Emerald Ash Borer and Camels Part II

June 17, 2016

Emerald Ash Borer & Camels - The Rest of the Story

Three weeks ago, I wrote a column about how treating your trees for Emerald Ash Borer (EAB) was like treating your trees to prevent camel damage. It wasn’t necessary at this time because EAB, or marauding camels, hadn’t been detected in Nebraska. I encouraged people to wait until EAB had been detected within 15 miles of their ash trees. That hasn’t changed! What has changed is EAB, but not feral camels, have been detected in Nebraska.

I told my co-workers I wondered how long it would take to get my first call from someone who was sure they had EAB following the Nebraska Department of Agriculture news release about EAB being detected in Nebraska. Sure enough, within hours I had an email from a concerned homeowner who heard the story on the news that evening, went out and looked at their ash trees, and was sure they had EAB. They wanted me to come look at their ash trees ASAP.

Just so I don’t build any false expectations, I did not look at those trees and I will not look at other ash trees unless there is a strong indication that EAB is present. What is a strong indication? Two things, the actual presence of the insect or D-shaped exit holes the insect chewed through the bark. Other indicators that EAB might be present, but are not as conclusive, include a thinning of the crown and suckers from the trunk or lower branches on the tree.

Other insects can be confused with EAB. If you have a suspect insect, capture it and put it in a jar or bottle with a tight sealing lid. Do not poke air holes in the lid. Also, do not put it in a plastic bag or envelope. If you do, you will likely bring me an empty bag or envelope with a hole chewed in it by the time you get to my office. Also, do not stick an insect in an envelope and mail it without putting it in some kind of protective container. You know how a road kill raccoon can look like it is 10 feet long on the highway? Automated letter handling machines do the same thing to insects on a smaller scale!

There are several borers that attack ash trees in Nebraska and have for many years. Although they are not good for an ash tree, their damage is less severe and won’t lead to as rapid a decline and death of the tree as EAB will. The big difference between them and the EAB is these other borers all leave an O-shaped exit hole while the EAB leaves a D-shaped exit hole.

As I mentioned a couple weeks ago, EAB are poor flyers and the majority will only fly a mile or two from the tree where they developed and even the hardiest flyers only flew up to 12 miles. That is why it is recommended to not consider treating trees until EAB has been detected within 15 miles of your ash trees. The current treatment consideration zone extends from near Fort Calhoun to Elkhorn to Plattsmouth.

Also, to help prevent the accidental spread of EAB, the Nebraska Department of Agriculture has established a quarantine area that includes Douglas, Dodge, Cass, Sarpy and Washington counties. Ash materials including trees, logs, branches, roots, green lumber; hardwood firewood and chips; and viable (live) EAB must not be transported out of quarantine areas.

Unfortunately, EAB will continue to spread across Nebraska. When it gets here is anybody’s guess, but there is no advantage to start treating a tree before it is close. In fact there are many good reasons to NOT start treating your ash trees for EAB until it is detected within 15 miles of you. Here are my “Top 10” things you should know about EAB before treating your ash tree.

10        Applying treatments before EAB is detected within 15 miles of your ash trees OR after the optimum treatment times when EAB is present is not effective, will not provide the desired results, and is generally a waste of time and money and puts pesticides in the environment unnecessarily.

9          The most common treatments a homeowner can apply is a soil drench which may not be adequate to protect large trees, especially trees with trunks over 15 inches in diameter.

8          Flowering plants near trees treated with a soil drench can pick up the chemical from the soil, exposing bees, butterflies, and other pollinators to the toxic materials.

7          Professional arborists have more options for EAB treatments including trunk injections, which are generally more effective (especially on larger trees over 15" in diameter) and limit pesticide exposure to non-target insects and the environment.

6          Tree injections are effective in controlling insect pests, but cause injury to the tree because drilling a hole for the injection opens the trunk to insect pests and decay fungi. Trees that are repeatedly injected will eventually show decline in tree health as a result of damage at the injection sites.

5          Different products can be used for injections. Some provide control for one year while another provides control for two years. However, the longer lasting product is about twice as expensive so you end up spending about the same amount per year. The cost will vary with the size of the tree. The advantage of products that last two years is over several years, half as many holes are drilled for injection sites.

4          Timing is critical for treatments to be effective. Soil drenches need to be applied in March or April, depending on the product. Injections need to be made by mid-June. Either kind of treatment made after the optimum date is less effective because it doesn’t allow time for the pesticide to be moved throughout the tree before insect damage has already occurred.

3          EAB will attack any ash trees, but seems to infest weak or diseased trees first. To prevent your tree from being at the top of the EAB's menu when it arrives, do everything you can to keep it healthy including a ring of organic mulch extending 10-15 feet out from the base of the tree and watering the tree during prolonged dry periods. This will not prevent EAB damage, but if your tree is healthy, it may buy you time to successfully treat a tree if it is attacked by EAB.

2          EAB generally requires a minimum of several years to kill an otherwise healthy ash tree. Treatments can be successful in protecting healthy trees, even after being attacked by EAB if the tree has not lost too much of its canopy. If you can see sky when looking through the tree’s canopy at a distance, recovery is less likely.

1          Applying treatments before EAB is detected within 15 miles of your ash trees OR after the optimum treatment times when EAB is present is not effective, will not provide the desired results, and is generally a waste of time and money and puts pesticides in the environment unnecessarily.

Many homeowners feel like they have to do something now. While treating a tree isn’t a good option, there are several things they can do. Homeowners can decide which trees are candidates to be treated and which ones will be removed. I would not recommend removing an otherwise healthy ash tree now. It might give you several more years of benefit before EAB arrives here.

Another thing you can do now is start other trees to take the place of an ash tree that you anticipate will be removed in the future. When selecting a replacement tree, I recommend homeowner use “Wilson’s Rule of 2.” (I can call it that because I made it up!) If you live in town, plant a different species than is planted within two blocks of you and if you live in the country, plant a different species of tree than is planted within two miles of you.

Obviously you are not going to inventory all the trees in these areas to know what is or isn’t planted, but the idea is to plant tree species that are different than those commonly planted. That way when the next tree epidemic like Dutch Elm Disease, Pine Wilt, or Emerald Ash Borer comes through attacking commonly planted trees, you will have something different that will be less likely to be affected.

This will give you an idea how much some trees are planted or overplanted. In the 1980's, the Nebraska Forest Service worked with local city tree boards to inventory the public trees in their community. Public trees include those found between the sidewalk (or where there would normally be a sidewalk) and the curb and also trees found in other public areas such as parks and cemeteries and around public buildings such as schools, libraries and city offices.

I realize this information is almost 30 years old, but it probably is still fairly representative considering how often we replace trees. This shows the percent of ash trees and actual number of ash trees in each community’s public tree survey. Remember, this is just the public trees. It does not include those in home landscapes that would be between the sidewalk and homes.

For more information on EAB, visit the Nebraska Forest Service EAB website at www.eabne.info.  There are images here to aid in identification of the insect or its damage, a map of the treatment consideration zone and quarantined area, and many other links that include helpful information on a variety of topics related to EAB. The maps will be updated in the future to reflect the spread of EAB across the state.