As far as invasions go, the emerald ash borer’s foray into Texas has so far been a ho-hum affair, and that’s a good thing for cities like Houston, where there are millions of susceptible ash trees.
Since foresters announced in May that four beetles had been trapped in northeast Texas, there have been no other confirmed reports of emerald ash borer, a voracious non-native pest responsible for killing millions of ash trees around the country.
“I am a little surprised to be honest,” said Shane Harrington, forest health manager for the Texas A&M Forest Service. “I’m hopeful that maybe our education efforts have paid off and people have gotten the message, especially about the transport of firewood, which is the primary way emerald ash borer move around.”
In February, the state forest service will resume setting out traps for the shiny green beetle, hoping they won’t find any more but banking on the probability that they will.
That’s because the emerald ash borer has quickly spread throughout the United States since first being found in southern Michigan in 2002.
Today, the beetle has been confirmed in 28 states, from the East Coast to Colorado.
A native of Asia, the beetle faces few threats from predators and has an abundant food source in ash trees, a species prevalent in urban cities.
“I promise you, you’re going to have more (emerald ash borer) than you have now,” said Deborah McCullough, an entomologist at Michigan State University.
Michigan is ground zero for the nation’s emerald ash borer infestation. The beetle turned up there after likely hitching a ride in wood-packing material that arrived via boat or airplane.
It has now killed more than 30 million ash trees in southeastern Michigan despite efforts to keep the infestation from spreading by doing things like initiating a quarantine of ash trees and ash-wood products.
“I compare our invasion to a wave,” McCullough said. “If you think about a wave in a ocean, it’s not something that you initially see in the water. But there is a force percolating under the surface that emerges over time.”
Texas officials have been anticipating the beetles’ arrival for years, setting traps across the state to provide an early warning.
That work paid off when a trap snared the four last spring south of Karnack.
It’s unclear how the beetles turned up there, but the fact that they were not far from Caddo Lake State Park might suggest they were inadvertently transported in firewood. The location also is not far from the border of Louisiana, which has its own emerald ash borer infestation.
McCullough said research has shown that most female beetles lay their eggs within a few hundred yards of where they hatched. But for reasons that scientists don’t yet understand, a few beetles have demonstrated they can fly great distances, making efforts to control their spread that much more difficult.
“One of the things that really concerns me about the emerald ash borers in Texas, and other parts of the Southwest, is the biodiversity of ash trees there,” she said. “You’ve got several different kinds of ash trees, including several the beetles prefer over other kinds.”
In the United States, 16 ash species are susceptible to the emerald ash borer. Texas is home to seven of those, most of which can be found in urban forests.
Ash trees were planted in many Texas cities – and in others around the country – as replacements for elm trees, which were wiped out by Dutch elm disease decades ago.
Ash trees comprise about 4 percent of the urban forest in Austin. It doesn’t sound like much, but 4 percent there equals about 33 million trees.
Harrington said Houston’s percentage of ash trees is slightly less than Austin’s, but not by much.
“One of the reasons why we have concerns about urban trees is because of the value they provide,” Harrington said. “Not only do they increase property value, they really add to the quality of life.”
Ash trees typically die within two to three years after being infested by emerald ash borer.
The good news for homeowners is that some insecticides have proven highly effective, especially if injected into a tree before borer damage is extensive.
However, foresters say, there’s no real need to treat trees unless you live 10 to 15 miles from a known infestation.
“Removal of poor quality ash, planting trees that aren’t susceptible to emerald ash borer, and protecting high value ash by treating them will help us weather this attack,” said Paul Johnson, urban and community forestry program coordinator for Texas A&M Forest Service.