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Colletotrichum blight

In the early 1980's, Colletotrichum acutatum and C. gloeosporioides caused blights on container-grown western hemlock (Figure 55) in British Columbia. Experiments showed that C. gloeosporioides affects several conifers, especially western and mountain hemlock. Colletotrichum blights are favored by high humidity and temperature. Symptoms include blanching of young needles, progressing from bases upward, followed by affected needles becoming brown. Advanced symptoms include needle browning on the entire shoot, crooking of lateral branch and terminal shoot tips, and stem and needle lesions. The disease spreads from infection centers, quickly affecting all seedlings within large, circular areas.

Both fungi overwinter as mycelium, sclerotia, and perithecia in diseased host tissue on living plants or soil debris. Culling and destruction of infected seedlings are recommended. Because spore production, spread, and germination all require high humidity and free water, cultural practices that reduce moisture are important in managing the disease. Where possible (e.g., in greenhouses) temperature should be reduced. Often it is necessary to apply fungicide sprays in conjunction with these cultural practices.

Selected References 

Griffin, M.S., J.R. Sutherland, and J.J. Dennis. 1987. Blight of conifer seedlings caused by Colletotrichum gloeosporioides. New Forests 1: 81-88.

Hopkins, J.C., W. Lock, and A. Funk. 1985. Colletotrichum acutatum, a new pathogen on western hemlock seedlings in British Columbia. Can. Plant Disease Surv. 65: 11-13.

Look Alikes

    Figure 55. Colletotrichum blight on container-grown western hemlock.