Stealthy damage threatens to destroy European conifer stands from the inside

To combat fungal diseases caused by Heterobasidion species, urgent action by decision-makers is needed: the fungi are a threat to European forestry and are already causing a significant loss of revenue.
Decision-makers should awaken to the need to fight the Heterobasidion fungi threatening pine and spruce stands.
’If we want to stop the spread of the Heterobasidion fungi, the EU and national governments should start thinking about regulation and aid measures in short order,’ says Lauri Lappalainen at Lallemand Plant Care, a company that manufactures a biological fungicide to combat Heterobasidion.
Heterobasidion species cause several diseases, primarily in pine, spruce and fir: butt rot, heart rot and Heterobasidion root disease. The annual financial loss caused by these in Europe comes up to EUR 800 million. In Finland, the figure is EUR 50 to 80 million.
If we want to stop the spread of the Heterobasidion fungi, the EU and national governments should start thinking about regulation and aid measures in short order.
The prevention of Heterobasidion should always be included in harvesting operations, yet it is often neglected for financial reasons and because the damage is slow to appear.
Information to forest owners should also be ensured. Heterobasidion can be combated by treating the tops of stumps with a biological fungicide or a urea solution. If stumps are left untreated, the fungus will spread into the root system and then on to adjacent healthy trees.
Heterobasidion is the worst plague of forests
The principal Finnish daily Helsingin Sanomat has called Heterobasidion an even worse plague of commercial forests than the bark beetles. Heterobasidion decays the roots and stem of spruce and pine, often to a height of several metres. In particular, it destroys valuable butt logs, but it may take decades for the damage to be revealed.
’Damage that only becomes visible some time in the future is not something that anyone is necessarily interested in treating right now,’ Lappalainen says.
Diseased trees are less capable of binding carbon dioxide, which is detrimental to combating climate change.

Heterobasidion also decreases the availability of raw material for the forest industry. In addition, decaying trees are more vulnerable to storm and insect damage. Last year, a Finnish study showed that three out of four trees plagued by Heterobasidion were infested with bark beetles.
Here’s how to fight Heterobasidion
In Finland, trees can be attacked by two different species: Heterobasidion parviporum, which specializes in Norway spruce, and Heterobasidion annosum, which mainly decays the roots of Scots pine. Both of these can also attack other tree species, but broadleaved trees are more resistant to them.
Having once arrived on a site, Heterobasidion will contaminate it for decades to come.
According to Natural Resources Institute Finland, ensuring the prevention of Heterobasidion is an investment in tree growth and future harvesting potential.
The best way to prevent Heterobasidion is to schedule fellings for the below-zero season, when the fungus produces no spores. Within the European Union, this is generally only possible in the northern parts of Finland and Sweden.

The second-best option, for harvesting in warmer weather, is to protect the exposed top surface of stumps with a fungicide.
An effective method is to use a biological fungicide containing spores of the Phlebiopsis gigantea fungus, a natural competitor of Heterobasidion. During harvesting, the exposed top surfaces of stumps are treated with the fungicide.
Finnish legislation requires that from the spring season until late autumn, Heterobasidion is prevented in all harvesting operations in conifer-dominated forests within a specified risk zone. Elsewhere in Europe the situation is less favourable.
In the Baltic republics and Poland, Heterobasidion is practically only prevented in forests owned by the state.
’If sufficient effort is not put into controlling root rot, future tree generations will suffer from increasingly severe decay, jeopardizing the future of conifer cultivation’ says Lappalainen.
Another way to combat Heterobasidion is to use specially bred seedlings. Swedish and Finnish researchers have observed that certain strains of spruce are resistant to the spread of Heterobasidion.
In these trees, the spreading of Heterobasidion was slowed down by up to 27 percent by allele B of the PaLAR3 gene. Using seedlings with this allele will bring a substantial benefit to the forest owner when the trees are felled, as valuable butt logs will be undamaged. However, the allele is not a protection against actual contamination.
Sources: Natural Resources Institute Finland, Tapio, Helsingin Sanomat, Verde/Lallemand Finland
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