Beware the Emerald Ash Borer


Since 2002 the Emerald Ash Borer has decimated urban forests across the Midwest. The Emerald Ash Borer (EAB) is a beetle native to northern China and Korea that was first discovered in the Detroit, Michigan/Windsor, Ontario area and is responsible for the loss of 18 million trees in southeast Michigan alone. Since being discovered in the south St. Anthony Park area in 2009 the EAB has spread across the metro area. Anoka, Chisago, Dakota, Fillmore, Hennepin, Houston, Olmstead, Ramsey, Scott, Washington and Winona counties are now under quarantine and most recently the EAB has been discovered in Island of Park Point in Duluth.

The Emerald Ash Borer is a small iridescent green beetle which lives outside ash trees in the summer months and lays its eggs on the bark. It is the resultant beetle larvae that does the direct damage. The larvae bore beneath the bark and chew their way through the layer between the bark and the wood, creating tunnels that interfere with the trees ability to transport water and nutrients. The tree eventually starves to death.

The flight season of the beetles begins around May 1. On its own the beetle travels only 1/2 mile from an infected site per year. So how has the EAB managed to spread to so far? The primary way has been through the transporting of ash firewood from infected trees.

Minnesota has the highest volume of ash trees in the U.S.–870 million. The urban canopy of Minneapolis includes 210,000 ash trees; 30,000 on boulevards, 10,000 in parks and the remainder on private property. EAB most likely arrived in the U.S. from Asia in solid wood packing materials in cargo ships or airplanes, and since it is not native it has no natural predators. The Minnesota Department of Agriculture is currently experimenting with two parasitoid wasp species; one that attacks the larva under the bark and another that destroys the eggs in the bark crevices. But until these can be proven effective and not harmful to other species or the environment, there are really only two ways to deal with EAB — treat or remove.

Treatment involves injections that are effective only one or two years. While that may be something that residents want do to with ash trees on their own property, is not a viable alternative for the Minneapolis Forestry Department. In 2014 the department began an eight-year effort to mark, remove and replace the 40,000 ash trees in the public realm. This is an effort to spread the cost of the tree removal over several years, reduce the impact of a sudden city-wide canopy loss and buy a little time for science to catch up with the EAB. The plan is to remove 5000 ash trees per year, 2-4 per block per season. The Director of Forestry will decide which trees will be removed on a block by block basis. Residents can also request that a boulevard tree in front of their property be removed at no cost to them. The identification and removal process runs from 2014-2021 and the tree replacement will take place from 2015-2022.

We are all pretty familiar with the orange “rings of death” that are applied to trees — mostly elms that are slated for removal. For the EAB the city is using green markings. You may have noticed trees across the city with green ribbons, green Xs or green rings. The green ribbons are being used to raise awareness about the effect that EAB will have on the urban canopy – so people realize how many of our boulevard trees are ash trees. Trees marked with a green X are trees that are unaffected by EAB, but are slated to be removed this year. A green ring means that the tree is infected and will be removed in five days. It is important to remove infected trees as soon as possible, not only to contain the spread of the EAB but because infected trees become hazard trees quickly. [Hazard trees are those that are in danger of falling over or dropping large branches that might injure people or damage property.]

It is estimated that the financial impact of dealing with the EAB in Minneapolis will be $152M; including removal, stump removal and replacement of 210,000 trees. Some of this cost will be borne by the City and some by the residents.