How to Identify and Treat Common Dogwood Diseases

For The Man of Steel and vampires, preventing harm is as simple as avoiding exposure.

But save for the occasional transplanting, species of dogwood are stuck in place, and escape from disease is not an option.

While these plants aren’t completely helpless – they can launch immune responses to pathogens – it’s up to us gardeners to keep our dogwoods as healthy as possible.

But how? How can a green thumb treat a diseased dogwood? And how can one keep these diseases from striking in the first place?

All these questions and more are answered in this guide. Upon reading it, you’ll be more than ready to maintain the health and vibrant appearance of your dogwoods for the long haul.

Let’s get to it:

Each of the following diseases come with their own causal pathogens, symptoms, and management techniques.

But there are definitely some general practices that’ll help keep your dogwoods healthy, no matter the particular disease that they face.

Choose only healthy seeds, cuttings, and transplants for use in your garden. Be sure to use disease-free soils, and always sterilize your tools before making any pruning cuts.

But the above tips won’t make much of a difference if your plants aren’t well cared for, or if they aren’t placed in the correct spot to begin with.

Ensure that your dogwoods are given the proper exposure, soil, irrigation, and fertilization, situated in hardiness zones that they’re suited for.

All of this, of course, depends on the species that you’re cultivating.

1. Armillaria Root Rot

Dogwood diseases come in many different forms, and Armillaria root rot, caused by fungi in the Armillaria genus, is a particularly nasty one.

After the onset of infection, disease symptoms manifest themselves all over the plant. Afflicted leaves turn yellow, are smaller than normal, and prematurely drop.

Branches die back, light fungal threads lie beneath the crown’s bark, dark fungal strands lie on or in the soil, and honey-hued mushrooms grow near the tree’s base in autumn.

There’s no known cure, and after the tree inevitably declines and ultimately dies, you’ll eventually have to remove and destroy the infected specimen.

And since the fungal pathogens can persist in the soil for years, you won’t be able to use the same growing site for a good long while, at least not until you sanitize or solarize it.

Prevention is best achieved by not doing certain things. Don’t place dogwoods in poorly-draining soil, irrigate excessively, or damage the trees.

And since this pathogen is often found in newly-cleared soils, avoiding planting in said soils for at least a year is often recommended.

2. Botrytis Blight

Caused by various fungal species within the Botrytis genus, Botrytis blight afflicts dogwoods and an assortment of species from other genera, such as begonias, chrysanthemums, and tulips.

Overwintering in dead plant debris, the causal fungi form spores in springtime, which spread via air currents and/or splashed water onto flower bracts and leaves.

Any infected structures are left with brown, wrinkled, and irregularly-shaped patches of tissue. In wet and humid bouts of cool weather, gray mold can form over these patches, hence the disease’s nickname “gray mold.”

As you can imagine, these problems lead to abnormal growth and development of the afflicted structures, and old flowers are prone to rotting rapidly.

Since warm, dry weather halts the disease before it can turn serious, any infection will most likely be a temporary cosmetic issue.

For prevention, rake up and dispose of nearby plant detritus, which will eliminate the fungi’s overwintering sites. Prune away infected tissues to slow further spread.

To allow for ample moisture-drying airflow, properly space out plants and prune within the canopy.

Avoid splashing the flowers and foliage with water to prevent excess moisture, and don’t over-fertilize with nitrogen, which can stimulate the growth of tender, vulnerable tissues.

For additional prevention, apply fungicides every 10 days during susceptible periods in spring. Copper, sulfur, and Captan are all fine choices.

3. Crown Canker

The trademark symptom of this disease is in the name: a discolored, oozing canker at the tree’s crown near the soil line.

In time, the canker becomes more and more sunken and exposed as the bark falls away, and can girdle the trunk or root crown. Eventually, the tree can weaken, become susceptible to other pathogens, and even perish.

But before all that occurs, you’ll probably notice diminished vigor and reduced foliage – both in size and in number.

Additional leaf symptoms include a lighter-than-normal hue, premature drop and color change, and overall distortion.

An infected tree may even produce more flowers than usual, which is an unusual way to respond to infection. Twigs and branches can also die back.

The causal pathogen, Phytophthora cactorum, overwinters in plant debris, spreads via wind or water, and typically enters the tree via trunk wounds, but it can also enter the root system.

