The severity of Sirococcus shoot blight in mature Norway spruce stands with regard to tree nutrition, topography and stand age

Abstract

In this study the impact of tree nutrition, topography and stand age upon incidence and severity of Sirococcus shoot blight was evaluated in a research area located in the Kobernaußerwald in Upper Austria. Investigations were carried out in uniform, even aged mature Norway spruce stands that were severely affected with Sirococcus conigenus. The impact of tree nutrition on the severity of Sirococcus shoot blight was tested in a fertilization experiment. Results indicated that disturbances in tree nutrition, especially lack of magnesium and calcium coupled with enhanced N/Mg and N/Ca ratios—increased susceptibility of mature Norway spruce to Sirococcus shoot blight. Furthermore, there were striking differences concerning Ca and Mg contents in green needles between trees on the fertilized and the control plot. Nutrient deficiencies were also found on non-affected unfertilized trees but nutrition was most unfavorable for Sirococcus damaged trees on the control plot. The application of a magnesite derived fertilizer amended with organic compounds balanced tree nutrition and mitigated severity of Sirococcus shoot blight. Terrestrial inventories indicated that intensity of the disease was highest on west exposed upper slopes as well as on hilltops. Stands of different age classes were severely affected by the disease.