Extension Communications
Extension 4-H Youth Building
Ames, Iowa 50011-3630
(515) 294-9915
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Extension Communications |
10/18/04
Contacts:
Mark Shour, Extension Entomology, (515) 294-5963, mshour@iastate.edu
Del Marks, Continuing Education and Communication Services, (515) 294-9807,
delmarks@iastate.edu
Garden column for the week of Oct. 22, 2004
By Mark Shour
Extension Entomologist
Iowa State University
Approximately two years ago, an exotic insect from Asia made headlines in newspapers across the Midwest. The emerald ash borer, Agrilus planipennis, was found to be the culprit behind ash tree deaths in Detroit, Mich. and Windsor, Ontario, Canada. Several research, eradication and survey efforts have ensued since the borer’s identification in 2002.
Identification and Life Cycle Refresher
Emerald ash borer adults are dark,
metallic and emerald green in color. The beetles are small and slender, measuring
one-half inch long and one-sixteenth
of an inch wide. Adult beetles feed on host foliage, producing a marginal notching
on the leaflets. In the United States, female beetles lay eggs in bark crevices
on white, green and black ash trees (Fraxinus species). Upon hatching, larvae
chew through the bark.
Immatures (larvae) feed just under the bark in the nutrient-rich cambial and phloem tissues. The creamy white larvae produce winding tunnels that girdle branches and the trunk, thus killing affected areas or entire trees. Mature larvae (approximately 1.5 inches long) overwinter in the host plant. The transition from larva to adult (pupal stage) occurs in early spring. Adult beetles chew their way out of the pupal chambers, producing D-shaped emergence holes about one-eighth of an inch wide. There is only one generation per year.
Known Infestation Sites
The beetle has been confirmed from sites in Michigan,
Indiana, Ohio, Maryland, Virginia and Ontario. Agencies in states neighboring
these areas are conducting
surveys to determine if this pest has reached their borders. Visual inspections
and sentinel “trap” trees (an ash tree with a section of bark removed
and a layer of the sticky, waxy product Tanglefoot® placed above the bark-peeled
area) have been the primary detection tools in these projects.
Detection Efforts
in Iowa
During the summer of 2004, Ryan S. Holl, graduate student in Horticulture
and Entomology at Iowa State University, visited communities, towns and cities
across Iowa looking for evidence of emerald ash borer. Although he was most
interested in recent industrial and residential landscape installations, he
also examined established ash trees. In addition, Steve Pennington, Forest
Health Coordinator with the Iowa Department of Natural Resources, visited sawmills
in Iowa, and the nursery inspectors of the State Entomologist’s office
of the Iowa Department of Agriculture and Land Stewardship inspected nursery
stock. Fortunately, no signs of this pest were located and Iowa is apparently
free of the emerald ash borer.
Potential Ramifications
If the emerald ash borer escapes quarantine areas,
this pest has the potential of exceeding the devastation caused by Dutch elm
disease. Unlike other borers,
which colonize weakened or dying trees, the emerald ash borer attacks healthy
ash trees of a variety of ages in landscape and forest settings. One Michigan
source indicated the attacks were 100 percent fatal. The United States Forest
Service estimates there are more than seven billion ash trees in the country;
all are considered susceptible to this beetle’s attacks. To date, roughly
six million ash trees have died from emerald ash borer activity in Michigan
and thousands more have been removed through eradication efforts. The cost
of containment efforts in Michigan is nearly $50 million.
Signs and Symptoms
Infestations of the emerald ash borer can be difficult to
detect. Symptomatic trees display thinning and dieback of the upper one-third
of the crown. Root
and stem suckers (epicormic shoots) are produced by affected ash trees directly
below borer activity. A definitive sign of this exotic pest is the D-shaped
adult emergence holes, first seen in the top of ash trees; native borers attacking
ash trees have round or oval emergence holes and often work near the bottom
of host trees. Woodpecker activity is a helpful indicator of the presence of
insect borers in a tree, since these birds can be seen from the ground.
Beetles
on the Move
Adult beetles can fly one-half mile from an infested host tree,
constituting natural spread from infested sites. People have inadvertently
spread this new
exotic pest. Satellite infestations in Maryland and Virginia resulted from
shipments of nursery stock. Infestations in Ohio were largely the result of
ash firewood, branches and log movement. Although there are quarantines on
ash trees and wood products in Michigan and Ohio, a recent inspection effort
in Michigan on Memorial Day weekend found nearly 5,000 pieces of ash firewood
carried in various vehicles.
Research Results on Management Tools
Researchers at Michigan State University
and the United States Department of Agriculture conducted experiments during
2003 to determine insecticide strategies
for management of the emerald ash borer. Detailed findings are posted at http://www.emeraldashborer.info/files/bulletin.pdf.
Since this exotic pest has not been found in Iowa, preventive insecticide applications are not recommended at this time. Unfortunately, these products are only effective during one growing season and would need to be applied each year to provide some degree of protection.
How You Can Help
Suspected sightings of emerald ash borer adults or symptomatic
trees should be reported to the State Entomologist’s office, any local
Iowa State University Extension office, or any district forester with the Iowa
Department
of Natural Resources. Remember, there are native insect borers that colonize
declining or dying ash trees and are not of special concern.
A photographic gallery for the emerald ash borer can be found at http://www.insectimages.org.
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ml: isugarden
Editors: Five color photos, suitable for publication, are available at below. Click on each thumbnail photo to download a high resolution photo.
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Caption: Epicormic branches on ash tree developing after emerald ash borer attack. Photo by Joseph O’Brien, USDA Forest Service, http://www.insectimages.org. High resolution photo is 1 MB. |
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| Caption: Emerald ash borer larval feeding galleries under bark. Photo by Ed Czerwinski, Ontario Ministry of Natural Resources, www.insectimages.org. High resolution photo is 1.3 MB. |  |
| Caption: Emerald ash borer larva. Photo by David Cappaert, Michigan State University, www.insectimages.org. High resolution photo is 1 MB. |  |
| Caption: Emerald ash borer larva. Photo by David Cappaert, Michigan State University, www.insectimages.org. High resolution photo is 350K. |  |
| Caption: Emerald ash borer adult. Photo by David Cappaert, Michigan State University, www.insectimages.org. High resolution photo is 350K. |  |