Hypoxylon canker
Entoleuca mammata

• Leaves on one or more branches are undersized, turn yellow then to brown and remain attached to stem
• Cankers begin near wounds or at the base of a branch
• Infected bark initially turns yellowish-orange; older infections are black at center with yellowish-orange margins
• Bark first appears blistered and raised, then falls off to reveal blackened wood
• Clusters of raised buff white to black bump like fungal stromata can be seen on 3 year old cankers
• Damage most common on trembling aspen

Management

• There are no fungicides that prevent or cure Hypoxylon canker.
• Avoid planting species that can become infected where existing Hypoxylon infections are found on neighboring trees.
• Prune to remove dead or dying branches during dry periods, before the canker reaches the main trunk.
• Remove structurally weak trees that have cankers along the main trunk in order to avoid damage to people and property from tree breakage.

Valsa and Leucostoma cankers
Valsa sordida and Leucostoma niveum

• Random dead branches seen throughout canopy
• Sunken irregularly-elongated cankers with cracked bark at the edges occur on branches or the main trunk
• Leaves on random branches wilt, turn yellow then brown
• Cankers are brown to black at the center with salmon to orange discoloration of the bark at the edges
• In wet weather curled tendrils of orange spores emerge from pimple like fungal structures within infected branches
• Common on trees stressed by drought, winter injury, wounds, insect feeding or other factors
• More information on canker

Cryptodiaporthe canker
Cryptodiaporthe populea

• Multiple thin weak adventitious shoots develop
• Bark on cankers may or may not be discolored, but the tissue beneath the bark will be brown to black
• Callus tissue formed around edges of cankers causing bark to fall off and expose the wood beneath it
• Leaves on infected branches turn yellow and drop prematurely
• Random dead branches caused from girdling cankers seen throughout canopy
• Common on Lombardy poplars

Wetwood or bacterial slime flux
Several species of bacteria

• Streaks/columns of water-soaked bark discoloration on the trunk or branches that is gray to yellow-brown when dry and black to brown when wet
• Discoloration commonly starts at bark cracks, wounds, or branch unions
• Fluid may ooze or bleed out of openings in the bark and may have a yeast-like odor
• More information on wetwood

Leaf spot and canker blights
Marssonina spp., Septoria spp., Colletotrichum
gloeosporioides

• Dark, sunken cankers can develop on stems of Septoria infected
• Irregular dark spots (angular to round) to large blotches on leaf surface
• Severe infestations may lead to leaf yellowing full defoliation by late summer
• Lower branches are infected first
• More information on Leaf spot and canker blights