The emerald ash borer, a shiny green beetle, is emerging from ash trees all over the eastern US and Canada. The beautiful little beetle, part of a group called “metallic wood boring beetle” was introduced in packing material from China around 1990. Carried throughout the region by people moving firewood, the beetle threatens to eliminate white, green and black ash. There is some hope that parasitic wasps introduced from China by the USDA may spread quickly enough to slow the beetle, but this is far from certain. Below you will find a slide show of the beetle and the damage done.
This is the year of death in central Kentucky. The emerald ash borer has been slowly expanding its population, and has now reached the point of mass destruction. You can see dead and dying trees all over town, most of which have died this spring. From here on, barring some miraculous change in ash borer populations, the fate of the remaining ash trees is sealed.
This is a predictable outcome of a biological phenomenon called the Great Curve of Growth. Mathematically, the Great Curve follows a logistic equation. It works like this:
- At first, ash borer numbers are very small and few trees die even as the borer population increases. This is called the lag period. Typically, the presence of the beetle is not observed for about 10 years after they arrive in an area.
- As beetle numbers increase, an explosion of death takes place, increasing steeply. This is the logarithmic phase. We are early in the logarithmic phase, and each subsequent year will bring approximately a doubling of the number of dead trees.
- Eventually, the beetles have killed most of the trees, and only a few live trees remain to be attacked. This is the stationary phase and ends with the elimination of white and green ash.
We can conclude from this analysis that the next few years will see an explosion of dead trees. Is there anything that can stop this explosion of tree death. Yes.
- Weather changes, especially extremely cold winters, could slow the beetle. However this beetle has thrived in the cold of Michigan, so this is unlikely to happen;
- Predators and pests of emerald ash borer could increase in populations and lower the population of beetles. This would slow the rate of death of trees. There are programs to releasepredatory wasps, but they are probably too little, too late.
- Treatment of trees is a known method to preserve important trees. The cost of treatment has gone down and treatment is affordable for more landowners. Contact a certified arborist for more information. In spite of the success of treatment, it is not possible to treat the majority of trees even in urban areas. Treatment should be focused on large or important trees.
- Blue ash trees appear to be resistant. Our large population of blue ash trees are probably, but not certainly, safe.
Trees with limited root systems often fair poorly, unless they are very deeply rooted. Here is a slide show of a white ash with a very limited root system that is doing well because it is deeply rooted in the limestone rock.
Have you noticed any ash trees in your neighborhood dropping green leaves? Several days of heavy rain over the last few weeks have allowed the development of a common ash disease called ash anthracnose. The disease is caused by a fungus, Gnomoniella fraxini. The fungus spends the winter on old petioles (leaf stalks) and branches. Spring rain splashes spores onto new leaves and the fungus quickly causes brown dead splotches, or lesions, on the leaves. In reaction, the tree casts off the infected leaves. Although emerald ash borer is spreading rapidly throughout eastern North America, early leaf loss is not a symptom of that insect.
Anthracnose makes some trees unsightly, but this is not usually a serious disease. New leaves will start popping out quickly to replace the lost ones. As long as we get a reasonably dry spell over the next few weeks, the disease is likely to disappear. In really wet years, some branches may be killed.
The slide show below shows the disease in a single ash tree. It is interesting that the ash trees in the background of the first slide do not have the disease. There is a lot of genetic variation in resistance of trees to anthracnose.
Thanks to Kimber Sternberg for bringing this to my attention.
In 1989, Bob Ramsey opened a little restaurant on the corner of E. High Street and Woodland Avenue in Lexington, Kentucky. The restaurant, with its excellent comfort food, soon became a landmark in Lexington. A patio behind the restaurant provided outdoor dining shaded by a large white ash tree that is as much a landmark as the restaurant. It is not as old as many of our Bluegrass venerable trees, but that does not diminish its significance.
Ramsey’s restaurant has moved to a new location after 25 years. The building had hardly been vacant for a month when a new restaurant, Chatham’s, began construction. Its owner, Charles Patterson, told me that he regards the old ash tree as critical to his business, marking the center of a renovated patio.
The tree is fascinating. As these pictures show, removal of the old patio shows that the tree had no fine roots in the little bit of soil – the small roots you can see in the pictures are from the English ivy that surrounded the tree. The roots of this ash tree must be deep below the ground, into the cracks in the Lexington Limestone, the layer of highly fractured rock that underlies the Inner Bluegrass.
We always preach that trees need the most space they can get to thrive, and that is generally true. However, some trees are deeply rooted and have relatively little contact with the surface of the ground in which they grow. While not unique to limestone, it is very common here to find deep-rooted trees with few surface roots.
This tree has lived a long time in the constraints of the tiny space in which it grows. Today, it needs some pruning and treatment to ward off the emerald ash borer. There is not reason to think that this tree will shade Chatham’s patio long into the future, just as it did for Ramsey’s restaurant. I certainly look forward to afternoons sipping iced tea in the shade of this fine old tree. When you go to Chatham’s for a nice dinner and sit on that patio, raise a toast to this fine tree.