A conservation department scientist said Wednesday difficulty in detecting the emerald ash borer adds to the threat it poses.
Bob Lawrence, a forest entomologist with the Missouri Department of Conservation, said while only 11 counties in Missouri have reported the invasive beetle, that does not mean the rest of the state is free of any pest problems.
"It takes a while to detect those low-level populations," he said. "It's probably in a lot more places than we know. It just hasn't been detected yet."
Lawrence said when the beetle reaches a new area, it takes several years for it to have any noticeable effect. Once the trees start dying, however, they die in rapid succession. He said removing dead trees in urban areas that pose safety risks can become expensive.
The emerald ash borer first arrived in the United States from Asia in 2002 and reached Missouri by 2008. So far, its reach has largely been confined to southeast Missouri, although scientists have found it in Pulaski County and the St. Louis and Kansas City metro areas. St. Charles and Clay counties both reported emerald ash borer infestations this year. Last week, Arkansas became the 24th state to report an ash borer problem.
Lawrence said emerald ash borer larvae kill a tree by burrowing through the inner bark layers that move water and nutrients. He likened the method to strangling the tree.
"If it was just one or two beetles, it wouldn't be a problem, but North American ash trees have very little resistance to this beetle. And so they overwhelm the tree's defenses," he said.
Lawrence said once the emerald ash borer has reached an area, there is little people can do to contain it. He said the best way to stop it from spreading is to burn firewood in the same area you buy it and not move it anywhere else. Missouri is one of several states currently under federal quarantine to keep the beetle from hitching a ride to a new location. Lawrence said the quarantine applies to logs, wood chips and all hardwood firewood.
Since ash trees are popular shade trees, he said cities should inventory their ash trees. Trees that are old, sick or poorly located should be removed. If they are worth protecting, he said cities can inject them with insecticide every year to ward off beetle attacks. He said such insecticides, which stay inside the ash trees, have been very effective at saving them from infestations.