The decline of oaks

Oak decline is weakening, progressive decline and subsequent death of oak trees. Trees experiencing oak decline will display die back of branches, usually starting from the top of the tree moving downward.

Oaks are an important component of Frederick County woodlands, found in nearly 70 percent of our forests. In some areas these large, majestic trees are suffering from oak decline.

Credit: - Mike Kay

Oak decline is the weakening, progressive decline and subsequent death of oak trees. Trees experiencing oak decline will display dieback of branches, usually starting from the top of the tree moving downward. They often develop small "sucker sprouts" along the main trunk and may develop large gray- to black-colored lesions (cankers) along the trunk as well. In two to four years the tree will die; sometimes these trees will blow over in a storm without much sign of a root system.

Oaks are vulnerable to decline when they are weakened. This can be the result of environmental factors, such as drought, storms or late-season frosts. Insects and disease can also weaken oak trees.

Widespread gypsy moth defoliation in 2008 has triggered much of the oak decline we are now experiencing. This caterpillar defoliates a tree early in the season when the oaks have spent most of their available energy leafing out.

Other factors that affect the health of oak trees include construction damage, damage to the root system and soil compaction, changing the soil grade around trees, cutting roots during trenching operations and changing the drainage patterns of the landscape. Finally, a forest may be so densely stocked that competition among trees may trigger oak decline.

A weakened oak tree sends out chemical signals that attract certain insects and diseases that will attack this unthrifty individual. These organisms are called "secondary" pathogens because they will not damage a healthy tree. Some of the more common secondary organisms that attack weakened oak trees include the two-lined chestnut borer and red oak borer insects, as well as the shoestring root rot and hypoxylon canker diseases.

The boring insects disturb the tree's vascular system, impacting the transport of water and food throughout the tree; this causes the tree to begin dying from the top downward. The shoestring root rot disease also impacts water and food transport while destroying the root system, making the tree unstable. The canker disease slowly girdles the tree causing a progressive death. A combination of all these factors causes the slow demise of the tree, and the dead oak oftentimes topples because there is not much of a root system to support it.

All of our native oaks are susceptible to oak decline, but the black and red oaks are more likely to come down with the disease than oaks in the white oak family.

Preventing oak decline

How do you prevent oak decline?

You do this by keeping oaks healthy. Some ways to accomplish this are by protecting oaks during construction, limiting foot traffic, car parking or any activity that could harm roots or compact the soil around an oak. Preventing gypsy moth or any other insect from defoliating or otherwise damaging a tree is another important strategy.

Finally, watering a landscape oak during a lengthy period of drought or thinning out a dense forest are other ways to keep oaks healthy and prevent decline.

What's in bloom?

A sure sign that winter's grip is loosening somewhat is that early-season flowering plants are now breaking bud. Look for the bright yellow flower of the forsythia bush, the large white flower of the saucer magnolia or the purplish bloom of the purple leaf plum tree.

The red and silver maples are also in bloom now, but their flower is not very large. From a distance you can see a red outline around a group of maples, up close you can see the flower. There should be a number of other trees joining this colorful parade in a week or so.

Article by FCFCDB

Nature Notes for 3/27/2011