Heterobasidion annosum infection of Picea abiles following manual or mechanized stump treatment

Heterobasidion annosum (Fr.) Bref. s. 1. colonization following thinning was studied in 1246 stumps of Picea abies (L.) Karst. trees from 14 previously unthinned stands in Sweden. Treatments included mechanized and manual application of (1) 35% urea solution, (2) Phlebiopsis gigantea (Fr.) Jul. spores, and (3) 5% solution of disodium octaborate tetrahydrate (DOT), and untreated stumps, cut in the summer and winter. Compared with untreated stumps cut in the summer, all stump treatments and winter cuttings significantly reduced the colonized stump area 6-7 weeks after thinning by 88-99%. Mechanized stump treatment provided as good protection as manual treatment against H. annosum infections. The probability of spore infection (p(ij)) was reduced by 53-83% in mechanized treatment and 79-98% in manual treatment compared with untreated summer thinning. In terms of p(ij), urea had significantly higher control efficacy than P. gigantea and manual treatment performed better than mechanized treatment.