If you’re driving in and around Boulder, don’t rubberneck at the green or purple boxes hanging in trees. Or at least, not to the extent of endangering other drivers.
The Colorado State Forest Service, along with Boulder and Boulder County, hung 65 new traps this week with two purposes: Finding the leading edge of the tree-killing insect’s infestation, still currently limited to the city of Boulder; and discovering which of four trapping methods is most effective at detecting it. The traps won’t dent the pest’s numbers.
Three more square-mile grids have been confirmed as hosting the bug, which has caused tens of millions of tree deaths in Midwest and Eastern states. That brings the total of infested square-mile grid blocks to 14 ( , go to eabcolorado.com)
But “we warn people, just because you happen to be on the other side of a grid line, doesn’t mean it’s not there,” said Boulder City Forester Kathleen Alexander.
“If you are living within Boulder, you about your ash.”
It can take two to four years for an infested tree to show any symptoms — years On the other hand, there’s also no reason to assume a damaged ash tree has the beetle, either — 2014 and 2015 have been a tough year for many tree species.
Alexander suspects that the insect is present in most areas of the city, though at low numbers. The reason for that is not the discovery of the new infestations, but how they were found.
In the City of Boulder, two of the recently identified infested grids were detected by trapping, Alexander said. Of the total of 15, five were found by branch peeling and six by foresters who saw symptoms of decline and climbed those trees to examine them closely. So getting up close and personal with the bug is still an essential method.
One of the new grids was found by a tree contractor doing seasonal pruning who found a live adult beetle in a bucket truck.
Detection remains a challenge with this insect. Adult borers are less than half an inch long and live in the tops of ash trees, camouflaged in the leaves. The larvae live inside the tree, eating its circulatory tissues and eventually killing it.
Earlier detection efforts focused largely on branch peeling. In the winters of 2013 and 2014, state, city and county workers and an army of volunteers laborious cut ash limbs and slowly scraped off the bark to try to find larvae inside. Trapping hadn’t been thought to be very effective as a detection method in the Midwest.
But in Boulder, a single trap has nabbed 100 adult beetles in the space of two weeks, said Dan West, a Colorado State Forest Service entomologist. It’s possible that traps are a more viable option in Colorado, where ash trees are less numerous.
“We’re looking for a better mousetrap, to see if one color or one kind of trap works best,” he said. To that end, the traps have been hung in ash and non-ash trees in infested areas, but also along likely routes of expansion, including roads, where it may travel in firewood. The traps contain pheromones that draw the borers to them.
“At this stage, we’re trying to figure out, are we different? We haven’t kicked any tools out of the toolbox,” West said.
Susan Clotfelter: 303-954-1078, sclotfelter@denverpost.com or twitter.com/susandigsin
