Flowering Dogwood – Problems and Alternatives

Cornus, commonly known as dogwood, is a genus of around 60 species, primarily of shrubs and small trees, with the flowering dogwood (Cornus florida) being one of the most renowned.

Native to the Eastern United States, these unique small trees thrive in Zones 5-9 and are celebrated for their beautiful blossoms in the spring, full canopy in the summer, red berries, and vibrant foliage in the fall.

However, flowering dogwoods are threatened by various pests and diseases that can adversely affect their health and longevity.

Flowering Dogwood Trees Under Threat

Dogwood Anthracnose

Dogwood anthracnose is a fungal disease caused by the fungus Discula destructive. It is particularly devastating because it can lead to the premature death of the tree. The disease was first identified in the United States in the late 1970s, initially in the northeastern states and then spreading to the Appalachian region. Over the years, it has become a significant concern in both natural forests and ornamental landscapes.

Symptoms:

• Leaf Spots: Initially, small, purple or tan spots appear on leaves, primarily on the lower canopy.
• Leaf Blight: As the disease progresses, the spots grow larger, and the leaves may curl and die prematurely.
• Shoot Dieback: New shoots and twigs can get infected, leading to their death.
• Branch and Trunk Cankers: The fungus can infect the woody parts of the tree, causing sunken, discolored cankers on the branches and trunk.
• Tree Death: In severe cases, the disease can girdle the tree by forming cankers around the trunk, ultimately leading to the tree’s death.

Dogwood Anthracnose

Dogwood Anthracnose Canker

Early detection and proactive management are key to controlling the spread of dogwood anthracnose.

Essential Steps to Prevent/Control Dogwood Anthracnose:

• Recognize the symptoms: Make it a habit to regularly check your trees to catch any early signs of disease.
• Choose Healthy Trees: Only plant disease-free trees obtained from a trusted nursery. If you spot any symptoms on your new trees, discard them immediately. Avoid relocating trees from forests, particularly those in mountainous regions.
• Pick the Right Site: Opt for planting locations with good drainage and fertile soil. Steer clear of areas near bodies of water like streams or lakes where moisture lingers on leaves long after sunrise. In areas prone to disease, make sure to plant your dogwoods in full sun.
• Prepare Planting Holes: Ensure the hole is larger than the tree’s root system and fill it with a nutritious mix of soil and organic matter. Position the root collar level with the ground surface.
• Mulching: Surround both new and established trees with a 2-4 inch (5-10 cm) layer of mulch. Make sure the mulch doesn’t come into contact with the tree stem, and refrain from using dogwood leaves or chips.
• Regular Pruning: Each year, cut away and dispose of any dead wood in the tree and fallen leaves. Avoid making flush cuts; leave the branch collar intact. Trim off any sprouting branches by late summer.
• Watering: During dry spells, water your trees once a week. To avoid leaf moisture, water in the early morning hours.
• Fertilization: Use fertilizer to enrich the soil. A soil test can provide guidance on the appropriate type and amount of nutrients required.
• Prevent Injuries: Be cautious to avoid mechanical damage to the trees, such as those caused by lawnmowers or string trimmers.
• Use Approved Fungicides: When necessary, use registered fungicides for treating dogwood anthracnose. Apply when buds are opening in spring, and repeat at least twice as leaves unfurl. Consult your local Extension Service for specific guidance on fungicide use.

Powdery Mildew

Powdery mildew is a common fungal disease that affects a wide range of plants, including dogwoods, vegetables, and ornamental plants.

While not usually fatal, this fungal disease can threaten the tree’s beauty, undermine its strength, impede growth, and reduce flower production. Repeated infections can seriously damage trees and make them susceptible to other pests and problems.

Symptoms:

• White Powdery Spots: The most prominent symptom is the appearance of white or light gray powdery spots on the leaves. This is usually the first sign that the tree is infected.
• Leaf Distortion: As the disease progresses, affected leaves may start to curl, twist, or otherwise distort in shape. The severity of the distortion can vary based on the extent of the infection.
• Color Changes: Initially vibrant green leaves may turn a duller color. Older leaves develop reddish or purplish irregular blotches on upper surfaces. Scorching of leaf tips and edges may also occur.
• Reduced Growth and Vigor: While less immediate, one longer-term symptom of a powdery mildew infection is a noticeable reduction in the tree’s overall vigor. You might see fewer blooms or less robust growth during the growing season.
• Spread to Twigs and Buds: In more severe cases, the powdery substance can also appear on the twigs and flower buds of the tree, which could compromise flower development and overall health.

