Spread

• To treat oak wilt, one must understand how it spreads. This occurs in one of two ways, either locally, through the tree's underground root system, or long distance, via overland spread. Underground transmission occurs when one tree in a close group of oaks with interconnected roots becomes infected. The fungus then spreads from that tree to the rest of the nearby trees via the interconnected roots. Overland spread happens when a sap-feeding insect, such as the Nitidulid beetle, eats from an infected tree and then carries fungal spores to a healthy tree on which it feeds.
  
  

Diagnosis

• Because it can be mistaken for other diseases and even infestation with certain insects, oak wilt is hard to identify. A certified arborist or forester can usually diagnose the disease, either through lab cultures or by detecting leaf symptoms, patterns of mortality or fungal mat. Tree experts look for such symptoms as necrosis or banding of the leaf veins or browning of the tips or edges of the leaves. A cluster of dead oaks, especially live oaks, which often have interconnected root systems, can be a tip-off, as can a large ring on the bark called a fungal mat. However, these mats do not form on all species of oak.
  
  

Controlling the Spread

• The only way to stop oak wilt from spreading is to disrupt the connection between the roots of infected trees and those that are still healthy. Trenching tools and vibratory plows are most often used to do this. These tools dig down into the ground and cut the interconnected roots, and infected trees usually die before the roots can graft themselves back together. The fungus that causes oak wilt does not survive longer than a few years in the roots of a dead tree.
  
  

Preventing New Infections

• New infections of oak wilt can be prevented in one of two ways: By removing and properly treating the infected trees or by using a fungicide to kill the cause of the disease. If a diseased tree is connected by its roots to other, healthy trees, care should be taken in its removal because as long as the infected tree remains alive, it offers some resistance to the spread of the fungal spores among its healthy neighbors. Non-connected diseased trees may be removed and then treated by debarking, chipping or splitting and then air-drying it to kill the fungus and any sap-feeding insects. Alternately, fungicides may be injected into healthy trees to prevent them from developing the fungus. Fungicides cannot revitalize trees already infected, and this treatment is expensive.