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Neighbors Growing Together | Nov 1, 2014

Garden Talk: Preparing for big problems

By JEAN THOMSON, Master Gardener | May 30, 2013

A very small insect poses a very big threat to Iowa landscapes. While the emerald ash borer is no more than 1/2 inch long, it is deadly to all varieties of ash trees.

Native to Asia, the emerald ash borer was first officially identified in the U.S. in 2002 in Michigan. Since then, it has spread inexorably throughout the Midwest. In 2010, its presence was confirmed in Allamakee County in northeastern Iowa.

When they are infested, ash trees typically die in 2 to 4 years, becoming hazardous if they are in populated areas. The first signs of damage are dieback and thinning foliage.

As it has spread over the last decade, the emerald ash borer has killed tens of millions of ash trees. The scope of the problem facing Iowa will be apparent from these numbers: we have approximately 52 million woodland ash trees and 3.1 million urban ash trees.

Towns and cities throughout Iowa, along with private landowners, will have to consider carefully the prospect of the death of many large trees. Anyone who does not budget for tree removal and replacement may face significant unexpected costs.

Research continues into chemical and biological control of the emerald ash borer. However, using insecticides to control insects that feed under the bark has always been difficult.

Iowa State University currently recommends preventive treatment only for street or yard trees, starting when the emerald ash borer is confirmed 15 miles away. Trees must be healthy enough to carry a systemic insecticide throughout the entire tree. Allamakee County is certainly more than 15 miles from Henry County, so no treatment is recommended here at this time.

Here are some common-sense recommendations for preparation:

1. Do not move firewood from its area of origin. Transportation of wood products, including firewood, has accelerated the progress of the emerald ash borer.

2. Inventory your own yard, woodland, and neighborhood street trees. Know where the ash trees are and what condition they are in.

3. Stay alert for updated information. Government agencies, universities, and horticultural organizations will be participating in public education.

Right now: The Plant and Insect Diagnostic Clinic at ISU is seeing plants with curling of leaves and tips of growing points. This damage has been noted in tomato, squash and bean plants and in trees.

The likely cause is exposure to growth regulator herbicides such as 2,4-D and dicamba, commonly used for weed control in lawns.

To lessen the risk of damage to sensitive plants, do not spray lawn chemicals on windy days, and do not use treated grass clippings as mulch.

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