Owners of ash trees are faced with some potentially big decisions about how to protect their trees against the destruction of emerald ash borer.
Although there is no perfect solution, insecticides are available to protect high-value trees.
To help Iowans better understand their options, a group of specialists with Iowa State University Extension and Outreach recently published a guide called “Emerald Ash Borer Management Options.”
In this four-page resource, the specialists explain how to determine the value of ash trees, the cost of treatment and how to compare the different treatment options available.
Once emerald ash borer is confirmed, ash trees within 15 miles are considered at risk, according to Laura Iles, director and extension plant pathologist with the Plant and Insect Diagnostic Clinic at Iowa State University.
“Once EAB is established in an area, all untreated ash trees will be killed,” she said. “You don’t want to wait until EAB is attacking your tree before you begin treatment.”
According to the publication, pesticides are effective at treating healthy trees in yards and parks. Treating large wooded areas is not practical or cost effective – and may exceed the per-acre pesticide application limits that must be followed.
Iles said it’s necessary for a tree to be healthy before treatment so the tree can transport the insecticide to the top, where the ash borers usually begin feeding. Trees with less than 30% dieback at the crown are considered the best candidates.
Depending on the size of your tree, pesticides can be applied as a trunk injection, soil drench, soil injection or basal trunk spray. The publication gives the pros and cons of each option and the range of time it takes for the tree to distribute the insecticide, which can be as little as one week or as long as eight weeks.
Iles said the question of whether to treat or not is commonly asked. The answer boils down to gathering information and making an educated decision. If the property owner wishes to have the trees removed, or replaced with something else, that option might make most sense. Or if there are a lot of ash trees on a property – such as a golf course, it might make sense to treat some trees and remove others.
“There is no right answer for every situation,” she said. “The best thing is to start making a plan for your ash trees and whether you want to protect them or remove them. Trees will need to be protected as long as you want to keep them alive since EAB will not disappear, but you can choose to protect a tree for any time period that best meets your needs. Some people plan to protect a tree for as long as they can, some people choose to protect their ash for a shorter time period as they establish new trees, and some people chose not to treat at all and remove their ash once EAB reaches their area.”
Other authors include Mark Shour, retired extension specialist in entomology; Donald Lewis, professor and extension entomologist; Jeff Iles, professor and chair in horticulture; and Billy Beck, assistant professor and extension forestry specialist at Iowa State University.