Infection of Sitka spruce stumps by spores of Heterobasidion annosum: control by means of urea

Abstract

Summary The ability of a 17 per cent solution of urea to protect Sitka spruce stumps against infection by spores of H. annosum was tested on 24 sites throughout Scotland and north England. After treatment, stumps were either inoculated with basidiospores or exposed to natural infection. Urea failed to reduce the incidence of infection arising from inoculation but it reduced the level of natural infection by two-thirds from a mean of 8.8 per cent to 3.5 per cent. In inoculated stumps that became infected, urea significantly increased the extent of colonization, particularly on peat soils, but this effect was not detected in naturally infected stumps. The fungus was largely confined to the heartwood and it is suggested that colonization may have been stimulated by the addition of nitrogen. It is concluded that urea provides an effective means of control against present ambient spore loads.