So you’ve finally given up hope that your ash tree(s) will miraculously recover from the damage inflicted by the dreaded emerald ash borer and you’re ready to replace trees. Fortunately, there are many excellent non-susceptible choices for northern Illinois municipalities and homeowners, and fall is a good time to plant most varieties. Before we get to that, let’s learn a little about the culprit responsible for attacking our beloved native ash trees which, according to The Morton Arboretum, made up about 18% of the street trees in the Chicagoland region.
The insect responsible for this arboreal carnage, which goes by the initials EAB, was suspected to have been inadvertently introduced in wooden crating from its native Asia and eastern Russia in the 1990s. It was first detected in Canton, Michigan in 2002. In its native lands EAB is kept in check by a variety of natural enemies that evolved with the insect. But in the U.S. and Canada EAB has few natural enemies, which has allowed the insect to spread rapidly. We have unwittingly helped its spread by moving ash firewood and other ash wood products containing its larvae. None of our native ash trees are resistant to EAB, but they seem to prefer green and black ash over white and blue.
In fact, it is the larvae that kill ash trees, not the bright metallic green adult. Here’s the EAB lifecycle in brief: The adult beetles burrow their way out of the tree, mate and soon lay eggs in the cracks and crevices of ash trees. After hatching the larvae burrow through the bark and into the phloem and cambium of the tree. The damage created by their feeding disrupts the nutrient and water flow in the tree, causing it to decline and eventually die. The larvae overwinters inside the tree, pupates, becomes an adult, and in spring the cycle begins again when the adult bores its way out of the tree, leaving the characteristic D-shaped exit hole.
Ash Replacement Tree Options
There is a wide variety of non-susceptible trees from which to choose that are well suited to our climate, and now is the perfect time to plant most varieties. The Illinois State Department of Agriculture web site contains an extensive list of recommended trees and their key characteristics. http://www.agr.state.il.us. What follows are just a few varieties that we at The Growing Place carry and recommend.
Oaks, including our native Swamp White Oak, Bur Oak and Red Oak can be surprisingly fast growing and become beautiful shade trees quickly. These oaks feature great fall color. Native oaks also support more than 500 species of wildlife and are host plants for many butterfly species.
The Triumph™ Elm is bred to be highly resistant to Dutch elm disease. Triumph Elms feature glossy green leaves that turn yellow in fall, a sturdy umbrella shape and medium growth rate. Its habit makes it an excellent street tree. It is also a larval host for many butterflies.
The Tuliptree is a fast growing, stately columnar tree prized for its unique foliage and unusual flowers that bloom high up in the canopy. It features spectacular golden fall color.
Sugar Maples including the varieties ‘Apollo’, and ‘Fall Fiesta’ are excellent choices for replacing ash trees. ‘Apollo’ grows very symmetrically and tops out at 20 to 25 feet, so it perfect for smaller spaces. ‘Fall Fiesta’ makes a great shade tree and grows faster than most other sugar maples. Both of these sugar maples feature brilliant fall color.
Another excellent maple variety featuring deep purple foliage all summer long is ‘Crimson Sunset.’ It makes a good small shade tree (30 to 40 feet) and develops maroon or reddish bronze fall foliage. Other Maple varieties with beautiful fall color include ‘Autumn Blaze‘ and ‘Redpointe’. Both grow to about 40 to 50 feet.
At The Growing Place, Ginkgo trees are always on our list of top trees for difficult sites because of their toughness and beauty. Considered slow growers; varieties such as ‘Autumn Gold’ display brilliant yellow fall foliage.
Ash Tree Treatment
There are systemic insecticides that certified arborists use to protect ash trees from infestation, but it is costly and must be done regularly in order to effectively protect the tree. Frankly, if you live in the region and you haven’t already begun treatments, it’s probably too late to begin—likely, your ash tree is already under attack.
If you are replacing a parkway tree make sure to check with your local municipality to make sure the replacement is on the acceptable tree list. You can also check your local township to find out if there is a replacement program for homeowners.
The lesson learned from the EAB disaster is that species diversity in the urban landscape is essential. We all mourn the loss of our beloved ash trees, but with so many great choices to replace them, the sooner we get planting the sooner we’ll be able to, once more, relax in the shade of our favorite tree.
Posted on 9/18/2014 at 3:00:00 AM