Terran's Tips

Trees and Boring Insects

This month’s Tree Tip was researched and written by Emil Peter, ISA Certified Arborist #SO-6363A and Forester.  He may be contacted directly via email with any questions concerning this article or any tree related issues.

Ladies and gentlemen, it is indeed a sad day in the world of Tennessee Forestry, but a day we knew was going to happen at some point. Last week it was reported by the Tennessee Department of Agriculture that Emerald Ash Borer (EAB) had been discovered near a truck stop in Knoxville. The most likely reason it has shown up here was the transportation of infected firewood from an area where EAB was on the back of a truck, the trucker had to stop to use the facilities, the insects came out of the wood, found an ash, and then: Boom - Infestation.

The Pest
Emerald Ash Borer is an invasive and destructive insect that has been plaguing the Midwest and Northeast region of our country for almost 25 years now. The adults are dark green or emerald, about one-half inch in length and 1/8” wide. They are known to fly from April until September, depending on the climate of the area, looking for trees to complete their life cycles. In Tennessee, most EAB adults would fly in May and June. After their emergence beginning in late April and May from their “D”-shaped holes, the adult females will lay their eggs soon after. Adult emergence continues through mid-summer so the eggs are continually deposited over an extended period. The eggs, light yellow in color, oval shaped, and about 4/100”, are deposited individually on the bark surface or in bark crevices on trunks and branches. Each female lays about 75 eggs in her lifetime and the larvae emerge from the eggs in about a week.

What’s Out There This Month  

  • Azalea caterpillar
  • Two spotted spider mite
  • Crape myrtle aphid
  • Citrus whitefly
  • Bagworms
  • Insect galls on oaks
  • Two lined spittlebugs
  • Orange striped oak worm
  • Green striped maple worm
After hatching, larvae bore through bark to feed on ash trees' vascular tissue which transports water and nutrients throughout the tree. Growing larvae zigzag through this delicate tree tissue as they feed, forming “S”-shaped tunnels that are flat and wide. These tunnels are packed with frass (excrement). The mature larvae are about 1” long, creamy white with a flat, broad-shaped body.  The larvae spend the winter under bark building their tunnels through feeding. As is evident, the faster they chew through the vascular system, the faster the tree dies. The more larvae that are chewing, the faster they go.

When warmer weather arrives, usually in March and April, larvae enter the pupal stage. During this stage they will transform from larvae into sexually mature adults. The larvae remain under bark as they pupate, continuing to feed. As soon as their development is complete the adults emerge from the tree.

Adults live about 20 days. They feed lightly on ash leaves, but not enough to cause real damage. Adults are about 1/3-1/2” in length and about 1/16” wide, bright metallic green with rounded bellies and flat backs. Their peculiar shape accounts for those distinctive “D”-shaped 1/8” wide exit holes from which they emerge.

Typically, the Emerald Ash Borer beetles can kill an ash tree within three years of the initial infestation. The infestation spreads as the beetles emerge and fly off to find other trees. Sometimes they use the same tree throughout their life cycle, hastening its demise. Other, though, will fly off to find nearby ash trees in which to live and mate. Stressed trees, whether it is from a current infestation of EAB, drought, lightning strikes, or other stress factor, will emit biological signals that are unknown to us, but insects and other trees can pick up on. This is one of the best means of prevention and helping to fight any EAB attacks: keeping your trees healthy to begin with.

What Can We Do
There are a number of treatment options for EAB. Research and arboricultural practices from around the globe are showing several promising insecticides and techniques that are specific to individual infestations. Our Plant Health Care Arborists can evaluate your particular situation and devise a plan catered to your section of the urban forest. As mentioned above, however, the best thing you can do is to keep your trees healthy before there is a problem. Healthy trees, like healthy people, are more resilient than stressed trees and therefore have a better means of fighting off things that plague them, the same as you or me.

Keeping trees strong and healthy is the best defense against EAB. Some of the easiest ways are listed here:

  • Right tree in the right place. If trees are suited to the site where they are planted, stress is reduced, lessening possibility of attack by borers and other insects and diseases.
  • Mulch your trees. Mulch protects from damage such as physical injuries from machinery such as lawnmowers or vehicles in addition to helping regulate soil moisture and lessen competition from grasses and other plants. 
  • Properly fertilize your tree. Overly fertilized trees & trees with nutrient deficiencies can develop weaknesses that boring insects will utilize as a vector to enter your tree.
  • Keep trees properly watered. Drought stressed trees will quickly be found by borers and colonized first.         

If you see these little guys on your ash trees, suspect their presence, want to prevent them before they start, or any other issues that need addressing, please contact one of our highly trained Plant Health Care Arborists to come and take a look and evaluate what we can do to help you enjoy your section of the Urban Forest.

Our arborists want to keep your trees healthy for years of your enjoyment. If you have any questions or need any assistance with your trees or pests, contact the experts at Woodland Tree Service. Please email Joanna@woodlandtree.com or call us at (901) 309-6779.

Posted by Mark Allen at 1:43 PM
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