Emerald Ash Borer: What to Look For

I attended the Minneapolis Home and Garden show last week, and after viewing the gardens and checking out all the cool gadgets, I stopped in the MSHS room to buy a few lily bulbs. While there I visited with a young woman from the Minnesota Department of Agriculture who was handing out information on the Emerald Ash Borer, which has been discovered in two places in Minnesota. While there are several signs of the borer’s presence, what’s the first thing most people see? Woodpecker holes. Apparently ash borer larvae are woodpecker candy, so if you see an ash tree that’s getting a real going over by woodpeckers, you may want to look further.

Other signs of an infestation include die-back at the top of a tree, especially if several ash are planted together and they all look bad; D-shaped exit holes in bark; and sprouts of leaves and branches from the base of the tree.

Of course, the first thing to do when scouting for Emerald Ash Borer is to make sure you are looking at an ash tree.  I put this guide up a couple of years ago, which might be helpful in determining if the tree you have is indeed an ash.

Emerald Ash Borer — Learn More About It

With the Emerald Ash Borer infestation in Minnesota now spreading to Minneapolis, this spring is a good time to learn more about the borer, how it spreads, and what can be done to slow it. With millions of ash trees in Minnesota, the borer presents a significant threat to both our forests and the urban landscape.

The Minnesota State Horticultural Society is partnering with the state Tree Care Advisors to present educational sessions on the borer all around Minnesota. Here’s a PDF file with a list of the class locations, dates and times. The same information can be found in the March/April 2010 issue of Northern Gardener.

Update on the Emerald Ash Borer

Saturday I had a chance to attend part of the Minnesota Master Gardener Conference at the University of Minnesota’s St. Paul campus. The campus is about a mile north of the St. Anthony Park neighborhood where Minnesota had its first confirmed infestation of emerald ash borer. Two borers recently were discovered in traps on the campus. So it seemed an appropriate place to be getting an update on this pest.

Entomologist Bob Koch, who has been one of the Minnesota Department of Agriculture’s point people on the borer, noted the importance of slowing the advance of the emerald ash borer. With about 900 million ash trees, the state would suffer economic, environmental and aesthetic damages if the borer spread rapidly. Moreover, unlike many other pests, borers are just as likely to attack a healthy ash tree as a sick one. Because ash trees are somewhat prone to illness and pests anyway, finding the borer has been a challenge. Generally, homeowners should look for these four signs of ash borer infestation on their trees:

  • Canopy thinning — when the top of your tree looks like it’s dying;
  • Sprouting at the base of the tree;
  • Woodpecker feeding — of course, woodpeckers could be feeding on lots of bugs, but the woodpeckers have proven to be pretty reliable, Koch said.
  • Bark splitting.

The borers themselves leave behind galleries in the cambium layer directly under the bark of the trees where their larvae eat and grow, and sometimes borers can be found through the presence of D-shaped exit holes that the grown borers make when they leave the tree of their birth to mate and spread havoc elsewhere.  Finding the holes is not as easy as it sounds, Koch said, and even on trees with a known infestation trained entomologists have difficulty detecting the holes. In other words, this is one tough, sneaky bug.

The Master Gardeners reported that, as the commenter on Locally Grown noted, many people do not know whether they have an ash tree. For more information on identifying whether you have an ash, check out this Michigan extension guide.

Master Gardeners also reported a lot of confusion about whether to treat for emerald ash borer with insecticides and when to treat. Generally, the ag department advises homeowners not to treat unless you live within 15 miles of an infestation — so basically, if you are in the Twin Cities, you might want to consider it. If not, probably not. The next question is what to use. There are a couple of chemical choices, but none of them have been tested on ash borer over a long period of time. Imidacloprid is the most commonly used active ingredient. (Koch noted that a chemical called Tree-age (Emanectin benzoate) has had better than average results.) Some insecticides are applied as soil drenches, but it seems the more preferred application is by trunk injection in early May to mid-June, which is the time the borers emerge from the tree.  For more information on insecticide options, check out the downloadable bulletin put together by the North Central Integrated Pest Management Center, which is a co-op of university bug experts.

Here’s what I took away from this helpful program. 1) Know if  you have an ash tree and how much you care about it. I’ve got two and one of them I would hate to lose. If I lost the  other, it would be too bad, but not a big deal. 2) Know the signs of ash borer infestation and watch your trees. 3) Start thinking about whether you want to treat your trees and how you would do that. We were approached about doing a soil drench of imidacloprid this fall and I said no. I’m not within 15 miles of the infestation and, if I do treat, the trunk injections seem more targeted and less likely to affect other plants or animals.

Finally, kudos to the U, the ag department, the feds and all the local government agencies around Minnesota who have really gotten on top of this issue. Minnesota had several years to prepare for EAB and clearly that time was used well. The quick action in St. Paul (all the infested trees were cut and incinerated within days), the thousands of purple traps around Minnesota, training folks like the Master Gardeners–these are all steps that will protect trees.

What an Ash Tree Looks Like

IMG_5876One of the commenters on  Locallygrownnorthfield.org, a community Web site where I live, noted that while she has seen lots of pictures of Emerald Ash Borers, she has not seen any of an ash tree. Good point! Ash are commonly used trees in Minnesota, so many people have them in their yards. The photo at left is a shot of a Marshall seedless ash in my yard. (Click on any of the photos for a bigger view.) It was planted as a mature tree 10 years ago, and as you can see, it’s a lovely shade tree, nicely shaped and taller than the roof of our house now.

IMG_5875IMG_5879At left here is the bark of an ash tree. The borer is usually discovered when homeowners notice thinning at the top of their tree and dieback. Arborists will remove some bark and look for the characteristic galleries of the borer. The photo at right shows a typical leaf cluster from an ash. The small dots and slight dieback on the leaves indicate I have a small insect problem with this ash — but it is not the emerald ash borer. (I checked with the folks at Knecht’s about it, but forgot what they said it was, except “don’t worry.”)

Hope this is helpful for those uncertain about whether they have an ash tree in their yards.

If You're Worried About Emerald Ash Borer…

EABcolumnMay08You may want to check out the attached PDF of an article written by plant pathologist Katharine D. Widin in the May/June 2008 issue of Northern Gardener. As you may know, the presence of EAB  in St. Paul was confirmed last week. Experts like Kathy, who is the magazine’s regular contributor on plant health issues and runs her own company helping individuals and organizations deal with pests, rots, diseases and other plant issues, have been expecting to find the borer here for awhile. The article describes the history of the EAB infestation in North America, tells how to spot an infestation and what to do about it, and includes pictures of both the borer and the galleries that it leaves in trees that have been infested.

For more information on this issue, check out the state site on Emerald Ash Borer.