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Save My Trees!

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hirl McMayon was enjoying her stay in Europe. As Director of Natural Resources (which includes all landscaping) for the Chicago Parks District, she was attending Nations in Bloom, an annual competition that honors cities throughout the world for excellence in developing liveable, sustainable communities. Finally, after entering four years in a row, Chicago was honored with first place in its category.?I got home on October 12th feeling pretty good, and picked up the Sunday paper,? she recalls. ?I saw that on the front page of the Metro section, there was a big picture of guys in trees ? and I knew it couldn?t be a good thing.? Indeed, the reason for the story was that the Asian longhorned beetle had been discovered in Oz Park ? definitely not a good thing. Urban trees are bombarded with stressors around the clock. Planted in less-than-ideal soils, often with limited root space, they endure inconsistent irrigation, airborne pollutants and even vandalism with stoic grace. Amazingly, they survive for years, offering shade and beauty to harried city residents. It?s no wonder that they can fall prey to a host of pests and diseases. Many of these maladies are seasonal or easily controlled ? others can mean decline and death. Oftentimes, the worst pests are those that come from other parts of the world. There are no natural predators for these interlopers so they have free reign, multiplying with breathtaking speed. Such is the case with the Asian longhorned beetle and the host of other exotic longhorned beetles and boring tree insects. We are under assault throughout the nation ? from the Pacific Northwest to the California coast to the Eastern seaboard. A little biology In order to devise a strategy for controlling these insects, we need to understand their lifecycle and biology. The Asian longhorned beetle, eucalyptus longhorned beetle, emerald ash borer, and most members of the Coleoptera (beetle) order, have a similar life cycle. Generally, these beetles have one cycle per year. The adults fly in the spring, looking for likely places to lay eggs. These are usually cracks and crevices in the bark of trees. There are theories that say that stressed trees emit pheromones that the insects can detect. Native beetles often lay eggs primarily in dead or dying trees, or even firewood piles. The frightening part about these imported insects is that they often lay eggs even in healthy trees. Although keeping a tree in good health is still a great way to keep the bugs away, it no longer guarantees that your trees will survive the onslaught. Adults can lay eggs through a relatively long period; spring through fall, depending on the species. After the eggs hatch, the larvae eats its way through the cambium and wood directly under the bark (the tree?s nutrient and water transport system is in the cambium, so this can cause a great deal of hidden damage). As the insect feeds, it grows larger ? causing more and more damage. The larva then pupates, manufacturing a hard shell and becoming an adult. Usually, the insects overwinter in this stage, although they can also overwinter as eggs or larvae. Finally, the insect emerges. As it tunnels its way out of the tree, it causes even more interior damage. When it finally sees daylight, it has its food source right in front of it ? a tasty meal including leaves, twigs and tender new bark. Then it flies off to lay eggs in the next victim. A rogue?s gallery Invasive species are becoming a crisis worldwide. According to the Nature Conservancy, more than 4,500 foreign species have gained a permanent foothold or taken root in the U.S. during the past century. Invasive species contribute to the decline of 46 percent of the imperiled or endangered species in the U.S. Invasive species are estimated to cost a total of $137 billion annually in losses to agriculture, forestry, fisheries and the maintenance of open waterways in the U.S. This staggering dollar figure doesn?t count the loss of urban trees, or costs that have been incurred to try to hold back the flood of aliens in cities and states. So, which ones are landscape professionals likely to come across? Needless to say, we don?t have room to cover all 4,500, but here?s a rundown of those that are causing the greatest impact on the green industry. Asian longhorned beetle Although the United States has many native longhorned beetles, Anoplo-phora glabripennis is one of the first that attacked healthy trees. The initial infestation in the United States was in New York in 1996, thought to be imported from Asia in pallets or packing material. It was found in Chicago in 1998 and in New Jersey in 2002. Most recently, it was discovered in Toronto, Canada. Millions of dollars have been spent on the required surveys and control programs. It affects a wide range of trees, including all species of maple along with elm, ash, poplars, alder, arbutus, willow, and various fruit trees. Chicago thought it might be able to breathe a sigh of relief at the end of this summer. The city had gone a year without seeing a new infestation ? or