What do baseball bats, bugs, and ash trees all have in common? (And no, this is not some lame, bar room joke.) Well, they are all part of the "Promise America" campaign initiated by the US Department of Agriculture. This campaign has been launched to educate everyday homeowners and gardening enthusiasts alike about the invasive insect pest called the Emerald Ash Borer (Agrilus planipennis) which is killing literally millions of ash trees across America. There are a handful of different species of ash trees that are native to the Midwest and the East Coast that are commonly planted as great urban street trees throughout the US, including Denver. Wood from ash trees has traditionally been used to make baseball bats. Unfortunately, all of our native ash, including White Ash (Fraxinus americana) and Green Ash (Fraxinus pennsylvanica), which are the two species planted in horticulture, are completely at the mercy of Emerald Ash Borer. This tree-killing beetle was first identified in the US in 2002 near Detroit, Michigan and is native to eastern Russia, northern China, Japan, and Korea. No one knows for sure how or when it got here, but most likely in the 1990s it came to the US in ash wood used for stabilizing cargo in ships or for packing or crating heavy consumer products. It has now spread into seventeen additional states and two Canadian provinces and continues expanding its range. Its spread has been accelerated by the movement of infested firewood. Last year it was discovered in Kansas for the first time, and people are worried that it will soon be in Colorado. Denver Parks & Recreation’s Forestry Division will begin monitoring for Emerald Ash Borer for the first time this season.
Photo: Adult Emerald Ash Borer
(Leah Bauer, USDA Forest Service Northern Research Station, Bugwood.org)
The Emerald Ash Borer is actually a relatively pretty insect (I say relative, because in my opinion all insects are kind-of gross.) The adult beetles are a bright, metallic green, a half-inch long, and have a flattened back. But the problem is not the adult beetles, it is their larvae. The larvae are a type of flatheaded borer. (By the way, “You are such a flathead!!” makes for a great insult!) Larvae hatch from eggs laid within bark crevices and under bark scales in the spring. They chew through the outer bark of the tree and into the cambium where they feed in the phloem interrupting the flow of nutrients within the tree, ultimately girdling it.
Signs and symptoms of Emerald Ash Borer infestation are yellowing leaves on branches and then dieback generally in the top of the tree canopy first. Sprouting from the base of the trunk can also occur. If you are lucky and look very very carefully, you may see small holes in the trunk that are 1/8” in diameter and that are D-shaped. Complete defoliation and tree death typically occurs within 2-3 years.
Photo: Green Ash dead due to Emerald Ash Borer
(David Cappaert, Michigan State University, Bugwood.org)
Unfortunately there is no simple cure for Emerald Ash Borer. This little beetle has had an enormous economic and ecological impact. The devastation of the insect is remarkable - over 53 million ash trees have died or are dying from the borer and all of North America's 7 billion ash trees are at risk. It is estimated that up to $26 billion has been lost due to the borer in just four Midwestern states. This took into account the cost of lost tree value, tree removal, and tree replacement.
Invasive pests have been incredibly problematic for our urban trees and native forests for the past century. From Dutch Elm Disease to Chestnut Blight to Asian Longhorn Beetle, invasive insects and disease have changed the composition and ecological functioning of our forests as well as their look and feel. So please, “Promise America” that you will not move firewood; that you will burn firewood where you buy it; and that you will plant a diverse selection of trees and not all the same species. Oh, and that old wooden baseball bat of yours may be more valuable than you think!
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