Perennial canker of stone fruit
Leucostoma cincta (Fr.:Fr.) Höhn
Leucostoma persoonii Höhn.
Small twig infections are usually found around winter-killed buds, leaf scars, and picking and pruning injuries. They appear as sunken discolored areas with alternating zonation lines and may ooze amber gum unless the twig is killed. On infected branches, the leaves often turn yellow, wilt and die (A). Dead twigs, branches, and canker margins become covered with pinhead-sized black pimples (pycnidia) that break through the bark (B). Pycnidia exude flesh- to orange-colored tendrils of spores under wet conditions. Main trunk and branch infections usually start at pruning wounds or winter-killed tissue. Cankers are elliptical and exude excessive amounts of amber-colored gum. Cankers often develop a series of concentric callus rings, reflecting the yearly alternation of callus formation and tissue invasion (C).
Widespread; but most damaging in cooler climates such as the northeastern US and Canada.
Can be confused with bacterial canker (particularly on sweet cherry) or constriction canker; however, these cankers do not form the alternating callus rings. Perennial canker is also known as Cytospora or Valsa canker
There are no fungicides registered specifically for Leucostoma control, and those applied for peach leaf curl and brown rot control give only minimal reduction in perennial canker infections. Pruning out cankers removes the source of disease for new cankers within an orchard, and eliminating wild hosts around the orchard periphery reduces disease pressure from outside sources. Training young trees to produce scaffold limbs with wide crotch angles is essential for avoiding infections that weaken crotches in older trees.
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