Tree Pests

The Emerald Ash Borer Found in Baltimore

Fear the emerald ash borer! This exotic pest of ash trees was found in our city in June in special beetle traps in Druid Hill Park and near Fort McHenry. In coming years, these shiny green beetles will be a death sentence for many of Baltimore’s ash trees, which make up a tenth of our urban forest. However, some Mid-western cities are saving their prime ash trees through pesticide injections, finding it to be far more cost effective to save the mature ash trees in all their glory than to pay for their removal.

The emerald ash borer (EAB), a shiny winged insect the size of a penny, is thought to have arrived in the United States in solid wood packing material from its native Asia. First detected in the Detroit, Michigan/Windsor, Ontario area in July 2002 and then in Ohio, infestation by EAB has has already killed millions of ash trees in the central and northeastern United States.

In August of 2003, Maryland became the third state to detect  EAB. That month, state inspectors found the emerald ash borer  on some of 121 ash trees at a landscape nursery in Prince George’s County. Despite measures to eradicate the pest, in 2008, EAB beetles showed up in Charles County. By 2011,

EAB had been detected in several more counties — Anne Arundel, Howard, Allegany, and Washington. At first, states tried to prevent EAB spreading by cutting down all nearby ash trees where EAB might breed. But now many cities have a mixed approach–cut down infested trees, but save and protect the rest by pesticide injections.

While no one has yet to see an emerald ash borer here in Baltimore, it is considered just a matter of time. City Forestry and TreeBaltimore have not been planting ashes for some years now, but the ash is the one of the most common trees in Baltimore – 293,000 trees, 10.4% of trees total population.

The good news for homeowners who have beautiful, old ash trees: “There is no reason for a landscape ash tree to die from emerald ash borer anymore,” says Deborah McCullough, a professor of entomology and forestry at Michigan State University. In 2009, Milwaukee started injecting trees with a pesticide called Tree-age.

Applying pesticides every two years costs about $250 a tree, while removal and replacement is $700 to $1,200 a tree, she said. “You can treat a tree for a lot of years before you reach the cost of removing that tree.”

“The treatment is so effective and so much cheaper than removal and replacement ,” said one Milwaukee Forestry Services manager, “that I can’t get a single elected official to weigh in on the side of removing healthy trees because we don’t have to, and that is never popular with the public.” Milwaukee could not afford to lose the 28,000 prime ash trees owned by the city all at once, he said. “The injections allow us to decide what happens to those trees, not the beetle.”

Hydraulic guns drive the pesticide into the tree through shallow holes drilled in the bark. Each tree is dosed every two years. Positive results are evident: Private ash trees that were not injected are dead, while treated ash trees on city property stand nearby in good health.

It has not been proven yet, but it may be possible to spread treatments farther apart once the main wave of beetles passes, thereby reducing future costs.

For more information from the state of Maryland,