Injections work to save ash trees from borer

Transcription

1 Injections work to save ash trees from borer A decade ago, when the emerald ash borer first was discovered in the U.S., a confirmed outbreak was considered a death sentence for every ash tree for miles around. By: John Myers, Duluth News Tribune August 27, 2013 An ash tree in Milwaukee is injected with an insecticide called TREE-äge. Officials there said it is effective in stopping emerald ash borers. (City of Milwaukee photo) Emerald ash borer A decade ago, when the emerald ash borer first was discovered in the U.S., a confirmed outbreak was considered a death sentence for every ash tree for miles around. The insect that came to the U.S. hitchhiking in packing pallets ate its way through ash trees in Detroit; Toledo, Ohio; and Evanston, Ill., without missing a tree, leaving millions of dead ash lining city streets and across backyards. The only defense recommended at the time was to cut as many ash trees down as fast as possible in infested areas to try to slow the spread. Still, in many cities, the ash borer was killing trees faster than crews could cut them down. Over the past few years, however, researchers and pesticide companies have developed new treatments that cost less and work better to stop the ash borer s larvae from killing trees. We haven t spent the last 10 years sitting on our hands, said Deborah McCullough, professor of entomology and forestry at Michigan State University and a leading expert on what works to kill emerald

2 ash borer. The early treatments often didn t work very well, or didn t last very long. But now we re seeing very high success with saving treated trees. Some treatments are spread on the ground or sprayed on the outside trunks of trees. But the most effective are injected directly into the heart of the tree where it works to kill ash borer larvae that otherwise would tunnel through the wood, starving the tree of nutrients. The pesticides work so well, at least for urban ash, that we re at the point where there s no reason for an ash tree to die from emerald ash borer, McCullough told the News Tribune. And there s certainly no reason to cut down a healthy ash tree because of emerald ash borer. That big change in strategy caught Superior officials off guard in recent weeks as much as the discovery of ash borers on the city s north side. Over the past two weeks, city crews began cutting infested and healthy trees in the neighborhood where the metallic green insect was prevalent. Passersby could see them flying from ash to ash. City crews have been cutting not just sickly trees apparently infested with ash borers, but also nearby healthy trees, figuring they were doomed. We were a week into that (infestation) and the decision we made at that point was to take the ash trees in that neighborhood, based on the best information we had, Mary Morgan, Superior Parks and Recreation administrator, said. But if we go in to cut on a block, it s just more efficient to take them all in that spot so we don t have to keep coming back. While everyone in the tree business expected emerald ash borers to show up sooner or later, Morgan said Superior, like many cities, simply didn t have the resources to take preemptive actions against the insect. But now she s weighing wholesale cutting as an option as well as treatment, and she said it may be time to stop cutting trees that appear healthy. To be honest, we were a little behind the times on assessing how far treatment has come, Morgan said. My plan is to present the City Council with the options for treatment and cutting at the next City Council meeting. Ultimately, it s going to be the council and mayor s decision on how we approach this. Morgan has called a meeting of the city s Tree Board for Thursday, hoping to move as fast as possible to get ahead of the borer. The City Council will get its briefing Sept. 3, she said. Do we spend money taking trees or treating them, and how much? Morgan said. Either way it s money we don t have in the budget right now. Milwaukee saving its ash Emerald ash borers were discovered in Milwaukee in That year city officials began a large-scale treatment program to inject ash trees with a special insecticide called TREE-age. The stuff worked

