Per Mpls Park and Rec we should wait to prune ash trees until fall because the ash borers are active now through Labor Day. Why is this important? “Emerald ash borers are a major concern because they have caused the deaths of millions of ash trees in 13 states, and approximately 20 percent of the tree canopy in Minneapolis consists of ash trees.” (per Mpls Park and Rec)
You may notice an increase in woodpecker activity (such as along Miss. River Blvd. in St. Paul)—this may be a sign of ash borers. Indeed, the trees along the blvd. are being monitored and treated for ash borer. You’ll notice tent treatments on the trees.