Management options

photo: Two-lined Chestnut borerHow you deal with a TLCB infestation depends on whether the trees are in your woodlot or back yard. In either case, we recommend replanting oaks to replace the ones that were lost.

Forested stands

Oak stands that have been stressed by drought and defoliation are vulnerable to damage and mortality by TLCB and Armillaria root disease. Manage stressed stands by:

  • postponing any activities in the stand
  • salvaging high-value, damaged trees to reduce economic impact.

Which option to choose depends on the potential for continued stress and the volume and quality of wood in the stand.

Cease management activities when oaks are under severe stress from drought and/or defoliation since any stand disturbance will further open up the stand and cause additional stress on the trees. Management activities could begin during the winter after a growing season with more normal precipitation patterns. However, oaks are vulnerable to TLCB for a few years after drought and defoliation end.

Salvaging does not control borers in outbreak situations, but it does reduce the economic impact by recovering timber while it still has its greater value. Salvaging is an option if dead oaks and oaks with 50 percent or greater dieback have a great enough volume to make a merchantable sale and the quality is high enough to produce veneer and grade lumber. Salvage the stand during the winter. Mark trees for salvaging during the leaf-on period, since dead trees and trees with severe dieback will be impossible to identify when dormant. When salvaging, do not extend the harvest into areas of the stand untouched or lightly damaged by TLCB.

If the main product is firewood, delay salvaging for at least a year after the oaks have died. Firewood quality will not deteriorate during this delayed period. This gives the borer larvae time to become adults and leave the tree. If infested firewood is moved into a backyard with oaks, the TLCB population will spread into the backyard oak trees.

Thinning will not control TLCB during an outbreak and should be avoided during an outbreak, particularly if the outbreak was triggered by drought. Thinning will open up the stand to drying winds that will increase the drought stress on the residual oaks. Thinning can also wound trees and damage roots. Even if thinning reduces stocking to optimum levels, the trees will not benefit from the reduced competition for a number of years, until the roots and crowns are able to occupy the spaces created during thinning. Thinning will also produce additional food for the Armillaria root disease fungus. It’s best to delay thinning for a few years until the oaks are more vigorous. Even at that time, thinning should be kept light; do not remove more than 30 percent of the basal area.

Sanitation will not control damage during an outbreak. A sanitation harvest cannot remove enough of the insect population to prevent future damage to the residual oak trees. The best practice is to postpone all management activities until the conditions that caused stress end.

Stump sprouting will be virtually nonexistent in borer-infested stands. In effect, the low vigor that created the TLCB problem will also decrease sprouting and enhance vulnerability to Armillaria root disease. To ensure future oak regeneration, count on advanced regeneration or oak planting stock, not stump sprouts.

Armillaria root disease, caused by an opportunistic soil borne fungus, attacks the root systems of weakened trees and often leads to tree mortality. If Armillaria root disease is damaging the root system, a white mat of fungal tissue grows between the bark and wood of the roots and root collar. These white mats, however, may not be found until after the tree is completely dead.

Yard trees

Homeowners may want to take additional measures to prevent the infestation of high-value yard oak trees. Here is what to do:

Water healthy and declining oaks on a regular basis during dry growing seasons. Trees, with less than 50 percent dieback, may be saved by heavy watering during droughty weather. If rainfall is inadequate, make sure trees get at least one inch of water per week from May through August. Water so the entire root system receives this amount of moisture and so it soaks deep into the soil. Remember the absorbing roots also occur beyond the drip line.

Strictly avoid using fertilizers and/or herbicides on lawns and gardens within 50 feet of an oak tree. Fertilizers will only hurt an ailing tree and herbicides kill tree roots, leading to more root system loss.

Avoid practices that destroy or smother roots. Root loss drastically affects tree vigor. Practices that damage roots include trenching or burying utility lines; driving and parking vehicles on root systems; paving or temporarily storing excavated soil over the root system; and changing soil grade by adding or removing soil.

Control other insects that cause defoliation before 60 percent of the foliage is lost. Once defoliation reaches this level trees may re-foliate, decreasing tree vigor further. Develop and implement spray plans if heavy defoliation is predicted to occur for the second or third consecutive year. The forest tent caterpillar population is declining but there will still be some areas with high populations and heavy defoliation this year.

You may be able to reduce TLCB populations by cutting and removing infested trees before the start of the growing season. However, if a lot of trees in your neighborhood are infested with TLCB, removing only a few trees is unlikely to reduce the overall population. If you decide to remove trees, remove the oaks that completely died last year and oaks with more than 50 percent crown dieback. Remember, TLCB can survive in cut and split wood and emerge the next spring, so remove all infested logs and branches by May 1.

The preferred methods of wood and slash disposal are removal to an approved landfill or sale of the trees for lumber. If any woody materials larger than 1 inch in diameter remain, pile and burn them before May 1. If you want to keep the wood for firewood, cover the woodpile with a heavy plastic tarp and bury the edges of the tarp in the soil for an airtight covering. Keep the firewood covered from May 1 until at least July 30. After that time the wood can be moved or burned.

Avoid bringing fresh oak firewood into your yard. Bringing more infested wood into an area will only compound the problem.

Chemical insecticides are usually not used against TLCB because of difficulties with timing and obtaining thorough coverage on large trees. However, certified arborists or commercial pesticide applicators may be able to treat high-value shade trees. Insecticides cannot replace good tree health. If trees continue to be stressed, insecticides will not save them from TLCB.