Emerald ash borer infestation alert issued

City Forester Sam Hogenson, in partnership with the City of Decorah Tree Board, is requesting Decorah residents help identify ash trees on their property. Over 400 ash trees have been removed from the City’s boulevards due to endemic emerald ash borer (EAB) infestation. Many ash trees had been planted to replace the American elms which were devastated by Dutch elm disease.

Hogenson said the emerald ash borer is a shiny green beetle native to Asia that has made its way to the United States in packing material. It is an invasive species that destroys white ash, black ash, and green ash trees. No natural predators exist in this country, but experiments are being done using a tiny European wasp which destroys the beetle in the larva stage. The larvae of this beetle feed under the bark of only ash trees. The infestation begins in the top one-third of the canopy and progresses until the tree loses all its leaves. Vertical fissures may appear in the bark. Larval feeding results in a serpentine (snake-like) pattern under the bark. The adult beetle emerges through D-shaped holes in the bark and then leaves to infest other trees.

Woodpeckers can remove large areas of bark and create holes when extracting the larvae. Light brown bark will be exposed where woodpeckers have chipped off the gray outer bark (the result is called flecking). Flecking is easily identified this time of year because woodpeckers are busy foraging for the larvae. In the early stages of the EAB infestation, flecking will appear in the upper canopy of the tree (on smaller branches). As the infestation progresses, signs of flecking will continue throughout the lower canopy and down the trunk of the tree. In most cases, when flecking is noticed on the trunk of the tree, the tree should be removed as soon as possible.

If caught early, emerald ash borer infestation can be treated with an insecticide administered by a professional arborist. Badly infected trees must be removed, and the wood should be chipped or burned. Treated trees may continue to decline in the first year after treatment but should begin to show improvement in the second year. Preventive treatment has not been recommended.

Rhree simple ways to identify an ash tree are 1) look for opposite branching of limbs, 2) compound leaves, and 3) diamond pattern bark. Opposite branching means the branches protruding from the tree limbs have a mate protruding from the exact opposite side of the same limb. A compound leaf has more than one leaflet per leaf connecting to a stem that has a bud at its base. Ash tree leaves typically have 5 to 9 leaflets per leaf. Though young ash trees have smoother bark, the bark on more advanced trees tends to have diamond shaped patterns.

If you have or suspect you may have an untreated ash tree on your property, you are encouraged to consult with a tree expert such as an International Society of Arboriculture (ISA) Certified Arborist.

For more information, please contact City Forester Sam Hogenson at: (563) 277-5153 or by e-mail at: cityforester@decorah.iowa.gov. Additional information is also available on the Decorah Tree Board website at https://www.decorahia.org/tree-board.

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