The pine weevil is the single biggest threat to newly planted spruce and pine in southern Sweden. On an untreated clearing it can kill more than half of the plants during the first two seasons. The good news is that most of the damage can be avoided with the right combination of plant treatment, soil preparation and timing.
In this guide we go through how to recognise pine weevil damage, when the attacks are at their worst, how to protect your plants and how to plan the planting so that the risk is kept down.
What is the pine weevil?
The pine weevil (Hylobius abietis) is a brownish black beetle about 8 to 14 mm long with lighter, yellowish patches across the wing cases. The adult beetle chews away bark on the lower part of the stem of young conifer plants. When the chewing goes right around the stem, the plant is girdled and dies.
The pine weevil is especially fond of fresh clearings. The scent from newly felled spruce stumps and leftover slash attracts the females, which lay their eggs in the root system. The adult beetles that later hatch can stay in the area and continue to damage plants for several years.
How to recognise pine weevil damage
The damage usually appears during the plant’s first two seasons. Go through newly planted areas several times during spring and summer, especially in the first years after felling.
Early signs, you can often still save the plant
- Light chewing wounds. Small, irregular wounds on the lower part of the stem where the beetle has chewed off the bark. Fresh, light coloured wood is often visible underneath.
- Resin flow at the wounds. The plant defends itself by releasing resin at the wound edges.
- The beetles themselves. Adult beetles can sit at the base of the plant or on the ground nearby, particularly at dusk and dawn.
Later signs, the plant is often lost
- Girdled stem. The chewing has gone right around the stem and the plant no longer gets nutrients up to the crown.
- Wilting, brown needles. The plant loses colour and dries out, usually during the summer.
- Dead plant. When the whole plant is dry and grey it has stopped living and usually needs to be replaced.
When is the pine weevil most active?
The pine weevil is active from late spring to early autumn. Attacks are especially heavy during the plants’ first two seasons on the clearing. The greatest risk is on areas that were felled one to three years ago, when the attractive scent from stumps coincides with a large local population. After four to five years the problem usually fades on its own, as the stumps stop giving off scent and the beetles seek out newer clearings.
How to protect your plants
- Choose the right plant treatment. Modern plant treatment places a mechanical or chemical shield around the lower part of the stem and is the single most important measure against the pine weevil. Read more about chemical and mechanical plant protection and why plant treatment is a must.
- Prepare the soil properly. Planting in clean mineral soil increases the plant’s resilience considerably. A patch of mineral soil around the plant makes it harder for the pine weevil to reach the stem. See our page on soil preparation.
- Use larger plants. Bigger, sturdier plants with a lignified stem cope better than small, weak ones. The right plant choice for the site is therefore a key part of the protection.
- Time the planting. Waiting one to two seasons after felling before you plant reduces the worst attack pressure. Read more about the right timing for planting.
- Follow up and beat up. Go out on the clearing during the first and second summer, check the plants’ condition and beat up where losses are heavy.
Combine measures for the best protection
No single measure carries the whole load. It is the combination of good plant treatment, thorough soil preparation, sturdy plants and thoughtful timing that gives you the low mortality you need to avoid expensive beat up planting. The better the foundation you lay at planting, the less work you get during the follow up years.
Frequently asked questions about the pine weevil
How do I know if the plant is attacked by the pine weevil?
Look for light chewing wounds with resin flow on the lower part of the stem. If the damage goes right around the stem the plant is usually lost. On fresh clearings you should check the plants during the first and second summer.
Is plant treatment enough on its own?
Plant treatment is the most important measure but works best in combination with proper soil preparation and sturdy plants. Together they give considerably lower mortality than any single measure on its own.
Is the pine weevil a problem here in southern Sweden?
Yes, the pine weevil is one of the biggest threats to regeneration across the whole of Götaland. On an untreated fresh clearing the mortality can be very high if plants are set without protection.
Need help protecting your plants?
Grimslövs Skogstjänst helps forest owners in southern Sweden with the entire chain from soil preparation and plant treatment to planting and follow up, so that your new plants get the best possible protection against the pine weevil. Request a free quote or contact us and we will plan a protection strategy that fits your property.
