Cherry trees, both sour and sweet varieties, are subject to a number of pests that can cause the leaves of the tree to curl, in many cases causing the tree to die prematurely. Leaf curl is typically a late sign of an advanced infestation, either from an insect pest or a fungal infection. Recognising what is causing leaf curl and taking steps to prevent or control it can help keep your cherry tree healthy and productive.
The black cherry aphid, a tiny, black, soft-bodied insect that often lives in large groups, is found in all areas where cherries grow. This insect pest usually attacks sweet cherries, but will also infest sour cherry varieties. The feeding behaviour of these insects can curl sweet cherry tree leaves, particularly young growth. Aphids feed by injecting their mouth parts into a leaf, then feed on the liquid inside. Though not considered a serious pest in commercial growing, in organic orchards, where chemical pesticides are not used, the aphid has become a significant problem. Dormant horticultural oils, natural insecticidal soaps and biological controls, such as introducing ladybirds or lacewing insects to cherry trees, may help reduce black cherry aphid numbers.
A fungal disease, powdery mildew attacks the leaves and stems of the cherry tree. A fine netlike mycelium will form on the leaves, followed by powdery, white patches. As the disease progresses, leaves will curl up and eventually fall off the tree prematurely. A fungicidal spray of benomyl can help kill powdery mildew spores and reduce the risk of spread. Rake the curled leaves that have fallen and destroy them by burning to also destroy the spores of this invasive fungus.
Peach Leaf Curl
Peach leaf curl is another fungal infection that can cause the leaves of a range of fruit trees to have curled leaves, including peaches, nectarines and cherries. The fungus Taphrina deformans is the pathogen responsible for this disease. When the fungus grows, it causes the leaves to become thicker than normal. This produces a characteristic curling deformation in the leaves with associated yellow to reddish-purple discolouration. The fungus eventually fruits and releases spores. Once this process is finished the leaf dies and drops of the tree. Left unchecked this fungus can entirely defoliate the tree. A fungicide applied late in fall or early in spring before leaf formation may help to reduce the risk of infection. Once leaves are infected and curled, there is no effective treatment.
Leafrollers are the larval stage of several species of moth, including the fruit tree leafroller (Archips argyrospilus), the European leafroller (Archips rosanus), the oblique-banded leafroller (Choristoneura rosaceana) and the three-lined leafroller (Pandemis limitata). These caterpillars commonly feed on fruit trees, including cherries. When the larvae reach the stage when they will pupate, they create cocoons using leaves of the cherry tree. The caterpillar will roll the outer edges of the leave together to form a case out of the leaf and will weave its cocoon inside. Prevention is largely focused on applying pesticides to cherry trees early in the season to eradicate the larvae before they form their cocoons, as the rolled leaves will provide protection against insecticide sprays.