According to a report from the Swedish Forest Agency, two new forms of harmful fungal attacks have been identified on contorta pine in Sweden. A fungus called Diplodia, which has never before been found on contorta, has caused damage in a stand in Gävleborg, while another previously common fungus now suddenly appears to be causing damage.
- "After extensive analyses by SLU, it is now regrettable that we have identified new types of fungal infestations that attack and reduce the growth of the contorta pine. We need to understand more, but of course it is a concern because we need healthy and vital forests," says Nils Frank, forestry consultant at the Swedish Forest Agency's district in Gävleborg, where the infestation was discovered.
The contorta pine (Pinus contorta) is a species from North America that was introduced to Sweden in recent decades, mainly because it grows faster than the native pine. Earlier this year, damage was reported to a contorta stand north of Hudiksvall, near Gnarp. A new report from SLU, which investigated the infestation, shows that the fungus Diplodia was found on some of the affected trees, marking the first recorded infestation of Diplodia on contorta in Sweden.
The impact of the attack on growth
The disease inhibits tree growth and causes damage that prevents the development of high-quality timber. Since 2012, Diplodia has been identified in various parts of the country, from Skåne to Jämtland. In 2017, Diplodia damage was found in young pine stands in several places, and the fungal disease was then considered to be established in Sweden. Now the disease has also reached Norway spruce. The extent and implications of these findings now need to be further explored.
In addition, examination of the damage to the lot outside Hudiksvall has shown that the fungus Sydowia was also abundant on the trees. This fungus, which is quite common, now also seems to be able to damage the contorta pine.
The importance of Forest Diversity
- It is worrying that the trees seem to be damaged by Sydowia, as it is so widespread in our forests. We don't yet know whether it causes the damage alone or contributes to it," says Mr Frank.
The Swedish Forest Agency is now disseminating this information to the forest industry and other stakeholders, urging forest owners to regularly check their forests and also to maintain as diverse a forest as possible (adapted to the site) to increase resilience.
- From many points of view, it is wise for forest owners not to put all their eggs in one basket, but to vary the forest and plant the trees where they thrive best. This way we get strong forests that grow well and are better equipped against various attacks and damage," adds Nils Frank.
Fact box: Diplodia
- Diplodia is a fungal disease that affects pine trees, including contorta pine.
- The disease disrupts the growth of the tree and hinders its development into a high-quality forest.
- Diplodia was first discovered in Sweden in 2016 and is now considered established.
- The first case of contorta pine was recorded in 2023 in Gävleborg County.
- The disease can be confused with Dutch elm disease because of similar symptoms, such as brown annual shoots on young pine.
- Diversified forest stands and stand adaptation of tree species increase resistance to pests.
- If the disease is confirmed, it is recommended that the most affected trees be removed.
- During the shooting of the trees, when the spores spread the most, no action should be taken.
- Well-grown pines that are given space and sun can heal from Diplodia's damage through proper clearing.
- If Diplodia is suspected, it is recommended to contact a claims coordinator for advice and confirmation of the disease.
