Eighty years ago a fungus carried by a beetle began infecting American elm trees, and within a few decades cities across the nation were
denuded of their beloved shade trees.
It’s about to happen again, but this time ash trees are in the crosshairs of a deadly plague spread by a tiny beetle called the emerald ash borer. All varieties of ash trees are at risk. It’s estimated that they account for 17 percent of the nation’s urban tree population, though the figure is considerably higher in many cities.
Iowans had been hearing about the spread of the insects from Wisconsin and other states to the east, but most may have assumed the threat was distant.
The problem is spreading faster than first thought, and complacency is no longer an option. State and local officials, businesses and homeowners need to implement an aggressive campaign to combat the spread of the deadly emerald ash borer. That strategy sadly must include preparing for the inevitable loss of millions of ash trees on public property, parks, residential yards, commercial lots and rural woodlands.
Based on a rough estimate, local governments in Iowa face an expense of at least $3 billion to remove infected and dead ash trees from public property. That doesn’t include the cost to homeowners.
The emerald ash borer larvae drill into the soft, inner layer below the tree’s protective bark and create a serpentine pattern as they eat their way along, cutting off the tree’s circulation of water and nutrition. That is a death sentence within two to three years.
The first Iowa infestation was spotted in Allamakee County in 2010. The disease was quiet for three years. Then — bang, bang, bang — trees infested with emerald ash borers were confirmed in three other eastern Iowa counties by experts from the U.S. and Iowa departments of agriculture, Iowa Department of Natural Resources and Iowa State University.
Then last month, the emerald ash borer team confirmed an infestation in Creston, in Union County, in southwest Iowa. In other words, in the span of three years, the emerald ash borer had moved across the state and was no longer confined to counties near the Mississippi River. It’s safe to assume the bugs have found their way into other parts of Iowa, too.
Although the emerald ash borer can fly up to five miles, experts say the infestation is more rapidly spread by humans hauling firewood and nursery stock.
In November, state officials established a quarantine in 25 eastern counties that restricts transportation of hardwood firewood, ash logs, wood chips and tree nursery stock out of those counties. State officials indicate the quarantine likely will be expanded sooner rather than later.
The Creston confirmation served as a “wake-up call” around the state, State Forester Paul Tauke said. That news, he said, made it clear that warnings about the ash tree blight “was not a lot of forestry Chicken Littles running around telling us the sky is going to fall.” As a result, communities across the state are beginning to recognize they have a problem on their hands, and a potentially expensive one at that.
It’s estimated that ash trees account for about 17 percent of Iowa’s urban tree canopy, according to figures from the U.S. Forest Service, or just over 3 million trees. At a removal cost of roughly $1,000 a tree, that adds up to a $3 billion challenge, mostly for Iowa’s cities and towns. The losses will be many multiples of the urban numbers when trees in rural areas are counted.
Burlington, for example, is one of Iowa’s worst-hit communities in numbers of infected trees. The city faces the task of removing an estimated 1,000 ash trees with a full-time city tree removal crew of two.
In Des Moines, City Forester David Jahn said the city estimates it has 6,000 ash trees on city parking right-of-way, 1,100 in mowed areas of city parks that get intensive public use and another 40,000 in forested areas of city parks. If Des Moines is typical, there are two to three times that number of ash trees on private property, or upward of 90,000 ash trees, Jahn said.
The state’s strategy for minimizing the loss of healthy ash trees in urban areas begins with the recommendation that communities do a detailed inventory of ash trees on public property. Communities should remove trees that are already in a “state of decline” and less able to withstand infestation.
As the infestation spreads, communities will have to decide when to initiate treatment using insecticides. Some suggest that should happen when infestations are confirmed within 15 miles; others say sooner. The treatment costs roughly a third the cost of removal, though it must be repeated every two to three years, Tauke said.
Chemical treatment may be effective, but Iowa will still be losing a lot of ash trees. With that inevitability, experts recommend that cities and private property owners take a lesson from the Dutch elm disaster: Don’t plant too many trees of one species. In fact, many Iowa communities replaced elm trees with ash and maples, and now yet another insect — the Asian longhorned beetle — is threatening maples.
Tauke’s advice is a bit like a good financial adviser who preaches the gospel of diversifying investment portfolios. “The best community forest is a diverse forest,” he said.
The ultimate goal is to minimize the chance of another devastating loss of urban shade like the one that wiped out 95 percent of Iowa’s elm trees. The time to begin is now.