The recent dry and warm climate has favoured the spruce bark beetle, which has now started to swarm in a serious way and is now attacking trees even in the northern parts of the country, especially along the Norrland coast. This is shown by the Swedish Forest Agency's monitoring of swarming.
During the summer, the Swedish Forest Agency empties spruce bark beetle traps every week across large parts of the country to monitor insect damage activity. The number of spruce bark beetles in the traps now indicates that swarms are also starting in the northern parts of the country.
- "During the last week we have seen large catches in all traps along the Norrland coast with records of about 7000 spruce bark beetles in the traps in Gävleborg, Västernorrland and Västerbotten. This indicates that the spruce bark beetles are now flying to find suitable spruces to breed in - spruces that will die from these infestations," says Mattias Sparf, spruce bark beetle expert at the Swedish Forest Agency.
In recent years, it is mainly the southern and central parts of Sweden that have been affected by extensive spruce bark beetle infestations. But last year we also saw infestations further north, for example in Gävleborg, which is probably due to increasing temperatures and decreasing rainfall.
- The spruce bark beetle thrives in dry and warm climates. This weakens the spruce trees and makes it difficult for them to defend themselves, while also favouring spruce bark beetle reproduction. If the dry weather continues in the northern parts of the country, we risk increased damage here too," explains Mattias Sparf.
An important measure to prevent infestation of standing trees is to take care of spruce trees that have been blown down or damaged by snow during the winter, as otherwise the spruce bark beetles can multiply massively there.
Since the extremely dry summer of 2018, it is estimated that around 32 million cubic metres of spruce, valued at around SEK 14 billion, have been killed by the spruce bark beetle.
Signs that a spruce has been attacked
Early spruce bark beetle infestations can be difficult to detect because the spruce still looks healthy from a distance. But one to two weeks after swarming has started, brown borer meal can be seen up close around the base of the tree, in bark pockets and in spider webs. After rain, however, it is more difficult to see the borers because they may have been washed away. Small entrance holes in the bark where the spruce bark beetle has bored in. Green needles on the ground around the spruce (usually later in the summer). Forest owners are advised to check their forests regularly and look for these signs at least every four weeks until the end of August. The risk of new infestations is highest in sunny locations and where there have been infestations in previous years.
Source: Swedish Forest Agency
