Some Observations on Imprelis Injury to Trees
Posted: June 26, 2011
Damage to trees due to leaching or drift of herbicides applied to turf is a rare event; but when it does occur, it can create a lot of anxiety and customer dissatisfaction. This year, professional turfgrass managers from Iowa to New Jersey experienced damage to certain tree species (primarily Norway spruce and white pine) following spring applications of a new herbicide called Imprelis. The following article provides information about Imprelis and tree injury resulting from spring applications.
Imprelis (aminocyclopyrachlor) was released by DuPont Profession Products in 2010 for use in the professional turf market. It belongs to a new class of herbicides called pyrimidine carboxylic acids. This class is similar, but not identical to the pyridine carboxylic acid herbicides, which includes aminopyralid (Milestone), clopyralid (Lontrel), triclopyr (Turflon, Garlon), fluroxypyr (Spotlight), and picloram (Grazon, Tordon). Herbicides in this class tend to have low mammalian toxicity, herbicidal activity at low rates, and slow decomposition rates in organic residue and manure where oxygen is limited (Hipkins, 2009).
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 of shoots and roots (Buken et al., 2010). Symptoms on target weeds are consistent with those of other herbicides in the synthetic auxin family (2,4-D, dicamba, clopyralid, etc.), and include petiole twisting, as well as bending, curling, and cupping of leaves.
Imprelis is labeled for broadleaf weed control in cool and warm-season turfgrass on lawns, golf courses, cemeteries, athletic fields, and sod farms. It is currently available as a soluble liquid formulation. In extensive research trials in turf, it has shown very good efficacy on dandelion, clover, plantain, wild violet, and ground ivy. It also has been reported to have foliar and soil activity on shrub and brush species (Rick et al., 2008).
Imprelis herbicide is active on target weeds at very low rates (3 to 6 fl oz product/A, or 0.047 to 0.094 lb ai/A), is taken up rapidly by foliage, and has immediate rainfast properties. It is considered to have a low volatility risk, and can undergo photoloysis (breakdown due to sunlight) under certain conditions. Imprelis is thought to have relatively long residual activity in soils (Oliveira et al., 2011), and a slow decomposition rate in compost. This herbicide is generally recognized as having positive environmental stewardship attributes, and low mammalian toxicity (>5,000 ppm oral and dermal LD50 in rats).
Little information is available in scientific journals regarding the behavior of Imprelis in soils. In a recent publication, Oliveira et al. (2011) stated that aminocyclopyrachlor should be very mobile in soil (based on its sorption properties); however, depth of leaching may be overestimated in models. The authors concluded that more information is needed on degradation and sorption of aged herbicide residue to better estimate potential mobility of aminocyclopyrachlor in soils. Until more information becomes available to the public, users should heed the Environmental Hazards portion of the Imprelis label, which states the following:
Surface water advisory:
This product may impact surface water quality due to runoff of rain water. This is especially true for poorly draining soils and soils with shallow ground water. This product is classified as having high potential for reaching surface water via runoff for several months after application. A level, well maintained vegetative buffer strip between areas to which this product is applied and surface water features such as ponds, streams, and springs will reduce the potential loading of aminocyclopyrachlor from runoff water and sediment. Runoff of this product will be reduced by avoiding applications when rainfall is forecasted to occur within 48 hours.
Aminocyclopyrachlor has properties and characteristics associated with chemicals detected in ground water. This chemical may leach into ground water if used in areas where soils are permeable, particularly where the water table is shallow.
Effects on trees:
I first heard about tree damage following Imprelis applications from Mr. Tom Ford, an extension educator in Blair County, PA. Other reports quickly followed from extension educators located in western, eastern, and central portions of Pennsylvania. Most of the reports involved damage to Norway spruce and white pines following April and May applications of Imprelis. Reports from several sites involved suspected herbicide damage to other tree species and ornamental shrubs (these reports are less common that those of spruce and pine). Notices of Norway spruce and white pine injury following Imprelis applications were issued from extension web sites in Nebraska, Iowa, Michigan, Ohio, Maryland, and other states. Turf managers and arborists in and around Pennsylvania are asking what happened, and what can be done to save injured trees.
First, not all applications of Imprelis resulted in tree injury. According to a letter sent by DuPont Profession Products to lawn care and golf course managers who used Imprelis, most applications resulted in no tree injury. In cases where injury occurred, symptoms to Norway spruce began as yellowing, curling, and browning of the current season’s growth.
This type of injury would be expected given that the active ingredient of Imprelis is translocated to leaf meristems. In some cases, injury does not progress much further than slight curling and browning of new growth; however, in other cases complete dieback is observed. In severe cases, the entire tree turns brown and begins to lose its needles. Trees of all ages have been affected to varying degrees.
The white pine injury I have observed involves severe twisting and curling followed by needle drop of the new season’s growth. Some landscape contractors and lawn care professionals have asked if the Imprelis damage is a result of drift or root uptake. Although it is difficult to determine the exact mode of entry into affected trees, most of the symptoms I have seen are more consistent with root uptake than drift.
