It's been more than 20 years since we put chemicals on our lawn.
I mention all of this because I only recently was made aware of an herbicide that was used in 2010 and 2011 that was once considered safe by the manufacturer, but has since caused so much damage to some trees and ornamentals that the EPA issued a stop-sell order and the manufacturer, DuPont, stopped producing the chemical.
Sold under the brand name Imprelis, the active ingredient, aminocyclopyrachlor, was once thought to be the safest chemical herbicide invented. Even though it was only approved for use by licensed lawn care professionals, it was used all across the country on lawns, golf courses and commercial properties, except California and New York.
Imprelis was approved for sale in October 2010 and was used primarily to kill broadleaf weeds, including dandelion and clover. By the spring of 2011, problems began to surface, particularly dying and damaged trees on properties where the chemical was used.
According to a 2011 article by The New York Times, DuPont officials first advised that perhaps the persons applying the chemical had mixed it improperly. Affected trees were thought to be able to withstand the damage and landscapers were advised not to remove the trees. It was believed that only Norway spruce or white pine were affected by the herbicide, but then other species of conifers and trees began dying.
After only a year, in August 2011, the herbicide was taken off the market.
While claiming Imprelis is safe for people and pets, DuPont has stated in the Frequently Asked Questions section of its website that clippings of grass and plants treated with the chemical cannot be composted. Injured trees shouldn't be chipped or mulched for use as compost. Lawn care operators who still have supplies of the chemical are instructed on how to return it to the company for refunds.
According to DuPont's website, the most common symptoms have been needle browning and curling of new growth on affected trees and shrubs, but evidence of distorted branches with small growths also have been reported.
The reason I mention this herbicide now, more than 18 months since its use was stopped and it was taken off the market, is that symptoms are still showing up.
According to the University of Minnesota in an article written in May 2012, a tree's recovery after exposure to this chemical depends on the amount of damage. Trees that show damage only to the tips of the branches shouldn't decline much more than that over the season. The article recommends further care by watering the trees well during dry periods and to avoid fertilizing for at least one growing season.
Unfortunately, trees that showed damage last year and are still showing signs of decline will likely continue to decline and won't recover. The trees that seem most susceptible to the chemical are white spruce and eastern white pine.
In yet another update from the University of Minnesota Extension Service, researchers say due to Imprelis' ability to mimic natural hormones that prevent plants from growing, trees that appear healthy might yet die from affects of the chemical.
If your trees are experiencing symptoms that you believe are the result of the chemical Imprelis, take samples of affected plants to The Ohio State University Extension in Cortland for a confirmation of the diagnosis.
DuPont also has answers to some questions at imprelis-facts.com and a hotline at 866-796-4783.