Dogwood trees (Cornus species) are highly sensitive to environmental changes, making them vulnerable to fungal diseases, insect attacks, and cultural mistakes. The decline of a dogwood is a common issue for homeowners and often indicates a deeper problem than simple aging. A correct diagnosis is the first step toward recovery, as the tree’s distress is usually the result of multiple, compounding factors working against its health.
Fungal Diseases and Pathogens
Fungal infections are a primary threat to dogwoods. The most destructive is Dogwood Anthracnose, caused by the fungus Discula destructiva, which can eventually kill the tree. Anthracnose begins with tan or brown leaf spots with distinct purple borders, often appearing first on the lower branches in cool, wet spring weather.
The fungus moves from the leaves into the twigs and branches, forming cankers that girdle the limbs and cause dieback. A sign of this disease is blighted, gray, or brown leaves clinging to the twigs throughout the winter instead of dropping normally. Powdery Mildew, while rarely lethal, can also significantly weaken a dogwood, especially on new growth.
This fungus appears as a fine, white, talcum powder-like coating on the surface of the leaves, causing the foliage to become distorted, turn reddish-purple, or drop prematurely. Powdery mildew is most prevalent during periods of warm, dry days followed by cool, damp nights and poor air circulation. Spot Anthracnose, caused by Elsinoe corni, is recognized by tiny, circular spots with purple borders on the flower bracts and leaves, but this infection is generally cosmetic.
Destructive Insect Pests
Insects that bore into the wood or feed on the sap can cause severe damage, especially when a dogwood is already weakened. The Dogwood Borer (Synanthedon scitula) is the most serious pest; its larvae tunnel beneath the bark, disrupting the tree’s vascular system. These borers, the larval stage of a clearwing moth, commonly target wounded areas of the trunk or lower branches (e.g., damage from a lawnmower or string trimmer).
Visible signs of a borer infestation include branch dieback, early leaf drop, and the production of suckers near the damaged area. Small holes in the bark, often accompanied by sawdust-like shavings or frass, indicate active feeding. Another common pest is the Scale insect, which appears as small, immobile, brownish or grayish bumps on the stems and branches.
Scale insects use piercing mouthparts to suck sap from the tree. Heavy infestations can lead to leaf yellowing, stunted growth, and branch dieback.
Environmental and Cultural Stressors
The most frequent underlying cause of dogwood decline is improper cultural care and unfavorable site conditions, which compromise the tree’s ability to defend itself. Dogwoods naturally grow as understory trees, preferring partial shade and protection from intense afternoon sun, which can cause leaf scorch. Planting the tree in an open, full-sun lawn without adequate moisture will cause immediate stress.
Improper planting depth is a common mistake; setting the tree too deep can smother the roots and lead to root girdling. Dogwoods have a shallow root system, making them highly susceptible to drought stress. Conversely, poor drainage and standing water will cause root rot, as the roots cannot tolerate heavy, saturated soils.
Dogwoods prefer slightly acidic soil with a pH between 5.5 and 6.5. Highly alkaline soil can lead to nutrient deficiencies like chlorosis, causing the leaves to turn yellow while the veins remain green.
Immediate Steps for Tree Recovery
Once the source of the stress has been identified, several actions can support the dogwood’s recovery. The first step involves careful pruning to remove all dead and diseased wood, which eliminates fungal spores and potential overwintering sites for pests. Pruned branches should be cut back to healthy wood, and the material must be removed from the site to prevent reinfection.
Adjusting the watering schedule is paramount, especially during dry periods, as dogwoods do not tolerate drought. A slow, deep watering that soaks the root zone is more beneficial than frequent, shallow sprinkling. Establishing a mulch ring is also beneficial for shallow-rooted dogwoods.
A two-to-four-inch layer of organic mulch helps retain soil moisture and keep the roots cool. Keep the mulch pulled back several inches from the trunk to avoid moisture buildup and potential canker formation. If the tree is suffering from sun exposure, a temporary shade structure may be necessary to reduce leaf scorch while the tree regains vigor.
For severe infestations or advanced disease, particularly Dogwood Anthracnose, consult a certified arborist for diagnosis and specialized chemical treatments.