Arbor Age Pest of the Month: Golden Oak Borer

Editor’s Note:
This article, by Jesse Lee, appeared in December 2008 issue of Arbor Age magazine. It is posted here with permission from Arbor Age and is not intended for reprint or republication. For more Arbor Age articles, visit www.arborage.com.

What does it look like?

The golden oak borer (Agrilus coxalis) larvae are long, white and slender. The larvae are legless, with two spines at the tip of the abdomen.
Adult golden oak borers are a metallic green color with distinctive golden-yellow spots on their forewings. The adult insects average about 3/8-inch in length and about 1/16-inch in width.

Host material and range

The golden oak borer was found in southern California in 2004 and has been previously found in Arizona and Mexico. It primarily attacks coast live and California black oaks found throughout the region.
Not much is known about the history of the species, and it is still unclear whether the discovery of the pest is due to range expansion, or if this is an introduction.
According to a report by the Pacific Southwest region Forest Health Protection Service, the golden oak borer may have been introduced in 2002, as oak mortality was first mapped that year and occurs over a period of years.

Current threat

The golden oak borer larvae feed on the sapwood causing patchy, cambium damage that leads to thinning crowns, leaf drop, twig and branch death. Staining of the trunk from the lower crown to the first scaffold branch is common and is often accompanied by woodpecker damage. Because this pest threat is recent, the extent of damages is still being recorded.

Prevention tips

Preventative insecticide and fertilizer applications can ensure tree health and keep outbreaks at bay. Increasing the tree’s vigor and health can often help it to fight off the pest on its own. In addition, thinning tree groups can lower stress on the trees and maximize tree health.

Treatment tips

When treating for golden oak borer infestation, it is important to pay attention to the foliage as well as the trunk and branches, treating the entire tree to reduce attack.

A single treatment with carbaryl has proven effective at keeping the golden oak borer at bay, and treatment should be repeated every year. Spray treatment of carbaryl will not impact larvae present under the bark in infested trees, however, and should be combined with a systemic insecticide if the tree is infested.

Micro-infusion, trunk-injected applications of imidacloprid have been found effective in preventing and eradicating golden oak borer. Treating trees early, in late April or early May, shows better results for killing both adults and larvae with one application. Treating affected or at-risk trees with a fertilizer application including chelated minerals, magnesium and calcium will also stimulate foliar and root growth — increasing vigor in defoliated trees.

What can you do?

As with all wood-boring insects, additional care and prevention should be taken when handling and transporting cut wood and logs. Transportation of cut wood can spread the insect into other areas.

Jesse Lee is with Epic Creative, Wis. Article provided by Mauget, a leader in micro-injection and micro-infusion tree care. Contact Mauget or visit www.Mauget.com to learn more about the golden oak borer, steps taken to prevent and control it, and proper pesticide application and use.