(Beyond Pesticides, July 13, 2011)
Millions of dollars’ worth of Norway spruce and white pine trees are mysteriously turning brown and dying this summer, and the chief suspect is a new lawn chemical. The product, Imprelis, a new herbicide manufactured by DuPont, is suspected by State officials and lawn care professionals who say they think Imprelis may be attacking pines and spruces. Once again, this new incident exposes the deficiencies in the registration process for new pesticides put onto the market without a full data set.
In what some say could be one of the biggest disasters of its kind since the emerald ash borer killed millions of trees, white pine and Norway spruce trees are turning brown or dying all around the country. Tree damage has been reported throughout the Midwest, in East Coast states and as far south as Georgia. Many landscapers in Michigan and elsewhere switched to Imprelis (See the MSDS here) this year to control weeds such as dandelions because it was touted as “safer” by DuPont for the environment than predecessors such as 2, 4-D. So many trees have died -from the East Coast west to Iowa – that the damage is projected to be in the millions of dollars, and now many states and the U.S. Environmental Protection Agency (EPA) are investigating the possible link to Imprelis.
Imprelis, whose active ingredient is the potassium salt of aminocyclopyrachlor, is a new herbicide conditionally registered in 2010. Conditional registration is allowed under Section 3(c)(7) of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), which allows pesticide registration to be granted even though all data requirements have not been satisfied, with the assumption that no unreasonable adverse effects on the environment will occur. When this occurs, pesticides are introduced to the market with unknown and unevaluated risks to human and environmental health. While all data must be eventually submitted, it often takes years before EPA acquires relevant data -often with data submitted for the 15-year reregistration review cycle that all registered pesticides must go through. It is rare that the regulatory decision will be altered once data has been submitted. Recently, EPA came under scrutiny recently since it was revealed that the conditionally registered pesticide, clothianidin, did not at the time it allowed the pesticide to be widely used have pertinent field data required on honeybees, even though the pesticide is known to pose risks to these vulnerable pollinators. This data is still outstanding even though clothianidin continues to be used in the environment.
The Michigan Department of Agriculture and Rural Development is studying sites of damaged trees and gathering samples of wood and soil. Michigan State University Extension is monitoring the situation and also has visited sites following complaints from landscapers. According to reports, landscapers appear to be following label directions and spraying Imprelis away from the trees, but they still have browning. In some cases, some white pines and spruces turn brown while others of the same species don’t, despite being in the same yard.
Landscapers switched to Imprelis this year to control weeds because it was claimed to be safer for the environment than predecessors. Amy Frankmann, head of the Michigan Nursery and Landscape Association, said she has not seen such widespread tree death since the emerald ash borer ravaged ash trees. “I’d say this is right up there as far as the significance and losses,” Frankmann said. “The customers are calling: trees are dying, what’s up?’ ” said Mark Underwood, a Michigan lawn care specialist. “We’ve never experienced anything like this.
In a letter to lawncare professionals, DuPont advises applicators, “Do not apply Imprelis where Norway Spruce or White Pine are present on, or in close proximity to, the property to be treated.” Furthermore, the industry giant suggests that, “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 root zone of trees and shrubs.” Spray drift which is typically the result of small spray droplets being carried off-site by air movement due to wind, humidity and temperature changes, can poison people and animals, injure non-target foliage, shoots, flowers and fruits resulting in reduced yields, economic loss and illegal residues on exposed crops.
Although drift has been suspected where symptoms appear on groups of branches, or on only one side of the affected tree, such symptoms are consistent with root uptake. Jim Sellmer, PhD, Penn State Department of Horticulture, pointed out that if only a portion of the root system was exposed to the herbicide, then foliar damage may be limited to the section of the plant that is serviced by those roots. Dr. Sellmer cautions that there may be no direct connection between the side of the tree exposed to the herbicide, and the side showing injury from herbicide uptake. Because of the spiral pattern of the vascular system in many conifers, damage from herbicide uptake may even appear as a spiral on foliage.
Imprelis is a post-emergent broadleaf weed control product controls a wide spectrum of broadleaf weeds, including difficult to manage invasive and noxious brush and herbicide-resistant species. Its active ingredient is the potassium salt of aminocyclopyrachlor which was granted conditional registration in August 2010. EPA, in its review of data submitted by the registrant DuPont, concluded that, “In accordance with FIFRA Section 3(c)(7)(C), the Agency believes that the conditional registration of aminocyclopyrachlor will not cause any unreasonable adverse effects to human health or to the environment and that the use of the pesticide is in the public’s interest; and is therefore granting the conditional registration.” However some data is still outstanding and are required in order to better characterize risk and “required in support of the new uses,” including data on environmental degradates, and certain environmental fate data.
According to EPA, aminocyclopyrachlor poses very low risk to humans, including workers and the general population, due to its low toxicity and low volatility. It is biologically active in soil and is rapidly absorbed by roots and leaves. Effects to target weeds include downward bending of leaves, severe necrosis, stem thickening, growth stunting, leaf crinkling and cupping, calloused stems and leaf veins, and enlarged roots. Symptoms may begin from a few hours to a few days after application, and plant death may take weeks to several months. Aminocyclopyrachlor is non-volatile, highly soluble in water, and highly mobile in soils. Due to its high mobility, this product has label advisories for surface and groundwater. Dissipation in the environment is expected to but aminocyclopyrachlor is environmentally persistent.
Aminocyclopyrachlor is in the chemical class of the pyrimidine carboxylic acids, which is similar to pyridine carboxylic acid herbicides which includes herbicides such as aminopyralid, clopyralid, and picloram. These chemicals have had repeated incidents where treated plant residues contaminated non-target plants. These chemicals persist in the environment, do not break down during composting, and have affected flowers and vegetables, such as beans, peas and tomatoes. Some states as well as the United Kingdom were prompted to take regulatory action due to these incidents.
Alternatives to Weed Management
There are some safer – though less widely used – options for weed control. To get started, read Beyond Pesticides’ “Read Your ‘Weeds’, A Simple Guide To Creating A Healthy Lawn” and “Least-toxic Control of Weeds.”
For more information on Imprelis’ effect on trees and what to do if your trees are affected, visit Penn State’s Cooperative Extension’s “Some Observations on Imprelis Injury to Trees.”