Oak Decline Syndrome in Korean Forests: History, Biology, and Prospects for Korean Oak Wilt

Abstract

Oak decline syndrome has been observed in South Korea and Japan and variously referred to as Korean oak wilt (KOW) and Japanese oak wilt (JOW). We reviewed aspects of the historical occurrence of KOW, disease cycle, and its potential causes. KOW has been seen principally in Mongolian oak (Quercus mongolica Fisch. ex Ledeb.). The first occurrence of KOW was in 2004 in Seongnam, South Korea. KOW is associated with the fungus Raffaelea quercus-mongolicae, which is vectored by the ambrosia beetle Platypus koryoensis. In addition, it has been suggested that yeasts have evolved a symbiotic relationship with the vector without antagonism for the pathogenic fungus. The number of trees in Korea killed by KOW increased to about 331,000 in 2011, but then decreased to about 157,000 in 2019. We hypothesized that trees infected by R. quercus-mongolicae accumulate phenolic compounds in the sapwood and the vector (P. koryoensis) beetles then avoid these trees. Therefore, the number of hosts available for the beetle after a KOW outbreak decrease due to accumulation of phenolic compounds in the wood, although most oak trees survive outbreaks. Therefore, P. koryoensis beetles move longer distances after outbreaks to find susceptible host trees. Novel occurrence of KOW in Korea may be due to either (1) an increase in tree age (size) in Korean oak stands, for which the beetle has a known preference or (2) climate change, which may be increasing the number of weakened or stressed trees, for which P. koryoensis also shows a preference.

Management of Forest Pests and Diseases

“…Fifteen papers are included in this issue, focusing on the monitoring and management of forest pests: Choi, et al [10] reviews Korean Oak wilt (KOW) (a new syndrome of oak decline in Korea) and describes its cause, distribution, history, disease cycle, and management. An increase in the number of stressed trees among the potential hosts of KOW has been the major cause of KOW in Korea due to an increase in the average age of trees in oak stands, as well as some effect of climate change.…”

Comparative Analysis of Secondary Metabolites in Diplodia corticola Strains with Different Virulence Degrees Associated with Canker and Dieback of Quercus spp.

“…In the last few decades, oak forests have been seriously affected by decline phenomena, causing global and local concerns. In fact, many studies describe the poor health of oak trees in many forests of the world [2][3][4][5][6][7][8][9]. The oak dieback or decline can be caused by a range of factors, including extreme climatic events, insects, and pathogenic fungi [10][11][12][13].…”

First record of two ambrosia beetle, Platypus quercivorus (Murayama) and Platypus koryoensis (Murayama) (Coleoptera: Curculionidae, Platypodinae) in Mainland China

“…Platypus koryoensis is the vector of Dryadomyces quercus-mongolicae (formerly Raffaelea quercus-mongolicae) which causes Korean oak wilt (KOW) (Kim et al 2009;De Beer et al 2022). The disease occurs mainly on Quercus mongolica and has mass killed mass oak species in Korea (Choi et al 2022). Its geographical distribution includes Korea and the Russian Far East (Beaver & Shih 2003;Hong et al 2006).…”