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Sirococcus blight

This disease, caused by the fungus Sirococcus conigenus, affects conifers throughout the North Temperate Zone, including all of British Columbia. Since being found on lodgepole pine seedlings at the Red Rock nursery in 1970, Sirococcus blight has appeared in nurseries throughout the province. It is more prevalent on container-grown than bareroot stock.

Hosts and damage

Seedlings of Sitka, white and Engelmann spruce, lodgepole and ponderosa pine, Douglas-fir, and, very rarely, western hemlock are affected. On Douglas-fir the disease has been found only on bareroot seedlings. Disease symptoms and time of their appearance differ for container-grown and bareroot seedlings. Although 2-year-old, container-grown spruce are sometimes affected, Sirococcus most often attacks very young seedlings in container nurseries (Figures 35 and 36) where killing of the primary needles from the base upward is a common symptom.

Depending upon how far the disease has progressed, the upper portion of diseased needles may be green. Killed needles are light to reddish brown. Dead seedlings remain upright. Examining the base of diseased needles with a hand lens often reveals the small, irregularly rounded, light butterscotch-colored pycnidia (Figure 37); these darken with age. In container nurseries, the disease affects random seedlings (Figure 38)  , usually within specific seedlots because the pathogen is seed-borne. In germination tests, 1-2% of the spruce germinants often become diseased from seed-borne inoculum. In container nurseries, mortality from secondary spread sometimes reaches 30% in some spruce seedlots.

In bareroot nurseries, symptoms usually appear in late summer through the fall on 1+0 bareroot seedlings or in the spring on 2+0 trees. The fall symptoms may be confused with early frost damage. Generally, the pattern of symptom development, color of diseased tissues, presence of pycnidia, and the random distribution of affected trees is the same as for container seedlings. The susceptibility of lodgepole pine varies among provenances. Whereas Sirococcus blight normally results in mortality of container-grown seedlings, it usually kills only part of the shoot on bareroot trees. A lateral branch then takes over as the terminal shoot (Figure 39). The desiccated terminal shoot of dead seedlings may assume a crozier-shape. In lodgepole pine, the pathogen's spread can often be traced from the primary needles, where infection may have occurred, to the base of the epicotyl and upward on the stem and secondary needles.

Note: New information suggests that Sirococcus can also cause stem lesions on pine.

Life history (Figure 40)

Because S. conigenus is seed-borne, initial disease centers in container nurseries develop from this inoculum and occasionally from spores outside the nursery. The latter inoculum is probably most important in bareroot nurseries. Secondary spread is via pycnidiospores produced on diseased tissues and disseminated in rain and irrigation water. Infection occurs through young needles and is favored by cool, moist conditions and low light intensity, all of which often occur simultaneously in the spring and early summer in coastal British Columbia. This probably accounts for the higher Sirococcus incidence in coastal container nurseries. Because the pathogen has no other known spore forms, it is assumed that each new disease outbreak originates from seed -or wind-borne pycnidiospores. In California, diseased trees and cones (Figure 41) adjacent to nurseries are known "Sirococcus sources."

Management

Because infested seedlots are probably the major source of Sirococcus inoculum in container nurseries, records should be kept of all seedlots with blight history. When infested seedlots are sown, a fungicide should be applied as soon as symptoms appear, to prevent spread of the disease. Prudent use of fungicides will help prevent the subsequent development of fungicide-resistant strains of pathogenic fungi such as Botrytis. Diseased seedlings should be rogued and burned when practical. Disease spread can be alleviated by reducing humidity in greenhouses, and perhaps by increasing temperatures. Increasing illumination may be helpful, as light-stressed seedlings are most susceptible. Disease severity usually decreases with the advent of bright, warm growing conditions. Bareroot seedlings should be sprayed with the appropriate fungicide when the disease first appears.

Selected References

Dennis, J. 1990. Stem Lesions on Pine Caused by Sirococcus conigenus. Seed and Seedling Extension Topics. Vol. 3, Number 2. p.1.

