Crabapple Diseases and Pests: 26 Potential Tree Problems

Crabapple trees are a captivating spectacle with their colorful blooms and abundant fruit. They bring a sense of refinement to any outdoor scenery and are adored by both avid gardeners and nature lovers.

However, they are susceptible to certain diseases and pests. Understanding these potential issues is key to maintaining the health and beauty of these trees.

The following list will provide a comprehensive guide to the most common diseases and pests that can affect crabapple trees.

We’ll explain the symptoms of each problem as well as prevention and treatment strategies, providing you with the knowledge you need to keep your crabapple trees thriving.

Boost your confidence and learn to care for your tree like a pro with my comprehensive Crabapple Tree Guide. It’s a must-read!

Crabapple Diseases

Crabapple trees can be affected by a variety of diseases, many of which are caused by fungi.

These diseases can cause a range of symptoms and can affect the leaves, fruit, and overall health of the tree.

Apple Scab

Apple scab is a common fungal disease that affects many types of apple trees, including crabapples. It is caused by the fungus Venturia inaequalis.

Symptoms include dark, scaly lesions on the leaves, fruit, and twigs. The disease is most severe in wet, cool weather.

Prevention

To prevent apple scab, choose resistant varieties of crabapple trees if possible.

Regularly clean up fallen leaves and other debris from around the tree as the fungus can survive in infected leaves and infect the tree the following spring.

Treatment

If your crabapple tree is infected with apple scab, fungicides can be used to control the disease.

These should be applied in the spring, starting when the buds begin to open and continuing until the leaves are fully expanded.

Fireblight

Fireblight is a bacterial disease caused by Erwinia amylovora. It affects a variety of plants in the rose family, including crabapple trees.

Symptoms include wilting, blackening, or “burning” of branches and a watery, light-tan ooze from infected areas. The disease can spread rapidly in warm, wet weather.

Prevention

To prevent fireblight, avoid excessive use of nitrogen fertilizer, which can promote susceptible new growth. Also, avoid wetting the foliage when watering, as the bacteria can spread in water.

Treatment

Prune out infected branches during the dormant season, making cuts well below the infected area.

Be sure to sterilize pruning tools between cuts to avoid spreading the disease. In severe cases, antibacterial sprays may be necessary.

Cedar-Apple Rust

Cedar-apple rust is a fungal disease caused by Gymnosporangium juniperi-virginianae. It requires two hosts to complete its life cycle: a cedar (or juniper) and an apple or crabapple tree.

On crabapple trees, symptoms include yellow spots on the upper leaf surface and orange, gelatinous spore horns on the underside of the leaves.

Prevention

To prevent cedar-apple rust, avoid planting crabapple trees near cedars or junipers or remove any nearby cedars or junipers if possible. Choose rust-resistant crabapple varieties for new plantings.

Treatment

Fungicide sprays can be used when the tree is flowering to protect it from infection. If cedars or junipers are present, removing the galls in early spring can also help reduce the disease.

Cedar-Hawthorn Rust

Cedar-hawthorn rust is similar to cedar-apple rust, but it is caused by a different fungus, Gymnosporangium globosum.

It also requires two hosts to complete its life cycle: a juniper and a hawthorn or apple tree (this includes crabapples).

Symptoms on crabapple trees include yellow or orange spots on the leaves, and, in severe cases, leaf drop.

Prevention

Preventing cedar-hawthorn rust involves similar strategies to those used for cedar-apple rust.

Avoid planting susceptible trees near junipers, or remove any nearby junipers if possible. Choose rust-resistant crabapple varieties for new plantings.

Treatment

Fungicide sprays can be used when the tree is flowering to protect it from infection. If junipers are present, removing the galls from the trees in early spring can help reduce the disease.

I talk about all the different types of rust that affect Crabapple trees in this article: Rust on Crabapple Trees: Identification, Prevention & Management.

Powdery Mildew

Powdery mildew is a common fungal disease that affects a wide range of plants, including crabapples.

It is caused by the fungus Podosphaera leucotricha. Symptoms include a white, powdery coating on the leaves, buds, and sometimes the fruit. The leaves may also become distorted or stunted.

