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Emerald Ash Borer Management

Overview

The emerald ash borer (EAB), Agrilus planipennis Fairmaire is a devastating exotic wood-boring pest threatening ash trees in North America. To date, EAB is responsible of killing more than 40 million ash trees in Michigan, Ohio, Illinois, Indiana and other surrounding states. Unfortunately, EAB can be easily spread either naturally as adult beetles can fly and travel to new areas, or by human assistance through the movement of infested firewood or ash logs from affected areas to neighboring places, including Minnesota. On May 13, 2009, EAB was confirmed in Minnesota (St. Paul). Because these beetles can wipe out all infested ash trees, it is our responsibility to work together to stop the aggressive movement of this invasive pest towards our parks, nurseries, forests, streets and backyards.

Facts

• EAB attacks only ash trees (Fraxinus spp.).

• EAB is native to eastern Russia, northeastern China, Mongolia, Taiwan, Japan and Korea, where it occurs on several species of ash.
• EAB was accidentally introduced into North America via infested ash crating or pallets.
• EAB was first detected in southeastern Michigan in June 2002.
• EAB attacks all species of ash of any size and age, and kills healthy ash trees.
• EAB can kill healthy and stressed ash trees.

Identification

• Adults are about 3/8 to 5/8 inch long, flattened back with metallic green wing covers, and coppery red or purple abdominal segments beneath wing covers.
• Adult beetles leave distinctive D-shaped exit holes in the outer bark of branches and the trunk.
• Larvae are creamy white, legless with flattened, bell-shaped body segments. The terminal segment bears a pair of small appendages.

• Larvae bore through the bark and into the cambial region making S-shaped feeding gallery becoming progressively wider as the larva grows. Galleries weave back and forth across the wood grain.

• Due to larvae feeding, canopy dieback begins in top one-third of canopy and progresses until tree is bare.

• Other signs of possible EAB infestation include:
  • The sprouting of epicormic shoots around the base of the tree or at the junction of live and dead parts of the trunk or branches.
  • Leaves of infested trees often look larger than normal.
  • Vertical cracks or spilt on bark due to callous tissue formation. Usually under this spilt, galleries are exposed.

Biology

• From mid May to mid August, adults are active and feed on ash foliage leaving small, irregularly shaped patches along the leaf margins. However, adult feeding causes little damage to the tree.
• Generally, adults live a total of three to six weeks. During this period, males and females feed for a few days prior to mating. The feeding is continued for an additional 1 to 2 weeks before females actually begin laying eggs.

• Females can mate multiple times during its lifespan and lay from 30-60 eggs.
• Eggs are deposited individually on the surface of the bark, in bark crevices or under outer bark or branches.
• After depositing, eggs soon darken to a reddish brown, and hatch in 7 to 10 days.
• After hatching, the first instar larvae tunnel into the tree and feed on phloem for several weeks, creating S-shaped galleries packed with fine sawdust-like frass (larvae debris). As a larva grows, its gallery becomes increasingly wider. 
• Larvae feeding are usually completed in autumn and pre-pupae overwinter in cells found about a half-inch into the sapwood or outer bark.
• Pupation usually takes place when it begins to warm up in the spring in April or May.
• It takes two to three weeks for EAB pupae to become adults, but adults often remain in the pupal chamber or bark for one to two weeks before emergence.
• From May to early July, adults chew a distinctive D-shaped exit holes in the bark and emerge from the ash trees.
• In northern states, a two-year lifecycle can occur in newly infested ash trees that are relatively healthy; whereas in stressed trees, the lifecycle takes only a single year to complete.

Habits

• EAB adults do not tunnel inside a tree, after emergence from a tree trunk; they typically fly within a ½ mile from their emergence tree to feed on ash trees leaves and lay eggs. However, they can fly up to 10 miles, especially when ash trees are not available within their normal flying zone.
• EAB larvae are the damaging stage. They live inside a tree and eat through the active phloem and xylem of the ash tree. This causes general yellowing and thinning of the foliage followed by canopy dieback and the eventual death of the tree in one to three years.

