I have been closely studying the spread of Emerald Ash Borer (EAB) for quite a while now, as you may know if you follow my posts here and on the Jacobs Tree Surgery Facebook page. I first saw EAB in person in 2010, shortly after their arrival in Pennsylvania.
Closer to home, EAB was first detected in Bucks County, in the Warrington area, in 2012. Over the past 5 years, I have watched the Bucks County EAB population increase to peak density – it would now be difficult to find a healthy ash tree in southern Bucks or the far eastern portion of Montgomery County.
Last summer, I saw infestations in the middle of Montgomery County for the first time (Center Point). I then began seeing evidence of them throughout the western part of the county. I started marking a map with personally confirmed EAB locations over the winter and soon realized it is now everywhere in the area I routinely service.
Mated EAB adults travel an average of approximately 2 miles, and up to 6 miles, from where they emerge (USDA studies). So you can see from the pins on the map that all of the ash trees in Montgomery County are likely to be attacked this summer.
EAB adults are just now starting to emerge. I found this one on Saturday in Horsham.
After they emerge from the tree where they have spent the immature portion of their life cycle, they will feed on the leaves of ash trees for a week or so before mating, and in about 3 weeks they’ll start laying eggs. Eggs will hatch in about another 2 weeks, and the young larvae will immediately bore into the tree and begin eating the tissue beneath the bark.
When a healthy ash tree is first attacked by EAB, it does not immediately die. Usually only a small number of eggs are deposited on it the first year, and the tree can survive the resulting damage. But the following season, each of the maturing females will lay many eggs, and the EAB population will rapidly increase. Within a few years, there will be so many EAB larvae feeding on the tree that they’ll completely destroy all the tissue beneath the tree’s bark, and the tree will die. Here’s what the progression looks like. This ash tree is on Rt. 611 in Willow Grove.
The oval areas are the damage from the first few beetle larvae to feed on the tree. The tree survived those injuries, walled them off, and they began to close, but the following year there were so many new eggs laid that the entire tree is riddled with larval galleries.
The most effective treatment to control emerald ash borer and keep an ash tree alive is the naturally derived insecticide emamectin benzoate, injected into the trunk of the tree. Because this treatment is invasive – it involves drilling holes in the tree – I have recommended reserving its use until the pest is actually present and infestation is imminent. That time has now come for all of Montgomery County. Valuable ash trees that are still healthy can be saved, but the window for taking action will soon close.