Apple Tree Diseases to Look Out For

Apple trees have semi-broad trunks, dark green foliage, and lusciously large green or red fruits. Not forgetting the glorious apple blossom, which signals spring and summer are on their way.

Unfortunately, while apple plants are beautiful, they are susceptible to diseases like powdery mildew and fire blight. On the bright side, however, there are ways you can treat such apple diseases.

In today’s guide, we’ll help you spot and treat the most common apple tree diseases. We’ll also reveal how to plant and grow healthy, prosperous apple trees.

The Most Common Apple Plant Diseases

Knowing what type of disease you will be dealing with is essential for successfully treating apple plant diseases.

In this article, we have researched some of the most common apple plant diseases that could affect your fruit trees .

1. Apple Scab

Apple scab is caused by the Venturia inaequalis fungus. It affects apples and crabapples. The result is infected fruit and foliage. The apple scab fungus overwinters on fallen, diseased leaves.

The warm, rainy weather in spring and summer creates the perfect environment for apple scab. During these seasons, the fungus will release spores transported by wind to areas of newly planted/developed foliage, flowers, green twigs, or fruit.

To identify apple scabs, monitor your apple trees, particularly in spring. Look for small, olive-green to black spots on your apple tree’s foliage. These spots can affect the whole leaf, causing it to turn brown and eventually fall off.

As the leaf spots age, they’ll turn black, and grow into larger clusters.

Infected fruit will also have olive-green spots that turn brown over time. Young apples that show symptoms of apple scab will form cracks and become deformed as they develop.

Another noticeable sign of apple scab is cracking and blistering on the twigs and black blotches on the emerging apples.

2. Fire Blight

Fire blight (Erwinia amylovora) is native to North America and was inadvertently introduced to the UK in the 1950s. It has since spread through many parts of mainland Europe. It primarily affects members of the Rosaceae, such as apple and pear trees. The fire blight bacteria will spend winter in the cankers of infected trees. During spring, the bacteria will multiply and seep out of the canker, resembling a sticky ooze.

This sticky ooze attracts pollinators, which carry the bacteria to other flowers or natural openings.

To spot fire blight, pay attention to your apple tree’s flowers and young twigs. If infected, they will appear wilted and shriveled, quickly turning black. During the period of active spread, you will notice  reddish/brown staining on the outer wood. This will give your apple tree a ‘fire scorched’ appearance on infected areas. Another sign is twigs that will bend, resembling the shapes of hooks.

Typically, these dead leaves and twigs remain attached to the dead branch. Fire Blight is a serious apple tree disease that requires treatment to prevent further contamination of other members of the Rosaceae family. 

3. Powdery Mildew

On apple trees, powdery mildew (Podosphaera leucotricha) is a fungus that forms a dense, gray-white growth.

The fungus overwinters in dormant buds on apple trees, spreading to their leaves and blossoms in spring via spores. Powdery mildew typically affects an apple tree’s leaves, buds, and shoots. However, you can expect to see infections more commonly on an apple tree’s foliage.

Look for white, felt-like patches of fungus on the lower surfaces of young leaves.

As the infection spreads, you can expect to see the fungus cover both sides of any affected leaves. Infected foliage is often narrow, curled, or distorted. In other words, infected leaves will show signs of stunted growth, becoming brittle with maturity.

The best time to inspect for powdery mildew is during dry periods when humidity is relatively high.

4. Sooty Blotch & Flyspeck

Although two different types of fungus, it’s not uncommon to find sooty blotch (Gloeodes pomigena) and flyspeck (Schizothyrium pomi) growing together on the same fruit. However, flyspeck can sometimes be found on its own.

These fungi overwinter on the fruit, leaves, and bark of apple trees. In warm, wet weather conditions, spores develop and germinate. Transported by wind and rain, the spores from these fungi spread onto developing fruits.

Flyspeck appears as small, black, slightly elevated dots on the apple’s surface. Sooty blotch appears in brown or black blotches on the surface of the fruit, too.

You can wipe both sooty blotch and flyspeck off the apple’s surface. However, unlike sooty blotch, flyspeck won’t discolor the apple’s surface once removed.

5. Honey Fungus

Honey fungus spreads underground, attacking the root system of many woody perennials. Honey fungus spreads through direct contact between the roots of healthy and infected plants.

This is a serious infection that can be difficult to treat as it could be spreading from the underground roots of nearby plants. Parts of the infected apple tree might die off in sections over a long period. The whole tree could also suddenly die off completely during hot, dry weather.

Symptoms include pale foliage, a lack of flowers, and cracking or bleeding bark. Because honey fungus grows underground and only sometimes produces mushrooms, it can be difficult to identify until it causes substantial damage.

During wet conditions, we recommend peeling back some of the bark at the base of your apple tree. Look for a thin layer of fungal tissue. If it’s cream/white and has the consistency of a mushroom, you’re likely dealing with honey fungus.

