Dogwoods (Cornus spp.) are popular ornamental trees and shrubs, appreciated for their branching structure, colorful stems, and seasonal interest.
Some dogwood species are known for their early spring blooms, while others stand out in the winter landscape with bright red or yellow stems.
They’re a popular choice for woodland gardens, borders, and native plantings thanks to their adaptability and visual appeal throughout the year.
But dogwoods can sometimes drop their leaves outside of the usual autumn shedding, and when that happens, it’s usually a sign that something is off.
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Our dogwood growing guide has an overview of how to cultivate species in the Cornus genus in your landscape.
In this guide, we’ll go over the most likely causes of premature leaf drop and what you can do to address the problem.
There are, unfortunately, many things that can cause dogwood leaves to drop.
The trick is to figure out which one (or more) is the culprit. Here is the list of potential causes we’ll be covering:
13 Causes of Leaf Drop in Dogwoods
The first one we’ll talk about is a doozy. It’s definitely not a disease you want to encounter, and acting fast is crucial:
1. Anthracnose
Dogwood anthracnose, caused by Discula destructiva, is a devastating fungal disease in parts of North America.
It came to the US in the 1970s and spread rapidly among the native dogwoods, which had no natural immunity to the disease.
It causes cankers in the wood and spots on the leaves and bracts. As the disease progresses, the leaves can drop from the dogwood.
Examine the leaves for angular tan spots with purple margins. Then, look for sunken, discolored areas and dead twigs.
If you see these symptoms, you have my deepest sympathy, and you can be reasonably sure the plant has dogwood anthracnose.
There are ways to deal with the disease, including pruning off severely affected areas and applying fungicides or biofungicides like those containing the beneficial bacteria, Bacillus subtilis.
2. Borers
Dogwood borers (Synanthedon scitula) are the larvae of clearwing moths and they’re incredibly destructive.
They’re not the only type of borer that attacks dogwoods, but they are the most prolific and damaging.
After the adult moths lay their eggs, the dogwood borer larvae hatch in the bark and start chewing their way through the cambium.
This feeding causes damage to the bark and it can result in the leaves dropping, as well as crown dieback.
Control can be difficult, but you can start by pruning out heavily infested areas and then treat the dogwood and the soil around it with beneficial nematodes.
These nematodes will kill the larvae, but the trick is making sure they come in contact with the pests.
That means spraying when the dogwood borers come near the surface to pupate. Contact your local extension for advice on timing.
You can also spray into any holes or damage that you see on the tree or shrub.
The beneficial nematode species Steinernema carpocapsae is effective at controlling dogwood borer larvae.
NemAttack Beneficial Nematodes
You can find this species available in a variety of packet sizes at Arbico Organics.
Apply according to the manufacturer’s instructions.
3. Botryosphaeria Canker
Botryosphaeria canker is a disease caused by the fungus Botryosphaeria dothidea.
In addition to causing cankerous growths, it also results in the leaves wilting and turning brown – before dropping from the dogwood tree.
Botryosphaeria canker is most noticeable on red bark dogwood types like Cornus alba, C. sanguinea, and C. sericea because you can easily see the dark areas that make up the sunken cankers.
But the pathogen attacks all species in the Cornus genus.
The disease is most active when temperatures are in the 70s and 80s and the humidity is high or there is plenty of rainfall.
The easiest way to deal with it is to prune out symptomatic branches.
You can generally avoid the disease taking hold by being careful not to damage the plants, keeping them adequately watered, and preventing pest infestations, which can expose the dogwood to fungal infections.
4. Inappropriate Moisture
Too much or too little water causes stress in dogwoods, and a stressed tree often drops its leaves.
Most dogwood species like a good amount of moisture, and while some can tolerate a bit of drought, prolonged dryness can be harmful.
That’s not to say that you can overwater your dogwood and everything will be fine. Too much water suffocates the roots and that makes it difficult for them to absorb nutrients.
You don’t need any fancy water measuring systems or try to calculate how many inches of rain you’ve received that week.
The easiest way to test soil moisture is to stick your finger in the soil.
