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How to Save a Dying Cherry Tree from Common Diseases

How to Save a Dying Cherry Tree from Common Diseases

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Cherry trees are among the first garden plants to signal the end of the winter weather. In early spring, these are the first trees to put out a burst of pink or white flowers.

It’s the welcome sign to the spring garden marking the start of colorful blooms and lush juicy fruits. Keep in mind though, the fruits only grow on mature cherry trees older than 4 years, or 3 years for dwarf varieties. Younger trees will still produce flowers.

If your cherry tree isn’t bursting with colorful blooms, showing signs of defoliation or starting to shrivel like its roots are rotted to the core, you’ll need a survival plan to attack the problem, rescue your cherry tree from the brink of death, and quite possibly, dig it up to replant it in a new home in a location.

Diseases that Can Appear Like They’re Killing a Cherry Tree

1 – Black Knot Fungus

Black knot is visible on twigs and branches. It looks like it sounds. Black knotted wood. It’s a wood infection that can only be remedied by cutting away the damaged branches and twigs.

This starts out looking like a tiny wart about an inch in size but if left to grow, it can cover as much as a foot of a branch or trunk. The worst part is that when it rains, the spores from the black knot carry the fungus to other parts of the tree (and other nearby plants) and it can transfer to them too.

The only way to prevent it from spreading is to remove the infected branch. Make the pruning cuts in winter when the tree is dormant. The infected parts will be easier to spot. Make the cut at least 4 inches below the gall because under the bark, it’s probably bigger than the visible part you’re seeing.

If the black knot fungus returns on new growth, it’ll probably need a fungicide treatment. Expect a two-year project at least. It takes a new cherry tree 4 years to produce fruit.

Do you want to spend two years on a spray and prune project with the chance of success? It might be worth considering starting over.

2 – Brown Rot

This will kill the twigs. Naturally, when those die, foliage won’t grow and without leaves, you’ll never get fruit. It may as well be dead.

The earliest sign of brown rot is cankers developing on the older wood. Those cankers are what cause the fungus to spread to neighboring branches. Insects spread it too.

You can eliminate the cause by cutting the branches off. Make the cut at least 4 to 6 inches below the lowest canker (that’s the dead wood on either the stem or trunk).

Brown rot is more likely to occur on twigs exposed to higher temperatures that stay wet for longer. Think heavy downpours with the rain resting on the twigs and the tree hasn’t been pruned to allow for sufficient air flow to help cool it down and dry faster.

Pruning is about more than keeping your trees looking pretty. It can help them survive. If you feel the tree canopy is too dense for sufficient air flow, make some thinning cuts while you’re removing the dead and damaged tissue.

3 – Cytospora Canker Disease

This is what happens to cherry trees that don’t have diseased bark removed. Those cankers caused by brown rot or other less lethal diseases weaken the plant tissue.

Weak tissue is susceptible to multiple fungi infections. Cytospora chrysosperma is among the worst. This is an airborne fungus that’ll infect any wounded bark on any nearby tree and branches. The canker girdles branches eventually killing it.

The good news is that it’ll take years to kill the tree. The bad news is it is a slow killer. Cankers will continually girdle, slowly strangling the tree, and it’ll spread to other parts of the tree too.

A sign of this fungus infestation is orange sap. That comes from pycnidia, which is a small fruiting body that only forms on dead tissue. Once you start seeing orange sap on the bark on your tree, that part of the tree is a goner.

To save the rest, you need to cut the branch off at least 6 inches beneath a canker.

Once you’ve removed all the cankers, take as much care as you can to prevent stressing the tree. Cytospora fungus only appears on stressed fruiting trees.

Typical stress factors on cherry trees are wounds (often accidental) like striking the lower branches with the gut of your lawn strimmer, or too many wounds from pruning.

4 – Cherry Leaf Spot

Unless you’re growing in an orchard, cherry leaf spot shouldn’t be an issue.

When it starts, it causes small spots (about a quarter inch in diameter) to form on the leaves.

The underside of the leaf usually shows a whitish pink spot. Eventually, the spots turn purple, holes form, the leaves yellow, then fall off. The fungus doesn’t die though. Splashes of water spread the fungal spores to healthy leaves and the problem spreads.

The solution is simply to clean your yard of fallen leaves. Keep your tree pruned for good air circulation and make sure it’s exposed to direct sunlight to prevent the problem arising.

5 – Powdery Mildew

This is not unique to cherry trees. It’ll infect nearly every type of outdoor plant imaginable. It’s not fatal, provided you treat it. Left untreated, it will suffocate the plant.

Find out more about treating powdery mildew here.

6 – Prunus Necrotic Ringspot Virus (PNRSV)

This goes by multiple names, the most common being shot-hole disease because it causes holes to develop on the leaves of fruiting trees. Other names include necrotic ringspot, cherry rugose mosaic, and recurrent ringspot.