How to Treat Apple Tree Diseases

Now that we have covered how to spot the most common apple tree diseases, let us look further at the best forms of treatment.

Below, we’ve revealed how to treat apple tree diseases effectively.

1. Apple Scab Treatment

To treat apple scabs, we recommend the following tips:

• Remove fallen leaves in autumn to prevent fungus from surviving the winter and reinfect new trees.
• Plant your trees spaced correctly in an area, allowing for good air circulation.
• Prune your trees and space out their branches to support consistent airflow. This will allow the leaves to dry quickly, removing the moisture the fungus needs to survive.
• Prune and destroy infected leaves.
• Grow scab-resistant apple varieties like Honeycrisp, Freedom, and Liberty.
• Use fungicides that contain captain, lime-sulfur, or wettable sulfur. Apply it when temperatures are above 60℃ and when the leaves/blooms are wet.
• According to Oregon State University, you could also add dolomitic lime to your soil after leaf drop. By using dolomitic lime in the fall, you’ll increase the pH of your soil. As a result, the dolomitic lime will help reduce the dispersion of fungal spores in the spring.

2. Fire Blight Treatment

Here are some tips to help you treat fire blight.

• Prune out fire blight by cutting branches and twigs 12-18 inches below any sign of infected tissue.
• Remove fire blight cankers during winter.
• Spray copper-based fungicides before autumnal periods of rain. Repeat fortnightly if needed.
• Disinfect pruning tools between cuts using a 10% bleach/90% water solution.
• For large infected areas, seek professional advice. Alternatively,  consider removing and burning the whole tree or take it to an appropriate land infill site.
• Grow fire blight-resistant apple varieties like Enterprise, Freedom, and Prima.

 3. Powdery Mildew Treatment

Read on to discover how to treat powdery mildew.

• Prune and discard infected leaves, buds, branches, and twigs.
• Spray your apple trees with Bonide Sulfur Plant Fungicide. Spray your fungicide before the blooms open and repeat every 2-3 weeks until new shoots stop growing.
• Make sure to plant your trees in a sunny area. Excessive shade and high humidity can increase the chances of infection.

Grow apple tree varieties resistant to powdery mildew, like Goldrush, Arkansas Black Apple, and Freedom.

4. Sooty Blotch & Flyspeck Treatment

Read below to combat sooty blotch and flyspeck.

• Prune your apple trees to promote improved air circulation in general.
• Thin out developing fruit to improve air circulation to these areas further.
• Store healthy fruit in cool and well-ventilated conditions to prevent the spread of sooty blotch.
• Apply a routine fungicide every two to three weeks.
• Grow apple varieties that are resistant to SBFS, like Enterprise and Pristine.

5. Honey Fungus Treatment

Lastly, we’ll discuss how to treat honey fungus.

• Dig out the entirety of the infected plant, including its roots and soil, and burn it/take it to a landfill.
• Remove a layer of soil around the base of plant stems if your apple trees are planted too deeply.
• Don’t leave infected stumps in the soil.
• Remove plants growing around the infected plant.
• Avoid planting anything in the soil of the affected area for 6-12 months. This will help to kill off the fungus completely.

How to Grow An Apple Tree

Knowing how to grow an apple tree correctly can help combat some of the most prevalent apple tree diseases. In general, apple trees  are easy to grow, with dwarf varieties suitable for pots and full-sized trees for the open ground. So don’t be put off by the list of potential diseases, as the rewards of harvesting fresh apples are worth the effort of growing your own.

How to Grow An Apple Tree in the Ground: By providing the best possible growing conditions, most diseases can be prevented or managed. Soil and sun are two vital requirements for healthy apple trees. 

Choose a sunny spot for your apple tree where it will receive at least eight hours of sunlight daily. An open location is essential to allow for adequate airflow, as this will help prevent or reduce fungal diseases and cross-contamination. However, some shelter from strong winds and late frosts is also ideal.

Apple trees thrive in fertile soil with a pH between 6 to 6.5. Adding plenty of well-rotted organic matter like manure or compost into the ground is essential before planting. Dig a planting hole large enough to accommodate the root ball and extra soil to backfill. After placing the root ball into the ground, gently backfill with soil or compost and water thoroughly. Your apple tree might also need staking, details of which we cover further in this article.

Many apple tree varieties require cross-pollination. To achieve this, it will be necessary to plant another apple tree nearby.

Growing Apple Trees from Seed: While it is possible to grow apple trees from seed, we don’t recommend it. Growing apples from seeds can take a decade to produce a mature tree. In addition, the fruit trees are likely to produce inedible fruits.

Grafted and Dwarf Apple Trees: Grafted apple trees come in all shapes and sizes, with a variety suitable for most gardens or yards. Thanks to dwarfing and semi-dwarfing rootstocks, there are dwarf fruit trees that are perfect for those who have small gardens, too.

1. Choosing Your Apple Tree

You can either purchase bare-root apple trees or potted apple trees.

