Michigan State University Extension is offering advice to superintendents who suspect that landscape trees have been injured by the herbicide Imprelis (aminocyclopyrachlor): Wait and see.
University Extension offices in several states, including Michigan, have received samples of conifers and woody ornamentals that have damage symptoms similar to those caused by synthetic auxin herbicides. These herbicides are growth regulators and may cause new growth to turn brown and die and needles, shoots and branch tips to become twisted and curled. At present, the exact cause of the damage has yet to be determined, and researchers are still investigating the problem.
Bert Cregg at Michigan State University Extension urges caution. In some cases, trees with this type of injury have recovered without drastic intervention (which may actually aggravate the situation). Cregg advises superintendents and others to make sure affected trees are lightly fertilized (avoid ammonium-based products) and well-watered but not water-logged, and then sit back and be patient because, he says "Trees can often overcome what appear to be devastating injuries and emerge relativley unscathed."
For more information and photos of the tree damage, visit the following sites: