Homegrown: Ash tree disease
I’m wondering if I should I invest in an ash tree with the ash tree disease I have read about? What can you tell me about them?
— Thank you, Laura
I think maybe what you’ve heard about is actually an insect called an emerald ash borer. This is an exotic beetle that was discovered in southeastern Michigan near Detroit in the summer of 2002. We think emerald ash borer arrived in the United States on solid wood packing material carried in cargo ships or airplanes originating in its native Asia. It has since spread to parts of Michigan, Ohio, Illinois, West Virginia, Pennsylvania, New York, Maryland, Missouri, Wisconsin, Minnesota, Indiana, Kentucky, Tennessee, and Ontario and Quebec, Canada.
The insect attacks only ash trees, with the adult beetles nibbling on the foliage but causing little damage. The larvae feed on the inner bark of ash trees, disrupting the tree’s ability to transport water and nutrients. It has been a big problem in those areas I mentioned, killing millions of ash trees. That sounds like a lot of trees, and it is, but remember that green ash is a native tree in those areas. The borer has been such a problem because it has abundant food sources, and it doesn’t have any natural enemies in its new environment to keep it in check.
There is a concerted effort by state and federal officials to stop its spread. This infestation has caused regulatory agencies to enforce quarantines in these states to prevent potentially infested ash trees, logs or firewood from moving out of areas where it occurs. Research is being conducted at universities as well, to understand the beetle’s life cycle and find ways to detect new infestations, control adults and larvae, and contain the infestation.
In addition to this, eradication efforts by state and federal agencies in Michigan, Ohio, Indiana and Canada are under way to prevent small infestations from growing into larger ones.
Though it’s a source of concern in the nursery industry, and I guess it could go out of control and spread to western Colorado, I don’t think it’s anything for you to worry about at this time. There’s some debate whether the insect will even make it to Colorado. And even if (or when) it does, the consensus is that it won’t be as devastating a problem as it is around the Great Lakes. We don’t have native forests of ash trees here, but only relatively scattered trees in landscaped and irrigated areas, so it shouldn’t spread as quickly and we should be able to utilize control measures more effectively.
Another borer here in the valley, called the lilac-ash borer, can affect ash trees. We’ve had it here forever, and it’s mostly a problem on ash trees that are weak or under stress for one reason or another.
A few years ago, I noticed more frequent problems with this borer. There’s still a relationship between stress and borer infestation, but it’s seeming to take less stress on a tree today to have borer problems.
I think the problem is that we’ve planted a lot of ash trees in the Grand Valley. And why not? They’re moderately fast growing and seedless and strongly branched. They thrive in our climate.
But we may have overdone it a bit. If you provide enough food for a pest like this, they’re bound to increase.
That’s not to say that we shouldn’t plant ash trees anymore. Far from it. I think, however, that we should be looking at more diversity in our tree planting.
If you want to plant two or three trees, don’t plant three ash trees. You may want to plant one ash, but plant a couple of different types of trees in the yard. If we all do this, we’ll have a more interesting urban landscape and hopefully avoid some of these problems.
There are some great alternative trees to consider. Purple leaf catalpa, Kentucky coffeetree, frontier elm, hackberry, linden, oaks, sycamore, to name a few, all are all wonderful, large shade trees.