Emerald ash borer addressed by expert
It’s small and green, but the emerald ash borer has Southeastern Michigan residents seeing red as it decimates the ash tree population.
Thousands of trees have already been lost, and more are expected as the insect’s larvae continues to feed on ash and destroy the tree’s ability to transport nutrients and water from the roots to the crown.
David L. Roberts, a Michigan State University Extension specialist and district horticulture agent, addressed a small audience of residents and officials from the Grosse Pointes about the growing threat during a talk March 4 at the Grosse Pointe Farms Pier Park.
Liz Brown, chair of the Farms Beautification Commission, which put the lecture together, said the city was “very lucky” to get Roberts — a leading expert on the pest — to speak.
Native to Asia, the emerald ash borer was identified by Roberts last year as he tried to uncover the reason for a rash of deaths among the normally sturdy ash trees in Michigan.
While Roberts said “we have a lot to learn” about the beetle, one thing researchers have already discovered is the speed at which it travels and kills trees, attacking healthy and troubled ash alike.
“It’s increasing tenfold each year, so it’s going to keep gathering speed,” Roberts said.
Although infestation symptoms aren’t always apparent until the tree is heavily infested, Roberts said residents should look for yellowing and thinning of upper branches, epicormic shoots emerging from the trunk, small D-shaped exit holes on the bark (from which the adult beetles emerge), bark splits and woodpecker holes. Woodpeckers frequently go after the larvae in winter, Roberts said. Unfortunately, the birds are only extracting an estimated 10 percent of the larvae — not enough to save the tree.
“One of the most important things: If you want to save ash trees, you have to detect [infestation] early,” Roberts said.
Once more than 10 percent of the canopy is lost, the tree can lose 40-50 percent of its canopy in the next two months, he said.
Roberts also stressed the need for maintaining a diverse tree population, as the Pointes have done. Many insects and diseases are species-specific, so a varied tree population can help a community stay green even if some of its trees are felled by a new invader.
He reluctantly recommended chemical treatments such as injections, sprays and ground applications, especially in combination. Although there’s no guarantee such treatments can ward off or save ash trees, they may buy time for researchers to come up with a more permanent solution. Roberts recommended ground applications in early April, and injections in May.
Roberts praised the Farms for opting to inject its city-owned ash trees last year.
“You’re setting the standard for the state, as people look to see if you can hold onto your ash,” Roberts said.
It’s crucial as well to take down dead or diseased trees to reduce the insect’s spread. Recommended disposal methods include chipping, burning or burying the wood. Roberts said if residents want to retain the wood for firewood, they should cover it to the ground with tarp, and weight the ends of the tarp down to keep any beetles left behind in the wood from escaping.
However, such wood cannot be transported outside of Southeastern Michigan. Last summer, the Michigan Department of Agriculture ordered a quarantine of ash trees and related products. The quarantine made it illegal to transport ash trees, firewood and other parts bigger than 1-inch in diameter outside of Wayne, Oakland, Macomb, Monroe, Washtenaw and Livingston counties, as well as Windsor, Ontario.
Experts are considering options such as introducing Asian ash varieties, which may be more resistant to the pest.
Roberts estimates a plan to contain and eliminate the insect will cost around $40 million to $50 million annually for at least 10 years. Although researchers have approached the federal government seeking funding, he said it’s unclear whether the government will authorize such a program.
For more information, visit http://www.msue.msu.edu/reg_se/roberts/ash/index.html.