An apple tree leaf coated with powdery mildew.

Prevention

To prevent powdery mildew, ensure your crabapple tree is planted in a location with good air circulation. Avoid wetting the foliage when watering as the fungus thrives in humid conditions.

Treatment

If your crabapple tree is infected with powdery mildew, fungicides can be used to control the disease. These should be applied as soon as symptoms are noticed.

Sooty Mold

Sooty mold is a type of fungus that grows on the honeydew excreted by certain insects, such as aphids.

It appears as a black, sooty coating on the leaves, branches, or fruit. While it does not directly harm the tree, it can block sunlight and reduce photosynthesis.

Prevention

Preventing sooty mold involves controlling the insects that produce honeydew. Regularly monitor your tree for signs of these insects, and use an integrated pest management approach to control them.

Treatment

If your crabapple tree has sooty mold, controlling the insects that produce honeydew will often allow the sooty mold to gradually weather away.

In severe cases, gently washing with soapy water can help remove the mold.

Leaf Spot Diseases

Leaf spot diseases are caused by various fungi and bacteria. They result in small, round spots on the leaves that may be black, brown, or tan. In severe cases, they can lead to early leaf drop.

Prevention

To prevent leaf spot diseases, ensure your crabapple tree is planted in a location with good air circulation.

Regularly clean up fallen leaves and other debris from around the tree to reduce the number of disease spores.

Treatment

If your crabapple tree has a leaf spot disease, fungicides or bactericides can be used, depending on the cause of the disease. These should be applied as soon as symptoms are noticed.

Phytophthora Root Rot

Phytophthora root rot is a disease caused by a soil-borne fungus, Phytophthora spp.

Symptoms include yellowing leaves, stunted growth, and the death of branches or the entire tree. The disease is most common in poorly drained soils.

Prevention

To prevent Phytophthora root rot, ensure your crabapple tree is planted in well-draining soil. Avoid overwatering, and do not plant trees too deeply.

Treatment

If your crabapple tree is infected with Phytophthora root rot, improving drainage and reducing watering can help. In severe cases, fungicides may be necessary, but they are often not effective once symptoms are advanced.

Cankers

Cankers are areas of dead bark on the branches or trunk caused by various fungi and bacteria. They appear as sunken, discolored areas and can girdle branches or the entire tree if not managed.

Prevention

To prevent cankers, avoid injuring your tree because wounds can provide an entry point for pathogens.

Also, ensure your tree is not stressed by drought or nutrient deficiencies as stress can make it more susceptible to cankers.

Treatment

If your crabapple tree has cankers, prune out the infected branches, making cuts well below the canker.

Be sure to sterilize your pruning tools between cuts to avoid spreading the disease. In severe cases, you may need to consult with a professional arborist.

Sooty Blotch

Sooty blotch is a fungal disease that causes dark, smudgy spots on the fruit and sometimes the leaves. It does not harm the tree but can reduce the aesthetic value of the fruit.

Prevention

To prevent sooty blotch, prune your tree to improve air circulation and ensure the foliage can dry quickly after rain. Also, clean up fallen fruit and other debris from around the tree.

Treatment

If your crabapple tree has sooty blotch, fungicides can be used to control the disease.

These should be applied when the fruit begins to develop and continued according to the fungicide label’s instructions.

Flyspeck

Flyspeck is a fungal disease that causes small, dark spots to appear on the fruit, resembling the specks made by a fly.

Like sooty blotch, it does not harm the tree but can reduce the aesthetic value of the fruit.

Prevention

To prevent flyspeck, prune your tree to improve air circulation and ensure the foliage doesn’t remain wet for long periods. Regularly pick up fallen fruit and tree litter from around the tree.

Treatment

If your crabapple tree has flyspeck, fungicides are recommended. Apply them when the fruit begins to develop, and follow the fungicide label’s instructions.

Crabapple Pests

While diseases can pose significant challenges to the health of crabapple trees, pests can also be a major concern.

These can range from tiny insects that suck the sap from leaves to larger pests that bore into the trunk.

