NEW LONDON — The news is not good for Midwest residents who have ash trees on their property, as tree-killing emerald ash borers slowly spread their way west and north.
“This is an insect that is probably the greatest non-native tree-killing insect that we’ve ever had in North America,” said Bill McNee, forest health specialist with the Wisconsin Department of Natural Resources. “It would rank up there with Dutch elm disease in terms of its total impact, but that’s caused by a fungus.”
McNee was among presenters in June at an EAB workshop at Mosquito Hill Nature Center in New London, where staff is working through a management plan for the center’s 430 acres of forested land with a large percentage of ash. Urban and woodland owners were invited to learn how to identify ash trees and what options were available for their management.
EAB was first discovered in Michigan in 1992 and gradually spread to 30 states east of the Rocky Mountains. The ash-killing insects are suspected of being imported from East Asia into Detroit with packing material. While infestations have been found in 41 Wisconsin counties, they haven’t been identified in Waupaca County, but it’s only a matter of time, McNee said.
“It has made its way down to places like east Texas, northern Louisiana and eastern Alabama, so if it can make its way that far it probably has made its way into Waupaca County, or the New London area or Shawano, and we just don’t know it yet,” McNee said. “This is a hard insect to find until a tree actually starts showing symptoms, so it’s very, very, very likely that we have other infestations in the state that we have not found yet.”
Adult emerald ash borer beetles lay eggs on the bark of an ash tree. When the eggs hatch, larvae tunnel into the nutritious floam layer where they eat their way in an s-shaped progression through the tissue and disrupt the tree’s ability to transfer water and nutrients upward to the branches. The larvae overwinter in the wood, pupate and chew their way out through the bark, leaving distinctive eighth-inch D-shaped holes.
Light-colored and smaller leaves high in the tree canopy are indicators of an early infestation. So are woodpecker activity, progressive die-back and thinning of leaves in the canopy, and shrubby branching at the bottom of the tree. Death is from the tree top down and takes one to six years.
“By the time we see galleries and adult beetles down in the trunk of the tree, usually that tree is either on its last legs or is dead and doesn’t know it yet,” McNee said.
Wisconsin has 42 quarantined counties from which ash material and hardwood firewood may not be transported into non-quarantine counties. Despite the quarantine, McNee said, people are probably the main means of long-distance mobility for emerald ash borers.
“On its own, this insect tends to be a lazy insect and will fly a few hundred yards in most cases, but some of them do fly several miles or more,” he said. “And, thanks to people, this insect can go 70 miles an hour and create a new infestation via the Interstate.”
McNee said the expectation is that more than 99 percent of Wisconsin’s ash trees will die without some kind of active prevention program. Roughly one of every 16 trees in the state is an ash, and most of them are north of the current quarantine area in productive forests where chemical treatments are not practical.
Roughly 20 percent of all street trees in the state and 12 percent of all urban trees on public and private property are ash. There, insecticide treatments might be of benefit, but there are factors to consider.
The closest known infestation to New London is Appleton, where EAB is widespread. That 15-mile distance is the point at which ash tree owners should start taking action.
“If (New London residents) did not treat this spring, you might want to next spring,” McNee said. “I would not go more than two years. Time is just not on your side.”
Determine the value of the tree in terms of its location and impact on the property. If it is healthy and vigorously growing, enhancing the landscape, and showing no more than a few outward signs of EAB infestation, it can be saved with insecticide treatment.
“What you will find is big trees provide much more of the benefits, and probably it’s the big trees people are going to spend the money to treat,” McNee said. “A big tree can cost a couple thousand dollars to remove and replace. (If treated), probably you can have that tree for 10 years or more and still have this nice big tree that provides shade, a view and increased property value, and spend less money than you would have spent to have that tree removed in the first place.”
If the tree is less than 20 inches diameter at breast height, the homeowner can try treating it annually with an over-the-counter product. If it is larger, a tree specialist should do the job.
“If you have a tree more than 15 inches in diameter, the homeowner products just don’t work very well,” McNee said.
If an ash tree is unhealthy, poorly situated on the property, will need maintenance to keep it clear of power lines or other structures, or poses a potential hazard when it dies, it should be removed. A live tree is less expensive to remove than a dead one.
Trees are a valuable asset to private property and woodlands. McNee’s message to property owners is to diversify.
“Whether you have yard trees or a woodlot, mix things up, because more of these (invasive) things are going to be showing up on shipping containers over the long term,” he said. “If you have five, six, seven species and you lose one, you’re still going to have a forest or yard trees. If you put all your eggs in one basket and some invader comes along and kills that one species, you’re going to have major problems. Hedge your bets and mix your species up.”