The Oak Wilt fungus is spread via two ways: above ground and below ground. The above ground movement is facilitated by a sap-feeding beetle that carries the fungal spores to new trees. The below ground movement occurs when the fungus travels from tree to tree through interconnected roots.
Establishment of New Infections
Red oaks play a key role in the establishment of new infection centers. The oak wilt fungus is spread overland by insect vectors and by humans through movement of wood from infected red oaks to other locations.
Fungal mats form beneath the bark of certain diseased red oaks in spring, but do not form on white or live oaks. Individual fungal mats produce spores for only a few weeks. The fruity odor of fungal mats attracts many kinds of insects, the most important of which are sap-feeding nitidulid beetles. The fungus is transmitted by these small beetles as they emerge from mats and visit fresh wounds on healthy oaks. Fungal mats are most commonly formed on standing trees, but they also can develop on logs, stumps, and fresh firewood cut from diseased red oaks.
Spread through Roots
Live oaks tend to grow in large, dense groups (called motts) with interconnected roots. The fungus is transmitted from one tree to another through these root connections. As a result, patches of dead and dying trees (infection centers) are formed. Infection centers among live oaks in Texas expand at an average rate of 75 ft per year, varying from no spread to 150 ft in any one direction. Occasionally, the oak wilt fungus is transmitted through connected roots between other oak species, called grafted roots, but movement through grafted roots is slower and occurs over shorter distances than in live oaks.