even a single specimen. A combination of quarantine (wood cannot be taken out of the zone unless it is chipped ? and then it?s taken to a specific dump site) and the tree is micro-injected with Imicide (containing imidacloprid). Mauget Company is the manufacturer of Imicide, which has contained the spread. ?You can?t find a beetle for two years before you can lift the quarantine, and we always seem to find one ? and only one,? McMayon explains. It?s also alarming to find an adult this late in the year ? eggs can be laid, which can mean an outbreak next spring. ?We?re figuring there has to be a tree that might be infested, and we need to find it fast.? Immediately upon detection, eight bucket trucks were sent out. Crews get as high in the trees as they can, then inspect the trees for exit holes, using binoculars to better see the tops. The insects favor the tender young tips of the trees, which make them even more difficult to spot. Although there is no guaranteed way to eradicate the beetle outside of destroying the trees it infests, research has shown that injecting healthy trees with Imicide can prevent infestation. The insecticide will kill adult beetles, preventing egg laying. However, it has little effect on the pupae, larvae or eggs of the pest. Emerald ash borer This beetle, Agrilus planipennis, has destroyed millions of ash trees in Michigan. ?We?re circling the wagons here,? says McMayon. ?It?s definitely moving toward us. They just found it in Ohio.? The beetle was first identified in Michigan in June 2002. Research-ers, however, believe the insect may have arrived in Michigan as many as 10 years earlier. It has also been found in southeastern Michigan and Ohio, as well as Ontario, Canada. Some six million trees in Michigan have died or are dying from infestation. Earlier this year, the U.S. Forest Service researched chemical controls. In April 2003, they treated trees with soil applications of imidacloprid. In late May, trees were injected with Imicide or Inject-A-Cide B (containing Bidrin). In early June, ash trees were treated with foliar cover sprays including Sevin, Orthene, Tempo and Talstar. In early July, half of the treated trees received a second cover spray. Leaf and twig samples were collected from all treated trees in mid-June and mid-July. Adult emerald ash beetles were caged on the foliage in the laboratory to assess leaf feeding and mortality. Adult mortality was found to be very high (up to 100%) on foliage from trees that were treated with Inject-A-Cide B or the foliar cover sprays. Emerald ash borer adult mortality was also fairly high on trees treated with Imicide. Larval mortality within the trees is now being evaluated. Other longhorned borers The first species of eucalyptus longhorned borer (ELB), Phoracantha semipunctata, was introduced to California in 1980. It rapidly spread throughout the state?s large population of eucalyptus trees. In 1995, a second species of borer, Phoracantha recurva, was discovered in Southern California in Los Angeles, Riverside, Orange, and San Bernardino counties. California agriculture officials have released predatory insects in an effort to control these insects. Many eucalyptus in California were grown with minimal irrigation and maintenance, and so were under stress. Officials recommend that trees be regularly irrigated in order to decrease infestations. Imicide injections are labeled to control the beetle. Valuable specimens should be treated on a preventative basis. Anoplophora chinensis, the citrus longhorned beetle, was first discovered near Seattle in August, 2001, by a nurseryman who knew it was trouble at first glance. The beetle had emerged from a maple tree in a shipment from Japan. A second and third beetle were spotted by agricultural officials and captured, but a fourth managed to elude capture. Shortly thereafter, another beetle in another nursery was found in a shipment of trees from Korea. Agricultural officials quickly devised a plan to contain the spread of the insects, which had a wide range of host trees; as well as citrus species, fruit trees such apple and pear, and hardwood trees such as maple, poplar, elm, oak and willow could be hosts. Potential host trees within an eighth of a mile from the nursery would be cut down and chipped, while trees in the next eighth mile would receive a systemic Imicide injection into the main trunk. At this point in time, no new beetles have been found. Officials are cautiously optimistic. As our global trade increases, so do assaults by alien species. As landscape professionals, there is little we can do to prevent these invasions. However, quick action with appropriate pesticides can offer hope for valuable specimen trees. In addition, careful maintenance, including regular irrigation, fertilization and proper pruning can also help you save that tree. EDITOR?S NOTE: Helen M. Stone is the owner of Stone Peak Services, a green industry communications and management company in Las Vegas, Nevada. She also currently serves on the board of directors of the Western Chapter of the International Society of Arboriculture.



November 2003
 
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