When to prune your trees, to protect them from Oak Wilt in Austin, Texas

By Jerry Naiser

Live Oaks, can get Oak Wilt by way of root transmission from another Live Oak, or from the sap feeding, Nitidulide beetle. This insect would first have to have fed from a tree with an infected fungal mat. A fungal spore can stick to its body, then be carried to the next tree that the insect feeds upon. Red Oaks are the most common tree to produce this infected fungal mat.

Insect transmission does not occur from Live Oak to Live Oak as Live Oaks are incapable of producing the infected fungal mat and fungal spore.

When Oak Wilt travels through the grafted root system of Live Oaks, it is at a rate of about 75 feet per year. Spread at a rate of 150 feet per year has been documented.

Spanish/Red Oaks primarily get Oak Wilt by insect transfer. Spanish/Red Oaks do not develop grafted root systems. Furthermore, Spanish/Red Oaks are one of the few trees known to produce the infected fungal mat and fungal spore, that can be transported by way of sap feeding beetles. This infected fungal mat most commonly forms in mild temperatures, for the first year following the trees death from Oak Wilt. Spanish/Red Oaks can not be salvaged once they have contracted the disease. They should be removed immediately upon decline.

Most Oaks develop mechanical problems which cause self inflicted wounding. This includes interlocking limbs, branches rubbing on roofs or other structures and trees growing up into and through the crown of susceptible Oaks. This type of abrasive wounding, will never heal, and will flow sap year around. The flow will be heaviest during peak insect and fungal mat formation periods. All pruning cuts made by man, even large or incompetent cuts, will stop flowing sap within a couple of hours. If these wounds are properly treated with pruning paint, there will be no sap flow at all and the wound will be unattractive to the insect. Therefore, properly pruned Oaks are less likely to become infected by sap feeding insects.

1. Trees that need to be pruned, should be pruned, by a professional Arborist, as soon as possible. This will significantly reduce the possibility of Oak Wilt infection by insect vector.

2. Needless to say, trees that don't need to be pruned, should not be pruned.

3. When pruning trees susceptible to insect transmission of any disease, a non-phytotoxic wound sealer should always be used.