3 immediately, and continues to work, David Sivyer, forestry services manager for Milwaukee, told the News Tribune. We treated street-side trees on a block where private trees also were infested and, within a couple years, all the private trees were stone dead and all of our trees on the block were fine, Sivyer said. Those treated city trees remain uninfested. Long after the city should have been overrun with emerald ash borers and dead and dying ash trees, it isn t. Nearly all of the city s street-side ash trees are healthy and standing, providing shade, soaking up stormwater and adding aesthetic value to homes and neighborhoods. The injections, usually done in June or early July as the tree expands its leaves, cost Milwaukee about $70 per tree, Sivyer said, and last for two years. Milwaukee has treated all 28,000 of its street-side ash trees that are 8 inches in diameter or larger, twice. And now we re on our third treatment cycle, Sivyer said. At $35 per year, it s so much cheaper than cutting, removing and replacing a tree; that cost is now north of $1,000. And we get the added benefit of preserving the shade and other values that bigger tree offers, he said. We don t believe that we re going to be able to perpetually hold off emerald ash borer. But we re saving our big ash for now and developing a solid replacement plan to fight this on our timetable, not on the beetle s timetable. Milwaukee still is cutting infested trees smaller than 8 inches and any dead or failing ash trees, especially along utilities or other less-visible locations. But he said city politicians and residents have been vocal against a large-scale cutting of trees that aren t yet dying just because emerald ash borers are around. We got Dutch elm here in 1956, and the city spent 17 years doing almost nothing else with trees other than cutting down dead elm trees, Sivyer said. We didn t want to go through that again. In fact, I have a hard time finding any support for cutting any ash when preemptive treatment is so effective. To treat or not St. Paul; Burnsville, Minn.; La Crosse, Wis.; Chicago and other Midwest cities are moving more to insecticide to save trees, in some cases allowing city crews to help homeowners treat their trees, for a cost. But Minneapolis, taking an opposite strategy, has chosen not to treat city trees and is cutting, with local officials citing widespread opposition to pesticide use on public lands. Superior, too, has an ordinance banning pesticide use, Morgan said. But she can get waivers for the City Council if they deem it s needed. Michigan State s McCullough says TREE-age uses the same compounds used by veterinarians to deworm dogs and other animals.

4 I m a forester before I m an entomologist, and I don t want a bunch of bad stuff going into our trees and water, she said. I wouldn t call it benign. But we re seeing that the treatments aren t killing a whole lot more than emerald ash borer. While Milwaukee is paying about $70 per treatment, small cities with fewer trees and unable to afford their own injection crews probably will pay more to hire private companies to do the work. Cities and private tree owners are paying about $10 per diameter inch per tree, McCullough and others said. An 18-inch tree would cost about $180 for a treatment that lasts up to three years. Meanwhile, a Canadian firm developed another low-toxicity pesticide called TreeAzin, which the company and its supporters say is an organic alternative. Morgan said TreeAzin appears not to last quite as long, requiring treatments each year. Made from the seeds of a tropical tree, it s considered to have a low impact on other living organisms. The injections target the tree just under the bark, about the first inch of wood where larvae spend most of their time. Another treatment involves pouring an insecticide at the base of the tree to soak into the root system. The drench is cheaper, $25 to $35 per tree, according to the University of Wisconsin-Extension, but it has been slightly less effective and may be affecting other organisms. The most common drench compound is imidacloprid, which can be found at hardware and lawn-andgarden stores. Because enough chemical is needed to find its way into a tree s root system, some critics say it may find its way into other plants and trees and inadvertently kill other insects, such as bees. The treatment must be repeated each year. Start now Whatever treatment is picked, McCullough has advice for public and private landowners, including those in Duluth: don t wait. While past advice figured the insects probably have been around for three or four years before they are discovered in any given place, McCullough says that it s more likely five or six years. That means they probably have spread for miles beyond Superior s north side, she said. The insects can expand their range a few miles each year on their own. But they have moved much faster by hitchhiking on firewood and nursery stock that s hauled down the highway at 65 mph. If you are within 15 miles of known infestation of beetles, start treating now or it will be too late, McCullough said, recommending that arborists and landowners first treat any green ash they want to save. If a tree shows more than 50 percent dieback, it s probably too late, and the tree should be cut and moved to an authorized holding yard. Each county where ash borers are found is placed in a federal quarantine, making it illegal to move ash wood or trees out. Each infested location has its own storage yard for infested and possibly infested cut wood.

5 McCullough said that TREE-age is working so well that researchers have yet to find any larvae in a treated tree. Moreover, there are some signs, although no proof yet, that large-scale treatment of ash might be holding down the overall population of emerald ash borers in specific areas. We haven t had the time or money to look closely at that yet, but it appears to be the case, she said. What is clear is that we are saving ash now that otherwise would have died, and, maybe, buying some time until a broader solution is found to stop this insect.