An Update on Tree Injury and the Status of Imprelis Herbicide
Posted: August 15, 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, the status of the herbicide, and what to do with all those dead trees.
Characteristics of Imprelis herbicide
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, and is 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). Other vegetation management herbicides containing aminocyclopyrachlor include DuPont’s Perspective, Viewpoint, and Streamline.
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 photolysis (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. A groundwater advisory on the Imprelis label cautions that aminocyclopyrachlor has properties and characteristics associated with chemicals detected in ground water.
Effects of Imprelis on trees:
I first heard about tree damage following Imprelis applications in early June 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 began asking what happened, what can be done to save injured trees, and what should be done with trees that must be removed.
Despite many reports of tree damage, not all applications of Imprelis resulted in tree injury. I visited one site in southeastern Pennsylvania where an application was made in early May directly under a row of mature white pines, and no visible injury resulted from this application. 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. Why some applications resulted in tree injury and others did not remains a mystery.
In cases where injury occurred, symptoms to Norway spruce began as yellowing, curling, and browning at the terminal portion 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 did not progress much further than slight curling and browning of new growth; however, in other cases complete dieback was observed. In severe cases, the entire tree turned brown and began to lose its needles. Trees of all ages have been affected to varying degrees. The white pine injury I have observed involved 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 soaking spring rains which may have leached the herbicide into the root zone, the fact that assimilates are moving mostly upwards in the tree’s vascular system in spring (along with any herbicide that may have been absorbed by the roots), 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 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. 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?
When attempting to determine if Imprelis caused tree injury, it’s important to make sure symptoms are 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.
Some state labs (Minnesota, Michigan, and possibly others) are offering to analyze for aminocyclopyrachlor in soils or plant tissue, but due to extensive laboratory renovations at the Pennsylvania Department of Agriculture, an analysis cannot be obtained in Pennsylvania. If a laboratory analysis cannot be secured, diagnosis of Imprelis injury will have to be based on visual symptoms (curling, twisting, yellowing, and browning of needles and leaves, mostly on the 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). Watering to alleviate stress may be useful on trees that received only slight damage. Irrigating during dry periods will minimize moisture stress and one good soaking per week may be beneficial if there has been no rain. Consider using “Gator Bags” during dry weather on smaller trees or newly established trees. For large and well established trees, the root system spreads well beyond the canopy. Irrigating with a soaker hose across the entire root system (including areas outside of the drip line) for one hour may help to reduce stress during drought. Changing the location of the soaker hose for the next irrigation will also provide stress relief for other parts of the root system.
Use of activated charcoal to deactivate the herbicide will be of little use at this point. On trees with minor 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 tree experts have indicated that dieback on conifers may ultimately destroy the shape and beauty of the tree, so it is questionable how much pruning will help.
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.
Reporting tree injury, and information from DuPont:
The Pennsylvania Department of Agriculture is aware of tree injury resulting from applications of Imprelis herbicide, and is collecting information and investigating reports of suspected damage. EPA is also collecting information on possible adverse effects to trees and is asking concerned individuals to fill out a form - forms can be obtained by emailing Peter Landschoot.
DuPont Profession Products has released letters to turf professionals and turf distributors who have purchased and sold Imprelis explaining the tree injury situation; offering the services of 20 independent, certified arborists for evaluation of claims; and providing directions on how to deal with injured trees. Representatives from DuPont have visited many sites to collect information and assess each situation. Recently, DuPont distributed a letter from Michael McDermott, Global Business Leader of DuPont Professional Products, on a voluntary suspension of sale of Imprelis, and a product return and refund program for this herbicide. The EPA followed this announcement with an order directing the company to immediately halt the sale, use or distribution of Imprelis. McDermott asked that individuals holding Imprelis not take any action until contact by DuPont representatives.
The product return and refund program is expected to be activated in mid-August. For questions on the recall, contact DuPont’s Customer Service Center at 1-800-342-5247 (prompt 99).
In a July 26 release, DuPont stated that individual businesses may need to decide soon on whether an injured tree should be removed due to a safety issue or a customer issue. If it is decided to remove a tree the company requests preparation of proper documentation including:
- Recording the size (height and trunk diameter at 12 inches above the ground), species, and physical location of the tree.
- Providing the name and address of the property owner.
- Spray records including date treated, application rates, application equipment, etc.
- Provide photos of each tree before it is removed including:
- A full picture to establish location, size and condition (include an object like a broom or yardstick to show perspective).
- A close up picture of branch terminals to record symptoms.
For more information from DuPont on the Imprelis situation, you can access their website or call their hotline at 866-796-4783. This number is not for filing claims.
Removal and disposal of Imprelis-damaged trees and replanting
Some extension educators have expressed concern that ground/chipped trees may still contain enough Imprelis residue to damage sensitive plants. Tom Ford (Blair County) cautions that nearly all conifer take-downs are disposed of at municipal sites where they are ground into mulch. Those responsible for disposing of dead trees may not be aware of the issues regarding Imprelis since they are generally not affiliated with the landscape and golf industries. The wood chips from these conifers may end up in the mulch stream and present a hazard if spread around sensitive plants. Ford advises that local solid waste and composting service agencies should be contacted and made aware of this situation.
Where burning is allowed, damaged conifers can be burned in late fall or winter. If allowed by local yard waste regulation, small trees may be disposed of in the trash. For Imprelis treatments applied at labeled rates prior to June 1, 2011, DuPont suggests waiting until after October 1, 2011 to replant. For Imprelis treatments applied at labeled rates between June 1, 2011 and June 30, 2011 trees can be replanted after November 1, 2011. As an additional precaution, DuPont advises not to use Imprelis-treated soil to back-fill around newly planted trees.
- 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 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 Rick Bates, Andy Beck, Jeff Borger, Nancy Bosold, Tom Ford, Jeff Fowler, Scott Guiser, Kerry Hoffman-Richards, Shawn Kister (Longwood Gardens), John Lake (PDA), Jay Matthews (Grove City CC), Eric Oesterling, and Jim Sellmer.