Ash borer confirmed in Decorah

The tree-killing pest has been found in 31 Iowa counties

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With the recent discovery of the emerald ash borer in Decorah, the tree-killing pest now has been confirmed in 31 of Iowa’s 99 counties.

After a consulting arborist noticed evidence of ash borer damage, further investigation revealed distinctive S-shaped galleries and a larva beneath the bark of the infested tree, according to the Iowa Department of Agriculture and Land Stewardship.

The U. S. Department of Agriculture Systematic Entomology Laboratory confirmed the larva was an immature emerald ash borer.

The Decorah discovery was the state’s second confirmation of the year, following last month’s confirmed infestation on the University of Iowa campus in Iowa City.

Andy Nimrod, director of Decorah’s Parks and Recreation Department, said the only surprise about the discovery is that it didn’t happen sooner.

“We thought it would be here last year,” said Nimrod, noting that Winneshiek County lies just west of Allamakee County, where the state’s first infestation was confirmed in 2010.

Though the city’s tree inventory is only partially complete, Nimrod said his impression is that ash trees are prevalent on some boulevards but much less so in city parks.

“We haven’t planted any in the last 25 years,” he said.

The plan going forward, he said, is to remove ash trees as they begin to show symptoms and replace them with a more diversified mix.

Symptoms of infested ash trees include thinning or dying branches in the upper canopy, evidence of woodpecker activity, S-shaped feeding galleries under dead or splitting bark, D-shaped exit holes and water sprouts along the trunk and main branches.

Federal quarantines are in place to restrict the movement of hardwood firewood, ash logs, wood chips and ash tree nursery stock out of Iowa into non-quarantined areas of other states.

Although the treatment windows remain closed through early April, landowners interested in protecting a valuable and healthy ash tree within 15 miles of a known infestation should have landscape and tree service companies bid on work and then review the bids before beginning the treatment.

l Comments: (319) 934-3172;

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