Powdery mildew on dogwood leaves and shoot.

Powder Mildew Mycelium on leaf surface

Causes:

• High Humidity: The disease thrives in conditions of high humidity but doesn’t require direct water contact to germinate, unlike many other fungi.
• Poor Air Circulation: Areas with poor air movement can encourage the disease.
• Shade: The disease is more prevalent in shaded areas where the air remains moist for longer periods.

Essential Steps to Prevent/Control Powdery Mildew:

• Plant Resistant Varieties: If you’re planting new dogwoods, choose varieties that are resistant to powdery mildew.
• Proper Spacing: Ensure adequate space between trees to facilitate air circulation, reducing the humidity that encourages mildew growth.
• Sunlight: Plant your dogwoods in areas where they can get enough sunlight, as shade tends to promote powdery mildew.
• Pruning: Regularly prune dead or overly dense branches to improve air circulation, thereby making it harder for the disease to thrive.
• Leaf Cleanup: Keep the area around the tree clean. Remove and dispose of fallen leaves that could harbor the fungus.
• Watering: Avoid excessive irrigation.
• Mulching: Apply organic mulch over the root zone
• Fungicides: Use fungicides that are specifically labeled for treating powdery mildew on dogwoods. They will protect healthy leaves from infection, but they will not cure already infected leaves.

Spot Anthracnose

Spot anthracnose is a fungal disease caused by the fungus Elsinoë corni. It is often confused with dogwood anthracnose, although it is generally less severe. Spot anthracnose primarily affects the aesthetic value of the tree rather than its overall health.

Repeated infections can weaken trees and cause sparse flowers and foliage.

Causes:

• Humid Conditions: The disease is more prevalent in wet, humid weather, typically during late spring and early summer.
• Fungal Spores: The spores can survive on fallen leaves and twigs, leading to reinfection in subsequent seasons.
• Poor Air Circulation: The fungus is more likely to thrive in areas where the air circulation is poor, which keeps moisture on the leaves.

Symptoms:

• Small Spots on Leaves: One of the earliest signs of spot anthracnose is the appearance of small, purple or reddish spots on the leaves. These spots may have a white or tan center.
• Blossom Blight: The disease can also affect the flowers, giving them a scorched or burnt appearance.
• Spotted Bracts: The bracts (the petal-like structures surrounding the actual dogwood flowers) can also develop spots, reducing the tree’s ornamental value.

Spot Anthracnose on Dogwood Bracts

Essential Steps to Prevent/Control Spot Anthracnose:

• Choose Resistant Varieties: When planting new dogwoods, select cultivars that are resistant to spot anthracnose.
• Planting Location: Opt for a shaded location with morning sun that allows moisture on foliage to evaporate early in the day. Provide good air circulation to make the environment less conducive to fungal growth.
• Proper Spacing: Ensure there is adequate spacing between trees to facilitate better air movement, which can help dry leaves more quickly.
• Sanitation: Keep the area around the dogwood free from fallen leaves, twigs, and other plant debris that could harbor fungal spores.
• Pruning: Trim away dense branches and foliage to improve air circulation. Remove any infected parts and dispose of them properly. Prune and destroy dead branches as they occur.
• Watering Technique: When watering, aim for the base of the tree rather than the leaves. This minimizes moisture on the foliage, making it less inviting for fungi.
• Fungicides: Use fungicides specifically designed for treating spot anthracnose on dogwoods. Follow the manufacturer’s instructions carefully.

Planting a Disease-Resistant Dogwood Tree

Planting a disease-resistant dogwood tree is an excellent proactive measure to ensure the long-term health and beauty of your landscape. Disease-resistant varieties are less susceptible to common problems like powdery mildew, spot anthracnose, and dogwood anthracnose.

Alternative Shrubs and Trees  For Flowering Dogwood

If you’re looking for alternative shrubs and trees to the flowering dogwood, there are many options to consider. These alternatives can provide similar aesthetic appeal, and many are resistant to the diseases that commonly plague dogwoods. Here are some alternatives: