Birch Trees Beset by Bugs

Scolioneura betuleti sawfly larvae in birch leaf.

Birch trees in the Reykjavík capital area are struggling following two waves of pests this spring and summer. While the trees made a comeback after moth larvae ate their way through new growth in the spring, they were soon beset by another hungry creature. Sawfly larvae, first spotted in Iceland in 2017, have done a number on local birch this summer, leaving behind brown leaves on many trees in the capital area.

“Many have noticed that the birch trees in our gardens are not doing well,” a press release from the Icelandic Institute of Natural History reads. According to the press release, Eriocrania unimaculella, moth larvae that mine birch leaves, ravaged the trees this spring. “In the short term, the trees managed to regain their foliage,” the release continues, “but a new pest has emerged which is greying the new leaves.”

The new pest is the larvae of the Scolioneura betuleti sawfly. The larvae was first spotted in Iceland in 2017, though it is not known when it first arrived in the country. Experts had noticed, however, damage to birch trees in late summer for several years prior which was similar to moth larvae damage in the spring. It was hypothesised that a second generation of moth larvae was to blame, but it has now been established that sawfly larvae is the culprit.

Scolioneura betuleti larvae behave similarly to Eriocrania unimaculella larvae, though they are not related. The sawfly lays its eggs in birch leaves in midsummer. Larvae live in and eat the leaf tissue, which is known as “mining” the leaves. The pests’ one-two punch can make it difficult for birch to grow healthy foliage all summer, “which will probably reduce the growth of the trees, seed ripening, and necessary preparation for the winter months.”

According to experts, green alder shrubs (Alnus viridis), a relative of birch common in Reykjavík gardens, may also be at risk from the Scolioneura betuleti larvae.

Wind Carries European Birch Pollen to Iceland

Pollen from birch trees in Europe and as far away as Russia reached Iceland last week. RÚV reports that the pollen was carried along with dust from the Sahara Desert on strong winds that originated in Eastern Europe. Much of the dust and pollen settled over the Mediterranean Sea, but a measurable quantity made the journey all the way to Iceland.

On April 25, the First Day of Summer in Iceland, a fair amount of the Saharan dust and a great deal of European pollen was caught in traps placed by the Icelandic Institute of Natural History in the municipality of Garðabær in the capital area and in Akureyri in North Iceland. According to an announcement on its website, the institute has only measured a higher pollen count twice since it began taking such measurements, that is in May 2006 and April 2014.

There was a veritable explosion of vegetation blooming over the last week in both North and South Iceland, although particularly around Akureyri. It’s expected then that there will be high levels of birch pollen circulating in the coming weeks, which may cause difficulties for people with pollen allergies.