For prevention, avoid wounding the trunk during transplanting and lawn care, as the smallest of vulnerabilities can lead to total demise, Death Star-style.

Similarly to Botrytis blight, you shouldn’t splash the leaves and flowers with water or leave plant debris nearby.

If your hands are steady and you have a sharp blade, feel free to remove small cankers from the trunk during periods of dry weather in summer.

To do so, remove all the diseased bark and sapwood you can, as well as two additional inches of healthy tissue as insurance. After the surgery, leave the area exposed to dry air.

If an infection spreads throughout the majority of the tree, you should excavate and pitch it.

4. Discula Anthracnose

Portobello mushrooms, hallucinogenic ‘shrooms, the red and green mushrooms from “Super Mario Bros.,” – there are plenty of famous fungi out there.

To take a closer look at a rather infamous one, let’s turn our attention to the Discula destructiva fungus.

Discula anthracnose, or dogwood anthracnose, both names for the sickness caused by this fungus, is arguably the most dangerous disease for a dogwood.

After its arrival in the US from parts unknown, the disease has significantly harmed and reduced native dogwood populations across the country, so it definitely warrants being taken seriously.

After trees leaf out in late spring, spots first form on infected leaves and flower bracts on lower branches before moving up the canopy.

These spots are tan to brown, with brown to reddish-purple margins, and are typically followed by sunken brown cankers as the disease spreads into the tree’s woody tissues.

Said cankers can girdle twigs, branches, and the trunk, all of which ultimately kills the tree in most cases.

The disease spreads via spores produced within the leaf spots that are dispersed by insects, birds, or splashes of water. Moving infected specimens into new landscapes can also lead to spread.

Preventing Discula anthracnose requires a multi-pronged approach.

Avoid shade and excess moisture by planting trees in sunny locations avoiding splashing the foliage and flowers.

Rake up fallen plant debris, and prune away water sprouts, which are prone to infection.

Any infected tissues should be pruned away as you happen to notice them. Burn them to prevent further spread, or dispose of them in the trash.

Regardless of the causal pathogen, the disease symptoms are pretty similar: the leaf spots are a quarter to an eighth of an inch in diameter, with sharp and irregularly-shaped borders.

Cercospora spots are tan to brown, while Septoria spots are a dark brownish-purple that later lightens or turns gray.

Severely infected leaves can drop prematurely, and multiple seasons of leaf spot can weaken trees, leaving them susceptible to other issues.

As the fungi overwinter in fallen leaves, these should be raked up and disposed of.

Applying fungicides preventatively at bud break can be helpful, especially if your tree is particularly at risk or already infected with fungal leaf spot.

6. Powdery Mildew

Caused by Erysiphe pulchra or Phyllactinia guttata, powdery mildew is a fungal disease that leaves foliage and tender new growth coated with a fine white powder.

It typically occurs during summer and fall in spots where air circulation is poor.

Secondary symptoms include chlorosis, reddish discoloration, marginal leaf scorch, premature defoliation, and patches of dead tissue.

If powdery mildew strikes in late summer, the impact is usually minimal.

The potential for early-season infections in specimens that you’re fond of can justify the use of fungicides, but your first step should be raking up nearby leaf and twig debris.

Additionally, prune away dead or infected tissues as you notice them.

For powdery mildew-resistant plantings, try specimens from the aforementioned Stellar series, along with kousa dogwood cultivars such as ‘Milky Way,’ ‘Milky Way Select,’ and ‘National.’

Durable flowering dogwood cultivars include ‘Appalachian Joy,’ ‘Appalachian Blush,’ ‘Appalachian Snow,’ and ‘Appalachian Mist.’

7. Spot Anthracnose

As if one type of anthracnose wasn’t bad enough…

Elsinoe corni is the fungus to blame for this one. Surviving for years on infected tissues, the pathogen primarily strikes in wet spring conditions, leaving flower bracts, leaves, and fruits with tan spots ringed with reddish-purple.

In severe infections, afflicted structures can become wrinkled and warped, and the small spots an eighth of an inch in diameter merge into larger spots.

To manage this disease, prune infected tissues and rake up fallen plant debris. You can’t control the weather to make conditions less moist, but you can improve inter-canopy airflow via pruning.