Bacterial cells act as nuclei for ice formation at temperatures slightly above freezing, causing frost injury to its host. Symptoms Symptoms may occur on leaf blades, petioles, flower buds, and young twigs. Leaf lesions begin as light yellow spots. They expand and become brown and water-soaked with yellow halos. Affected tissue eventually turns black.
Young leaves turn black and die quickly.
Lesion expansion occurs slowly on older leaves. Affected leaves may also exhibit black streaks along midribs and veins. Leaves displaying this symptom may al be crinkled along the midvein or margin. Petioles and stems may be girdled by black lesions and the tissue beyond this point withers and dies. Tissue directly affected by syringomycin turns black and exhibits water-soaking while those that die as a result of girdling turn brown.