State foresters say the discovery of Iowa’s fourth emerald ash borer infestation – confirmed this week in Mechanicsville in Cedar County – may herald a widespread emergence of the tree-killing invasive beetle.
“I think we will see it start to fill in the gaps between the confirmed infestations,” Paul Tauke, chief of the Department of Natural Resources Forestry Bureau, said Wednesday.
“I would not be surprised to see it surface in many Iowa counties within the next year,” added State Urban Forester Emma Hanigan.
Tauke said the ash borer likely has been active in the infested areas for several years.
The combination of the progressing infestation and drought-induced stress has “made it pop in places like Burlington and Fairfield,” he said.
Ash trees can mask their symptoms with vigorous growth until weather-related stress makes them more noticeable, Hanigan explained.
This year’s flash drought, following last year’s prolonged drought, made the ash tree’s already impaired vascular systems more vulnerable to the lack of rainfall, she said.
After the initial confirmation in Burlington on July 16, DNR foresters in mid-September surveyed the approximately 700 ash trees on city property and found ash borer symptoms in about 40 percent of them, according to Hanigan.
The state’s first infestation was confirmed in 2010 on a Mississippi River island in Allamakee County. Rigorous monitoring found no additional infestations until July, when infested ash trees were confirmed in both Burlington and Fairfield.
State Entomologist Robin Pruisner said a Mechanicsville resident contacted local officials about a declining ash tree along the right-of-way. Several larvae were pulled from at least one street tree and another tree in a nearby yard on Sept. 26.
The USDA then confirmed the larvae were emerald ash borer, making Cedar County officially infested.
Pruisner said all Iowans are urged not to transport firewood across county or state lines. Most ash borer infestations have been started by people unknowingly moving infested firewood, nursery plants or sawmill logs, she noted.
The adult beetle also can fly from two to five miles, ensuring a more gradual spread of the pest.
Pruisner said state and federal agriculture officials soon will issue a regional quarantine that will restrict movement of hardwood firewood, ash logs and wood chips out of the quarantined counties.
State foresters said it’s too soon to tell how much of a toll recent droughts will take on other species of Iowa trees.
“We’re seeing symptoms of stress,” Hanigan said.
Urban trees with confined root space and more disturbed soil are more vulnerable than rural trees to drought stress, Tauke said.
Drough-impacted deciduous trees tend to shut down and drop their leaves early to conserve energy, he said.
Prolonged stress drains trees’ energy reserves, weakening their resistance to disease and pests, which eventually can kill trees long after the drought has ended, said DNR forester Mark Vitosh, whose district includes Linn and Johnson counties.
Stress has been less noticeable in northeast Iowa, where rainfall has been more abundant this year, according to DNR forester Bruce Blair.
It also remains to be seen whether drought-related stress will affect the onset and intensity of fall colors, state foresters said.
Last year’s fall colors, following the worst drought in 50 years, came earlier than usual and provided especially spectacular scenery, Blair said.
From his office in Des Moines, Tauke said most leaves remain green.
“Things are going to have to change pretty quickly” to attain peak color by the normal date of Oct. 12, he said.
Mechanicsville, as with more than 180 other Iowa communities already had been the site of a DNR tree inventory, which in 2010 found 559 trees of more than 40 species.
Maple at 39.8 percent was the top genus, followed by ash at 32 percent.
About 8 percent of the city’s trees were considered in need of management, and 16 trees were recommended for removal.
“There is a strong possibility that (all of Mechanicsville’s city owned ash trees) will die once (emerald ash borer) becomes established in the community,” stated the report that accompanied the inventory.
Ash, one of the most abundant native tree species in North America, has been heavily planted as a landscape tree in yards and other urban areas. Iowa has an estimated 52 million rural ash trees and approximately 3.1 million more ash trees in urban areas, according to the USDA Forest Service.
If they all die, the cost of removing and replacing them would be staggering.
That cost, coupled with the lost benefits of energy savings, property value and storm water retention, has been estimated at $2.5 billion.
With the recent addition of Colorado to the list, the emerald ash borer is now found in 22 states, 5 of them contiguous to Iowa.