Aphids

Aphids are small, soft-bodied insects that suck the sap from the leaves and stems of crabapple trees.

They can cause the leaves to curl and become distorted, and they also excrete a sticky substance called honeydew, which can lead to the growth of sooty mold.

Prevention

Encourage beneficial insects, such as ladybugs and lacewings, which are natural predators of aphids. Avoid overuse of nitrogen fertilizer, which can promote lush new growth that aphids prefer.

Treatment

If your crabapple tree has a heavy infestation of aphids, you can use an insecticidal soap (find it here) or a strong spray of water to dislodge the aphids. In severe cases, a targeted insecticide may be necessary.

Japanese Beetles

Japanese beetles are a common pest of crabapple trees. The adult beetles feed on the leaves and flowers, often leaving behind skeletonized leaves. The larvae, or grubs, feed on the roots of grass and other plants.

Prevention

Hand-picking beetles can be effective for small infestations. Traps are available but should be placed away from the tree, as they can attract more beetles to the area.

Treatment

If your crabapple tree has a heavy infestation of Japanese beetles, insecticides can be used. However, these should be used cautiously, as they can also kill beneficial insects.

Whiteflies

Whiteflies are tiny, white insects that suck the sap from the leaves of crabapple trees.

They excrete honeydew, which can lead to the growth of sooty mold. Heavy infestations can cause leaf yellowing and drop.

Prevention

Encourage beneficial insects, such as ladybugs and lacewings, which are natural predators of whiteflies.

Keep the area around the tree clean of fallen leaves and other debris, which can provide a hiding place for whiteflies.

Treatment

If your crabapple tree has a whitefly infestation, insecticidal soaps or a strong spray of water can be used to dislodge the whiteflies. In severe cases, a targeted insecticide may be necessary.

Thrips

Thrips are tiny insects that feed on the leaves and flowers of crabapple trees, causing discoloration and distortion. They can also spread plant diseases.

Prevention

Regularly monitor your tree for signs of thrips, and use an integrated pest management approach to control them.

This includes promoting beneficial insects and using targeted pesticides as necessary.

Treatment

If your crabapple tree has a thrips infestation, insecticidal soaps or a strong spray of water can be used to dislodge the thrips. Use a targeted insecticide when necessary.

Scale Insects

Scale insects are small, immobile insects that attach themselves to the stems and leaves of crabapple trees and suck the sap. They can cause yellowing of the leaves and reduced vigor of the tree.

Prevention

Monitor your tree regularly for signs of scale insects. Encourage beneficial insects, such as ladybugs and parasitic wasps, which are natural predators of scale insects.

Treatment

If your crabapple tree has a scale insect infestation, horticultural oil can be used to smother the insects. In severe cases, a systemic insecticide may be necessary.

Sawflies

Sawflies are small, wasp-like insects whose larvae feed on the leaves of crabapple trees. They can cause significant defoliation if left unchecked.

Prevention

Monitor your tree regularly for signs of sawfly larvae, and hand-pick them if found. Encourage birds and other natural predators, which can help control sawfly populations.

Treatment

If your crabapple tree has a heavy infestation of sawflies, insecticidal soap or a targeted insecticide can be used.

Spider Mites

Spider mites are tiny arachnids that suck the sap from the leaves of crabapple trees. They can cause the leaves to become speckled and, in severe cases, can lead to leaf drop.

Prevention

Ensure your crabapple tree is not stressed by drought as dry conditions can promote spider mite populations.

Regularly rinse the leaves with water to dislodge mites and reduce dust, which can provide a favorable environment for spider mites.

Treatment

If your crabapple tree has a spider mite infestation, horticultural oil or insecticidal soap can be used. In severe cases, a miticide may be necessary.

Caterpillars

Various types of caterpillars can feed on the leaves of crabapple trees, causing defoliation.

These include tent caterpillars, which create a web-like tent in the branches, and gypsy moth caterpillars, which can defoliate entire trees.

Prevention

Monitor your tree regularly for signs of caterpillars, and hand-pick them if found. Encourage birds and other natural predators, which can help control caterpillar populations.

