Westminster City Forester John Kasza said he was instantly worried about the city’s trees when he learned that the Emerald Ash Borer had slipped past a six year quarantine last month.

“They found it Broomfield, pretty much right across the street,” Kasza said. “That’s why we began looking, even more closely than we normally do.”

Sure enough, Kasza said, inspections and later testing proved his concern: the green pests, responsible for killing Ash trees in cities across the eastern United States, had spread to Westminster.

“It wasn’t bad enough to kill all the trees there, but it will shortly,” he said.

Kasza said he and his crews inspected the trees in the Willow Run Shopping Center parking lot, pulling back bark from trunks and cutting sample branches for laboratory testing.

On Aug. 29, they confirmed that the shopping center’s trees were infested with Ash Borers.

“We did one inspection closer up in two trees and found it,” he said.

No predators

The Emerald Ash Borer is a non-native wood-boring beetle responsible for the death and decline of tens of millions of ash trees in the United States and Canada. As a non-native insect, it lacks predators to keep it in check.

Westminster has about 69,000 ash trees in the city limits — about 15 percent of the city’s total tree population.

“It’s like saying one out of every seven trees in Westminster is an ash tree,” he said. “There are a lot of them out there and we know that not ever ash tree is going to die.”

He recommended homeowners remove small, younger ash trees or old and diseased trees.

“But if you have good healthy tree, it’s much less expensive to treat the tree instead of replacing it,” Kasza said.

He recommended homeowners apply emamectin benzoate, an insecticide that was invented in 2001.

“It’s the most effective, up to 99 percent, and has the fewest environmental risks,” he said. “It’s too late in the year to do it now, but next summer they should have their ash trees treated.”

He said it’s best to apply the insecticide once the trees have leafed out.

Boulder quarantine

The pest was first discovered in the U.S. in Michigan in 2002 and has been detected in Boulder, Gunbarrel and Longmont since 2013. The pest was found on private land in the vicinity of in Lafayette in 2017. That was still within the quarantine.

The state forest service began the quarantine around Boulder County to help prevent human-assisted spread of the pest.

Property owners with ash trees should be on the lookout for thinning of leaves in the upper tree canopy, 1/8-inch D-shaped holes on the bark and vertical bark splitting with winding S-shaped tunnels underneath. People that find suspicious trees should report them by calling the Colorado Department of Agriculture at 1-888-248-5535 or filling out the EAB Report Form at https://www.colorado.gov/pacific/agplants/eab-identification-and-reporting.

The pests were found near 136th Avenue and Main Street in Broomfield on Aug. 20. State state agriculture officials said they didn’t know if it spread there naturally — the insects can spread a half-mile each year on their own — or if it was brought in by people accidentally, on firewood or infected ash bark.

He said scientists removed sample branches, placing them in isolation for several days to determine if they were infected with the Emerald Ash Borer, and they were. The testing is important because there are other problems locally with ash trees.

“There are other insects, like the lilac ash borer that doesn’t kill the tree outright but causes some dead branches and most ash trees in Westminster have that,” Kasza said. “And there are other issues, with the drought or freezes and stresses that make our ashes not look so healthy. So it can be hard to determine that you actually have the Emerald Ash Borer.”

The Colorado and U.S. departments of agriculture could move to end the Boulder County-centric quarantine now that the pest have escaped the quarantines’ bounds. That quarantine included firewood and decorative bark used for landscaping.

Kasza said the quarantine did help slow the spread and gave other Colorado counties time to prepare.

“It’s been hard to enforce, and the state really doesn’t have much of a budget, so we expect it to end this winter,” Kasza said. “What that’s meant is that tree companies have been having to go to a greater expense to keep their ash wood within Boulder County. Once the quarantine ends, they’ll be able to bring that wood outside of the county and all throughout the metro area.”