They all point to the same issue. Holes in the leaves that are usually mistaken for insects nibbling on the leaves. That’s often the first suspect when you find holes in your plant’s foliage. For the leaves on fruiting trees, bacteria and fungi spores can cause holes to appear on leaves.

With this virus, the holes are around 1/8th of an inch in diameter, and they appear sporadically with multiple holes per leaf.

The result is not pretty but it’s not lethal either. It might look like it is, and while the tree won’t die, it won’t produce as much fruit either.

Cherry trees infected with PNRSV lose up to 15% of their fruit yield.

The most susceptible leaves are the young and healthy ones just coming through in early spring. Monitor those and remove any that appear with holes.

Often, vigilant removal of damaged leaves is enough to keep this under control. Similar to cherry leaf spot, prevention is done by discarding the leaves that fall from the tree, and/or the ones you remove before they get a chance to fall.

7 – Silver Leaf Disease

Sounds innocent, doesn’t it? What’s the big deal of silver leaves? Cut them off, and they’ll grow back green, right?

Wrong.

Silver leaves are caused by an infection in the bark of the trees. What you’re seeing is a symptom of the layers of leaves separating because of a bark disease.

Now, if all the leaves on a cherry tree have a silvery sheen to them, it’s probably light reflections playing tricks. But, when silver leaves are concentrated around one or a few branches only, that’s probably silver leaf disease in the wood of those branches.

The only way to get rid of it is to remove infected wood.

You can tell a branch is infected by cutting it. Make a cut on a branch that’s at least an inch in diameter. Infected wood will have dark brown spots.

You may need to add some water to notice the color differences. If you have dark and light brown on the inside of a branch, chances are, it’s infected with chondrostereum purpureum, the fungus in the wood that causes silver leaf.

Depending on the severity of the infection, a hard pruning of every infected branch might do more harm than good as it’s rarely wise to cut away more than a third of a tree in one go.

If the problem is widespread, consider marking and monitoring the tree so you know to continue making cuts to infected branches, then while waiting for new branches to emerge, check to make sure they’re growing in healthy and continue to regularly prune infected parts. It isn’t a guarantee that the infection won’t spread to new branches, but it is a possibility.

Always remember when pruning diseased branches, or leaves from trees, to disinfect your tools thoroughly before using them on other plants. Fungus diseases will spread.

The Last-Ditch Effort to Save a Dying Cherry Tree

Provided your tree has healthy bark, it’s probably showing signs of decay due to lacking the growing conditions it needs. That’s plenty of sun (8 hours full sun daily), a well-draining soil, and regular pruning to promote good air circulation.

If the problem’s related to the growing conditions, perhaps inadequate drainage or inefficient acidity levels, all is not lost. You can dig it up, amend the soil, aerate some roots and replant it in the right type of soil at the right depth.

Here’s how you do it…

Test the soil to make sure it is right first. Dig a hole that’s 12” x 12”, fill it with water, leave it overnight to dry, then fill it again and this time, time it. You want to drain within a few hours. If it takes longer, it’s lacking the drainage cherry trees need.

The ideal soil for cherry trees is loam. An easy mistake to make is to pop a plant into the ground before checking the type of soil you’re working with.

Loam soil has good drainage. Clay heavy soils are deadly (for cherry trees anyway).

Depending on the extent of clay in your ground soil, it might be worthless. For the level of drainage and depth (4 feet) that cherry trees need, it’s best to have no more than 10% of the soil mix be clay.

You can generally tell by the soil’s texture. If it has chunks of rocks and stones, it’s going to be clay heavy. These can take hours to drain water away. Too long for cherry trees.

The roots don’t bode well in standing water, or in moist soil that takes hours to drain.

Soil amendments that help improve drainage include adding organic materials that tend to compost fairly quick. Thin leaves, green plants, and well-rotted manure.

If you’re new to composting, greens compost faster than browns, but a quality compost is made with a mix of greens and browns.

When adding directly to ground soil, use more greens than brown. Brown materials will be bark, sawdust and healthy twigs pruned from shrubs (not the diseased riddled branches discussed above – burn those), preferably cut to short pieces to similar sizes as bark chippings.

The quicker solution to remedy clay heavy soil is to dig a hole that’s 4 feet deep at least and double the diameter of the rootball of your tree, fill some in with new loam soil (or sandy loam soil) plant your cherry tree, then backfill the hole and water the soil thoroughly.

Going forward, it needs 8-hours of sun daily, the soil drying between watering and watered at soil level rather than overhead irrigation that causes the leaves to be wet for too long.

Regular pruning to maintain good air flow and decent humidity can prevent many of the fungus diseases that are more likely to kill cherry trees off early.