A severe infection can cause reduced yields. Symptoms and Diagnosis Symptoms first appear in spring. New leaves become curled and develop reddish areas. The reddish areas become thickened and puckered resulting in severely distorted leaves. As the disease progresses the thickened areas turn yellowish grey and become covered with velvety spores.
Affected leaves turn yellow or brown and fall prematurely.
Affected shoots usually send out new leaves which often are unaffected by the disease unless rainy weather ensues. In more severe infections shoots may become thickened and die. Aphids can also cause leaves to curl but if present, the insects or cast skins will be evident to the naked eye. The fungus overwinters on bud scales, on twigs and on fallen infected leaves. In spring the fungal spores are moved on to newly developing leaves by splashing water.