Heterobasidion annosum: Development of Butt Rot following Thinning in two young First Rotation Stands of Norway Spruce

Severe butt rot caused by Heterobasidion annosum (Fomes annosus)developed in two stands of first rotation Norway spruce on oldagricultural land within 11 years of first thinning. At SiteI (Devon), 11 per cent of thinning stumps and 23 per cent ofclear felled stumps were found to be decayed when examined soonafter the crop was felled at age 37 years. It is estimated thatbetween 4.4 per cent and 6.6 per cent of potential volume waslost on clear felling. Significant butt rot had also developedin a 33-year-old stand of Norway spruce in Site II (Aberdeenshire)11 years after a Scots pine nurse crop was removed. Here, thedisease was found to be widespread on an area of 2 ha, and 73per cent of trees had butt rot. Decay extended 3 m up the stems,and occupied significant areas of the butt. In both cases, thepresence of butt rot in the crops led to premature clear felling,which resulted in additional loss of potential revenue. It seems most likely that the disease became established followinginfection of thinning stumps by airborne spores of the fungus:at Site I, the thinning stumps were not protected whilst atSite II it would appear that a chemical or biological treatmentapplied to the pine stumps failed. The subsequent rapid developmentof the disease was due, in part, to a variety of environmentaland edaphic factors.