With their big, beautiful pink foliage, crabapple trees make for an excellent addition to any front lawn. If one of the many crabapple tree diseases out there were to infect your beautiful plant, it could sadly destroy it.

Under the right conditions, crabapple trees can thrive outside your home for decades! But, just like any other fruiting or ornamental tree, they are susceptible to diseases that can stunt their growth or, in some cases, take down the whole tree.

This guide will help you identify and prevent common crab apple tree diseases.

So, if you want to learn more about keeping your crabapples healthy, keep reading.

Fireblight

One tricky crabapple tree disease is fireblight.

Fireblight is a contagious bacterial infection (Erwinia amylovora) that primarily infects members of the Rosaceae family.

If you aren’t familiar with the Rosaceae family, it includes more than just roses! Laurels, pears, peaches, almonds, strawberries, brambles, apples, and other related fruits and ornamentals are all members of the Rosaceae taxonomy.

Fireblight is largely influenced by seasonal weather as it festers in bark over winter, then spreads and infects the tree during warm, wet weather.

Fireblight is spread by water, wind, and insects, making it an easily transmittable crabapple tree disease.

It typically affects a crabapple tree’s leaves, fruit, and petals but can eventually spread to the whole tree.

Luckily, all symptoms of this crabapple tree disease are above ground, therefore, easy to recognize and isolate.

Symptoms

Fireblight gets its apt name from the scorched appearance the leaves take once an infection has set in.

Starting from the end of the crabapple tree branch and moving in, the pretty pink foliage shrivels up and turns dark brown or black. The dead leaves don’t fall off, though. They stay attached to the tree as they wilt.

If the infection has spread to the rest of the crabapple tree, cankers will be visible on the bark.

Sometimes, a white or orange liquid may be visible on the plant, especially in wet and humid conditions.

Treatment and Prevention

Unfortunately, no proven chemical treatments like fungicides or antibacterials help get rid of a fireblight infection.

However, liquid copper is thought to help reduce the spread of fireblight in some cases.

If your tree has already fallen victim to fireblight, prune back all the affected areas until no signs of infection are present. Then, burn the refuse to avoid the bacteria spreading elsewhere.

It’s hard to prevent bacterial infections, but one way to do what you can is to ensure your gardening tools are frequently cleaned.

Cedar-Apple Rust

Rusts are a category of crabapple tree disease that require living hosts called biotrophs, as opposed to necrotrophs, which live off dead organic matter.

Thankfully, this means that rust diseases won’t kill your plant. However, that doesn’t mean it can’t severely impact your garden or yard.

One of the biggest effects of crabapple tree diseases like rust is that it ruins the beautiful fruit or blooms of your ornamental trees.

Cedar-apple rust is a unique kind of rust – it requires two different living hosts to thrive.

The spores of the rust fungi develop in the fall of a member of the Cupressaceae family, Eastern red cedars.

In the spring, the spores are released and carried by the wind to a member of the Rosaceae family, such as a crabapple tree.

Symptoms

Primarily, cedar-apple rust damages the tree leaves by growing spots and spores on the leaf’s surface. Thus, this crabapple tree disease impacts the tree’s ability to absorb sunlight.

Sunlight is a crucial element for photosynthesis. Without sunlight, the tree cannot develop and grow properly.

Disrupting photosynthesis will weaken the crabapple tree’s ability to grow fruit and produce new growth.

While this particular crabapple disease won’t directly kill the plant, it will greatly weaken the tree over time until it becomes too damaged to survive.

Treatment and Prevention

Your first line of defense against cedar-apple rust is to avoid planting cedar trees and crabapple trees near one another.

Cedar-apple rust can’t transfer from crabapple to crabapple or from cedar to cedar. It needs both types of trees to propagate.

Keeping these two trees separate from one another is the best preventive measure in keeping this crabapple tree disease at bay.

Once you spot the symptoms of cedar-apple rust, it’s usually too late to control this crabapple tree disease with chemical treatments. Rather, your best bet is to prune away the infection and clear the surrounding area of any dead plant matter.

However, if you know your trees or area is susceptible, you can treat the crabapple disease early on with sterol inhibitor fungicide.

Botryosphaeria Canker

Botryosphaeria dothidea Black rot Canker

Botryosphaeria canker infections are the B company of crabapple tree diseases. It’s a fungus that will only grow on trees that are already weakened or suffering from another pathogen.

Botryosphaeria canker is a pretty common fungal disease that generally impacts trees and shrubs with lots of bark area.

