Gardening with Gary

Gardening Advice from an Expert

Modesto Ash Trees

Sheila writes~ I have an 8 year old Modesto Ash tree that has insects eating the bark away. There is 1' long, 2" deep, and 4" wide hole starting. The tree looks healthy every place else. I live in central Ohio. Is there anyway I can repair the hole and keep it from dying?

A. Fraxinus velutina glabra

These trees can be severely damaged on many of the limbs by cicadas. The cicadas leave saw-tooth damage when they laid their eggs in the summer. Boring insects can cause a great deal of damage to landscape trees, but infestations are treatable if caught in time. Early indications of an infestation are sap running down the trunk, yellow leaves or sawdust at the base of the trunk. The larvae of the round-head borer kicks out long strips of wood that resemble 'Shredded Wheat.'

Certain beetles lay their eggs in tree bark. Once the larvae hatch, they begin eating their way into the tree. You can kill the insects by sticking a piece of wire into the holes adult insects have bored in the bark, but that works only for areas of the trunk you can reach. Borer infestations may be treated with parasitic nematodes, which attack the larvae. Boring insects usually lay their eggs in spring and summer. The tunnels boring insects carve inside a tree provide a direct route for pathogens to enter.

To protect trees susceptible to attack from boring insects, apply an insecticide when the pests are active. Insecticides with a residual effect, e.g., Lindane, control insects throughout the season. Only the bark of the tree should be sprayed. Insects can bore tunnels under the bark and girdle a tree. Borers enter trees through wounds in the bark. To protect trees, keep them well watered so the sap runs freely, avoid damaging the bark with string trimmers and mowers, and make sure the area under the tree is free of debris. If you see signs of insect damage, begin a spray program.

Frank Hale, UT Agricultural Extension

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Caterpillars and other crawling insects cause enormous damage to mature trees and shrubs by defoliating leaves and boring into the bark. The result is unsightly and can be fatal to a tree. Even if the tree does not succumb to the insects, they can be severely weakened making them more susceptible to serious diseases.

You can prevent insect damage by wrapping your trees with TreeHelp Bug Band. It can be applied at any time of the year to control immediate problems. For annual ongoing control, apply one TreeHelp Bug Band in the late fall and another in the early spring to prevent many crawling pests from breeding and creating infestations on your trees.

http://www.treehelp.com/shopping/product-detail.asp?Product_ID=2198

Most borers attack only trees that are stressed due to drought, injury or disease. Consequently, any means of promoting vigorous tree growth should be considered the primary approach for borer management. A few borers, particularly clearwing borers, are considered more aggressive and are capable of damaging apparently healthy trees.

Borers within trees cannot be successfully treated with insecticides because the insects are in a protected site. Insecticidal control is best achieved if sprays are made during periods of adult activity and egg laying. Trunk sprays can kill the adult borers during egg laying and also may be effective against newly emerged larvae before they enter the trunk. Adults often feed on twigs and foliage before laying eggs. Timing of trunk sprays varies with different borer species. Check your local nursery.

Insecticide applications must be done for one to two months and may need to be reapplied if egg laying occurs over a long period. For a few borers, the larvae remain exposed on the bark for a considerable period. For these insects, treatments can be effectively applied from late summer through mid-spring.

In the past, Lindane has been the primary insecticide used for borer prevention. However, it is becoming increasingly restricted. Chlorpyrifos (Dursban, Lorsban) currently is the most widely labeled insecticide for borer management. Permethrin (Astro) and carbaryl (Sevin, etc.) have some labeled uses for borers. Thoroughly wet the wood with trunk sprays along areas where borers enter. Most borers typically attack lower trunks, but others can affect the upper crown areas of the tree.

Because many borers are attracted to recent wounds, try to avoid pruning during periods when the adult insects are laying eggs. Concentrating insecticide applications around wounds, cankers and callous growth also may be useful in managing borers that use these sites to enter trees. Systemic insecticides, applied to the root zone or injected into trunks, generally do not control existing borer infestations. These treatments may give some control when applied just as young borers first enter trunks. However, injections leave wound sites that can allow entry of disease organisms.

Fumigants have been used for some rescue treatments. Paradichloro-benzene (PDB) moth crystals can kill tree borer larvae when they are located within the base of trunks. Crystals also may be inserted into the tunnels of borers that leave external openings while feeding, such as carpenter worms.

For more information and pictures, go to: http://www.ext.colostate.edu/pubs/insect/05530.html