated promptly.

Common symptoms of ARRV include yellow rings or spots on the leaves, which are visible when held up to light; these may also appear as concentric circles on the fruit surface. Infected fruits will often have a rough texture and may become discolored or mottled in appearance due to secondary infections from other fungi or bacteria, such as powdery mildew. Additionally, infected leaves may curl up and fall off prematurely, causing reduced yields in affected apple varieties.

To reduce the risk of ARRV infection, resistant cultivars such as Delicious, Honeycrisp, Empire, Granny Smith, and Golden Delicious should be chosen for planting when possible. Nevertheless, even these varieties can still become infected so it is important to stay on top of management practices like clearing away fallen leaves during harvest season and pruning off dead wood prior to bud break in springtime to help ensure a reinfection-free orchard year after year.

Apple russet ring virus is a serious disease that can cause severe damage to apple trees, so it’s important to be aware of the signs and take preventative measures. Fortunately, there are also other diseases like Apple green crinkle-associated virus, which may affect your tree as well.

7. Apple green crinkle-associated virus

Apple green crinkle-associated virus (AGCAV) is a serious disease that affects apple trees. AGCAV is transmitted by airborne spores and can infect both orchard-grown and home-garden apple trees, manifesting in yellowed leaves, stunted growth, curled foliage, and misshapen fruit with raised bumps. AGCAV is spread through airborne spores and can be found in both orchards and home gardens. Symptoms of AGCAV include yellowing of leaves, stunted growth, curling leaves, and discolored fruit with raised bumps on the skin. The virus also causes brown spots on the bark which may eventually lead to collar rot if left untreated.

The best way to prevent infection from AGCAV is to choose resistant cultivars when planting an apple tree. It is essential to get rid of any dropped leaves or fruit near the tree’s base in order to avoid new contamination. Pruning away any dead branches will help reduce potential sources for reinfection as well. Additionally, keeping your soil healthy with adequate amounts of organic matter will help keep your trees strong enough to resist infection from this virus.

Monitoring trees regularly is essential to spot any signs of illness during the growing season so that action can be taken quickly. Catching problems early makes them much easier to treat. While there are no chemical treatments available for AGCAV specifically, fungicides may be used in some cases depending on what type of fungal infection has taken hold in your tree’s tissues. Keeping up regular maintenance such as pruning away dead wood and removing fallen debris will go a long way towards preventing future outbreaks in your apple orchard – prevention is indeed better than cure.

Apple green crinkle-associated virus can cause serious damage to apple trees if left untreated, so it is important to be aware of the signs and symptoms. Apple stem pitting virus is another disease that affects apples and requires careful monitoring for successful management.

8. Apple stem pitting virus

Apple stem pitting virus (ASPV) is a serious disease of apple trees that can cause significant damage to the tree and its fruit. It is caused by an insect-transmitted virus, and it affects both young and mature apple trees. The symptoms of ASPV include small yellow spots on leaves, twig dieback, stunted growth, premature leaf drop, and distorted or misshapen fruit. In some cases, infected apples may have deep pits in their flesh which are difficult to detect until the fruit has been cut open.

In order to prevent ASPV from infecting your apple tree, it’s important to practice good pest management techniques such as removing dead wood from around the base of the tree where insects can hide and using insecticides when necessary. Additionally, you should always prune your trees properly so that there are no weak branches or overcrowded areas for pests to congregate in. Ensure that any newly-acquired trees are confirmed to be free of illness before placing them in your garden or yard.

If you suspect that your apple tree might be infected with ASPV, then it’s important to act quickly before the infection spreads further throughout the plant. Start by inspecting all parts of the plant for signs of infection, including discolored leaves or fruits with deep pits in them. If you find any evidence, immediately remove all affected parts from the plant and dispose of them safely away from other plants so they don’t spread further infections.

The best way to treat an ASPV infection is with a combination approach involving both chemical treatments, such as fungicides as well as cultural practices like proper pruning and sanitation methods mentioned above. Future generations can be spared from this vexing issue through a combined strategy of chemical treatments and cultural practices. With careful attention paid to prevention strategies combined with prompt treatment if needed, homeowners can keep their prized apple trees healthy for years without worrying about this dreaded disease ruining their harvest season.

Apple stems pitting virus is a disease that affects apple trees, causing premature fruit drop and poor quality fruits. Perennial canker is another serious issue for apple tree health; it’s caused by a fungal infection of the bark or woody tissue.

9. Perennial canker

Perennial canker is a fungal disease that affects apple trees. It usually starts with the leaves and fruit of infected trees becoming mottled or discolored, then gradually turning brown. If not treated, the infection can spread to the bark and wood of the tree, leading to its weakening and eventual death. The fungus thrives in moist conditions and is spread through airborne spores from other infected plants.

10. Anthracnose

Anthracnose is another fungal disease that affects apple trees. This fungal pathogen causes spots on the bark that eventually turn dark as tissue dies and separates, often exposing the inner fibre of the branch.

Infections typically happen during autumn rains, starting as small red circles on the bark. They’re easiest to see when the bark is wet. The color spreads deeper into the tree, reaching the sapwood which has important vessels. The infected spots get bigger and longer, changing to orange or brown, with a clear border between healthy and dead tissue. The bark cracks around the infection. In winter, the disease-causing organism takes a break, but restarts in the spring.

FAQs about apple tree diseases

Before you go…

In conclusion, apple tree diseases can be a serious issue for homeowners. Realizing the fundamentals of these typical illnesses is key to preserving your trees from contamination and keeping them in good health. Fire blight, apple scab, cedar apple rust, powdery mildew, and various viruses are all possible threats that you should look out for when caring for an apple tree. By being proactive with preventative measures such as pruning and monitoring regularly you can help reduce the risk of disease affecting your apples.

Resources

• Apple tree spacing guide
• How long does it take an apple tree to grow?
• When to pick apples: A harvest season guide
• How often to spray apple trees?

References

• Sutton, T., Aldwinckle, H., Walgenbach, J., & Agnello, A. (2014). Compendium of Apple and Pear Diseases and Pests. Amererican Phytopathological Society.
• Chand, G., MD, Akhtar, N., & Kumar, S. (2020). Diseases of Fruits and Vegetable Crops: Recent Management Approaches. CRC Press.