Root rot caused by Heterobasidion spp. is one of the most important pathogens in Norway spruce (Picea abies (L.) Karst.) stands in Latvia. It is estimated that in Latvia on average 22.9% of Norway spruce stumps are infected with Heterobasidion spp. The aim of this study was to compare four different electronic devices for Heterobasidion root rot detection in Norway spruce. In the autumn of 2009, in a sample plot located in the forests of Kalsnava district 27 trees were used to compare the possibility of instruments to detect root rot. The results show that IML-RESI F400 accuracy for detecting root rot in Norway spruce is high and the instrument is usable for detecting root rot, but additional accumulators are needed for large sample plots. Rotfinder’s accuracy for detecting root rot varies from probe to probe taken from one tree. Conditiometer AS-1 and Arbo-Sonic decay detector show slightly higher average values for infected trees, but the difference for both instruments between healthy and decayed trees is not significant, thus leaving the usage of instruments questionable.

Heterobasidion spp. is an important pathogen in the Northern Hemisphere, causing root and butt rot mainly in conifers. Norway spruce (Picea abies (L.) Karst.) is one of the most common tree species infected by Heterobasidion spp. In Latvia, 22.9% of Norway spruce stumps are infected. Heterobasidion spp. decreases timber quality, but what impact it has on Norway spruce growing in understory of dominant stand is not known. The aim of the study was to evaluate incidence of Heterobasidion spp. on understory Norway spruce in Myrtillosa forest type and impact on radial growth of trees. In autumn of the year 2011 in a sample plot located in forests of Kalsnava district a total number of 258 trees were examined for presence of Heterobasidion spp. Results showed that 54% of examined trees were rotted. In 30% of trees Heterobasidion spp. was detected. It is concluded that Heterobasidion spp. does not impact radial growth on understory Norway spruce trees.

The biological control agent Rotstop, composed of spores of Phlebiopsis gigantea, is used for treatment of conifer stumps to reduce the spread of Heterobasidion root rot in commercial forests. Two experiments were conducted to compare the antagonistic ability of the Rotstop isolate and nine Latvian isolates of P. gigantea against root rot fungus Heterobasidion, in wood of Scots pine and Norway spruce. Billets of conifer trees were first sprayed with a spore suspension of P. gigantea and then with Heterobasidion at different concentrations. The presence of fungi in billets was evaluated by morphological characteristics of mycelium. The Latvian isolates of P. gigantea showed similar or even higher values of efficacy against Heterobasidion (average efficacy 84% in spruce and 89% in pine) than the commercially manufactured Finnish preparation Rotstop (61% in spruce and 90% in pine). Latvian isolates of P. gigantea have a potential to be used for preparation of biological control agents in the future.