Illingworth, K. 1973. Variation in the susceptibility of lodgepole pine provenances to Sirococcus shoot blight. Can. J. For. Res. 3: 585-589.

Smith, R.S., Jr., A.H. McCain, M. Srago, R.F. Krohn, and D. Perry. 1972. Control of Sirococcus tip blight of Jeffrey pine seedlings. Plant Dis. Rep. 56: 241-242.

Sutherland, J.R., W. Lock, and S.H. Farris. 1981. Sirococcus blight: a seed-borne disease of container-grown spruce seedlings in coastal British Columbia forest nurseries. Can. J. Bot. 59: 559-562.

Wall, R.E., and L.P. Magasi. 1976. Environmental factors affecting Sirococcus shoot blight of black spruce. Can. J. For. Res. 6: 448-452.

Look Alikes

Other Fungi

Insects

Environmental

Colletotrichum blight
Diplodia
Fusarium
Gray mould
Phoma blight
Phomopsis canker and foliage blight
Sclerophoma
Top blights and cankers

 

Chemical burn
Frost
Sunscald

Summary

Sirococcus blight

Principal, locally grown hosts

Host age and season when damage appears

 

Nursery type and location

 

 

 

     

Bareroot

 

Container

 
 

Age

Season

Coastal

Interior

Coastal

Interior

All spruces

1+0
2+0

Spring and early summer

Yes

No

Yes

Yes

All hard pines

1+0
2+0

Late summer
Fall through spring

Yes

Yes

Yes

Yes

Douglas-Fir

1+0
2+0

Late summer
Fall through spring

Yes

No

No

No


Figures

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Click on this image to see a larger versionFigure 35. Sirococcus blight on container-grown spruce. Note that needles are killed from base upward.
    

 

 

 


Click on this image to see a larger version     Figure 36. Sirococcus blight on container-grown spruce. Note dark pycnidia on needles.

 

 

 

 

Click on this image to see a larger version     Figure 37. Pycindia of Sirococcus on 2+0 Douglas-fir.

 

 

 

 

 

 

 

 


Click on this image to see a larger version     Figure 38. Sirococcus blight on container-grown lodgepole pine. Note how the disease spreads outward from a central point.

 

 

 

 

Click on this image to see a larger version     Figure 39. Sirococcus blight on bareroot spruce. Note that the leader was killed in the preceding year and a lateral has become dominant.

 

 

 

 

Click on this image to see a larger version     Figure 40. Life history of Sirococcus blight.

 

 

 

 

 

 

 

Click on this image to see a larger version     Figure 41. Pycnidia of Sirococcus on a Sitka spruce cone.

 

 

 

 

 

 

 

Click on this image to see a larger versionAdditional Figure. Sirococcus pycnidia on a Sitka spruce cone.

 

 

 

 

 

 

Click on this image to see a larger version Additional Figure. Sirococcus on lodgepole pine

 

 

 

 


Click on this image to see a larger version  Additional Figure. Sirococcus tip blight on Ponderosa pine.

 

 

 

 

 

 

Click on this image to see a larger version     Additional Figure. Sirococcus conigenus on 2-month-old white spruce.

 

 

 

 

 

Click on this image to see a larger version     Additional Figure. Lodgepole pine needles affected by Sirococcus.

 

 

 

 

 

 

Click on this image to see a larger version     Additional Figure. Atypical Sirococcus stroblinius affection. Note the leader does not show the usual curved tip

 

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Click on this image to see a larger version     Additional Figure. Stem lesion on logdepole pine caused by Sirococcus

 

 

 

 

 

 

Click on this image to see a larger version     Additional Figure. Stem lesion on logdepole pine caused by Sirococcus

 

 

 

 

 

 

Click on this image to see a larger version     Additional Figure. Sirococcus on Douglas-fir.

 

 

 

 

 

Click on this image to see a larger version     Additional Figure. Sirococcus spores.