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Wednesday, October 30, 2013

A Very Unwelcome Guest

     Maybe it was just a matter of time until the Emerald Ash Borer (E.A.B.) arrived in Colorado.  It had already killed tens of millions of ash trees in 21 other states east of here. Now it's official:  the
Emerald Ash Borer is in Colorado.

     Thankfully, it has not been confirmed in any ash trees outside of the one small and specific area where it was found in northeast Boulder.  But because of its discovery there in September, all of Boulder County is now officially under quarantine.  No live ash trees or untreated ash lumber, firewood or wood products can be moved outside of the county's boundaries.

      Experts with the Colorado State Extension office seem fairly well convinced that the borers came here on infested firewood.  Their best advice?  "Burn it where you buy it!"   Never bring ash or any firewood from one part of the country to another.  That free ride is the perfect way to give an otherwise slow-moving insect a whole new world of tree-killing opportunities.

     By the way, the good folks at Tagawa's are not known for blowing their own horn, but I'm not shy.  Tagawa's nursery staff realized years ago that ash trees in Colorado would likely to be attacked by this borer sooner or later.  Tagawa's quickly began phasing out ash trees as part of our nursery stock.  As a matter of conscience, ash trees were no longer a good choice.   We haven't sold them in many seasons.    One more reason I'm proud to work there.

A pretty, but deadly bug

     The Emerald Ash Borer is a strikingly pretty bug:  bright metallic green, about half an inch long.  The borer's purple body can be seen when its wings are unfolded.  But as my mother used to tell me, "pretty is as pretty does."  Based on what the E.A.B. does, this is one of the ugliest bugs to hit Colorado in decades.

     The E.A.B. is unforgiving.  Once it has infested a tree, it's usually just a matter of time.... two to four years... until the tree dies.  All species of ash are susceptible.  ("Mountain ash" is not a true ash, and is not a target.)  More than fifty-million ash varieties have died since the borer arrived in Michigan and parts of Canada in 2002.

     Experts at Colorado State University estimate that one in five trees in our Front Range  "urban forest" are subject to attack.  Nearly 100,000 trees in Boulder.... and more than 1.4 million ash trees in metro-Denver, could be at risk.  One state official calls it "the greatest threat to Colorado's community forests since the introduction of Dutch elm disease in 1969."

Signs and symptoms

     Unfortunately, it's common for a lot of trees in our Front Range community or urban forests to look stressed.  Poor care, and putting the wrong tree in the wrong place, result in
trees that don't look their best.   To the untrained eye, a tree that's been hit by E.A.B. may be hard to distinguish from other trees that are simply struggling.

     But there are things we can look for.  The first symptom of an E.A.B. infestation is a tree that's thinning in its crown.... its upper branches.  Even if the rest of the ash tree is fully leafed out, the crown can already be failing.  During the next season or two, the foliage will continue to thin out.  Branches will die.  The Emerald Ash borer claims another victim. 

     There are two sure-fire symptoms we can look for.  First: examine trees for distinct D-shaped exit holes made by the adult beetles as they mature and fly off. 

     And near the exit holes, examine the tree for S-shaped tunnels or "galleries" underneath the bark.  It's this tunneling that damages the trees vascular system and shuts down the tree's ability to carry water and nutrients.  The tree slowly starves to death.

What can we do about E.A.B.?

    Opinions vary about how we as tree-owners and tree-lovers should respond to the arrival of the Emerald Ash Borer, but experts all agree on one fact:  the E.A.B. will not attack any trees other than ash.  Know what trees you have in your yard.  (You might be surprised how many people don't....)  Feel free to bring a bagged sample of a leaf cluster to Tagawa's to have your trees identified.  Tagawa's nursery staff would be happy to help.

     Crews of tree experts are surveying the neighborhood in northeast Boulder where the E.A.B. has been confirmed.  For now, unless you're within five miles of that neighborhood, or unless further infestations of the bug are confirmed, there's only one thing you should do for your ash trees:  give them the very best care you can!!  The less stress, the stronger the tree. 

     That means proper watering, including winter watering.  Be careful not to compact the soil over the root zone or damage the bark or roots during routine yard work.  


     The jury is very much out on the use of chemicals to fight back against the Emerald Ash Borer.   Some tree experts says systemics can help protect an otherwise healthy ash tree.  Systemics are insecticides taken up by the tree's roots or injected directly into the tree by licensed professionals.  Other experts say that in the case of E.A.B., the effectiveness of systemics is far from proven, and may not be worth the cost every year for the life of the tree.  Also, the chemicals most often used for E.A.B. are suspected of damaging beneficial insects like honey bees. 

     While the research continues, know that C.S.U., the Colorado Department of Agriculture, the U.S. Department of Agriculture and many other groups are working hard to organize the best defense possible against this invader.  Links to their websites are listed below. 

Colorado State University Extension

Colorado Department of Agriculture

U.S. Department of Agriculture

Multi-agency Emeral Ash Borer website (E.A.B. elsewhere in U.S.)