This disease is caused by the fungus Endocronartium harknessii. The term "rust" designates both the disease and causal fungus. To date, the rust has been found in most bareroot nurseries in British Columbia where its hosts are grown. Although recent disease losses have been small, infected nursery stock can disseminate the rust to disease-free areas. Infection of nursery seedlings often occurs on the main stem; thus, if diseased stock is outplanted, the gall continues expanding and the tree dies, or may suffer wind-breakage.
Hosts are two- and three-needle (hard) pines, of which only lodgepole and ponderosa pines are grown locally. Since there is an interval between infection and development of conspicuous galls (Figure 51), the disease is rarely noticed on stock until late in the second growing season, or it may go undetected until the lifted trees are graded or after they are outplanted. Locally, in recent years, seldom more than 1%, and often none, of the stock has been affected. Since seedlings are not killed, the only direct losses are the culling of lifted stock. Because these losses have been inconsequential, the disease has been largely ignored; however, western gall rust epidemics are cyclical and the potential for serious losses always exists.
In spring and early summer, masses of orange-yellow spores are produced by and released from galls on diseased trees. When these wind-dispersed spores land on succulent current year's shoots or needles, they germinate - especially during rainy periods - and penetrate. The rust stimulates proliferation of the host's tissue so that 1.5-2 years later, irregular, rounded to pear-shaped swellings appear. These woody, perennial galls grow and release spores (Figure 53) annually, which can re-infect pines. Consequently, no alternate hosts are involved in this rust's life cycle. Eventually the stem or branch dies. Since the interval between infection and sporulation exceeds the usual period that most seedlings are in the nursery (except perhaps some transplants), there is no danger of disease spread among nursery seedlings. Instead, all inoculum originates from older infections on trees outside the nursery (Figure 54).
Because of the interval between infection and sporulation, it is obvious that (i) the galls seen on 2-year-old trees originate from infections occurring early in the first growing season, and (ii) trees infected during the 2nd year will be symptomless while in the nursery. The concern with these seedlings is that they mask the true incidence of the disease in the nursery, with the result that infected trees get outplanted unknowingly.
Because spores are blown into the nursery from outside, all gall rust infected pines should be cut for 275 m around the nursery. The unreliability of current prediction techniques makes fungicidal spraying of nursery seedlings impractical. Diseased seedlings should always be culled to lessen spread of the disease to new areas.
Hiratsuka, Y., and J.M. Powell. 1976. Pine stem rusts of Canada. For. Tech. Rep. 4, Dep. Environ., Can. For. Serv., Ottawa, Ont.
Ziller, W.G. 1974. The tree rusts of western Canada. Dep. Environ., Can. For. Serv., Publ. No. 1329, Ottawa, Ont.
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Other Fungi |
Insects |
Environmental |
|---|---|---|
|
Root disease |
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Herbicide damage |
|
Principal, locally grown hosts |
Host age and season when damage appears |
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Nursery type and location |
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|---|---|---|---|---|---|---|
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Bareroot |
Container |
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Age |
Season |
Coastal |
Interior |
Coastal |
Interior |
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|
Lodgepole and ponderosa pines, other hard pines |
2+0 |
Mid - to late summer |
Yes |
Yes |
? |
? |
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Figure 51. Western gall rust on 2+0 lodgepole pine.
Figure 52. Life history of western gall rust.
Figure 53. Western gall rust on 2+1 lodgepole pine. Note masses of spores which can vary in colour from white to yellow.
Figure 54. Globose galls on trees in windbreaks or adjacent to the nursery produce western gall rust inoculum (courtesy of Forest Insect and Disease Survey, P.F.C., Victoria, B.C.)