Landscape - Canker Diseases of Conifers

With the stress of last year's drought, we are likely going to see increased amounts of canker on conifers this year. The following is an article on the subject.

Atropellis and Cytospora cankers of conifers

From a moisture standpoint, the extended period of drought last summer severely affected landscape trees and shrubs, field nursery stock, and Christmas trees. The drought also predisposed affected plant material to many problems with diseases and insects. One such disease, called canker, commonly occurs on all trees stressed by extremes in soil moisture. Cankers are large, elliptical lesions on twigs, branches, and trunks. The fungi that cause cankers are opportunistic organisms that infect plants through wounds and at the base of dead branches. As cankers enlarge, affected tissue becomes girdled, and tissue distal to the canker dies. A cut made into the wood with a pocketknife at the edge of a canker reveals a sharp transition between wood that appears white and healthy and wood that is brown and infected. Canker diseases on conifers are most noticeable in nursery, landscape, and Christmas tree plantings at this time of year. Fungi that commonly affect conifers in Delaware include Atropellis (pine) and Cytospora (spruce). Since trees affected by drought stress, mechanical injury, or winter injury are susceptible to canker development, expect to see more canker problems this growing season. To manage cankers, maintain or improve plant vigor, avoid wounding, water during periods of drought, and prune moderately affected trees at least 6- to 8- inches below discolored tissue during dry weather. When pruning for disease control, surface sterilize pruning tools between cuts. Severely affected trees should be discarded. Fungicides are ineffective against such fungi and are, therefore, not recommended.

Extracted from "Diseases of Conifers" by Ann B. Gould, Ph.D., Plant Pathology in the Rutgers Plant and Pest Advisory, Landscape, Nursery, and Turf edition.