Oak Wilt - Hosts and Symptoms

Hosts and Symptoms

Oak wilt affects all oak species, but affects different groups differently. Oaks in the red oak group (black, northern red, northern pin and others with pointed leaf edges) are particularly susceptible and, when infected, generally die over the course of a single summer. Infected red oak wilt 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, Nebraska 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.

Live oak susceptibility is somewhat variable depending on environmental conditions but wilt and death usually occur within six months of infection. Live oak foliar symptoms differ from those of red and white oak. Infected live oak leaves develop chlorotic veins that eventually turn necrotic before falling off the tree.