The biocontrol efficacy of Chondrostereum purpureum is not sensitive to prevailing environmental conditions in boreal forests

Abstract

Sprouting of deciduous trees is problematic in forest regeneration areas, alongside roads and railways, under electric power lines and above gas pipe lines. A decay fungus Chondrostereum purpureum is a potential biocontrol agent against sprouting of deciduous trees. However, before this method can be utilized in practice, the effects of environmental factors on the efficacy of the fungus, i.e., its ability to cause stump mortality, should be understood. Thus, in this study, the effects of environmental factors on the efficacy of C. purpureum in controlling birch stump sprouting were investigated. Fungal inoculum was spread on 342 freshly cut birch (Betula pendula and B. pubescens) stumps at 17 sites, which were thereafter used to investigate the effects of solar radiation, temperature, precipitation, and soil properties on the efficacy of C. purpureum treatment. In the control plots, 318 birches were cut but no fungal inoculum was spread on their freshly cut stumps. The results revealed that solar radiation had no effect on the mortality of treated birch stumps, but an increasing proportion of hot days after the fungal treatment and an increase in precipitation within one week prior to the treatment reduced the mortality rate of stumps by the end of the first growing season following stump treatment. Furthermore, an increase in precipitation after the treatment and high soil moisture were also related to an increase in stump mortality. However, these effects were only temporary as by the end of the second growing season only precipitation that has occurred prior to the treatment had slight effect on birch stump mortality, while other investigated environmental conditions, i.e., proportion of hot days, amount of precipitation after the treatment and soil moisture, had no effect. Furthermore, application of the fungal inoculum immediately after cutting was essential for efficient sprout control. Even a delay of 15–30 min has significantly reduced stump mortality rates. Taken together, this study revealed that the presented method of biological stump sprouting control is not very sensitive to the investigated environmental conditions, suggesting that it can be used also during hot and rainy periods as long as requirement for a minimal delay between the cutting of trees and stump treatment is considered.