Oak Decline and the Future of Missouri’s Forests

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Published on: Jul. 2, 2002

Last revision: Nov. 12, 2010

the next two years.

Red oak borer larvae, which look like white grubs, create a 1- to 2-inch wide cavity in the phloem layer just under the bark during the first summer and the following spring. By the middle of the second summer, larvae begin burrowing into the sapwood and often go deeper into the heartwood of the tree.

Each larva creates about a 3/8-inch diameter tunnel that extends several inches, first angling upward away from the bark and then turning straight up through the wood.

The adult red oak borer emerges from the tree in the third summer by chewing an oval hole in the bark near where it entered the tree as a larva.

Most adult red borers emerge from their host trees in June and July of odd-numbered years. Huge numbers of these adult beetles are expected to emerge in 2003. Trees still stressed at that time will be at high risk for increased attacks.

Despite its name, the two-lined chestnut borer commonly attacks stressed oaks. Adult beetles are small, black and bullet-shaped and have two yellowish stripes down their back. Larvae of the two-lined chestnut borer are wormlike creatures that grow to about an inch long. They spend all of their time tunneling in the phloem layer and outer sapwood just under the bark. Their tunnels wind around the trunk of the tree, disrupting the flow of food, water and minerals, but they do not go deeply into the wood.

Reducing the Impacts of Oak Decline

Periods of reduced oak growth, mainly due to drought, have occurred in the Ozarks about every 14 years. Mortality due to oak decline was common in southern Missouri following droughts of the 1980s, although not on the scale of current conditions. Droughts and the resulting effects on our oak forests are always going to be with us, so we need to manage our forests so they can best withstand these stresses.

You can prevent or reduce oak decline by taking steps to improve the health and vigor of trees on your property. Start by increasing the diversity of tree species on your property. Select species appropriate for the conditions of the site. Remove poorly-formed trees and trees with unhealthy crowns, but keep some standing dead trees and trees with cavities for wildlife habitat. Some cavity nesting birds, woodpeckers for example, are important predators of wood-boring insects.

Landowners may avoid effects of oak decline by regenerating oak stands before trees

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