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The Journal Gazette

Saturday, April 14, 2018 1:00 am

Arborist diagnosis should be trusted

Ricky Kemery

Q. An arborist last year told us our large Colorado spruce tree has a disease called cytospora canker. How do I know this is the correct diagnosis?

A. You don't know for certain. Only by culturing the diseased tissue in a laboratory can one determine if indeed cytospora is the issue. However, many certified arborists and extension agents have one thing on their side: experience.

In today's world, people want quick answers at low cost. The reality is that many homeowners don't want to send samples to a lab at a higher cost that will take more time for results.

The consumer is often willing to bet that a landscape professional's experience will provide the correct answer – most of the time.

Professionals know cytospora canker is a common disease of Colorado blue spruce in our area. These trees are native to the mountain areas of Colorado – areas with low humidity, cooler weather, good drainage and adequate rainfall.

Our area is characterized by high temperatures and humidity during the summer, periods of drought or over wet conditions. Add incorrect planting, volcano mulching and poor maintenance and the stress on blue spruce is tremendous. This stress incurred by the tree leads to infection by diseases such as cytospora canker.

Cytospora canker is seldom a problem on young, vigorous trees. The canker first infects random lower branches and gradually progresses upward. Needles on affected branches turn brown and die. Branch cankers (infected areas) are generally located on branches near the trunk. A bluish white resin or pitch frequently coats the cankered area of the branch and is an important diagnostic symptom of cytospora canker. This sticky resin frequently will drip onto the trunk and branches below often producing an extensive accumulation of resin.

I would encourage residents to inspect Colorado spruce trees early in the spring. If one sees areas of white resin on the main trunk or branches, then contact a certified arborist or extension professional.

There is no cure for cytospora canker. Avoid using Colorado spruce in our area. Black Hills spruce, Norway spruce and white spruce are less susceptible to the disease. Because older, weakened trees are most susceptible to cytospora canker, it is important to improve tree vitality.

Work with a certified arborist to maintain tree health with fertilization, using compost as a mulch and soil builder, and pruning away infected branches when necessary during summer or late fall. Fungicide sprays are generally not effective, though there is some disagreement on this issue.

Often if tree health is maintained, the tree can live for many years. After the spruce succumbs to the disease, use other species of trees more adapted to our area.

The Plant Medic, written by Ricky Kemery, appears every other Saturday. Kemery retired as the extension educator for horticulture at the Allen County branch of the Purdue Extension Service.