Prevention of Oak Mortality by Wrapping Trunks With Vinyl Sheeting

27 Mar Prevention of Oak Mortality by Wrapping Trunks With Vinyl Sheeting

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Abstract

1980年以降, 口本海側の各地においてカシノナガキクイムシの穿入を受けたナラ類の集団枯損が拡大し, 問題となっている。被害発生地において, ナラ類の枯死を防ぐために幹をビニールシートおよび麻布で被覆する実験を行った結果, 枯損率は低下したものの無処理木と有意差は認められなかった。次に, 被害拡大を阻止する目的で, 林分内のすべての穿入木をビニールシートで被覆する実験を行った。しかし, 無被害木の被害発生は阻止できなかった。ビニールシートを被覆した穿入木を割材して, 生存虫数の調査とナラ類病原性未同定菌の分離調査を行った。その結果, 74%の虫が生存し, ほとんどの材片から菌が分離されたことから, 殺虫と殺菌の効果は低いと考えられた。しかし, ビニールシート被覆木からの羽化脱出虫の捕獲調査で, わずかの成虫しか捕獲できなかったことから, 羽化脱出防止効果は認められた。また, 樹皮へのクレオソート塗布により, カシノナガキクイムシの穿入を回避できることが示唆された。

English Abstract

Since 1980, mass mortality of oak trees (Querucus serrata and Q. crispula) caused by boring by the beetle Platypus quercivorus has become a serious problem in districts along the Japan Sea. We wrapped oak trunks with vinyl sheeting or linen cloth to protect the trees from dieback in a damaged forest. The results showed that the mortality of oak trees which had been wrapped with vinyl sheeting declined, but the mortality compared with untreated oak trees was not significantly different. To stop the damage spreading to undamaged trees, all trees that had been bored by the beetle were wrapped with vinyl sheeting, yet damage to undamaged trees was not prevented. We counted the number of beetles living in the trunk of a damaged oak tree which had been wrapped with vinyl sheeting, and isolated an unidentified oak pathogenic fungus from the tree to investigate its effects on the beetles and the fungus in the oak trunk. However, both effects were found to be small, because 74% of the beetles lived in the oak trunk and the fungus was isolated from most of the wood fragments of the trunk. We also collected beetles that emerged from oak trees which had been wrapped with vinyl sheeting to investigate the effect of the sheeting on preventing the emergence of the beetle. Because few beetles were collected, it was clarified that the sheeting was effective for preventing the emergence. Moreover, it was also suggested that painting the bark with creosote oil prevented the beetle’s attack.