Oak wilt

Oak wilt is a disease affecting oak trees caused by the fungus Bretziella fagacearum (previously known as Ceratocystis fagacearum). Symptoms vary by tree species but generally consist of leaf discoloration, wilt, defoliation, and death. The fungus spreads from diseased to healthy trees overland by insect or other airborne vectors and underground by naturally grafted tree roots. Management of the disease historically meant preventing infection by not wounding oaks during certain time periods, removing diseased oaks that will produce spores (sanitation) and breaking root connections with vibratory plows, trenchers, rock saws or hoes. Present methods focus on reducing or eliminating monocultures and restoring ecosystems correctly using soils baseline information. Fungicides are used for preventive treatments in urban areas. Oak wilt is an important disease of oak for wood products and of shade trees in urban areas. Oak wilt is one of three devastating North American vascular wilt diseases and was first seen in Wisconsin in the 1940's. Within the last decade, it has spread into new counties northwest and northeast of the Twin Cities in Minnesota and also new locations in northeastern states. The other two vascular wilts and their destructive time periods are Chestnut Blight (1900-1950) https://en.wikipedia.org/wiki/Chestnut_blight and Dutch Elm Disease (1928 - 1980) https://en.wikipedia.org/wiki/Dutch_elm_disease . It is important to note that vascular wilts, including oak wilt, kill by fooling the tree into killing itself; the fungus or pathogen does not kill the tree or host. The tree's reaction-to fungus entering into sapwood, by walling off the fungus, causes shutdown of water supply upward, then wilting. Killing off the fungus doesn't get to the heart of the problem. Keeping the water supply open and flowing upward is the main problem. Certain elements like Boron are crucial to the trees' physiological well being, especially with translocation of fluids. Additionally, copper and chemotherapies have been used to keep the tree or plant from killing itself via wilting. Oak wilt infects and kills all oak species but affects the two main groups, red and white oaks, differently. Oaks in North and Central America are sorted into two groups based mostly upon the porosity and corresponding leaf shape. The white oak group have rounded leaf edges and the pores or water-conducting vessels in the wood (aka xylem or sapwood) are clogged with tyloses. The red oak group have pointed leaf edges and pores are large and open/not clogged. Because of this difference in porosity, red oak group trees die faster from oak wilt disease than white oak group trees. 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, known also as spore pads or pressure pads. Overland spread of oak wilt from white oaks is not a problem because white oak group trees rarely produce spore mats. When infected, oaks in the red oak group 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; oak wilt specialists call this stage II. Oaks in the white oak group (white, swamp white, bur) die slower when infected (white oak in particular) and can live for several years after infection, losing a few branches each season, from the top down. Bur oaks tend to die faster than others in the white oak group, although not as fast as trees in the red oak group. Symptoms in white oak are similar to those in red oak. Quercus virginiana, the southern live oak, is the most common of 31 species of evergreen - or live - oaks and is in the white oak group.