|Colorado Emerald Ash Borer Myths
September 23, 2015, will mark the two year anniversary of the detection of emerald ash borer (EAB) in Colorado. It is estimated that the insect was present in Boulder for at least 4 to 6 years prior (2007 – 2009) to its detection in 2013. Efforts to detect EAB and ‘find the edge’ of the infestation continue to dominate the efforts of those responding to the invasive pest. But the insect has proven to be very difficult to find in the early stages of infestation, frustrating those of us who work in arboriculture, pest management, diagnostics, and support sustainable urban landscapes. As such there is much confusion and misinformation circulating regarding EAB. It’s time to set the record straight.
Myth #1 – All declining and dead ash in Colorado must have emerald ash borer.
This statement is far from true. Many ash all over the Front Range are exhibiting symptoms indicating signs of distress, which include the tiny clusters of new growth, thinning of the canopy (dropping leaves), suckering or growth of stems and leaves at the base of a tree, splitting of the bark and signs of boring insects.
There are many boring insects that affect ash. The most common insects causing holes in the bark of ash trees are lilac ash borer and ash bark beetle. It has been surprising to tree experts at how much damage lilac ash borer, ash bark beetle, and other pests, such as flatheaded apple tree borer, ash trees can tolerate. These naturalized pests cause similar damage to EAB in ash trees. The big difference is ash can coexist with the naturalized pests, while an infestation of EAB will kill any ash tree within 3 or 4 years.
The naturalized boring insect pests we commonly find in our declining ash trees are not working alone, environment plays a major role. Mother Nature has not been kind to Colorado trees of all kinds, ash included, in the past few years. Much of the damage expressed by ash and other trees throughout the Front Range was caused by damage suffered in November 2014, when we experienced a 77 degree drop in temperature over just a few days. This was extremely damaging to ash and many other tree species in our area that had not ‘hardened off’ appropriately.
The fact remains that as of September 2015, EAB has only been detected within the city limits of Boulder. And even in Boulder, many declining ash are being attacked by the naturalized pests, not EAB.
Myth #2 – Pesticides labeled for EAB won’t work once a tree is infested with this pest.
Not completely true. Multiple research studies on EAB in the Midwest have proven that several pesticides will control EAB even after an ash has become infested. This is not to say that pesticides will save every ash or that pesticides should be used in all cases. The decision to use a pesticide is a personal choice of the land owner/manager and should be based on the following:
· Health or condition of the tree. Ash trees with more than 30-40 percent canopy dieback, or damage or injury to the trunk of the tree, including severe frost cracking or splitting, will not respond well to treatment. If you have ash trees with canopy dieback or severe trunk injury, consider removal and replacement with a species other than ash.
· Location of the tree. On a regional level, the current recommendation is to only consider applying pesticides for EAB management if the tree is located within the quarantine area or is close to the known area of infestation (City of Boulder). On a site-specific level, if a tree is located under power lines, is too close to a structure, is in a parking lot or other area with limited root space, or just plain poorly sited, consider removal and replacement with a species other than ash, rather than use of prolonged chemical treatments.
· Economics or value the tree provides. Trees provide value and services to our landscape. They increase property values, shade and aesthetics, and provide services to our communities by helping to mitigate storm water run-off and reduce cooling costs by shading our buildings and reducing temperature. They also filter the air and help mitigate pollutants.
Myth #3 – All pesticides labeled to control EAB are harmful to pollinators.
Not true, as long as the law and label directions on the product are followed. The pesticides used to control EAB are insecticides, and an insecticide can potentially kill a wide variety of insects, including those that are pollinators. However, pesticides are highly regulated and researched so that misuse and harm to non-target organisms (pollinators and other animals and plants) is minimized. All of us are bound by law to follow the label on an insecticide. The label will tell us if there is risk of harm to pollinators when using a particular product, and how to use that product to minimize that risk. For example, if a product is potentially harmful to honeybees, the label directions will tell us to avoid applying the product to flowering plants when bees are present.
Here is an example of the label instructions on a commonly used insecticide for backyard settings: