On Thursday the U.S. EPA ordered E.I. DuPont de Nemours (DuPont) to immediately halt the sale, use or distribution of Imprelis. The order, issued under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). http://www.epa.gov/pesticides/regulating/imprelis.html
DuPont’s Imprelis Herbicide (aminocyclopyrochlor) was approved by the EPA in August 2010 for use to control dandelions, ground ivy, violets, clover and other weeds in lawns after they emerged from the ground. Imprelis was developed and marketed to kill emerged weeds and control future weed growth in lawns, and works by both direct uptake through the leaves as well as root uptake by interfering with a plant’s normal hormonal balance. It was designed to be long lasting and does not break down easily, in other words, it is environmentally persistent. Imprelis was never approved for use in New York and California because both states have separate review procedures for new herbicides. New York State officials were concerned that the herbicide does not bind with soil, and may leach into groundwater. California never completed its review.
Beginning in June 2011, EPA started receiving complaints from state pesticide agencies about evergreen damage related to the use of Imprelis. University Extension Offices across the country reported injury to evergreens on lawns and golf courses treated with Imprelis. Homeowners, lawn service operators and others reported browning of shoots and needles and twisting and stunting of shoots, especially near tops of trees on current year growth on tree tops and outer branches. The damage occurred quickly, within two to three weeks of application of Imprelis. The most commonly affected trees were Norway spruce, Colorado blue spruce and eastern white pine. There were also reports of damage to firs and yews. http://news.msue.msu.edu/uploads/files/122/Imprelis%20homeowner%20factsheet_Bert%20Cregg.pdf
By the end of July, DuPont officially acknowledged to the EPA that there has been damage to trees associated with Imprelis use. By the first week in August 2011, DuPont had submitted to the Agency over 7,000 adverse incident reports involving damage (including death) of trees impacted by Imprelis. Test data from DuPont has confirmed certain coniferous trees, predominately Norway spruce and white pine, as susceptible to being damaged or killed by the application of Imprelis. On August 4, 2011, DuPont voluntarily suspended sales of Imprelis and announced a forthcoming product return and refund program. The DuPont website has recommendations for trying to save impacted trees. It is the same advice given to me by the local extension office and if you have impacted trees you might try to save them.
The EPA order to stop the sale and distribution of Imprelis is based on a technical violation of FIFRA labeling, not the fact that an environmentally persistent herbicide had unexpected consequences. This was a consequence that occurred within three weeks of application, and would have been hard to miss in appropriately designed field testing. The testing performed for Imprelis appears to have been inadequate to evaluate impact to and protect non-target species, such as conifer trees. New York state officials concern for potential impact to groundwater does not even appear to have been addressed by the EPA approval process. The fate and transport of chemicals sprayed into the environment should be evaluated before the chemical and its commercial formulation are approved for sale, not after.
The studies originally submitted were found to be adequate to allow for the conditional registration of the herbicide. The conditional registration required that an additional toxicity study be performed to evaluate environmental degradation and (re)submission of avian and invertebrate reproduction studies to evaluate animal endocrine disruption. The EPA web site states that Aminocyclopyrachlor is a low-risk pesticide. The human health and ecological risk assessments found that the herbicide posed low risk to both humans and other terrrestrial and aquatic organisms, except for plants. Aminocyclopyrachlor is related to other herbicides, including clopyralid and aminopyralid, which have caused plant damage when present in compost or manure as a result the label recommended against use of grass clipping for compost, but the tree deaths were unexpected.
Disclosure: In the 1970's and 1980's I worked for both the US EPA and DuPont as a Chemical Engineer.