Sirococcus tip blight, caused by the fungus Sirococcus conigenus, occurs on a wide variety of conifers. In Minnesota, this disease most seriously affects red pine (Pinus resinosa) and Colorado blue spruce (Picea pungens). The fungus infects new shoots (candles) causing tip blight, and may also kill seedlings.

Sirococcus overwinters in infected shoots, needles, cones, and seeds. Spores are dispersed from infected tissue during rainy weather in the spring and summer, coinciding with the new growth of conifers. Infections occur on or next to the base of new needles. First symptoms of infection include a small purplish lesion and small resin droplet at infection points. Infections on expanding shoots often cause the shoot to curl downward. Infected red pine needles often droop conspicuously. Lesions eventually expand, killing the shoots. Dead shoots become apparent from June to August.

Sirococcus tip blight Photo: U of MN Department of Plant Pathology

Small brown to black reproductive structures are produced on newly infected shoots, cones, and needles in the fall or early spring after infection. On spruce, these structures are most common on the shoots whereas on red pine they are most abundant under needle sheaths. Spores are disseminated by rain splash and most new infections occur within a few yards of previous infections.

This disease is most damaging on smaller landscape or under-story trees that are near larger, infected trees. Damage on large, established trees is usually confined to lower branches and does not significantly impact their overall health. On red pine, infections may spread upward killing branches over several years when favorable conditions for disease persist.

Cultural control methods should include proper pruning and site selection. Prune out infected shoots and branches during dry weather. When planting trees, provide adequate space between trees to encourage air movement and promote drying of branches and foliage.

Under severe conditions, a protective fungicide containing the active ingredient chlorothalonil (trade names include Daconil 2787 and Multi-Purpose Fungicide) may be used. When using fungicides, be sure to read and follow the directions on the label. Generally, two applications of chlorothalonil should provide adequate control of this disease. The first application should be made in the spring when new growth is ½ to 2 inches in length. The second application should be made three to four weeks later. If favorable conditions for disease persist, a third application three to four weeks after the second may be warranted.

Representative trade names may be included along with generic names. This information is supplied with the understanding that no discrimination is intended and no endorsement is implied.

References

Pscheidt, J.W. (ed.) 1997. Pacific Northwest 1997 Plant Disease Control Handbook. Corvallis, OR: Extension & Station Communications, Oregon State University.

Sinclair, W.A., H.H. Lyon and W.T. Johnson. 1987. Diseases of Trees and Shrubs. Ithaca, NY: Comstock Publishing Associates (Division of Cornell University Press).

P438S
Revised 2/99
Chad Behrendt, Crystal Floyd