After Broomfield and Westminster confirmed the presence of emerald ash borer — a deadly invasive pest that targets all 60 species of ash trees, which make up 15% of Colorado urban forests — the Colorado Department of Agriculture announced this week it will repeal a federal quarantine put in place in 2013 to slow the proliferation of the invasive pest.
“We knew that this pest could not be eradicated,” said Laura Pottorff, the plant health and certification section chief for the Colorado Department of Agriculture. “The decision to put the quarantine in place was collectively made by a group of agencies to try and slow down the pests spread and allow other communities to become prepared.”
Courtesy of Colorado State Forest Service
An emerald ash borer beetle is seen emerging from a tree in Westminster.
Emerald ash borer was first confirmed in Boulder in 2013. It spread to Gunbarrel, Longmont, Lafayette, Lyons and Superior before the quarantine, which largely encompassed Boulder County, was put in place that same year.
While it’s unknown whether emerald ash borer arrived in Broomfield and Westminster naturally or via accidental human transport, such as in firewood or other raw ash material, the quarantine’s repeal is largely due to the insect’s ability to fly upwards of a half-mile a year and spread to new areas without the movement of infested wood.
Though it was unable to stop the spread of emerald ash borer, the quarantine did allow communities along the Front Range to prepare for the invasive species’ arrival.
During that time the Westminster, which has approximately 1,700 public ash trees, identified 1,100 trees for protective treatments, 700 of which have already been treated, and another 200 less valuable ash trees that have have been removed and replaced.
Before Broomfield initiated its management plan in 2016, the county had approximately 2,900 public ash trees that were susceptible to emerald ash borer, comprising roughly 10% of the total public tree population. Since implementing its management plan, the city has reduced the ash population to just 1,500 trees. It also has treated 931 ash trees identified as being of high value and planted nearly 900 replacement trees.
The most effective treatment, however, is biocontrols, which in this case is comprised of four types of wasps that feed on the larvae of the emerald ash borer.
The wasps, which only target emerald ash borer, have been highly effective in the ash tree’s native environments on the East Coast and Midwest. Boulder, in partnership with the Colorado Department of Agriculture, has been deploying wasps since 2015 and while Dan Bean, director of the Colorado Department of Agriculture’s Palisade Insectary, said its too early to tell if the wasps are equally effective in Colorado, there are signs of optimism.
“At this stage, it’s too early to say these biocontrols are highly effective, but it’s late enough to say these wasps are now established in the environment and will most likely suppress the populations of the emerald ash borer,” he said. “But I don’t want to be overly optimistic.”
The current study site in Boulder showed 28% of emerald ash borers are being parasitized by the wasps and another 45% are being eaten by local woodpeckers, but John Kaltenbach, a biological control specialist with the Colorado Department of Agriculture, said in order to see any real effects on the population, those number would need to be somewhere around the 90% range.
While the biocontrols will help to slow the spread of emerald ash borer, the most effective plan, according to the Colorado Department of Agriculture, is to either treat the tree with protective insecticides or to replace ash trees with a diverse array of tree species so future pests don’t threaten such a large swath of the urban forest.
While treatment can be effective, Pottorff said it does not work in trees that are struggling with drought conditions or other health issues, and those considering it should consult with an expert before taking any action.
Cliff Grassmick/Staff Photographer
Levi Coleman, of the Colorado Department of Agriculture, introduces small wasps, tetrastichus planipennisi, as a biocontrol for emerald ash borer last month at the Mayhoffer Singletree trail in Superior.
She also said those who decide to replace some or all of their ash trees, should do so before they die. If done afterward, the branches become very brittle, forcing contractors to use heavy machinery rather than taking them down by hand.
According to Boulder Forestry, the emerald ash borer attacks and kills both stressed and healthy ash trees. It is so aggressive that nearly 100% of infected trees trees typically die within two to four years, according to the department.
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 as signs of ash borer infestation . Those who suspect tree is infected can report it to the Colorado Department of Agriculture at 888-248-5535 or filling out an EAB Report Form at colorado.gov/pacific/agplants/eab-identification-and-reporting.
Source link