|
Oak wilt is a fungal disease that can quickly kill an oak tree. It is caused by the fungus ''Ceratocystis fagacearum''. Symptoms vary by tree species but generally consist of leaf discoloration, wilt, defoliation, and death. The fungus is spread from diseased to healthy trees by insect vectors or via connections between tree roots. Management of the disease consists mainly of preventing infection by avoiding tree wounds, removing diseased trees and digging trenches that disrupt root connections. Fungicide treatments are available and are mostly preventive as well. Oak wilt is an important disease of oak for timber production and of oak trees in urban areas. ==Hosts and symptoms== Oak wilt affects all oak species, but affects the two main groups differently. Oaks in North and Central America are sorted into two groups based mostly upon cell structure and corresponding leaf shape. The white oak group are diffuse-porous hardwoods and have rounded leaf edges. The red oak group are ring-porous hardwoods and have pointed leaf edges. Ring porous (red oak group) oaks die faster - from oak wilt disease - than diffuse porous oaks. Common names of oaks are based upon common folklore or customs, which leads-to black oaks being in the red oak group. In the upper midwest, red oak group trees like black, northern red and northern pin are most threatened-by oak wilt for two reasons: they die faster and they produce spore mats. White oak group trees rarely produce spore mats, so overland spread of oak wilt from white oaks is not a problem. Oaks in the red oak group (''pointed leaf edges'') are particularly susceptible and, when infected, generally die over the course of a single summer. These oaks typically die from the top of the tree down as leaves become a bronze color and fall off the tree. Another symptom is discoloration of the vascular tissues. Brown streaks or spots can be seen under the bark in the sapwood. Oaks in the white oak group (white, swamp white, bur and others with ''rounded leaf edges'') are somewhat less susceptible when infected (white oak in particular) and can live for several years after infection, losing a few branches each season, from the top down. Some oaks in the white oak group, such as bur oak, are more susceptible than others, although not as susceptible as red oaks. Symptoms in white oak are similar to those in red oak. Oaks with oak wilt stand out with their dead crowns compared to a green canopy in the summer, so much so that oak wilt infections can be spotted from the air. Northern pin oak (''Q. ellipsoidalis'') susceptibility is extreme when monocultures exist. Northern pin oak forests are typically found on entisol soils (aka barren sands or lakebed sands) in Wisconsin and Minnesota, and these forests are often misidentified as oak savanna. Mistaking northern pin oak forest monocultures for oak savanna, then burning them for oak savanna restoration, has made state and federal lands north of Minneapolis-St Paul the largest oak wilt disease reservoirs in Minnesota.〔Nelson, Steven (2011). ''Savanna Soils of Minnesota.'' Minnesota: Self. pp. 21-22,29-30. ISBN 978-0-615-50320-2.〕 See: https://commons.wikimedia.org/wiki/File:Cedar_Creek_2007_Oak_With_County_Line_Wiki_Version.jpg 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oak wilt」の詳細全文を読む スポンサード リンク
|