Development of Sirococcus shoot blight following thinning in western hemlock regeneration.

Abstract

Shoot mortality from Sirococcus strobilinus Preuss. and other causes was recorded by crown position from April 1978 through October 1979 in younggrowth western hemlock (Tsuga heterophylla (Raf.) Sarg.) crop trees released in a 1977 thinning at Thomas Bay, Alaska. All study trees contained some infected shoots, but no terminal leaders were killed by shoot blight. On individual trees, the number of shoots killed by S. strobilinus between April 1978 and October 1979 was significantly correlated with the level of shoot blight mortality present in April 1978. Disease occurrence was highest in the lower crown, but differences in the level of shoot mortality between lower, middle, and upper crown locations were not significant. Disease occurrence during 1978 and 1979 was markedly lower than that in 1976 and 1977. After thinning, shoot blight appears to be causing little damage to hemlock crop trees; suggesting that thinning operations can proceed at Thomas Bay with confidence that the selected crop trees will suffer little, if any, damage from the disease.

Citation

Shaw, Charles G., III; Laurent, Thomas H.; Israelson, Spencer. 1981. Development of Sirococcus shoot blight following thinning in western hemlock regeneration. Res. Note PNW-RN-387. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 6 p