New Tools Aid Fight Against EAB

By P. Kerr

As fast as there is a story to print, there are new developments in the war on the emerald ash borer. And although no one has any expectation that this insect can be eliminated from North America, there are new promises for control available with the potential to slow the spread of EAB, at least in select trees.

The lastest tool involves emamectin benzoate, a product used successfully in Canada in preventing sea lice in farm-raised salmon. In the U.S., the same chemical is used in insecticide sprays for agricultural products. In both cases, the end product is fit for human consumption. Emamectin benzoate has broad spectrum control for both native and exotic pests.

Arborjet, Inc., working with Syngenta, a Swiss agrochemical company, used a 4 percent solution of this well known chemical (emamectin benzoate is already used in Syngenta’s Proclaim insecticide, and a similar product, avemectrin, is used in its Avid insecticide) and reformulated it to be used with their tree injection systems. Called TREE-äge, this new product already has emergency licensing in Michigan, Indiana, West Virginia and Ohio and it is pending in other EAB-infested states. It is in the EPA queue for full federal registration. It should now be available for purchase in registered states.

“In preliminary studies conducted by Michigan State University, the pesticide killed more than 99 percent of the ash borer larvae in treated trees and 100 percent of the adult beetles that nibbled on their leaves,” according to an April press release from Arborjet.

This statement refers to the research of Michigan State University’s Dr. Deborah McCullough and her colleagues at the university, USDA’s Animal and Plant Health Inspection Service (APHIS) and the USDA Forest Service. They are conducting ongoing experiments with TREE-äge and other products licensed for use against EAB.  

Groups of ash trees from different sites were treated in 2007 with TREE-äge and other chemical formulations. Some trees were left untreated as controls. In the fall of 2007, some of each group were cut down, debarked and the EAB larvae counted. Right now, it appears TREE-äge did well the first year.

In 2008, some of each group will receive a second treatment. In the autumn, more trees will be cut and the larvae counted. That data will tell if there is residual effectiveness the second year after one treatment compared to two treatments. But answers won’t come until 2009. Because of studies on other insects, Arborjet believes a residual effective period will be shown in the second year.

Dr. Cliff Sadof, entomologist from Purdue University, is conducting a separate study. With colleagues, he first did a review of Michigan State’s literature on past efforts in the battle against EAB. His comparison study involves half a dozen products claiming success with EAB. He is measuring the results of each product with defoliation levels. They are studying 300 ash trees in an EAB infested campground. New applications of each of the six products were applied in June 2007, but indicators were insufficient to produce results last year. He expects to see differences this season as the study continues and infestation progresses.

After reviewing the literature, Sadof believes TREE-äge runs through the tree slower than other products and that its toxicity lasts longer in the adults. If this proves true in field trials, TREE-äge could slow the spread of the beetle.

Toxicity
Random observers in Ohio and Canada have reported woodpeckers feeding in EAB infested areas during and after various EAB treatments. No one noted which of the treatments were used on the trees the birds and rodents were feeding on. They only made observations about an increase in feeding in the area. They saw no dead birds or animals and have no scientific data to discuss what they saw. Homeowners may notice increased feeding on infested trees and ask environmental questions about the treatment options.

Dr. Don Grosman, an entomologist with the Texas Forest Service, has studied emamectin benzoate for about 10 years and its effects on seed and cone insects, bark beetles and wood borers (not EAB). He says it is highly improbable the woodpeckers are feeding on larvae from a tree treated with emamectin benzoate because there are no living larvae present to attract the birds or rodents. Their tests with bark beetles (Ips and Dendroctonus spp.) showed that when beetles tunnel into trees, as soon as they bite into the phloem (innermost part of the bark where nutrients are conducted in the tree), the beetles die and cannot produce brood larvae or adults.

Theories for the observations made in Ohio and Canada are that woodpeckers could be feeding on untreated trees, trees treated with other products that were unsuccessful in controlling the EAB, or on beetles on the bark surface that have not contacted the emamectin benzoate in the phloem at the time of the observation.

A Japanese study (2003) found very low concentrations (in the order of parts/billion) of the emamectin benzoate in the treated trees.

Grosman has been testing emamectin benzoate on beetles that kill trees across North America. In initial tests, they treated 6- to 8-inch (dbh) trees with different concentrations of emamectin benzoate and cut them down at intervals of one, three and five months. Each series of logs was exposed to Ips engraver beetles for three weeks. Later the bark was removed and the logs examined for insect activity. In another test they studied emamectin benzoate activity against Dendroctonus species (bark beetles).

