TWIG CANKER
Vermicularia ipomearum (imperfect fungus)
All American and Siberian elms are effected throughout the United States: Western Plains states and central California.
Wet spring seems to favor development.
Seen as Small, black, girdling cankers on small twigs, leading to limited dieback (not significant).
Tiny, hairy, black fruiting structures (pycnidia) at edges of small, round, grayish cankers on small twigs in late spring. These cankers enlarge each season until the twigs are girdled. The pycnidium is globose, leathery black, with dark-colored bristles. The conidia are elongate, single-celled, slightly curved. They are produced abundantly, reinfecting the tree.