Abstract
Japanese oak wilt, which is caused by the ascomycetous fungus Dryadomyces quercivorus and its vector, the ambrosia beetle Platypus quercivorus, has been spreading across Japan, resulting in massive mortality of Quercus crispula on Honshu Island. However, there have been no recorded cases of Japanese oak wilt in Hokkaido, the northernmost island of Japan. In 2023, field surveys were conducted at five locations in Matsumae and Fukushima, situated at the southern edge of Hokkaido. The surveys revealed 10 damaged trees (16 damaged stems), attacked by P. quercivorus. The damaged trees were identified as Q. crispula. Dryadomyces quercivorus was isolated from the entry holes of P. quercivorus in two damaged trees. The number of entry holes in the nine dead trees ranged from 1 to 17, with many holes located near the ground. The number and density of entry holes in dead trees were higher than those in surviving trees. The number of entry holes was greater in damaged trees with larger basal area at breast height. However, damaged trees were not necessarily larger than surrounding undamaged trees when comparing their diameters at breast height. The characteristics of the first Japanese oak wilt damage in Hokkaido were consistent with previous studies in Honshu in that the number of entry holes was greater in dead trees than in surviving trees. However, there were some characteristics different from those of Japanese oak wilt in Honshu, such as the death of trees with few holes and attacks on trees other than large diameter trees.
