You have probably heard of or read about a relative newcomer to the local insect population.
The emerald ash borer, or EAB for short, came to the United States from Asia about 15 years ago.
It was first discovered in Michigan and has now spread through most of the eastern part of the country. It has been found in areas all around Danville, and while there have not been any reports I am aware of in the city itself, it is only a matter of time.
Since this insect in only known to attack North American species of ash trees the damage will be somewhat limited. However, for those who have ash trees providing shade in their yards, this will be a serious problem.
The adult EAB is a shiny, metallic looking green color. There is a dark read thorax under the wings that is visible when they fly. They are very small. A fully grown adult can rest on a penny with room to spare. Their bodies are long and narrow and the head is hard to distinguish from the rest of the body.
There is another shiny green insect called the six-spotted tiger beetle that is common in this area that bears a close resemblance, but it has an easily identifiable head and six light-colored spots on the edge of its body toward the rear.
The adult EAB is known to feed by eating out small notches in leaves but that does not really cause much in the way of damage. It is their children who pose the most serious problem.
Over the next four to six weeks, the adults will emerge from where they have been living under the bark of ash trees. When they come out they leave a small hole, about ¼ inch in diameter in the bark. Most borers leave a perfectly round hole, but the EAB hole is always flattened on one side and looks similar to an upper case letter “D.”
They will fly and feed for a while and then, around mid-summer, they will start mating. In September, the females will each lay about 50 eggs. The eggs are laid one-at-a-time in crevices in the bark of ash trees.
About a week after the eggs are laid they will begin to hatch. The larvae, or baby EABs, will bore through the bark and begin feeding on the green, moist layer of tissue just under the bark. This tissue is called the cambium layer and it is where most of the sap flows up and down in the trees. As the larvae feed, the movement of sap between the root and the crown of the tree is reduced and can be stopped completely.
Early symptoms of EAB in ash trees show up as dead branches and limbs in the crown. This is accompanies by a growth of small branches that sprout along the main trunk of the tree as it is fighting for survival.
Eventually the tree will be killed almost to the ground. But there will be numerous sprouts growing from the stump because the roots are still alive.
The larvae will stay under the bark through the winter. In the spring, just about now, they will pupate and turn into the green adults.
Then the process starts all over.
Control if this insect is very difficult. In most cases, when they are discovered it is already too late to save the tree. Infested trees should be removed to prevent the spread of EAB to other trees. Do not haul off the firewood to some other place as that will only help to spread the problem.
Researchers are testing a species of parasitic wasp as a natural predator to control the EAB but that is in the early stages and we need to make sure we are not introducing yet another problem insect.
There are some insecticides that can be used as a preventative measure to protect ash trees when EAB is known to be nearby. A soil drench applied on the ground to be taken up by the roots has shown some success. A systemic formulation of a recommended insecticide must be used in April or early May when the roots first become active. Treatment of the trees with a contact insecticide while the adults are present can also reduce the numbers of this insect if they are used in early May and again in early June.
Fortunately, these insects are only known to attack ash trees at the present time. Therefore we can still use maples and other shade trees in our lawns. We can also use most species of Asian ash trees as they seem to be resistant to the EAB.
Enjoy your garden.