Efficacy of Phlebiopsis gigantea treatment on spore infections of Heterobasidion spp. on Larix X eurolepis

Abstract: The effectiveness of Phlebiopsis gigantea to prevent spore infections from Heterobasidionannosum and Heterobasidion parviporum on hybrid larch stumps were investigated in fivestands in southern Sweden. All sites are former forest land and the age of the trees wasbetween 9 and 13 years.The study was implemented in August 2010, a month where spore dispersal should be great.The five sites were located in previously un‐thinned monocultures of hybrid larch. The sporeload in the air was studied with the help of spore traps from three different tree species;Norway spruce, Scots pine and hybrid larch. A total of 146 spore traps, evenly distributed inall five sites were analyzed. The spore traps were exposed for three hours then brought backto the laboratory for incubation and analysis. The hybrid larch trees were randomly selected,cut down and every second stump was treated with Rotstop® S and the others were left ascontrols. No visible signs of infections were discovered. Roughly 60 days after felling andtreatment, disc samples were collected for further analysis in lab.The study indicates an abundant amount of basidiospores of Heterobasidion spp. in the air.63,7 % of all spore traps was infected with Heterobasidion spp. Most infections were foundin Södra Rörum II, with 83 % infected spore traps. Out of 263 colonies, 61,2 % of theisolations were infections of H. annosum and 38,8 % were H. parviporum. Scots pine andhybrid larch were most attacked by H. annosum whilst Norway spruce was equally attackedby H. annosum and H. parviporum. The mean percentage of infected stumps for all five sitesper tree species was; larch 52 %, Norway spruce 58 % and Scots pine 72 %.A total of 176 hybrid larch stumps were analyzed and 20 % were infected by Heterobasidionspp. Both H. annosum and H. parviporum were isolated from the hybrid larch stumps. 60 %of the isolations were H. parviporum and 40 % were H. annosum. Highest infection rate wasfound in Fulltofta and Klippan where 24 % of the stumps were infected.There is a significant difference of infection rate and infected area between treated stumpsand un‐treated control stumps, where p < 0,000 and p < 0,024 respectively. This resultmakes Rotstop® S an interesting stump treatment alternative also on hybrid larch.