What Is Killing Our Oak Trees?

There are a large number of diseases that can affect trees. An arborist can distinguish between sudden oak death, oak wilt, or various other diseases. It is also possible that it is not a disease or insect at all. Factors like drought, damage, lightning strikes, and extreme temperatures can also cause stress on oaks, leading to further decline in their health. Increases in air and soil pollution have made oak trees more vulnerable to disease, bacterial infections, and fungal blight.

Oak wilt is found in 21 states. It is a fatal and fast-spreading disease caused by the fungus Ceratocystis facacearum. This disease affects the tree’s vascular system, preventing the proper flow of water and nutrients and eventually killing it. Although all oaks are susceptible to oak wilt, the red oak is more susceptible to the disease than the white oak species. White oaks tend to develop symptoms more slowly and often recover, while red oaks usually die three to four weeks after symptoms appear.

The oak fungus spreads in one of two ways: Fungal spores are either transported to healthy trees by insects, or the fungus travels from a diseased tree to a healthy one via interconnected root systems or root grafts. Therefore, once the disease affects one oak tree, others nearby will soon follow.

Wilting symptoms are observed most commonly in July and August. Symptoms can vary in different oak species. Signs that a red oak is infested usually include the following:
Discoloration of leaves or tip burn
Wilted or curled leaves
Complete leaf drop occurring mid-summer
Dead crowns
Suckering at the base of the tree
Fungal mats
Tree death

Trees infected with oak wilt should be removed and destroyed immediately before the disease spreads to healthy trees.

Prevention is key with oak wilt, as there is no cure for the disease.
Seasonal fungicide injections into the tree’s trunk can be applied by a professional.
Prune only during the winter months when beetles are less active.
Avoid transporting infested red oak logs and firewood; white oak logs can be used safely as firewood.

Weather conditions have been hard on Arkansas’s trees. Many hardwoods, especially oaks, have rapidly turned brown this summer. According to the Arkansas Department of Agriculture, this may be “overnight flagging,” more commonly known as “scorching.” This decline syndrome does not actually occur overnight but takes several months, if not years, to appear.

This decline event is not “sudden oak death,” which is the common name associated with a specific fungal infection not present in Arkansas. This fungal infection tends to affect the trunk and branches of the tree. Neither is it “oak wilt,” a fungal infection that affects the leaves and is often confused with oak decline complex. Both sudden oak death and oak wilt can be spread by bringing plant material, soil, or water that is infected to a new area.

Oak decline is a chronic dieback with no single identifiable cause. It may occur when a tree has experienced multiple stress events. Trees are resilient and attempt to overcome stressors. Factors that might precipitate a decline event include snowstorms in February, extreme flooding in late spring to early summer, extreme fluctuations between wet and dry growing conditions during the summer, excess soil moisture and root rot pathogens or pathogens that infect the leaves and branches, twig pruner/girdler longhorn beetles, or gall-forming wasps.

During normal conditions, those individual events would not likely kill the trees. However, with continued stressful events and changing climatic conditions, there may be an increase in mature hardwoods dying seemingly overnight.

Now, in the hottest weeks of the summer, trees experience a great amount of transpiration, water movement through the tree, and escape into the air through the leaves. The demands of transpiration coupled with the expenditure of stored carbohydrates can cause rapid scorching.

What does that mean for the current flagged trees? Some may survive if the roots capture enough energy for next spring. A professional arborist or forester should be consulted for a tree health assessment.