Curled leaves on a cherry tree are a common observation, signaling that the tree is reacting to stress from its environment or a biological agent. This leaf distortion is a visible symptom, not a specific disease, often indicating the tree is attempting to protect itself, perhaps by limiting water loss. Identifying the shape of the curl and the context of its appearance is the first step in determining the underlying issue affecting the tree’s health.
Curling Caused By Insect Pests
The most frequent biological agents responsible for leaf curling are sap-sucking arthropods. Black cherry aphids (Myzus cerasi) are a primary culprit, clustering densely on the undersides of new leaves and tender shoots. As they feed, they inject toxins that disrupt normal cell growth, causing the leaves to tightly curl inward and downward. A secondary sign of an aphid infestation is honeydew, a sticky, sugary liquid the insects excrete. This residue often leads to the development of sooty mold, a black fungus that coats the leaves, fruit, and branches.
Another group of pests, spider mites, also cause leaf distortion. Their damage often appears as fine stippling or bronzing before the leaf cups upward. Mite infestations are accompanied by fine, silken webbing, particularly visible in the joints of the leaves and stems.
Pathogens That Induce Leaf Distortion
Leaf curling can also manifest from a pathogenic infection, most notably from fungi or bacteria that directly attack the foliage. Fungal leaf curl, caused by Taphrina deformans, affects leaves shortly after bud break during cool, wet spring weather. Infected leaves become noticeably thickened, puckered, and blistered, often displaying a reddish or pinkish coloration before turning yellowish-gray. The fungus infects the developing leaf tissue while the buds are swelling, leading to the characteristic distortion.
Bacterial Canker, caused by Pseudomonas syringae, is a severe threat that involves woody tissue, though it also affects leaves. Leaf symptoms manifest as small, dark, angular spots that may dry out and fall away, creating a “shothole” appearance. Although curling is not the primary symptom, bacterial toxins can cause wilting or death of new shoots, resulting in distorted or curled leaves. A distinguishing feature of this issue is the presence of cankers—sunken, darkened areas on the trunk or branches that often ooze a reddish-brown, gummy substance (gummosis).
Environmental and Cultural Stress Factors
When no pests or diseases are visible, curling is likely a physiological response to non-living environmental stress factors. Water stress is the most common non-biological cause, resulting from either severe drought or overwatering that leads to root saturation. In drought, the tree rolls the leaf margins inward to reduce surface area exposed to the sun and wind, minimizing water loss. Conversely, soggy soil suffocates root hairs, impairing water absorption, which mimics drought stress and causes the same protective curling response.
Extreme temperatures, such as intense heat or sudden frost after bud break, can also damage new foliage, resulting in temporary cupping or scorching. Another cause is accidental exposure to growth-regulating herbicides, such as 2,4-D or Dicamba, commonly used on lawns. These chemicals mimic plant growth hormones, causing distorted cell elongation that results in leaves that are cupped, twisted, or puckered. Symptoms from herbicide drift are often uniform across the tree or appear on multiple plant species nearby, providing a strong clue.
Diagnosing the Cause and Treatment Steps
Effective management begins with a systematic inspection to accurately determine the source of the leaf curling. Examine the affected leaves closely, noting the location of the curl and any associated signs. If the leaf is tightly rolled and sticky, unroll it to check the undersides for colonies of aphids. If you observe a blistered, thickened, and reddish leaf texture, especially in the spring, the issue is likely fungal leaf curl. If the leaves are distorted but clean, the issue is likely environmental; evaluate soil moisture and consider whether nearby areas were recently treated with a broadleaf weed killer.
Treatment is categorized based on the diagnosis. For aphids, a strong jet of water can dislodge them, or a targeted insecticidal soap application can be used. Fungal disease treatments are largely preventative, requiring fungicide application in the late fall or early spring before bud break, as treatment after symptoms appear is ineffective. For cultural stress, adjusting the irrigation schedule is necessary. For herbicide damage, the tree generally needs time to outgrow the symptoms, though a professional arborist should be consulted for severe cases.