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Extension Line

Wednesday, May 26, 2010

The recent discovery of the emerald ash borer (EAB) in Allamakee County has increased interest in this invasive insect and what Iowans can do to protect ash trees (Fraxinus species) on their property. Iowa State University (ISU) Extension is collaborating with Iowa state regulatory agencies and local officials to limit the spread of EAB into other areas of Iowa.

Treatment options to protect ash trees from this destructive pest are available, but careful analysis is needed to prevent the spread of false information and excessive and needless use of insecticides. Forest, horticulture and insect specialists with ISU Extension have developed a guide that outlines your management options against EAB.

The first step is confirming that you do have an ash tree. Only ash trees are susceptible to EAB attack; all species and varieties of ash trees are at risk. Second is determining if the ash tree is in vigorous health. Trees must be healthy and growing for insecticide treatments to be effective.

Compromised trees that have mechanical injuries, loose bark or thin canopy or are struggling to grow in poor sites with limited rooting area, compacted soil or other stresses are not worth treating. If the tree is apparently healthy and is valuable in your landscape, then preventive treatment options may be considered.

Insecticide control measures against EAB should not be used unless you live within 15 miles of the confirmed EAB infestation. Based on the May 14th announcement of finding EAB in Iowa, the upper portion of Allamakee County is within this risk zone. However, due to the isolated incidence and associated remote terrain of the infested site, treatment in Iowa is still not recommended at this time.

Protecting ash trees with insecticides is a long-term commitment. Most treatments will need to be reapplied annually or twice per year for an interminable number of years to protect the tree. With that in mind, many homeowners would be money ahead to remove and replace susceptible trees.

ISU Extension has a publication on this topic, PM 2084, "Emerald Ash Borer Management Options," released June 2009. The publication can be downloaded from the ISU Extension Online Store at www.extension.iastate.edu/store. The North Central Region IPM Center's "Insecticide Options for Protecting Ash Trees from EAB" was issued May 2009 and is available on the ISU emerald ash borer website, along with a full list of EAB detection and education activities, www.extension.iastate.edu/pme/EmeraldAsh....

It is estimated that there are approximately 90 million ash trees in Iowa. Over the next several years, let's enjoy the ash trees in the landscape while we can. Begin checking the condition of your ash trees and note those that are declining or otherwise in poor health. Such high-risk trees should be considered for future removal and replacement.

When replacing ash trees consider species diversity and site conditions. Stop by the local ISU Extension office for a list of recommended trees for the Iowa landscape.