Lawn Herbicide and Trees

Watch for Possible Broadleaf Lawn Herbicide Injury to Trees
Damage to trees due to broadleaf lawn herbicides is a rare event; but when it does occur, it can create a lot of anxiety and customer dissatisfaction. This year, damage has been observed on certain tree species (primarily Norway spruce and white pine) following spring applications of a new herbicide called Imprelis. Pete Landschoot, Professor of Turfgrass Science, recently provided an update on this situation. Here’s a brief summary of his report.

Effects on trees:
First, not all applications of Imprelis result in tree injury. The recently observed injury seems to be related to the soaking spring rains we experienced in April and May. We are not aware of any tree injury following fall applications.

In cases where injury did occur, symptoms to Norway spruce began as yellowing, curling, and browning of the current season’s growth. 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. White pine injury appears as severe twisting and curling followed by needle drop of the new season’s growth. Because of the spiral pattern of the vascular system in many conifers, damage from herbicide uptake may even appear as a spiral on foliage.

What can be done about injured trees?
Since a number of factors can cause symptoms similar to Imprelis injury it’s important to make sure tree injury is a result of herbicide uptake. Call a qualified arborist or bring in samples to your local Penn State Extension office.

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. Place 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 additional active ingredient being taken up by the tree. 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.

Penn State Cooperative Extension will provide updates as more information becomes available. To find the latest updates go to http://extension.psu.edu/ and search on the term Imprelis.

To read Dr. Landschoot’s full article go to http://extension.psu.edu/greenindustry/giec/news/2011/some-observations-on-imprelis-injury-to-trees Or contact your local cooperative extension office. In Lackawanna County ask for the Garden Help line at 963-6842 or email LackawannaMG@psu.edu


Terry Schettini, Extension Educator
Penn State Cooperative Extension in Lackawanna County