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ISA Board Certified Master Arborist Drew Stevenson offers advice and treatment plans for EAB and ash trees in Decorah

Posted: Wed, Jun 6, 2018 12:59 PM
Infested Ash Tree

Decorah residents have either experienced ash trees being removed from their own property or noticed ash trees being removed throughout the city due to the emerald ash borer infestation. ISA Board Certified Master Arborist Drew Stevenson, owner of Stevenson Tree Care, believes Decorah is likely in the 6th year of EAB and offers's reader's advice on EAB and treating ash trees.

"The historic mortality cycle of past EAB infestation is about a 10 percent mortality in the 1st through 5th years, followed by a 60 to 70 percent mortality in the 6th through 7th years, with the remaining 20 to 30 percent of ash trees succumbing to the infestation in the 9th or 10th year. Decorah is likely in the 6th year of the EAB infestation and will see significant tree loss in the next 24 to 36 months," said Stevenson.

Stevenson explained the first sign of an infested ash tree is woodpecker flicking, when pieces of bark are stripped from the tree as the woodpeckers are searching for EAB larva. As the tree starts to decline from the infestation, the trees will begin to have smaller leaves in the upper quarter of the canopy. These smaller leaves will give the impression of a thinning canopy. As the infestation grows, the terminal twigs will begin to die, epicormic sprouts (which is a shoot growing from an epicormic bud, which lies underneath the bark) will develop in the lower canopy and the tree will decline from the upper canopy to the ground.

According to Stevenson, the cost of treatment for EAB is no longer extremely expensive. Ash trees with up to 30 percent canopy decline can still be treated and effectively saved from an EAB infestation. Ash trees that are treated before showing signs of an infestation are more likely to be saved from an infestation. Stem injected systemic insecticides are effective at suppressing EAB infestations for up to two years.

Stevenson says insecticide treatment of ash trees to protect against EAB is extremely effective and consistent, even under intense infestation pressure. Stem injected systemic insecticides have a success rate of almost 100 percent in protecting ash trees from EAB, he says.

Just because you see some of the symptoms of an EAB infestation does not mean that the tree is no longer able to be saved.

Stevenson Tree Care offers free estimates for EAB treatments, which includes a structural inspection as well as a health and vigor inspection to determine if a tree is healthy enough to take up a treatment and structurally sound enough to warrant treatment.

"Along with the health and structural integrity of a tree, I believe an ash tree needs to pay for its treatment in energy savings or increased property value.  An ash tree in the correct location can easily save a homeowner the cost of treatment in energy savings. Treatment cost is determined by the size of the tree as well as the level of infestation.  The average 20-foot tree would cost somewhere between $160 to $240, depending on the infestation level, for a 2-year treatment.  Basically $80 to $120 each year to protect a 20-foot ash tree," added Stevenson.

Stevenson concluded with, "The key to replacing our ash trees is diversity, planting no more than 10 percent of trees from one species.  There are many great trees to choose from, but some good options for Decorah would be Ginkgo, Hybrid Elm, Swamp White Oak, Red Oak, Sugar Maple, Hackberry, Sycamore, Linden, Kentucky Coffee Tree, Catalpa, and Quaking Aspen."

As woodpeckers search for EAB larva they pull chunks of bark off of the tree