Landscape - Cytospora or Leucostoma Canker of Spruce

With last year's stress, expect to see more canker diseases in the landscape in 2008. Cytospora or Leucostoma canker of spruce is a common canker disease to watch for. The following is a factsheet on the subject from Bob Mulrooney, UD Extension Plant Pathologist.

Cytospora canker is the most prevalent and destructive disease of mature Colorado blue spruce and Norway spruce in the northeastern United States. Douglas-fir, eastern white pine, Japanese larch, European larch, and rarely hemlock may also be affected. This disease is very common in all three counties of Delaware.

Cause

The fungus, Cytospora kunzei, more properly identified as Leucostoma kunzei causes this canker disease. It is also known as Valsa canker. Cytospora can infect branches through wounds and branch stubs, but does not actively develop a canker unless the tree is stressed by drought. Most cankers on spruce remain on the branches, but Norway spruce is found with trunk cankers. Cankered areas on branches or trunk produce spores in small fungus fruiting bodies that are exuded during periods of wet weather. Rain splashes the spores onto nearby branches and infections occur through wounds.

Symptoms

The most noticeable symptoms are the browning and eventual death olower branches of older trees. The disease progresses upward at a slow rate until the entire tree may be infected. Infrequently, branches high in the tree may be the first to turn brown and die.

Dead, brown needles persist through much of the growing season and drop during the winter, leaving bare twigs and branches. Another conspicuous symptom is the presence of large amounts of bluish-white pitch or resin on the bark of dead or dying branches. It may run and drip onto the lower branches. Fresh resin from an active infection is amber-colored. This usually appears as scaly patches as the resin dries out. Typically the actual cankers appear first at the base of lower branches near the trunk of the tree. Damage usually does not occur until the trees are 10-15 years old. On the more susceptible species (Norway spruce), trunk cankers develop which may result in girdling and death of the tree. The bark of the cankered areas is not usually visibly different in color, nor does it become depressed as in other cankers on deciduous trees. Resin flow from these cankers is a good diagnostic tool, but resin flow can occur from any injury to branch tissue. So you need to be sure the fungus is associated with the resin flow.

Control

Although no control measures are completely effective, the following suggestions should help to reduce the spread of the disease if it has not already caused extensive damage and if action is taken immediately.

1. Keep trees growing vigorously by fertilizing periodically. Water trees during dry periods since drought predisposes trees to canker development and expansion. Control insect pests such as spider mites and gall aphids. Poorly maintained trees, in low vigor, are usually more susceptible to the disease. When replanting with a spruce, choose a site that is not prone to drought and may be watered during droughty periods.

2. Prune out and destroy diseased branches since they cannot be saved. Prune back to the main trunk or nearest healthy lateral branch. Pruning tools should be disinfected between cuts by swabbing with a 10 percent solution of household bleach or 70 percent alcohol. This helps prevent spread of the disease. Also, never prune when the branches are wet.

3. Avoid injuries to the bark from lawn mowers, tools, etc. since Cytospora may enter the tree through such wounds.

4. Fungicides cannot be properly timed to prevent this disease, and have been ineffective.

Caution. The information and recommendations in these fact sheets were developed for Delaware conditions and may not apply in other areas.

Reprinted from the factsheet Cytospora Canker of Spruce by Bob Mulrooney, Extension Plant Pathologist, UD.