Botryosphaeria canker infections can cut through the bark of a tree into the tissue, disrupting the flow of water and other nutrients throughout the plant.

Symptoms

The infection site of this crabapple tree disease appears like a spore, blister, or vacuole. Underneath, the tree bark will appear almost rotted, darkened orangey-black as opposed to a healthy light brownish-green.

As the Botryosphaeria canker cuts off the tree’s nutrient supply through the bark, the crabapple tree foliage begins to wilt, shrivel, and die.

Individual canker spots can weaken branches one at a time, making it slightly easier to identify and treat this crabapple tree disease.

Treatment and Prevention

As is the case for most crabapple tree diseases, the best way to ensure your tree is safe from fungal damage is through preventative measures.

Drought can make a crabapple tree more susceptible to Botryosphaeria canker since it weakens the plant. However, overwatering, especially on the tree’s trunk, can cause the fungi to grow and spread.

To prevent crabapple tree diseases like Botryosphaeria canker, ensure the growing environment is appropriate for your tree. Too little sun, too little water, or too much water in the wrong places causes Botryosphaeria canker to thrive.

Once symptoms have been spotted, prune away as much of the impacted area as possible. However, if the cankers have broken through the layers of bark into the tree’s tissue, this may not help.

Fungicides for ornamental plants or fruit trees won’t be able to save the branches or reverse the damage, but they can help prevent the infection from spreading further.

Powdery Mildew

Like cedar-apple rust, powdery mildew is a biotrophic pathogen, and it impacts all kinds of crabapples worldwide.

This particular fungus differs from most other fungi that cause crabapple tree disease in that it doesn’t grow or travel by water, earning it the nickname “dry weather disease.”

Instead, the spores travel by wind, making it a highly transmittable crabapple tree disease.

Symptoms

This crabapple tree disease takes the form of a dusty white layer all over buds, blossoms, shoots, fruit, and leaves, hence the powdery mildew name.

The white fuzz-like surface is produced by fungal threads called mycelia, and it’s a symptom that’s difficult to miss.

If this crabapple disease has impacted your tree, the buds will be slowly open and covered in white fungal fluff.

Though powdery mildew won’t necessarily kill your crabapple, it will prevent it from fruiting. Part of the allure of the crabapple tree is its lovely foliage and sweet smell, which powdery mildew wipes out.

Treatment and Prevention

Unlike some of the other crabapple tree diseases, powdery mildew can be effectively treated by fungicide. But it’s so contagious that you may find yourself playing a game of catch-up with the mildew.

To further bolster your crabapple tree’s powdery mildew defenses, make sure your tree gets plenty of sun.

Since this crabapple tree disease winters inside of the buds, prune your crabapple tree’s overwintering growth before the blooming season.

Frogeye Leafspot

Also known as “black rot,” frogeye leafspot is a crabapple tree disease that lives up to its name.

Frogeye leafspot is caused by the obtusa fungi, which winters in dead plant matter or cankers. As the blooming season comes around, the infection points will release spores into the air and infect surrounding crabapples.

This particular crabapple disease is enduring and can impact your crabapple’s production the following year.

Symptoms

Frogeye leafspot appears differently on the leaf than on the fruit. The infected fruit will start to form brown, black, and purple bands of rot from the calyx end of the apple up.

As it spreads, frogeye leafspot leaves withered, wrinkled fruit in its wake. Finally, the fruiting fungal spores will appear on the apple’s skin.

On the leaves of your crabapple tree, frogeye leafspot looks like small, purple dots. Over time, the dots will widen, with a wilted brown area in the center and a purple ring around the edge.

Where the fruit leafspot moves from top to bottom in one wave, the leaves are polka dotted with the disease that grows from the center outwards.

The developing frogeye leafspot infection sites on the leaf begin to look like a frog’s eye, hence the name.

The impacted leaves and fruit then begin to drop off the tree, weakening the tree all over and reducing productivity and harvest for the next year.

Treatment and Prevention

Not to fret! As intimidating as frogeye leafspot might look and seem, it is treatable and preventable.

The best thing you can do for your crabapple trees is to prune them well during dry periods in the winter. Then, get rid of any signs of frogeye leafspot and dispose of the plant waste properly.

Use a fungicide that fights frogeye leafspot from early spring to harvest to slow down or stop any infection left on the tree.

To the Rescue of Your Crabapple Trees

This guide to crabapple tree diseases is here to help you identify, treat, and prevent future issues and keep your trees healthy for years to come! You’re now well-equipped to rejuvenate your beautiful crabapples.For even more information, visit our post about the care and keeping of crabapple trees.