Treatment

If your crabapple tree has a heavy infestation of caterpillars, a targeted insecticide, such as Bacillus thuringiensis (Bt), can be used.

Apple Maggot

The apple maggot is a type of fruit fly that lays its eggs in the fruit of apple and crabapple trees. The larvae feed on the fruit, causing it to become distorted and often drop prematurely.

Prevention

Clean up and dispose of fallen fruit promptly to reduce breeding sites. Traps can be used to monitor the presence of apple maggots and to reduce their numbers.

Treatment

If your crabapple tree has an apple maggot infestation, insecticides can be used. However, use them with caution as they can also kill beneficial insects.

Apple Tree Borers

Apple tree borers are a type of beetle that lays its eggs on the bark of apple and crabapple trees. The larvae bore into the tree, causing wilting and sometimes death of branches.

The grub of an apple tree borer and the damage to the tree trunk.

Prevention

Keep your tree healthy and unstressed as borers are more likely to attack stressed trees.

Regularly inspect the trunk and branches for signs of borers, such as sawdust-like frass or holes in the bark.

Treatment

If your crabapple tree has an infestation of apple tree borers, insecticides can be used. In some cases, borers can be physically removed from the tree with a thin wire inserted into their holes.

Leafhoppers

Leafhoppers are small, wedge-shaped insects that suck the sap from the leaves of crabapple trees. They can cause the leaves to become stippled or yellowed, and they can also transmit plant diseases.

Prevention

Encourage beneficial insects, such as ladybugs and lacewings, which are natural predators of leafhoppers. Regularly rinse the leaves with water to dislodge leafhoppers and reduce dust.

Treatment

If your crabapple tree has a leafhopper infestation, insecticidal soap or a targeted insecticide is recommended.

Mealybugs

Mealybugs are small, soft-bodied insects that suck the sap from the leaves and stems of crabapple trees.

They excrete honeydew, which can lead to the growth of sooty mold. Heavy infestations can cause leaf yellowing and drop.

Prevention

Encourage natural predators of mealybugs, such as ladybugs and lacewings. Keep the area around the tree clean of fallen leaves and other debris, which can provide a hiding place.

Treatment

If your crabapple tree has a mealybug infestation, insecticidal soaps or a strong spray of water can be used to dislodge them. In severe cases, opt for a targeted insecticide.

Leafminers

Leafminers are the larvae of certain types of flies, moths, and beetles. They feed inside the leaves, creating winding tunnels or blotches.

While they rarely cause serious harm, heavy infestations can reduce the aesthetic value of the tree.

Prevention

Monitor your tree regularly for signs of leafminers. Hand-pick and destroy affected leaves if found. Encourage beneficial insects, which can help control leafminer populations.

Treatment

If your crabapple tree has a heavy infestation of leafminers, a targeted insecticide can be used.

Lacebugs

Lacebugs are small insects that suck the sap from the undersides of leaves, causing them to become speckled or bleached in appearance.

They can also excrete honeydew, which can lead to the growth of sooty mold.

Prevention

Encourage beneficial insects, such as ladybugs and lacewings, to help control the population. Regularly rinse the leaves with water to dislodge the pests.

Treatment

If your crabapple tree has a lacebug infestation, use either an insecticidal soap or a targeted insecticide.

Springtail Insects

Springtail insects are tiny, soil-dwelling insects that can sometimes be found on the leaves or fruit of crabapple trees, especially during wet weather.

They are generally harmless and are more of a nuisance than a threat.

Prevention

There are no specific prevention measures for springtails as they are generally not harmful to crabapple trees.

Treatment

No treatment is generally necessary for springtails. If their numbers are high and they are causing a nuisance, a general-purpose insecticide can be used.

Final Thoughts

Crabapple trees, with their stunning blossoms and vibrant fruit, are a wonderful addition to any landscape. However, they can be susceptible to a variety of diseases and pests.

By understanding these potential issues and how to prevent and treat them, you can help ensure the health and beauty of your crabapple trees.

Regular monitoring, proper watering and feeding, and timely pruning can help keep your crabapple trees healthy and vibrant.