Landscape and Nursery - Botryosphaeria Canker

With the extra stress placed on woody landscape plants this year by the drought you can expect to see increased incidence of Botryosphaeria canker. The following is an article on the subject from Rutgers University.

Botryosphaeria canker is a commonly occurring disease that affects woody plants in over 100 genera. Although the disease is very important in fruit and nut crops, it can be troublesome in ornamental species such as ash, birch, cotoneaster, crabapple, dogwood, elm, firethorn, hop hornbeam, mountain laurel, locust, magnolia, mimosa, photinia, pieris, privet, rhododendron, and wax myrtle. The causal agent, Botryosphaeria dothidea, is an opportunistic fungus that attacks trees and shrubs wounded or weakened by environmental stress, particularly drought. The disease can result in a branch dieback that may kill trees or severely reduce their aesthetic value. Indeed, Botryosphaeria canker is quite evident now on older, stressed rhododendrons.

Symptoms of Botryosphaeria canker vary with the species and age of the host and the severity of the predisposing stress. The fungus kills bark and sapwood tissue, causing areas of dead tissue called cankers to form. Cankers range from small, elliptical lesions that coalesce into large diffuse areas of blighted tissue, to large, elongate cankers delimited by callus tissue. Affected bark turns dark, rough, and may peel away. Multiple cankers of various sizes often develop on branch tissue, growing slowly until the limb is girdled and killed. The entire plant may be killed once the canker moves from the branch into the main stem. Disease cycle Botryosphaeria survives the winter in small, round “fruiting bodies” (or structures that produce spores) embedded near the surface of cankered tissue. Infections occur when spores called conidia are splashed by rain from these fruiting bodies to susceptible tissue. Spore dispersal can occur during most of the year, but is most extensive during late spring and early summer. Infection occurs when fungal spores penetrate wounds or other openings in the bark. Pruning wounds, cracks, leaf scars, sunscald lesions, and senescent branches are all good entry sites for the fungus. Symptom development can take anywhere from 3 months to a year.

Through careful monitoring and early detection, Botryosphaeria canker can be eradicated before a significant reduction in the aesthetic value of the tree occurs. Branches with symptoms of canker should be promptly pruned during dry weather at least 6 to 8 inches below affected tissue. If possible, remove the branch from the tree by properly cutting the limb flush to the branch collar, not flush to the trunk. To prevent the spread of this disease on pruning tools, surface-sterilize tools between cuts with denatured alcohol or 10% bleach. Since the fungus can persist and sporulate in dead plant material for extended periods, branches cut from diseased trees should be taken from the site and, if possible, composted. Fungicides or wound paints have not proven to be an effective control of most canker diseases and are not recommended.

Reprinted in part from "Botryosphaeria Canker: Troublesome to Plants in Dry Weather" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, in the October 9, 2008 edition of the Plant and Pest Advisory, Landscape, Nursery, and Turf Edition from Rutgers University.