Imprelis (aminocyclopyrachlor) was released by DuPont Professional Products into the turf market this spring as a broadleaf control. It is part of a new chemical subclass called pyrimidine carboxylic acids. We have studied this product experimentally at Iowa State for the past couple of years and have found it to be very effective against a broad spectrum of broadleaf weeds. Its advantage is that it is effective against several hard to control weeds such as ground ivy, violets, and henbit. It also has the advantages of being applied at very low rates of active ingredient and is rainfast, meaning that it does not need to remain on the weed leaves for a period of time. It's safe on most cool-season grasses and some warm-season grasses, including zoysiagrass.
In early June, a number of reports on tree damage on areas treated with Imprelis began to come in. The first reports that I heard were from the east coast. Then pictures and reports started coming in from Chicago. Yesterday, I heard that there are several reports from the Atlanta area. The two most commonly damaged trees have been Norway spruce and white pine.
It is important to note that there are many locations where the product was used and no tree damage has occurred. Also, not all trees on the treated areas are damaged.
The pictures below are Norway Spruce and were taken in the Chicago area. The damage appears to be systemic, meaning that the material is being taken up by the roots and translocated to new growth. On this site, about 20 trees out of approximately 120 susceptible plants were damaged. In this case, there was heavy rain after treatment that may have increased movement of the product into the rootzone.
Dupont released a letter last night to users of the product. Their recommendation is as follows:
"As a precaution, until we can more fully understand the circumstances, and whether Imprelis may have contributed to the observed symptoms, do not apply Imprelis where Norway Spruce or White Pine are present on, or in close proximity to, the property to be treated. Additionally, when applying Imprelis, 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 rootzone of trees and shrubs. Consult a certified arborist if you are uncertain about the root zone of specific tree species."
My personal recommendation is to be very cautious with the use of this product until we know exactly what is going on. This story is just developing and I will keep you posted as new information is released.
Here are some additional links.