Oak Wilt Home2018-11-14T01:20:55+00:00



Why is Protecting Your Trees So Important?

Bretiziella Fagacearum

Bretiziella Fagacearum is a type of fungus found in oak trees that is responsible for Oak wilt and the eventual death of the oak. The fungus is similar to yeast and this is carried along the vascular system in the tree sap. It excretes digestive substances, which once in the vascular system are fatal to the oaks. Red oaks, once infected, are guaranteed to die. White oaks have cells in the wall of the sap-vessels that react to it by producing gum-filled enlargements (tylosis-a white rubbery substance), which then clog the vessels. This possibly may be an effort of defense by the tree to control the spread of fungi, but in doing so it suffocates/ starves itself. (A defeatist attitude, kill yourself, kill the disease and the effect is like a serious cholesterol problem in humans). The flow of nutrients and water is stopped and soon the outwards signs of the disease can be seen: yellowing leaves, tips of the leaves turn brown, and venial necrosis (the main venial rib turns brown, the area between the veins remains green or yellow) within a few weeks a dying branch or the entire tree. There are different forms of the fungus, which may exist side by side. One is non-aggressive, whereas the other causes the death of the tree in a short time.

How it’s spread:

The diseases primary transfer of infection is through the root system at a rate of 50 to 100 feet per year. All oaks can spread the disease via inter-grafted root systems, usually between their own species. The secondary transfer is by the sap sucking bark-beetle (Nitidulidae species). The beetle, a long distance vector, carries the fungal spores from a spore mat developed only on red oaks that have succumbed from Oak wilt. During warm spells in the early spring the young beetles emerge from fungal mats and are able to fly several miles to find an oak tree that has cuts or wounds and feed on the sap. If successful it gives off a scent to alert its little friends to the find. This is the beginning of the end for the tree because the beetles infect the sap with the fungal spores.

Gestation in Live oaks can take about four to six months(less in some cases) and there are no noticeable effects of the disease until you see the start of the foliar effects. Red Oaks will die within weeks of becoming infected. Leaves usually begin to shed from the top down in rapid discoloration.

The pathogen has to have a healthy living host to survive. It cannot live in the soil or dead wood tissue.

Also during pruning, fresh cut wounds through molecular evaporation emit an oak sap odor, which is like a loud dinner bell to the beetle. The larger the wound, the greater the molecular evaporation.

Prune your oaks ONLY during the hottest or coldest times of year, usually June thru February and spray the cut with paint IMMEDIATELY! The nitidulid beetle has been found to be active almost year round in the Texas hill country and could still infect oaks that have be trimmed or pruned. It is also recommended that you sterilize your cutting equipment between trees. Although there is no scientific evidence of transfer, we encourage good pruning practices at all times.
What can be done

All oaks are at risk of contracting Oak wilt, with white oaks such as Bur and Monterey being less susceptible. It is important to monitor the health of your oak for broken limbs, leaf abnormalities, pest infestation, etc and contact a certified arborist for a consultation. Preventative and therapeutic treatments are available, as well as Do-it-Yourself kits. There is no known cure for Oak wilt, but that doesn’t mean they cannot be protected from getting it. It is a small investment when you consider the other alternatives.


New Leaves and VN

Old leaves showing veinal necrosis coexist with new leaves (not showing symptoms yet) put on in the spring.

Classic VN

This is an example of how veinal necrosis is typically presented on a leaf.

VN on a Red Leaf

Some Live Oaks turn a dark red color prior to dropping their leaves in the spring. Veinal necrosis on this leaf shows up bright red.

Veinal Necrosis (VN)

This example shows how the veinal necrosis can be finely detailed throughout the leaf.

VN and VB

This leaf has a combination of both VN and VB.

Classic VB

When veinal banding occurs, the veins remain a normal green color and the remainder of the leaf turns pale.

Veinal Banding (VB)

Veinal banding or inter-veinal necrosis is shown here. The yellowing of the area between the veins is not common but really helps to illustrate the symptom.

Margin Burn

Margin burn is a symptom of oak wilt where the edge of the leaf turns brown. These leaves also have veinal necrosis.

Tip Burn

This symptom is similar to margin burn, but only the ends of the leaf turn brown.

Bronzing Red Oak

One of the symptoms of Oak Wilt in red oaks is an apparent bronzing of the leaves as shown here.

Tip Burn in Red Oak

Another common symptom of Oak Wilt in red oaks is tip burn.

Fresh Fungal Mat

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Fungal Mat Remnant

Shown is the remnant of an Oak Wilt fungal mat on a long dead red oak. This spore mat is no longer an infection hazard because it has dried out.

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