Oak Wilt in Minnesota

elm leaf Rainbow Treecare has again started to see symptoms of this deadly diseases in the Twin Cities. Oaks are one of our most highly prized shade trees, by monitoring them closely we can make sure they will be around for generations yet to come. Preventive treatment is the most effective way to protect your trees.

Oak Wilt

Characteristic browning on leaf margins, moving inward

This is a lethal disease that invades and disables the water-conducting system in oaks. Red oaks typically die within 4-6 weeks of initial symptom development, while white oaks may survive or take 1-6 months to defoliate and die.

Oak tree showing decline in canopy due to oak wilt disease

Most oak wilt disease is spread through root grafts. We see approximately 90% of all new infections transmitted in this manner. Whole groves of oak trees can be decimated in this manner within a very short time. Root graft disruption and fungicidal treatments aid in the prevention and spread of oak wilt.

Trenching to sever grafted roots

Oak wilt can also be spread through sap feeding beetles. These beetles feed on fungal spore mats and then carry the oak wilt spores to wounds on healthy trees. This form of transmission takes place during the spring and early summer months. Because beetle vectors (carriers) are attracted to fresh wounds, it is very important not to prune oaks during the months when spore mats are present. We recommend pruning oaks only during the cold weather dormant season.

Oak wilt is easily transmitted through the roots of trees of the same species. Trenching helps to prevent root graft transmission.

The primary symptom of oak wilt is the wilting of leaves, discoloration, and defoliation. Browning appears on the margin of the leaf and moves inward.

An important aspect in controlling this disease is physically cutting (trenching) grafted roots between infected and healthy trees. Trees that cannot be trenched and small groups of trees are good candidates for Alamo Macro-Infusion fungicide treatments. These fungicide treatments are effective for two full growing seasons.