Over the past few weeks, numerous accounts of injury to trees and shrubs have been reported. Some of this damage is suspected to be a result of herbicide applications made to turf areas. Several reliable sources have indicated that the use of Imprelis™ (aminocyclopyrachlor), a post-emergent broadleaf herbicide, has caused damage to some woody ornamentals, in particular Norway spruce, blue spruce and white pine. The damage is consistent with growth regulator herbicide type injury and includes twisting and curling of new growth. The following is a collection of useful resources about this developing situation.
Reports include those from Ohio State University through the Ohio State Buckeye Yard and Garden Line (see newsletters for June 9 and June 16, 2011: http://bygl.osu.edu ), as well as from Michigan State University:
This situation has also been reported by the diagnostic lab at Purdue University where the damage seen appeared to be a result of root uptake:
In addition, there have been similar but unpublished reports from some mid-Atlantic states regarding comparable situations and damage.
DuPont, the maker of Imprelis™, is in the process of investigating the situation and has sent out precautionary information about the material, including the following statement based on their preliminary investigations:
"In most cases, Imprelis™ was not applied alone, but in a mixture with other herbicides, either pre-emergent, post-emergent and/or with a liquid fertilizer. Some reports indicate there may have been errors in use rates, mixing practices and/or applications to exposed roots, or the tree."
DuPont advises to not apply Imprelis™ where Norway spruce or white pine are present or in close proximity to a property being treated. In addition, DuPont advises:
"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 rootzone of trees and shrubs."
The full text of the letter from DuPont can be found at:
Applicators who suspect that this type of injury has occurred or is occurring should work with their pesticide distributor. Distributors have contact information for area manufacturer representatives who are responsible for addressing suspected problems and concerns.
Note that there are many factors that can cause needle browning and similar damage to evergreen landscape plants. Pictures of the injury suspected to have been caused by Imprelis™, can be viewed at the Purdue University Diagnostic Lab website:
In addition, Michigan State has information on what to do with trees that may have been injured by the herbicide:
General information for avoiding ‘non-target’ damage from pesticide applications
- Pesticide applicators should make themselves aware of factors that may inadvertently lead to non-target effects of pesticide applications. Some broadleaf turf herbicides, including aminocyclopyrachlor and dicamba, are soil active. Applicators should know if the herbicides they are using are soil active and whether they may be prone to movement in the soil profile. Many areas of the country, including the northeast, experienced above average rainfall this spring. This combination of soil active materials and high levels of precipitation may lead to unintentional herbicide injury.
- Make every effort to use dedicated sprayers and to properly clean all spray equipment. In an ideal world, those that apply pesticides as part of their business would have dedicated sprayers for each type of pesticide that they apply. In other words, they would have a sprayer that is just for herbicides, another for fungicides and also one used just for insecticides. Having separate spray equipment for each type of pesticide is usually not practical, expensive and would cause a logistical nightmare when trying to get equipment to and from a job site. The application of a turf insecticide followed by an application of a turf herbicide to a turf area has little to no potential of causing plant injury or death to the grass. The potential for big problems exists with applicators that switch back and forth between turf and landscape pesticide applications, particularly when the use of an herbicide is involved. In this situation it is crucial that the spray equipment receives a thorough cleaning before the new pesticide is added to the tank and the application begins. For example, if a postemergence broadleaf herbicide was applied first to turf and shortly thereafter an insecticide was applied to landscape ornamentals using the same equipment, there is a great potential for herbicide injury or death to landscape ornamentals from the herbicide left in the sprayer if it was not properly cleaned. In this situation, simply running the spray equipment until the tank is empty does not remove all the herbicide spray solution from the pump, lines and hoses. In addition, herbicide mixtures should never be allowed to dry in a sprayer. The pesticide label for the product being applied and the sprayer manual are two important sources of information on how to properly clean the sprayer. During very busy and hectic times of the growing season it can be very tempting to try to cut corners with the objective of saving time and money. Proper spray tank cleaning between pesticide applications and at the end of the workday is not any area in which it is wise to cut corners. Applicators must be responsible for sound pesticide application practices.