Emerald Ash Borer

 

Emerald ash borer (Agrilus planipennis Fairmaire), an invasive insect native to Asia, has killed untold millions of ash trees (Fraxinus species) in urban, rural and forested settings. This beetle was first identified in 2002 in southeast Michigan and Windsor, Ontario. As of April 2014, emerald ash borer (EAB) infestations were known to be present in 22 states, including Ohio and West Virginia, as well as two Canadian provinces. Surveys continue and additional infestations will be found as EAB continues to invade North America. Ash trees are common in urban landscapes and residential areas across much of the continental US. Many homeowners, tree care professionals, and municipalities would like to protect valuable ash trees from EAB.

 

 

Symptoms

The symptoms an ash tree shows when it is infested with emerald ash borer are similar to symptoms caused by other ash pests or diseases. For example, crown dieback can occur due to EAB damage, but can also be the result of drought stress, soil compaction or verticillium wilt, just to name a few. Therefore, it is important to look for a combination of at least two symptoms or signs when trying to figure out if emerald ash borer is in your ash tree.

 

  • Crown dieback: Dieback of the upper and outer crown begins after multiple years of EAB larval feeding. Trees start to show dead branches throughout the canopy, beginning at the top. Larval feeding disrupts nutrient and water flow to the upper canopy, resulting in leaf loss. Leaves at the top of the tree may be thin and discolored. An example of this is shown below.

 

  • Epicormic Sprouting: When trees are stressed or sick, they will try to grow new branches and leaves wherever they still can. Trees may have new growth at the base of the tree and on the trunk, often just below where the larvae are feeding. An example of this is shown in the picture above, where small branches are growing on the trunk, about 6 feet off the ground.

 

  • Bark splits: Vertical splits in the bark are caused due to callus tissue that develops around larval galleries. Larval galleries can often be seen beneath bark splits.

 

  • Woodpecker feeding: Woodpeckers eat emerald ash borer larvae that are under the bark. This usually happens higher in the tree where the emerald ash borer prefers to attack first. If there are large numbers of larvae under the bark the woodpecker damage can make it look like strips of bark have been pulled off of the tree. This is called "flecking." An example of this is shown below.

 

  • D-shaped emergence holes: As adults emerge from under the bark they create a D-shaped emergence hole that is about 1/8 inch in diameter. An example of this is shown below.

 

  • S-shaped larval galleries: As larvae feed under the bark they wind back and forth, creating galleries that are packed with frass (larva poop) and sawdust and follow a serpentine pattern. An example of this is shown below.

 

  • Larvae: Larvae are cream-colored, slightly flattened (dorso-ventrally) and have pincher-like appendages (urogomphi) at the end of their abdomen. By the time larvae are done growing they are 1 1/2 inches long. Larvae are found feeding beneath the bark. It’s the larva that does all the harm to ash trees. Larvae tunnel under the bark and disrupt the tree’s systems that transport food and water, eventually starving and killing it.

 

  • Adults: Adult beetles are bright, metallic green and about the size of one grain of cooked rice (3/8 - 1/2 inch long and 1/16 inch wide). Adults are flat on the back and rounded on their underside. It has purple abdominal segments under its wing covers. The EAB can fit on the head of a penny, and is hard to spot in the wild.

 

 

Where Can The Beetle Hide

Infested ash materials can include any part of an ash tree including logs, stumps, branches of almost any size, composted or uncomposted chips, nursery stock and especially firewood.

 

 

How Does It Spread

EAB adults are strong flyers, but most of them only fly short distances (about 1/2 mile). So they don’t spread far on their own. Most new infestations are caused by people unknowingly taking infested ash to an uninfested area.

 

 

Control

Several insecticide options are available to effectively treat landscape ash trees threatened by EAB. Products have been evaluated by university and government scientists in field trials. Some products may not be labeled for use in all states. This does not imply that it is endorsed by the authors or has been consistently effective for EAB control. Keep in mind that controlling insects that feed under the bark with insecticides has always been challenging. This is especially true with EAB because most of our native North American ash trees have little natural resistance to this pest. Effective control of EAB requires some care when selecting an insecticide product and application method to ensure the product is applied at the proper rate and time.

 

Insecticides that can effectively control EAB fall into four categories:

  • systemic insecticides that are applied as soil injections or drenches

  • systemic insecticides applied as trunk injections

  • systemic insecticides applied as lower trunk sprays

  • protective cover sprays that are applied to the trunk, main branches, and (depending on the label) foliage

 

 

When is the best time to treat my trees

As with any pest management effort, optimal timing is required to achieve best control. Two life stages of EAB are targeted by treatments:

 

  • Young larvae: Systemic insecticide applications should be made in time to allow for uptake and distribution of the insecticide within the tree to ensure adult beetles and very young larvae encounter the toxin. Peak egg hatch and larval establishment occur between early June and mid-August, depending on location and weather. As a general rule, young larvae are more susceptible to insecticides than are older larvae. Moreover, controlling young larvae pre- vents damage to the tree caused by older larvae that feed in larger galleries and thus injure more area on the tree. The efficacy of insecticide treatments will likely decline if they are applied later in the growing season when larger, more mature larvae are present. Consistent with this, MSU scientists found that imidacloprid trunk injections made in mid-May were 70% more effective against EAB than those made in mid-July.

 

  • Adult beetles: Non-systemic cover sprays, which are less commonly used, should be applied to foliage to target adult beetles, as well as the trunk and branches to help control newly hatched larvae. Thorough coverage is critical for achieving successful control. Adult EAB feed on ash foliage throughout their life span and females must feed on leaves for at least 14 days before they begin laying eggs. This provides a window of opportunity to control the adults before any new eggs or larvae are produced. The onset of adult beetle emergence begins from early May for southern Ohio and peaks two to three weeks later. Beetle emergence may begin sooner at locales farther south or later in more northern areas.

 

 

My ash tree looks fine but EAB has been detected in the vicinity?

Detecting new EAB infestations and identifying ash trees that have only a few larvae is very difficult. Ash trees with low densities of EAB larvae often have few or even no external symptoms of infestation. In addition, scientists have learned that most female EAB lay their eggs on nearby trees, i.e. within 100 yards of the tree from which they emerged. A few female beetles, however, property is within 10-15 miles of a known EAB infestation, your ash trees are probably at risk. If your ash trees are more than 10-15 miles beyond an infestation, it is probably too early to begin insecticide treatments. Treatment programs that begin too early waste money and result in unnecessary use of insecticide. Conversely, treatment programs that begin too late will not be as effective.

ADULT BEETLE

Adult beetles are bright, metallic green and about the size of one grain of cooked rice (3/8 - 1/2 inch long and 1/16 inch wide). Adults are flat on the back and rounded on their underside. It has purple abdominal segments under its wing covers. The EAB can fit on the head of a penny, and is hard to spot in the wild.

S-SHAPED LARVAL GALLERIES

As larvae feed under the bark they wind back and forth, creating galleries that are packed with frass (larva poop) and sawdust and follow a serpentine pattern. An example of this is shown below.

LARVAE

Larvae are cream-colored, slightly flattened (dorso-ventrally) and have pincher-like appendages (urogomphi) at the end of their abdomen. By the time larvae are done growing they are 1 1/2 inches long. Larvae are found feeding beneath the bark. It’s the larva that does all the harm to ash trees. Larvae tunnel under the bark and disrupt the tree’s systems that transport food and water, eventually starving and killing it.

CROWN DIEBACK

Dieback of the upper and outer crown begins after multiple years of EAB larval feeding. Trees start to show dead branches throughout the canopy, beginning at the top. Larval feeding disrupts nutrient and water flow to the upper canopy, resulting in leaf loss. Leaves at the top of the tree may be thin and discolored. 

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