New Herbicide Suspected of Causing Tree Injury - August 3, 2011
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

The herbicide, Imprelis (aminocyclopyrachlor), has been in the news over the last few months. The selective herbicide was introduced by DuPont Professional Products into the market this spring to control broadleaf weeds in turf areas. Most of the reported damage has been on white pine and Norway spruce grown in or near treated turf areas in the Midwestern and eastern U.S. Other reports have included effects on willow and poplar too. The damage observed ranges from slight distortion of the leaves to death of mature landscape trees.

DuPont continues to sell Imprelis, which is registered for use in all states except New York and California, and the company maintains that there are many places where the product was used and no tree damage has occurred. At this time, I am unaware of any plant damage that occurred in Arizona. This may be partially due to the fact that it is not recommended for use on bermudagrass. In northern Arizona, we plant bermudagrass (a warm season species) below 3,200 feet elevation. Imprelis is labeled for use on cool season turf species (Kentucky bluegrass, fescue, and ryegrass) which are typically planted on sites above 4,000 feet in northern Arizona. The Verde Valley falls between these elevations and, subsequently, we have both warm and cool season turf grasses.

Turf managers often apply post emergence, selective broadleaf herbicides to manage dandelions, clover, and similar weeds without damage to the desirable grasses. Prior to the introduction of Imprelis, turf managers used 2,4-D, dicamba, clopyralid, and other products to reduce broadleaf weeds in turf areas. Like these products, the active ingredient of Imprelis is absorbed through foliage and roots of target weeds. Once in the plant, it is translocated in the xylem and phloem, and accumulates in meristematic regions (growing points) of shoots and roots. The result is abnormal growth (twisting, curling, and cupping of leaves) and subsequent death due to excessive cell division within the plant.

According to experts at the U.S. Environmental Protection Agency and DuPont, Imprelis went through about 400 trials, including tests on conifers, and performed without problems. The EPA reviewed the herbicide for 23 months before granting its conditional approval, meaning that all of the safety data was not yet in but the agency judged Imprelis to be a reliable product.

So far, DuPont representatives have placed some of the blame on workers that have applied Imprelis. Michael McDermott, a DuPont products official, said that workers might not have mixed the herbicide properly or might have combined it with other herbicides. DuPont officials have also suggested that the trees may come back, and have asked landscapers to leave them in the ground. Green industry professionals in some areas have been overwhelmed by damage reports from their customers. All one need to do is conduct an Internet search on “Imprelis” to see that law firms are expressing a willingness to represent clients that suspect tree damage from the herbicide.

The issues related to Imprelis also have implications for composting. On May 25, 2011, the United States Composting Council informed the composting industry and consumers that grass clippings from Imprelis-treated lawns could end up in a compost pile. Unlike most herbicides, Imprelis survives the composting process and is still active in the finished compost. Preliminary research has shown that Imprelis does not break down significantly faster than the leaves and grass in the compost, so the concentration stays about the same. An unsuspecting gardener using contaminated compost could end up damaging their flowers and vegetables, most of which are also broad-leafed. Dicamba and clopyralid are also known to persist in composted materials, so the persistence of Imprelis in compost should come as no surprise.

Many home gardeners that I interact with do not have significant lawn areas. Those that do are either not applying any herbicides or using 2,4-D for broadleaf weed control. It will be interesting to follow the “Imprelis issue” as more information becomes available. Herbicides are tools which have value to agriculture and society. They are not illegal and once informed, we can make our own decisions as to their relative merits or shortcomings.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: November 21, 2011
Content Questions/CNovember 21,

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