A new commercial lawn care chemical by DuPont called Imprelis has been linked to damage to coniferous trees, primarily white pine and Norway and Colorado blue spruce. Firs and yews also may be affected.
The herbicide with the active ingredient aminocyclopyrachlor was released this spring for use by commercial applicators.
The first damage reports came in late May/early June from the East Coast. Damage has now been reported in Chicago, Iowa City and Cedar Rapids, Iowa, but there has been none in the Quad-Cities, Iowa State University/Scott County Extension horticulturist Duane Gissel said.
Symptoms include twisting and curling, followed by the browning of needles, shoots and branch tips.
Although university Extension horticulturists say it is too early to determine whether affected trees are dead or will die, several nurserymen quoted in a July 14 New York Times article said they know of trees that are dead.
Bert Cregg, an associate professor of horticulture and forestry at Michigan State University, said in a Extension bulletin that it is possible affected trees could recover if they are left in place for a year to a few years, even if damage appears severe.
"Based on experience with other forms of herbicide injury and other types of environmental damage, trees with minor browning (less than one-third of the crown affected) on new growth will likely be able to push new growth and eventually ‘grow out' of the damage, though this can take one or two growing seasons," he wrote.
"A lot of it comes down to the homeowner's tolerance," he told the New York Times. "How long can they stand to look at this thing in their yards? This is going to be a large-scale problem, affecting hundreds of thousands of trees, if not more."
The U.S. Environmental Protection Agency has begun gathering information on the damage and "is taking this very seriously," according to a statement it provided to the New York Times.
Quad-City, Iowa angle
Has the product been used in the Quad-Cities?
A representative for Service Master, whose brands include TruGreen, said her company has used the product, but not in Iowa and only in "isolated" areas of Illinois.
Representatives of Greenspace Associates, Bettendorf, and River Valley Turf, Davenport and Silvis, said they have not used the product. Representatives of two other area companies did not immediately return telephone calls.
The product was studied experimentally at Iowa State University for the past couple of years and was found to be very effective against a broad spectrum of broadleaf weeds, including ground ivy, violets and henbit, Nick Christians of Iowa State said.
It also has the advantage of being applied at very low rates of active ingredient and is rain-fast, meaning that it does not need to remain on the weed leaves for a period of time, he said.
"It is important to note that there are many locations where the product was used and no tree damage has occurred," he said. "Also, not all trees (in damaged areas) are damaged."
DuPont released a letter to its users in June saying that "as a precaution ... do not apply Imprelis where Norway spruce or white pine are present on, or in close proximity to, the property to be treated."
The letter also cautioned applicators to "be careful that no spray treatment, drift or runoff occurs that could make contact with trees, shrubs and other desirable plants, and stay well away from exposed roots and the root zone of trees and shrubs."
To be approved by the EPA, the herbicide went through 400 trials, and the agency reviewed it for 23 months.