Dogwood trees are prized for their beautiful spring blooms and attractive foliage, but when their leaves begin to curl or cup, it signals that the tree is under duress. This leaf distortion is not a disease in itself but rather a physical symptom, a protective mechanism employed by the plant to conserve moisture or minimize exposure to a threat. Diagnosing the underlying cause requires careful observation, as the issue could stem from environmental conditions, insect activity, or a fungal infection. Understanding the specific type of stress your dogwood is experiencing is the first step toward restoring the tree’s health and appearance.
Environmental Causes of Leaf Curling
The most frequent cause of dogwood leaf curling relates to issues with water availability or excessive heat, which together induce a condition known as leaf scorch. When the tree cannot absorb enough moisture from the roots to match the rate of water loss through the leaves, the foliage rolls upward along the midvein. This response effectively reduces the leaf’s surface area exposed to the sun and wind, slowing transpiration to conserve the remaining water supply. Curled leaves can be a sign of drought stress, which is particularly common in young trees that have not yet developed an extensive root system to draw water from the soil.
Conversely, while less common, overwatering or poorly draining soil can also lead to curling because saturated roots are unable to function properly, causing a physiological drought. Another cause of distortion is exposure to certain chemical compounds, specifically herbicide drift from nearby lawn or garden applications. Herbicides containing plant growth regulators like 2,4-D can cause new dogwood growth to emerge with a characteristic twisted, cupped, or gnarled appearance, often affecting multiple plant species nearby.
Curling Due to Pests
Small, sap-sucking insects are a common culprit that can directly cause dogwood leaves to curl or distort as they feed. Aphids, which often cluster on the undersides of new leaves and stems, extract plant sap, leading to the deformation of the tender foliage as it expands. The presence of aphids is often indicated by a sticky, clear residue called honeydew, which is their sugary waste product, and may also attract ants.
Spider mites, tiny arachnids that thrive in hot, dry conditions, cause leaves to curl and roll tightly as they damage the leaf tissue. Mites feed by piercing individual plant cells to suck out the contents, leaving behind a fine, speckled pattern known as stippling on the leaves. A heavy infestation of spider mites can be identified by the fine, silken webbing they weave across the leaves and branches, especially near the tips of the shoots.
Curling Caused by Fungal Issues
Fungal pathogens can also cause dogwood leaves to curl, typically as a secondary effect of tissue damage. Spot Anthracnose is a common disease characterized by small, tan spots with distinct reddish-purple borders that appear on the leaves and flower bracts. When these spots become numerous and merge, the surrounding healthy tissue forces the leaf to wrinkle and distort, resulting in a curled or cupped appearance.
Dogwood Anthracnose is a more serious disease that initially appears as purple-bordered spots, often starting at the leaf margins. As the infection progresses, the lesions expand, causing the entire leaf to shrivel and turn black, often leading to premature leaf drop and dieback of the twigs. Powdery Mildew covers the leaves in a white or gray coating, and in severe cases, the affected foliage may exhibit twisting and distortion.
Actionable Steps for Recovery
Addressing environmental stress usually involves adjusting watering practices to ensure the tree receives deep, slow applications of water directly over the root zone. When the top few inches of soil are dry, provide enough water to soak the top 10 inches of soil to encourage deep root growth. Applying a two to three-inch layer of organic mulch around the base of the tree, kept a few inches away from the trunk, helps to conserve soil moisture and moderate soil temperatures.
Managing pest infestations often requires non-chemical treatments, such as a strong jet of water to dislodge aphids and mites from the foliage. For more persistent problems, applications of horticultural oil or insecticidal soap can be effective, provided they are applied thoroughly to the undersides of the leaves where pests hide. When fungal diseases like Anthracnose are present, pruning out and disposing of infected twigs and leaves will improve air circulation and reduce the source of fungal spores. Fungicide sprays, such as those containing chlorothalonil, can be applied in early spring as new leaves emerge to create a protective barrier against infection, especially during wet weather.