They learned that temperature affects the rate of chemical movement in the trees. At colder temperatures or high elevations, extra time is needed for the chemical to be circulated throughout the tree. The tree must fully circulate the formulation in order for the treatment to be completely effective.

“We suspect the chemical is stored in the wood tissue of the tree, but we don’t know exactly how, when or where.”

A request was made by Syngenta Crop Protection to EPA in January 2008 for a full section-three registration of emamectin benzoate across the U.S. The company believes the product is effective against bark beetles, woodborers and moth defoliators.

Several years ago, an early formula of emamectin benzoate showed phytotoxicity problems. Michigan State’s McCullough says, “These problems have apparently been resolved. There is no evidence at this time of any harm to the tree in 2007” using Arborject’s TREE-äge.

Even at this early stage of research, McCullough believes there are indicators to support the residual effectiveness of emamectin benzoate in the TREE-äge formula. She believes it may be possible to get full coverage with a biannual treatment, with a soil drench on the alternate years. APHIS has already done leaf collections from the trees in Michigan and McCullough had received the raw data when we talked with her for this article, but needed time to compile it and provide the residual analysis.

The amount, if any, of residual emamectin benzoate levels in the leaves when they fall in the autumn is not known, but the potential is lower than with either soil drenching or spraying, according to Peter Wild, president and CEO of Arborjet. McCullough believes there is little risk that TREE-äge will affect bees and other pollinators because ash is wind pollinated and bees don’t feed on leaves.

“TREE-äge,” McCullough says, “is another option to save valuable landscape trees.”

Canadian option
In March 2008, emergency licensing was received in Ontario for injection of TreeAzin, a new product using azadirachtin from the oil of Neem seeds, for use against EAB.

Research has shown that, at very low doses, TreeAzin inhibits emerald ash borer larval development, prevents adult emergence, and provides prophylactic and remedial treatments. Taylor Scarr of Ontario’s Ministry of Natural Resourses calls TreeAzin “environmentally safe.”

TreeAzin was developed by the Canadian Forest Service in collaboration with BioForest Technologies Inc. and is owned by the Canadian Forest Service. Field trials of tree injections to fight emerald ash borer in ash trees are ongoing in Canada. Early results of the Neem experiments on emerald ash borer are expected in the fall of 2008.

Parasitoid release
In early April, Dr. Leah Bauer of USDA forest service was about to start tree cutting to determine if the 2007 release of the EAB parasitoids Tetrastihus planipennisi (Tetra) and Oobius agrili (Oobi) was successful.

Tetra lays its eggs in EAB larvae. Oobi lays its egg in an EAB egg. Dr. Julie Gould of USDA plant health is involved with the release of the third parasitoid, Spathius agili (Spath). These different insects live by consuming EAB at different stages in the EAB’s life cycle.

“We recovered 87 gregarious ectoparasitoids (collections of wasp larvae) from one tree at the release site,” says Gould. “Confirmation whether or not these are Spath will be received in a few weeks.”

Construction and hiring to expand the release program in the fall of 2008 is starting.

As EAB continues to march across North America, more and more options are progressing toward market that may finally control this pest and save the continent’s ash forests. The next year will provide substantial clues as to whether science or borer will win the race.

About the Emerald Ash Borer

Emerald Ash Borer is a deadly threat to ash trees, killing host trees within three to five years of infestation. The pest belongs to a group of insects known as the metallic wood-boring beetles. Adults are dark metallic green in color, 1/2 inch in length and 1/8 inch wide, and fly only from early May until September. Larvae spend the rest of the year developing beneath the bark of ash trees, and when they emerge as adults, leave D-shaped exit holes in the bark about 1/8 inch wide.

Note the characteristic D-shaped exit hole. Once they become adult beetles, they crawl through the bark, leaving these exit holes.	EAB larvae choke the Ash tree by eating through the cambium layer just under the bark.

The pest is difficult to detect in its first year of infestation, as it first infests the tops of ash trees and works its way down. Infested ash trees are essentially choked to death by larvae feeding on the cambium layer -- the live tissue just beneath the bark responsible for transporting nutrients throughout the tree. Signs of EAB include dieback at the tops of ash trees, D-shaped exit holes, S-shaped larval galleries, epicormic sprouts, woodpecker damage, and bark splits.

Research has shown that the natural spread of the pest is less than one-half mile per year. However, EAB can be easily, yet unknowingly spread through the movement of infested ash material such as logs, nursery stock, firewood, etc. The majority of infestations were introduced through the artificial spread of this insect.

Many states and provinces are now aggressively spraying ash trees to stop the spread of this deadly pest.