If you’re like me and you live in an area where the hard-packed clay becomes cement-like in the summer, you will need to dig a small hole with a trowel and then stick your finger in that.
If it feels dry, it’s time to water. In general, try to water in the morning and do it infrequently if you can. A good, deep soak is better than lots of shallow, frequent waterings.
5. Leaf Scorch
Too much sunlight and high temperatures can cause leaf scorch, which results in leaf drop.
This goes hand-in-hand with underwatering. When temperatures are high and direct sunlight is hitting the foliage, it can cause the margins or tips of the leaves to turn brown.
If the problem continues, the entire leaf turns brown and drops from the tree.
In the case of small dogwood trees or shrub types, you can cover them with some shade cloth or an umbrella during a heatwave.
I’ve been known to scoot my patio umbrella near susceptible plants during unusually high temperatures.
If you know that you regularly experience heatwaves during the summer, it might be best to plant your dogwood in partial sun to provide protection during the heat of the afternoon.
Whether you cover the dogwood or not, make sure it receives enough water during very hot weather.
6. Leaf Spot
In addition to anthracnose, there are several diseases known as “leaf spot” that can cause spots or areas of discoloration to develop on the leaves, and all of these can cause the foliage to drop.
Fungi in both the Cercospora and Septoria genera cause spotting.
In the case of Cercospora leaf spot, the areas are tan or light brown with reddish-purple borders. There might be a chlorotic, pale yellow border around them, as well.
Spots caused by Septoria are gray with a brown border.
When the foliage is heavily symptomatic, the leaves will drop from the plant. You’ll need to address the cause to stop the falling foliage.
Both thrive in humid, rainy conditions when it’s warm.
Spray the tree with fungicide as soon as you notice symptoms. Copper, sulfur, or thymol are all tried-and-tested options.
I always keep copper fungicide in my gardening toolkit since it’s useful for treating so many different plant diseases.
You can find copper fungicide available at Arbico Organics. It lasts longer in dust form than liquid, and you simply mix it with water whenever you need it.
Follow the manufacturer’s directions for application and continue to spray throughout the season.
7. Midges
Clubgall midges (Resseliella clavula) cause ugly galls on your dogwood.
The adults are tiny flies with orange abdomens and black and yellow wings, but these aren’t dangerous. It’s the larvae that you need to watch out for.
After the females lay eggs in the springtime in the developing twig buds, the maggots that hatch feed on the plant material and their saliva causes a protective gall to form, protecting the larvae so they can feed and grow.
The galls can cause the twigs to die and the leaves on it to fall to the ground. The rest of the leaves on the tree will typically remain healthy.
They feed all summer and then emerge in the fall, chewing their way out of the galls. The larvae then drop to the ground and overwinter in plant debris before pupating in spring.
When the larvae are present and hiding out in the galls, you can’t do much about them unless you want to prune off each and every one. There can be dozens on a single tree, so this can be a challenge.
The other option is to spray in the spring to kill the adults and again in the fall to kill the young as they emerge.
Bonide Captain Jack Deadbug Brew
A product like Bonide’s Captain Jack Deadbug Brew which is available at Arbico Organics is effective.
Spray on a windless day in the spring and again in the fall when you see holes appearing in the galls. Make sure to spray the ground around the tree too!
8. Nitrogen or Iron Deficiency
Nutritional deficiencies can also cause leaf drop in dogwoods.
When it’s a lack of nitrogen that’s the problem, the older leaves will first turn pale green or pale yellow before they drop.
Iron deficiency shows up in newer leaves, generally turning them yellow, while the veins remain green. They will eventually drop from the tree as well.
If you suspect a nutrient deficiency is the cause of the leaf drop, test your soil. You can do this by contacting your local extension office or by purchasing an at-home test kit.
When you get the results, amend accordingly.
9. Powdery Mildew
A mild case of powdery mildew won’t cause leaf drop, but as the symptoms progress, infected leaves will drop from the tree.
Typically, the foliage will turn yellow or brown before this happens, with a powdery white or grayish coating.
