Disease

Canker diseases

Cytospora, Nectria, Botryosphaeria and others

Fungi that kill patches of bark and the wood beneath, mostly on trees stressed by drought, wounds, winter injury or a poor site. A canker that circles a branch kills everything beyond it.

Signs

• Sunken, discolored, cracked or dead bark, often with a sharp edge against live bark.
• Tiny pimple-like dots in the dead bark; bluish-white resin on spruce.
• Branches beyond the canker wilt and die; on spruce, often the lower branches first.

What favors it

Stress from drought, winter injury, sunscald, wounds, poor sites and the wrong species for the climate.

Prevention

• Water deeply in dry spells, fall included, and mulch the root zone.
• Avoid wounds from mowers, trimmers and poor pruning cuts; prune in dry weather.
• Plant species suited to the site, such as Norway or white spruce instead of Colorado blue spruce on dry sites.

Crops it shows up on

Shade & ornamental trees; Evergreens & conifers (pine, spruce, juniper); Apple, pear & stone fruit; Roses & ornamentals.

Often confused with

Sources

• Cytospora CankerMontana State University Extension
• Nectria CankerMontana State University Extension
• Cytospora cankerUniversity of Minnesota Extension
• Cytospora Canker on SprucePenn State Extension
• Cytospora CankerColorado State University Extension

Why →