For more than two decades, the face of many golf courses across North America has changed thanks to an invasive pest no larger than a dime.
Since it was detected in southeastern Michigan in 2002 after arriving in Detroit in packing material aboard a cargo ship from China, the emerald ash borer has cut a swath of devastation across the continent, and has left a trail of millions of dead ash trees in its wake, according to the U.S. Department of Agriculture Forest Service.
Finally, help is on the way that might prevent a virtual wipeout of ash trees across North America by the emerald ash borer, and could result in repopulating forests and other areas, including affected golf courses, with naturally resistant trees.
In 2010, U.S. Department of Agriculture Forest Service officials in Ohio identified healthy ash trees scattered in an area populated with other dead, dying and infected trees. They wondered why some trees remained viable among such widespread devastation. Ensuing research indicates that those trees exhibited natural immunity to the ash borer.
That research has led to scientists cloning trees from the most resistant stock that they hope can be used to repopulate forests that have been decimated during the past two-plus decades.
The cloned trees exhibited increased resistance to EAB, compared with parent trees, with some even killing the larvae, a finding that has surprised forestry officials.
"The mantra at the time was no co-evolution, no resistance, meaning that since this insect was from a whole other continent and our trees didn't grow up exposed to them that they didn't evolve any sort of mechanisms to defend themselves," U.S. Forest Service geneticist Jennifer Koch, Ph.D., told PBS in Detroit.
"Now, we're convinced (cloning resistant trees) works."
Adult ash borers lay their eggs in the tree's cambium layer between the bark and the wood. Larvae hatch and as they feed create a series of tunnels and channels through the cambium layer, cutting off the tree's circulatory system and preventing the flow of water and nutrients.
Cloned trees exhibited increased resistance to EAB, compared with parent trees, with some even killing the emerald ash borer larvae.
To date, EAB has been confirmed in 38 U.S. states and five provinces in Canada. Adult EAB can fly only a short way. Their main mode of transportation is as a stow away in infested firewood.
EAB recently was detected in Oregon's Willamette Valley, and researchers at Oregon State University in Corvallis wrote that the pest "will likely kill most of the ash trees in forests and urban plantings in Oregon over the coming decades."
Researchers at Penn State, however, believe that there is enough genetic diversity in the Oregon ash that it too can be used to breed naturally resistant trees. The Oregon ash populates forests from California to Canada.
Koch said reforesting could begin in the next decade, however, the USFS will have to identify geo-specific resistant parent trees to maximize the chances of success.
"We're working with trees from Ohio and Michigan, so I can't take those trees and the resistance they produce and plant them all the way down to Mississippi. They won't be adapted to grow there," Koch told PBS. "So we have to do what we're doing over and over to make seed orchards for each separate region."
The USFS needs help, however, identifying other resistant trees for potential parents.
"We need other people out there who are in the forest, keeping an eye open looking for large, surviving, healthy ash trees," said Kathleen Knight, Ph.D., research ecologist with the USFS. "Because there's not enough of us to survey every forest and there are a lot of important trees out there that could be missed if people aren't watching out for them."
