The sudden appearance of brown and curling leaves on a dogwood tree signals an underlying problem. While these symptoms are visually alarming, they are a general distress signal, not a diagnosis in themselves. A dogwood’s response to environmental, pathological, or entomological threats frequently manifests as wilting, browning, and leaf deformation. Identifying the precise cause requires careful observation of the specific pattern of damage, leaf coloration, and location on the tree.
Environmental Stressors
Dogwoods are understory trees adapted to filtered light and moist, well-drained soil, making them highly susceptible to environmental imbalances. The most common cause of leaf browning and curling is leaf scorch, which results from the tree losing water faster than its shallow root system can supply it. This condition is triggered by drought, high temperatures, or excessive wind exposure, particularly when trees are planted in full afternoon sun. The tree conserves moisture by shutting down water flow, causing leaf margins and tips to turn brown and dry out.
Heat stress can also cause an upward rolling of the leaves, known as leaf roll, where the undersides may take on a purplish hue. This curling is a defense mechanism to reduce the leaf’s surface area exposed to the sun, limiting transpiration. Improper soil conditions can mimic drought stress. Poor drainage leads to root stress and reduces water absorption, while over-fertilization can cause a salt burn that draws moisture out of the roots, manifesting as brown leaf edges.
Fungal and Bacterial Diseases
Several fungal pathogens target dogwood foliage, causing lesions and tissue death that lead to browning and curling. The most serious concern is Dogwood Anthracnose, caused by the fungus Discula destructiva, which thrives in cool, wet spring weather and often begins on lower branches. Symptoms include large, irregular tan or purplish blotches that spread down the leaf vein, eventually blighting the entire leaf and causing premature drop and twig dieback. This fungus can move into the twigs and branches, forming sunken cankers that may ultimately girdle and kill the tree.
A less severe but more common issue is Spot Anthracnose, caused by the fungus Elsinoe corni, recognizable by its distinct small, circular spots. These spots are typically an eighth of an inch or smaller and feature a tan center surrounded by a reddish-purple border. When numerous, these spots cause the leaves and flower bracts to wrinkle and distort, leading to a curled appearance, though this disease rarely poses a threat to the tree’s survival.
Powdery Mildew, caused by Erysiphe pulchra, also results in leaf curling and distortion. It presents first as a fine, white or grayish coating on the leaf surface. The fungus saps nutrients, leading to marginal leaf scorch, premature leaf drop, and a weakened state.
Insect Activity and Damage
Certain insect pests cause symptoms similar to disease or environmental stress by damaging the leaves or disrupting the tree’s vascular system. The Dogwood Borer, the larva of a clearwing moth (Synanthedon scitula), is a threat because it feeds just beneath the bark, primarily targeting stressed or wounded trees. This feeding damages the cambium layer, hindering the flow of water and nutrients. This causes the foliage on affected branches to turn red and brown prematurely, often leading to branch dieback.
Scale insects, such as the Cottony Maple Scale, appear as small, immobile bumps on stems and leaves. These pests suck sap from the tree, and heavy infestations deplete resources, causing leaves to yellow, brown, and drop prematurely. Dogwood Sawfly larvae feed voraciously on leaves, often skeletonizing them by consuming the tissue between the veins. This damage causes the remaining leaf structure to brown, curl, and fall off.
Remediation and Long-Term Care
Addressing brown and curling leaves begins with adopting cultural practices that reduce tree stress and improve site conditions. For environmental issues like leaf scorch, consistent water management is necessary, especially during dry periods, using deep, slow watering to soak the root zone. Applying a two-to-three-inch layer of organic mulch over the root area, keeping it away from the trunk flare, helps conserve soil moisture and regulate temperature.
In cases of fungal disease, cultural controls involve improving air circulation and removing sources of infection. Prune out all dead or infected twigs and branches during dry weather, cutting several inches below the visible canker or dieback. Raking up and disposing of all fallen leaves in the autumn is also important, as many fungal pathogens, including Anthracnose, can overwinter in this debris. For serious fungal issues like Dogwood Anthracnose, a protective fungicide application may be necessary, beginning at bud break in early spring and repeated every ten to fourteen days while new growth is emerging.
To manage insect pests, maintaining tree vigor is the best defense, since borers primarily attack stressed dogwoods. For scale insects, horticultural oil sprays applied in the spring before new growth emerges can smother overwintering adults and eggs. If dogwood borers are present, removing the infested branches is the primary remedy. Avoiding trunk wounds from equipment like lawnmowers or string trimmers prevents entry points for the pest.