Powdery mildew won’t usually kill a tree, but you’ll want to avoid excessive foliage loss.
Our guide to controlling powdery mildew has all the info you need to address this common fungal condition.
10. Root Rot
Many dogwoods do well in wet areas, but that doesn’t mean all will, nor does it mean that problems can’t develop from constantly wet soil.
In soggy conditions, certain fungi and oomycetes can take hold and cause the roots of the plants to rot. Drought stress can also make a plant more susceptible to pathogens that cause root rot.
Scientists aren’t exactly sure which pathogens cause the problem in every case, but water molds in the Phytophthora genus are a top culprit.
Regardless of the label, the pathogen will cause the roots to literally rot away, turning black or dark brown and slimy. If you were to dig down and take a big whiff, it would smell really gross.
Most of us don’t make a habit of checking our plant’s roots, though. We have to watch for the symptoms aboveground. Usually, by the time the plant is showing symptoms, the root rot is extensive.
One of the first signs is leaf drop, usually coupled with the foliage turning yellow or brown. You might also see twig death or the entire tree might eventually die.
There are ways to avoid the problem in the first place. The most important one is to plant your tree at the appropriate depth.
Dogwoods have shallow roots and if you plant too deep are prone to rot. You should also be aware of how moist the soil is and avoid overwatering.
A thick layer of organic mulch can help retain moisture.
While you can use a fungicide to slow the progression of this disease, once it takes hold, there’s little you can do. Eventually, the tree will die and you’ll need to remove it.
11. Scale
Scale insects are small, sapsucking pests that latch onto the plant and feed. One or two of them won’t harm a big tree, but they don’t travel alone.
If you see one or two, you can be pretty sure there are many, many more that you can’t see, since they often hide in protected spots like the undersides of leaves or where the leaves meet the branch.
More than once, I didn’t even realize there was a scale problem until I discovered the sticky substance called honeydew that they excrete.
Feeding draws nutrients out of the plant, which can cause the leaves to turn yellow and drop.
You might also notice a black coating on the foliage – this is known as sooty mold, a fungal infection as a result of the honeydew.
Sooty mold can also cause leaf drop because it deprives the plant of the ability to photosynthesize.
Learn more about how to manage scale here.
12. Spot Anthracnose
Spot anthracnose shares a common name with the dreaded dogwood anthracnose, but they are caused by different pathogens and have different symptoms.
Spot anthracnose is caused by the fungus Elsinoe corni and results in spots with tan centers and reddish borders on the bracts and leaves.
On young leaves, these spots can have chlorotic borders, but older leaves typically won’t have this.
In a severely impacted plant, the leaves and bracts might fall off.
This disease is very unlikely to kill the dogwood unless it’s very young or already stressed and sickly.
If you seem to encounter anthracnose year after year, you’ll need to treat it with a product that contains beneficial bacteria, potassium bicarbonate, or citric acid.
My personal favorite is a product called Mycostop. It harnesses the power of the beneficial bacteria Streptomyces Strain K61.
You can find Mycostop available at Arbico Organics. Apply according to the manufacturer’s instructions.
13. Transplant Stress
When we purchase new trees or shrubs for our yard, if you’re anything like me, you undoubtedly choose the largest specimen you can afford.
The problem with this is that the tree can often end up suffering from transplant shock after planting, causing it to drop its leaves.
In other words, a large dogwood is very likely to suffer from transplant stress which can cause it to drop its foliage.
But even small plants are likely to suffer, as well. That doesn’t mean they will necessarily die, but you can expect some leaf drop after transplanting.
You can try to mitigate this by transplanting when the tree is dormant and doing so on a cool, misty day. If you transplant when the weather is dry, be sure to keep the soil moist.
Reserve the Falling Leaves for Autumn
Leaves gently dropping from trees in autumn is such a beautiful sight.
But falling leaves as a result of disease or stress is ugly. It’s also a sign that something is wrong with your dogwood.
Were you able to determine the cause of the problem? Or do you need a bit more guidance? Let us know in the comments section below! We’re happy to help if we can.
And for more information about growing dogwoods, add these guides to your reading list next:
