Spruce and pine is normally in focus when assessing pine weevil damage. Preliminary results by PhD student Sezer Olivia Kaya however show that planted birch seedlings are also affected by weevils, although the damage is often less severe than on conifers.
After the first growing season PhD student Sezer Olivia Kaya and supervisor Michelle Cleary, both enrolled with Trees For Me and the Southern Swedish Forest Research Centre at SLU in Alnarp, have, together with Gudmund Vollbrecht, coordinator within Trees For Me and at SLU’s Unit for Field-based Forest Research, identified Hylobius abietis and Hylobius pinastri (both snytbagge) as well as Strophosoma melanogrammum (ögonvivel) and Otiorhynchus scaber (öronvivel) as the most common species encountered causing damage to newly planted birch.
Several weevils found
While the pine weevils Hylobius abietis and Hylobius pinastri primarily cause damage to the bark by girdling the trees, other weevils found on the planted birch seedlings show more interest in the leaves.
Strophosoma melanogrammum feeding on birch leaf. Photo: Sezer Olivia Kaya
“Strophosoma melanogrammum and Otiorhynchus scaber primarily cause damage to the leaves. While this type of damage usually does not result in mortality, it can affect seedling growth and the overall quality of development”, Sezer Olivia Kaya explains.
Age of clearcut less important
The researchers compared the weevil damage on newly planted birch seedlings in fresh clear-cut sites to seedlings in one-year-old clear-cut sites.
“The assessment in 2024 revealed no significant difference in seedling mortality between fresh and one-year-old clear-cut sites, indicating that the age of the clear-cut did not influence seedling survival on the year of planting”, says Sezer Olivia Kaya.
Mortality and treatment
Previous studies have highlighted that while pine weevils cause significant damage to pine and spruce trees, leading to mortality rates as high as 80-90 % due to bark feeding, their impact on birch is comparatively lower. However, according to the researchers it is not well understood how much damage pine weevils actually cause on birch.
“Birch seedlings treated with the pine weevil treatment Hylonox exhibited significantly lower mortality compared to untreated seedlings (2 % vs. 16 %) which demonstrates the effectiveness of the treatment in reducing damage on the year of planting the seedlings”, Sezer Olivia Kaya says.
Future focus
In 2025, the researchers will continue to follow the experiment in Tönnersjöheden’s experimental forest outside of Halmstad, to examine how the incidence and severity of damage changes in the second year, if seedlings show signs of recovery, and whether the treatment remains as effective as it was in the first year.
The researchers also look to scale up the research from the pilot project in Tönnersjöheden to several locations to be able to assess the incidence, severity and expected impact of weevil damage but across Sweden. They will also compare the damage with Norway spruce, Scots pine and larch to study differences between the species and if and how they recover after being damaged.