In the Fall, Ash Tree Leaves Take on a Bluish Cast
Nature Notes By

Patricia Martin

It’s fall on Mackinac and many of our trees, shrubs, and vines are going through their annual color change. The vine known as Virginia Creeper is already a brilliant red, the Smooth and Stag Horn Sumac is beginning to show color, and the Sugar Maples are starting to show orange, yellow, and red tinges.

Some of the colors that appear are pigments that have always been there and are now becoming visible because the chlorophyll, which gives plants their green color, is being broken down in the fall and revealing the other colors. Short day length and cool weather cause some plants to start producing a pigment known as anthocyanin. This is the pigment that is responsible for the brilliant reds in much of our fall foliage. It is also responsible for some of the much more subtle color change.

Ash Leaf (above) and Fruit of Green Ash (right).

This pigment in a sap that is acidic (pH less than seven) turns reddish, but in a sap that is more basic (pH greater than seven), it becomes bluish. This is what happens with Ash trees when, in the fall, the leaves take on a bluish cast.

Yes, we have Ashes on Mackinac. I’m not talking about the Mountain Ash, which is in the Rose family, but of the true Ashes, those in the genus Fraxinus , which is part of the Olive family. Lilacs are also in this family.

Ashes are not particularly common on Mackinac. I’ve found perhaps two to three dozen trees on the Island. Most of the larger ones appear to have been planted and generally the ones that I’ve found in the woods are fairly small. Both the Green Ash ( Fraxinus pennsylvanica ) and the White Ash (F. americana) may be found here.

By the way, what we used to call Red Ash is now considered just a variation of the Green Ash.

I have not found Black Ash on the Island.

Ashes are deciduous trees, which have their leaves arranged opposite each other along the branches. They have compound leaves (made up of a number of leaflets) and the leaflets are arranged along a central petiole. On the species of Ash found on the Island, there are usually five to nine leaflets, with the average being seven. The flowers are small, but are somewhat conspicuous as they appear before the leaves. The fruits that are produced are elongated-winged seeds known as sumaras. The wings help in seed distribution, as they do in Maples. The bark on adult Ashes is thick and furrowed. The root system is fibrous and shallow. These trees prefer a rich, moist, loamy soil, but will also grow in well-drained situations and are often common along river banks.

Because they’re easily transplanted, grow rapidly when young, and, traditionally, have been fairly immune from insects and fungi, these trees have been heavily planted in urban areas and for landscaping. This immunity, however, has changed in Michigan and several other states in the Midwest. An insect has come into the state in the last five years that is wiping out the Ash trees and has been making headlines. It is known as the Emerald Ash Borer.

The Emerald Ash Borer (EAB) ( Agrilus planipennis ) comes from eastern Russia, Northern China, Japan, and Korea. Before 2002, it had not been found in North America. It was discovered in southeastern Michigan in the Detroit area. How it arrived is unclear, but most likely it came in ash wood used for stabilizing cargo in ships or for packing or crating heavy consumer products. So far, it has killed at least 15 million Ash trees in Michigan, Ohio, and Indiana, with most of the destruction being in southeastern Michigan.

The Emerald Ash Borer, as an adult, is a dark metallic green beetle about one-half inch long and about 1/16 to 1/8 inch wide, but it’s not the adult beetle that does the damage. The adults may nibble on the leaves of the ash, but it is the larval stage that kills the trees.

The female ash borer lays its eggs in the bark of the ash tree, which hatch in about 10 days. The worm-like larvae emerges, tunnels under the bark to feed and grow and change through the summer and fall. It is this feeding and tunneling that will eventually kill the tree by damaging the conductive tissue that bring water and nutrients to the leaves and branches and returns food (sugars) to the roots, etc. for the following year’s growth. The larvae winter over in the sap wood or the bark and pupate in the late spring to become an adult.

Evidence of EAB in a tree begins with the canopy of the infested tree becoming thin above the infestation owing to lack of nutrients and water. The top 1/3 to one-half of the tree’s branches may die in a year. Most of the canopy will be dead within two years of the first symptoms. The ash tree may send up sprouts from the trunk after the upper portion of the tree has died. The adult borer leaves behind a small D-shaped hole in the bark when it exits the tree.

Our species of Ash have no resistance to this insect and, as of yet, there is no effective control, though woodpeckers do like the larvae. One hundred percent of the infected trees will die.

On their own, these insects do not travel long distances (they fly less than a half mile), so it is people that have been transporting them around the state.

The state has a ban on moving Ash trees and firewood in hopes to contain the spread, though this has not been completely successful. If you’ve crossed the Mackinac Bridge this year, you probably have noted the State firewood collection area. No firewood was to be brought into the Upper Peninsula, but this hasn’t stopped the spread. The Emerald Ash Borer has been found in Cheboygan and Presque Isle counties in the northern Lower Peninsula and recently there has been a report of EAB in Brimley in the U.P.

It only takes one careless individual to spread this insect.

To date, we’ve had no infestation of these insects on the Island, though one tourist thought he had found one. The insect in question was collected and was later identified as a common weevil by Michigan Technological University students studying Norway Maples here.

It will probably not be long before other states are facing infestation of EAB, and research is ongoing.

This infestation will cost municipalities, property owners, nursery operators, and forest products industries tens of millions of dollars. It will also have a cultural impact on traditional arts produced by local tribes. Black Ash is used in making baskets, cradle-board, snowshoes, and bows and arrows. Some people are collecting Ash seeds for the future and are storing wood for future projects.

For more information on the Emerald Ash Borer, you may contact the Emerald Ash Borer Hotline at 866-325-0023 or visit the Web sites at www.michigan.gov/eab or www.emeraldashborer.info.

Trish Martin is a year-around resident of Mackinac Island, has earned a master’s degree in botany from Central Michigan University, and owns Bogan Lane Inn.