Oak wilt

Oak wilt
Aerial photograph of an oak wilt center (St. Paul, MN). Robert L. Anderson, USDA Forest Service, Bugwood.org
Causal agents	Ceratocystis fagacearum
Hosts	oaks
Symptoms	leaf discoloration, wilt, defoliation and death

Oak wilt is a fungal disease affecting oak trees caused by the fungus 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 from insects or by connections between tree roots. Management of the disease historically meant preventing infection by avoiding tree wounds, removing diseased trees and breaking root connections with vibratory plows, trenchers/rocksaws or hoes. Present methods focus on the area of monocultures and restoring correct ecosystems using soils. Fungicide treatments, used in urban areas, are available and are mostly preventative as well. Oak wilt is an important disease of oak for timber production and of oak trees in urban areas.

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 porosity and corresponding leaf shape. The white oak group have rounded leaf edges and the pores 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. 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 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) 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.