Phomopsis canker and foliage blight

In British Columbia nurseries, Phomopsis occulta (perfect state = Diaporthe conorum) and P. lokoyae (perfect state = D. lokoyae) occasionally cause cankers and foliage blight.

Hosts and damage

These two fungi are widely distributed, occurring on many conifers, particularly western larch and spruces. Needle loss and shoot blight (Figure 44) can occur on 1+0 and 2+0 seedlings. Older seedlings may develop stem or branch cankers resulting in dieback of laterals, seedling death, or culling due to terminal shoot death. Cankers appear to be sunken, because of the growth of healthy tissue surrounding the dead tissue. Foliage and branches distal to the infection become yellow and die quickly. Sometimes seedlings die (Figure 45), but most losses are due to culling.

Life history (Figure 46)

These fungi are common saprophytes occurring on dead tissues of living seedlings, fallen cones, and dead stems and needles. Phomopsis occulta may be seed-borne on western larch. Cankers form on young stems and branches of winter-dormant seedlings and grow for one season. If the stem is not girdled, lesions eventually heal and no permanent damage results. Small, black spherical pycnidia develop in cankers during spring or summer, producing spores that are spread by rain or irrigation water. Under favorable conditions, spores germinate on young branches or stems in late summer and infection results. The fungus moves through the bark to the cambium where it develops during the winter. The fungus' perfect state may occur in the fall on infected branches, releasing wind-borne spores that lead to within-nursery spread of the fungus.

Management

Several cultural practices are important in Phomopsis management. Thinning seedlings and decreasing watering reduces humidity. Removing diseased seedlings decreases the amount of inoculum for spread of the fungus. Top pruning, which creates infection courts, should be avoided and stressed seedlings (e.g., from drought or frost) should be kept under careful surveillance as they are prone to infection. Under extreme conditions, applying a fungicide regularly to protect new growth from the time of germinant emergence through the fall has also proven to be effective.

Selected References 

Funk, A. 1968. Diaporthe lokoyae n. sp., the perfect state of Phomopsis lokoyae. Can. J. Bot. 46: 601-603.

Hahn, G.G. 1930. Life history studies of the species of Phomopsis occurring on conifers. Part I. Trans. Brit. Mycol. Soc. 15: 32-93.

Kliejunas, J. 1986. Evaluation of fungicides for control of Phomopsis canker of Douglas-fir at Humboldt Nursery. U.S. Dep. Agric. For. Serv., Pac. Southwest Reg. Rep. 86-18.

Smith, R.S. Jr. 1975. Phomopsis canker of Douglas-fir. In Forest nursery diseases in the United States. In G.W. Peterson, and R.S. Smith, Jr. (editors). U.S. Dep. Agric. For. Serv. Agric. Handb. 470, Washington, D.C., pp. 42-44.

Look Alikes

Summary

Phomopsis canker and foliage blight

Figures

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    Figure 44. Phomopsis blight on western larch.

     Figure 45. Container-grown western larch killed by Phomopsis blight.

     Figure 46. Life history of Phomopsis canker and foliage blight.