There is one significant difference between bare-rooted and potted apple trees. Bare roots are best planted in winter, during their dormant season (November to March). Potted apple trees can be planted all year round.

Both bare-rooted and potted  apple trees require the same planting conditions. Start by choosing an area that receives full sun and isn’t prone to late frosts. Ideally, your chosen site should have ample shelter from strong winds and enough space to accommodate branch development.

There are many varieties of apple trees to choose from. We recommend that you consider disease-resistant varieties as a first choice. Self-pollinating varieties are good for small gardens or patios as in theory, you only need one tree. However, planting two trees for pollination is better, as relying on one self-pollinating variety could result in smaller apples and harvests.

2.  Growing Apple Trees in Pots or Containers

Apple trees grown in pots or containers are an ideal solution for a small garden or yard. The added benefit is they can be moved to different locations during bad weather conditions.

A number of varieties have been specifically grown for this purpose. When grown in pots or containers, dwarf apple trees can reach a height of 6-10 ft.

 Ideally, your pot should have a diameter of at least 18-22 inches and have good drainage holes at the base.  Also, ensure your pot is stable enough to support the tree’s canopy when in full leaf and fruit.

To replant an apple tree, you’ve purchased in a pot, remove some of the soil around the edges of your tree’s roots. Place some small stones or gravel to the base of the new pot. Then add some general-purpose, granular plant food and perlite to the pot’s base and cover with a 2 to 3 inches layer of multi-purpose compost. Place your tree on top.

Fill in the pot around your tree with more multi-purpose compost until the top of the soil is 5cm below the rim of the pot. All you need to do from here is firm the compost down and water in.

For bare-root trees, prepare the pot in the same way. Soak the rootball in a bucket of water for an hour prior to planting your apple trees. You may also need to spread out the roots if they appear bunched together. 

Listed are just a few variety of apple trees suitable for growing in pots and containers:

• Honeycrisp: Grows to 10 ft tall and produces sweet, crisp apples around mid-September
• Ambrosia: Produces very sweet red apples with an eventual height of 12 feet.
• Pixie Crunch: A truly petite variety, growing up to 8 feet tall. It is a disease-resistant good choice but needs a pollinator companion. gardenerspath.com/plants/fruit-trees/best-dwarf-apple-trees/

Tip: Some dwarf   apple trees can be grown as ‘step-over’ trees and planted as mini hedges or dividers in your vegetable or flower borders.

3. Staking Your Tree

For this, you’ll need a stake and a tree tie.

Staking an Apple Tree in a Pot: Push the stake into the compost approximately 3 inches away from the edge of the apple tree’s trunk. Continue to gently work the stake downwards until it hits the base of your pot. Tie your stake to the tree’s trunk using a tree tie.

Once your stake and tree are planted and positioned securely, you can firm down any loose soil around them.

Staking Apple Trees in the Ground: It is essential to stake when planting. Position the stake at a 45-degree angle to the tree’s main stem. Ensure the rounded end of the stake is facing into strong wind directions. The pointed end of the stake should be beyond the edge of the root ball. Hammer in the stake to a depth of 12 to 18 inches, taking care not to damage the roots. Secure with a tie, fixed approximately one-third the height of the tree. Keep a gap of 1 inch between the stem and tie to allow for growth. This will need monitoring and readjusting from time to time. The tree should be supported but allow for some gentle movement to encourage a robust root system.

4. Watering Your Tree

Give your tree a generous watering to help the tree’s roots establish. Most apple trees need an inch of rainwater every 7-10 days. Young or potted apple trees will need watering more frequently.

The exact amount of water your apple trees need will depend on your climate, weather, and soil. For that reason, we suggest using a trowel to dig 1 inch into the soil to check if the soil is damp. If it’s not, your apple trees need water. Make sure to check the soil frequently for dryness.

5. Adding Mulch

Add a layer of mulch to the top of your compost. By doing so, you’ll improve moisture retention and suppress weed growth.

Wood chips make for an ideal mulch for fruit trees. Alternatively, you can also use pine needles, shredded leaves, and grass clippings as mulch.

6. Caring For Your Trees

Below, we’ve provided some tips to help you keep your apple trees healthy.

• Every two years, check to see if your trees need repotting. You can generally tell a tree needs repotting if roots are poking out through the pot’s drainage holes.
• Water generously during long, hot, and dry spells.
• Apply an organic fertilizer to the base of the apple tree once a year, either during late winter or early spring.
• Prune dead, damaged, or diseased branches to stimulate root growth between November and early March, when the tree is dormant.

Follow the advice in our earlier sections to identify and treat apple tree diseases.

Apple Tree Diseases: Concluding Thoughts

Following the advice in our guide will enable you to successfully grow healthy apple trees all year round.

You will also find it much easier to spot and combat the most common and dangerous apple tree diseases.

Remember always to follow the instructions on the packaging of any fungicides you use.

We wish you luck on your journey of growing strong and healthy apple trees.

For more advice relating to plant growth and care, check out our blog!

Frequently Asked Questions