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. Dr. Jim Sellmer (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. He 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 (Freucht, 1988).
Imprelis injury seems to be related to the soaking spring rains of April and May (I am not aware of any tree injury following fall applications), and to some particular characteristics of the herbicide. Even though applicators I have spoken with did not apply the herbicide within the “drip line” of affected trees (as directed on the Imprelis label), injury still occurred. Research has shown that root spread of trees far exceed the branch spread; thus, root uptake from leached herbicide residue can occur outside of the drip line (Freucht, 1988). Although leaching of herbicides is more of a risk in sandy soils with low organic matter content, Imprelis-related damage occurred in several locations on heavy, clay soils. Right now, there is much speculation about the details surrounding tree damage due to Imprelis applications, but the exact reasons still need to be sorted out.
What can be done about injured trees?
First, it’s important to make sure tree injury is a result of herbicide uptake. Freucht (1988) stresses the importance of recognizing symptoms that mimic growth regulator herbicide injury on trees. For example, eriophyid mites can cause deciduous tree leaves to twist or curl (mostly upward); however, their feeding does not result in twisting of the petioles. Leafhoppers and aphids may produce petiole twisting and leaf curl, but will usually leave stippled patterns from feeding.
In conifers, biotic or abiotic factors can cause symptoms similar to Imprelis injury. Diplodia blight and injury due to environmental stress are two factors that can cause browning of new growth. Mr. Scott Guiser, extension educator in Bucks County, noted that portions of Pennsylvania experienced severe drought in 2010, and Norway spruce were especially affected by this stress. Drought injury to spruce results in branch dieback, but current season’s growth does not exhibit curling and distortion associated with synthetic auxins. An extension educator in southern PA recently sent pictures to Penn State tree specialists showing tip dieback of Douglas firs from an area that had not been treated with herbicides. The injury was diagnosed by Penn State specialists as being caused by high heat and light intensity following a prolonged period of cool, cloudy conditions during needle expansion.
Currently, I know of no commercial or private laboratory that can analyze for aminocyclopyrachlor in soils or plant tissue. Until laboratory analysis procedures become available, diagnosis of Imprelis injury will have to be based on visual symptoms (curling, twisting, yellowing, and browning of needles and leaves, mostly on new-season’s growth).
In cases where injury is clearly herbicide induced, do not fertilize trees for at least one growing season (excess growth can compound injury). If drought begins to set in, watering to alleviate stress may be useful on trees that received slight to moderate damage. Officials from DuPont suggest placing a soaker hose on the soil near the trunk of injured Norway spruce trees that have low hanging branches. This allows slow irrigation of the soil directly under the tree, and reduces the risk of bringing additional active ingredient into soil solution where it would be available for uptake. Use of activated charcoal to deactivate the herbicide will probably be of little use at this point. On trees with dieback, pruning should be delayed for up to a year to fully assess the extent of the damage, and to allow for recovery (Patton et al., 2011).
Some turfgrass managers have expressed concern about increasing tree damage as the summer progresses. Although no one knows for sure, Dr. Charles Silcox from DuPont Professional Products points out that the average half life of aminocyclopyrachlor in turfgrass systems is 44 days, so a large proportion of the active ingredient has probably been degraded, and will continue to dissipate over the next few weeks.
The Pennsylvania Department of Agriculture is aware of tree injury resulting from applications of Imprelis herbicide. DuPont Profession Products has released a letter to turf professionals and turf distributors who have purchased and sold Imprelis, explaining the situation. Representatives from DuPont are also visiting sites to collect information and assess each situation. Penn State Cooperative Extension will try to provide updates on the Imprelis situation as more information becomes available.
- Buken, B., R. B. Lindenmayer, S. J. Nissen, P. Westra, D. L. Shaner, and G. Brunk. 2010. Absorption and translocation of aminocyclopyrachlor and aminocyclopyrachlor-methyl ester in Canada thistle (Cirsium arvense). Weed Science 58:96–102.
- Freucht, J. 1988. Herbicide injury to trees - Symptoms and solutions. J. of Arboriculture 14:215-219.
- Hipkins, Pat. 2009. Pyridine herbicide carryover: Causes and precautions.
- Imprelis Herbicide Label. 2011.
- Oliveira, R.S. Jr., D. G. Alonso, and W. C. Koskinen. 2011. Sorption- desorption of aminocyclopyrachlor in selected Brazilian soils. J. Agricultural and Food Chemistry 59:4045-4050
- Patton, A., G. Ruhl, S. Weller, and J. Becovitz. 2011. Herbicide damage on spruce and pine. Turf Tips.
- Rick, S. K., R.G. Turner, and J.H. Meredith. 2008. Biology review of
aminocyclopyrachlor. North Central Weed Sci. Soc. Proc. 63:202.
This article was prepared by Pete Landschoot, Professor of Turfgrass Science, Penn State. Much of the information in this article comes from first hand observations by the author, and from conversations, photos, and reports from Andy Beck, Jeff Borger, Nancy Bosold, Tom Ford, Jeff Fowler, Scott Guiser, Jay Matthews, Eric Oesterling, and Jim Sellmer.