Management

Typically, management options for managing EAB include three treatment technologies. Soil treatment, trunk injection and cover treatment.

Soil Treatment

• Soil treatment with systemic insecticides (i.e., Merit®) is recommended from mid-April to mid-May.
• Research studies have suggested treating trees with soil treatment if EAB is detected within 20-30 miles.
• A number of studies propose that for small trees (<6'' Diameter Breast Height (DBH)), a soil application every two years may be sufficient; otherwise, for high value trees or for larger trees, continue to treat annually.
• The initial dieback of the tree is an important factor for the tree recovery. For example, if less than 50% canopy dieback is detected in the tree, soil treatments will promote recovery in ash trees after two years of treatment. If dieback is more than 50%, it is hard to save the tree.
• There are two major methods of soil treatment for EAB management:
  • Basel soil drench: in this method of treatment, the appropriate amount of a systematic EPA approved insecticide for EAB management will be mixed and poured around the base of the tree within 2 feet of the trunk. This tactic is simple and requires no special equipment to apply, but a bucket or watering can. However mulch or leaf litter can attach to the insecticide and reduce uptake and distribution of the insecticide. Before treatment, remove any mulch or dead leaves and pour the insecticide solution directly on mineral soil.
  • Soil injection: The soil injection technique involves the injection of the insecticide solution into holes in soil surrounding and near the base of the tree. Studies have indicated that soil injections made immediately adjacent to the trunk (within 6-18 inches) are more effective than those made on a grid pattern under the tree canopy.

Trunk Injunction

• Trunk injection is the most effective management method that provides the fastest knockdown of existing EAB infestation according to studies conducted at four universities. This technique can be carried out in spring from mid-May to mid-June.
• Several systemic insecticides, such as TREE-äge^TM (Emamectin Benzoate) or Merit® (Imidacloprid) can be injected or implanted directly into the trunk of ash trees.
• A single trunk injection provides at least two years protection against EAB infestations.

Cover/ Trunk and Foliar Treatment

• A trunk and foliar application of systemic insecticides (i.e., Merit® or Tempo SC Ultra Tempo) in both mid May and mid to late June will manage visiting beetles and newly hatching larvae.
• In this method, EAB adults ingesting or coming into contact with treated foliage will be managed.
• Foliar application is recommended for prevention of EAB infestation, as it provides no effects on the developing larvae inside the tree.
• Researches have shown that treating the whole tree is more effective than treating only the trunk and large branches.

Frequently Asked Questions

Q: What options do I have for treating my ash trees?

A: Since EAB is not native to North America, our ash trees have little natural resistance to this pest. If you choose to treat your ash trees, there are a variety of insecticide treatment options available and research has shown that treatments can be effective.

Q: My backyard ash trees are infested with EAB. Will application of insecticides still be effective?

A: It depends on the initial level of the infestation. This because the EAB larvae feed inside a tree and damage the phloem and xylem, which make up the plant's circulatory system. This damage will hinder and weaken the capability of a tree to transfer the water, nutrients and the insecticides up the trunk and into the branches and canopy. Most of the insecticides used for EAB management act systemically. This means the insecticide must be transported within the tree through its circulatory system. Researches have been shown that if a tree has lost more than 50% of its canopy, it is probably too late to save the tree. In this case, the insecticide application is not justified. Otherwise trees with the most effective treatments averaged less than 20% canopy thinning and dieback. In many cases, the tree canopy will begin to improve in the second year of treatment giving a tree some time to recover.

Q: Why do I need to hire a professional to treat for the EAB?

A: Because the pest management professional is licensed and trained on the proper method, placement, dosing, and timing of applications, as well as, because products for professional use give better overall management, and longer residual effects, often times using less products and fewer applications.