By Rob Gorden
Emerald Ash Borer is creeping into our ash trees undetected, destroying them from the inside, and threatens to devastate our urban forests, leaving many neighborhoods without trees. The financial impact to cities will be enormous if these trees come down. This pest, a hitchhiker on packing materials originating in Asia, was discovered in the United States in 2002 and has spread to 13 Midwestern states and Canada. Left untreated, Emerald Ash Borer, or simply EAB, is expected to kill every unprotected Ash tree in the country. Considering that Ash trees make up from 20-30 percent of the canopy of our boulevards, with residential ash trees accounting for 4-5 times a city’s tree population, this is an environmental and economic crisis that bears immediate attention.
Trees are generally considered indestructible, so damage from EAB is often severe by the time physical signs are apparent, and hope for saving the tree has diminished. In the space of 2 – 3 years, a tree’s defenses become overwhelmed by the sheer number of these pests which destroy the tree’s vascular system, making it unable to transport food or water. When a tree dies, and the borer’s source of food is gone, they move to the next tree, and the cycle of destruction begins again.
The impact of tree loss to a community is well documented, as countless cities removed trees in the early days of EAB. Tree loss means warmer homes in the summer, and less protection against winter winds, costing you more to heat and cool. Outdoor watering use increases, as have water use rates. Loss of these trees will increase storm water runoff, affect drinking water, increase local street flooding, reduce stream clarity, and hasten habitat decline. Property values are inextricably linked to lush landscaping, and many neighborhoods now lament the removal of their stately trees, replaced by 1-2” saplings.
The good news is that researchers have worked aggressively to find practical solutions to save our trees. Some treatments can be purchased directly by homeowners, but those proven most effective are only available through trained and licensed tree care professionals. Emerald Ash Borer kills every unprotected tree it attacks, so ignoring the pest is not an option. After evaluating your trees, and determining which are ash trees, there are several options including, removal and replacement, or treatments which include; soil drenching, bark spraying and trunk injection.
Removal and replacement. Deciding to remove your ash tree is complicated by many factors, not the least of which is cost. Cities have estimated that to remove, stump grind and replace a street tree averages $750- $1000 when performed by city personnel. Having a commercial tree service remove your tree could be considerably more, especially if the tree is situated in your backyard.
Consider removing those with physical damage, or in decline from other pests, or environmental conditions. Small trees, up to 4 inches diameter, can be removed at a lower cost and may not warrant the attention you will employ to save them. Some trees have sentimental value and only you can assess their true value.
Soil Drenching – Available directly to homeowners, the pesticide is poured into the soil at the base of the tree. This method requires two treatments per year to prevent trees from declining, however, homeowners may legally make only one treatment per year with soil drenches. Research has shown inconsistent results in stopping EAB damage with this treatment. Additionally, these chemicals can bind to the mulch around the tree, further reducing efficacy. Soil Injection, used by contractors, is similar to soil drenching, except a tool is used to inject the chemical below the soil surface allowing legal treatment to be performed twice per year. For cities, and residents, there are legal limits to the number of trees which can be treated per acre. Inconsistent performance and bi-annual treatments make this a less appealing solution.
Other Methods -– Many other methods have been proposed, but few have provided consistent, affordable, and environmentally sound alternatives.
Trunk Injection – is widely considered to be the most effective and consistent method available for preventing EAB from attacking a tree, or killing EAB in an infested tree. It can stop damage even if the tree is already under attack without harming the surrounding environment. A special injection tool places and seals the insect control directly into the trunk where it is immediately taken up by the vascular system and distributed throughout the tree. Research has proven that this method effectively protects trees for two years following a single injection.
The largest Midwestern cities, including Chicago and Milwaukee, chose and are currently using trunk injection with its two years of protection, for over 115,000 boulevard trees, following careful evaluation of the alternatives.
The bottom line: treatment is always less costly than removal and replacement, cities can treat for 40+ years before treatment cost equals the cost of removal. If EAB has been confirmed within 15 miles of your community, don’t wait to treat your trees. Call your local tree care professional and discuss which treatment options they offer, before the damage is irreversible.