News and Information
What to do with Imprelis-affected trees
Patience and time are preferred to hasty action that may only compound the problem.
Bert Cregg, Michigan State University Extension, Departments of Horticulture and Forestry
Recent reports that the turf herbicide Imprelis may be responsible for damage to landscape trees, especially conifers, has generated numerous calls to MSU Extension specialists and educators as well as MDA officials (see Kevin Frank’s article Imprelis herbicide may injure evergreens). One of the most common (and most vexing) questions is what to do if you suspect trees have been affected by Imprelis.
Imprelis (active ingredient aminocyclopyrachlor) is classified as a synthetic auxin herbicide. In addition to foliar activity, Imprelis can also be taken up by plant roots. In the current rash of reported tree damage, it appears that trees are taking up Imprelis that has been applied to turf outside the tree’s drip line. Affected trees are showing symptoms commonly associated with herbicide injury: twisting or stunting of new growth and needle browning.
So, what do you do if you suspect Imprelis application has damaged trees? Unfortunately, the best advice we can offer at this juncture is “wait and see.” Imprelis is a new product on the market and there is relatively little information in the literature to guide us. In soils, Imprelis adsorbs most tightly to organic matter. Therefore, it should leach most readily from soils with low organic matter, especially sandier soils. Soil adsorption of Imprelis decreases as soil pH increases, so it should leach faster on alkaline soils. Rainfall and irrigation may help to leach Imprelis through soils. However, the active ingredient is broken down by soil microbes, so it is important to avoid water-logging soil since that would inhibit microbial activity, not to mention increase stress on trees that are already struggling.
Herbicide injury to trees can sometimes appear worse initially that it is in the long term (Photo 1). Landscapers and lawn service operators should try to avoid knee-jerk reactions in response to client calls. Trees can often overcome what appear to be devastating injuries and emerge relatively unscathed. The best plan for an affected tree at this point is to try to keep the patient comfortable and let the tree’s recuperative abilities kick in.
If possible, irrigate trees during warm, dry weather, but avoid water-logging. Light fertilization may also improve tree vigor and its ability to recover. Based on what little we know about Imprelis, avoid ammonium-based fertilizers that may reduce soil pH and therefore increase Imprelis adsorption. Removing sod or contaminated soil over tree roots may trigger additional tree stress and should be viewed as a last-ditch effort to save trees.
Photo 1. Many of these red maple trees were slated for removal after the
surrounding mulch beds were mistakenly treated with the herbicide Sahara in
June 2009 and the trees suffered severe die-back. Most of the trees had essentially recovered when this photo was taken in June 2011.