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Emerald Ash Borer

Emerald Ash Borer

Emerald ash borer (EAB) forces tree owners and managers to ask how ash trees can be saved, within a climate of limited tree care budgets.  Categorizing ash trees by treatment priority can lead to difficult but necessary decisions in creating an EAB treatment plan for your property.

“Can my ash tree be saved from emerald ash borer (EAB)?” We’ve been getting that question a lot since the emerald ash borer was detected in Colorado in September of 2013. The answer is yes. But a more important question to ask is, should I save my ash tree?

First some background. As of this writing, the emerald ash borer has only been detected in one place, and that’s Boulder.  Colorado is now the 22nd state to detect it.  EAB has killed over 50 million ash trees and could threaten the Denver metro area which has around 1.4 million ash trees.

Those are some macro-level numbers but what about your ash trees? Should you try to protect everyone on your property? The answer I give to folks is that not all the ash trees in your yard are of equal value.

Consider letting nature takes its course or removing your ash tree if it meets some or all of the following criteria.

If your ash is 50 or more years old.

The average ash in Colorado can live 40 to 70 years. If your ash is in that range, you could spend thousands of dollars on preventive ash borer trees and then just have it die on you from old age. Is that worth it versus perhaps planting a new tree nearby? In most cases, it’s not.

Your ash is brand new

If you just planted ash, you could spend literally tens of thousands of dollars to keep it alive for the next 50 years. Starting over with a better tree species will almost certainly save you time and heartache. Because while ash trees can be protected from ash borer, nothing is guaranteed. While arborists are not entirely sure how long EAB inhabits an area once it appears, the history of other invasive pests suggests it will be here for a long time.

Your ash is in a bad spot

If your ash is planted too close to your house or under a power line, it may be best to remove it and plant a new tree.

Your ash is already infested with lilac/ash borer

In Colorado, we’ll need to approach emerald ash borer differently than in many other states. That’s because ash/lilac borer a similar pest of ash trees is already boring holes and killing ash trees. While not as aggressive as EAB, it does reduce the effectiveness of treatments designed to prevent EAB.  So if your tree is heavily infested with ash/lilac borer already, it may be best to remove and replace it.

What about the ash trees I do want to save?

Before thinking about what to do about EAB which has not yet been detected in Denver or neighboring cities,  I recommend tackling lilac/ash borer first.  Here is what will need to be done.

  • Controlled with a trunk spray.
  • Recommended timing April to May.  Cost is minimal
  • Control depends upon complete coverage of the trunk

Once the lilac/ash borer is controlled, there are four insecticide options for EAB control.

Best Practices for Emerald Ash Borer Control

  1.    Preventive bark and foliar cover spray.
  • The cost is minimal.
  • Control depends on the complete coverage of the canopy, branches, and trunk.
  • The two-part application did 4-to 6 weeks apart.
  • Recommended timing 1st spray April to May with a follow spray 4-6 weeks later.
  1.  Soil injection
  • The cost is moderate.
  • Control depends on getting full uptake of the active ingredient from the soil to the leaves. Winter water helps move the active ingredient into the tree.
  • Recommended timing is mid to late spring or mid-fall.
  1.   Systemic bark spray
  • The cost is moderate.
  • Control depends on getting full uptake of the active ingredient from the soil to the leaves. Winter water helps move the active ingredient into the tree.
  • Recommended timing early May to June.
  1.   Trunk injection
  • Cost is expensive
  • Control depends on getting full uptake of the active ingredient from the soil to the leaves. Winter water helps move the active ingredient into the tree.
  • This treatment effectiveness is weakened if the clear winged ash borer or ash bark beetles are already in the tree.
  • Recommended timing early May to June.

Executing these methods will be very important.  A quality tree service that has an ISA-certified arborist, and is properly trained to apply insecticides will affect how well EAB treatments work. Look to see if the tree service has a QS designation through the Colorado Department of Agriculture.

Hiring an amateur tree service that is not legally licensed by the state of Colorado will result in the only solution they can provide you, tree removal.  It’s like the age-old adage “if the solution you have is a hammer, every problem looks like a nail.” If a tree service is not legally capable of providing ash borer treatment, the only thing they’ll recommend is to remove the tree.

How You Can Prevent the Spread of Ash Borer

Federal and state agencies have established quarantine areas that restrict the movement of ash materials (nursery stock, logs, mulch) and firewood across certain state and county lines. To be safe, buy your firewood locally and make sure you burn it before spring. This will not only help prevent the spread of EAB but also mountain pine beetle, IPS engraver beetle, and 1000 canker.

There is a thought, put forth by Whitney Cranshaw, Professor of Entomology at Colorado State University, that since all ash trees in Colorado stem from human planted trees, there may exist natural barriers that prevent emerald ash borer (EAB) from spreading as vigorously as it has in states like Michigan, which have hundreds of millions of naturally occurring ash species. This may give us the possibility to truly quarantine it in Colorado.

Tree services that tell you that EAB is in Denver already should be avoided, as that is simply incorrect. Until the State Department of Agriculture makes a definitive statement of detection, a reputable arborist should disclose that EAB is not yet confirmed in the metro area.

However, it pays to consider your options now, as the frightening thing about EAB is how quickly it can go from being present in spots to being a full-on epidemic. High-profile and high-value ash trees need a plan of action now.

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