What is it? How bad is it? What do we do about it?
Emerald Ash Borer is an invasive beetle that found its way from China or eastern Asia to the US, stowing away in shipping crates. It was first identified in 2002 and has since spread to 22 states. In September 2013, Emerald Ash Borer (EAB) was discovered in the city of Boulder, which is the first known presence in Colorado. Since then a team has been stripping the bark from samplings of ash trees in Boulder to determine the extent of its spread. It is suspected that EAB has been in Boulder for three to four years.
The beautiful, emerald green beetle is only a half inch long and an eighth inch wide. The adult causes little damage feeding on leaves. It lays eggs in bark crevices starting in the upper branches of ash trees which then hatch mid-May to mid-June. The tiny larvae then bore into the tree and feed on the inner bark. This damages a tree’s capacity to transport water and nutrients and within 2-4 years, the tree will die. Spread of the infestation is at first very slow, but as more and more trees are affected, the spread becomes very rapid. It only harms ash (Fraxinus) trees.
This beetle is responsible for the deaths of tens of millions of ash trees around the US. It is considered by some to be one of the most destructive tree pests ever seen in North America, worse than Dutch Elm Disease. As an exotic invader, the only natural enemies are woodpeckers and certain parasitic insects, but these cannot slow the spread of EAB.
Ash trees have been planted in great numbers in Colorado, because they are tough and tolerant of our difficult conditions. Green Ash, Fraxinus pennsylvanica, is by far the most common ash here. It makes a strong, fairly fast-growing shade tree that tolerates poor soil, some drought, wind and cold. The second most popular is the Autumn Purple Ash, Fraxinus americana, with gorgeous reddish purple fall color. This species is not as tough or well-adapted to Colorado, but has been doing well under cultivation. Right now around 12% of the city trees in Boulder and 14% in Longmont are ash trees, which amounts to about 7,800 trees. In the Denver Metro area there are about a million and a half ash trees. This does not include the trees growing on private property. If even half of these trees die, it will have a profound impact on our shade, temperature (inside buildings at least) and quality of life.
At present there is a quarantine in effect for Boulder County and the city of Erie. Nurseries within these areas are not allowed to sell or move ash trees out of the quarantine area, and are required to keep records of names and addresses of the buyers. Also, all hardwood firewood (regardless of species) cannot be moved outside the quarantine area. Firewood is probably responsible for EAB entry into Colorado, so it is best not to move it very far and to burn or debark it before spring hatching. Ash makes a high quality firewood.
What can be done about this destructive pest? I interviewed two city foresters, three arborists, an Extension entomologist and a director from the CO. Dept of Ag. All of them are waiting for the final word from State Entomologist Whitney Cranshaw who is dancing as fast as he can to learn from the experiences and studies done in the Midwest, and to prepare his report which is expected to be published about the same time as this magazine issue.
In the meantime, here is what I have learned and heard: Everybody agrees that prevention is the best strategy. Once 40% (some say 30%) of a tree is dead from Emerald Ash Borer, it is not wise to invest in treatment. Mitch Yurgert, director of the CO. Dept. of Agriculture Division of Plant Industry, recommended that people begin by determining the value of the ash trees on their property. Ash trees that are unhealthy, broken, growing under wires or not valuable for shade, may not be worth the expense of treating them.
Ken Wicklund, city forester of Longmont said there are some beautiful ash trees in parks and along streets that he will try to save. He said our trees are stressed and may be very vulnerable to EAB. Since Longmont is 12 miles from Boulder, and since the beetle rarely travels more than a half mile to a mile a year, he is not going to start treatments yet. One of the chemical treatments he is looking at is Tree-age because one injection can last 2 or 3 years, which would be more economical.
Steve Pfeiffer, a Boulder arborist who has been doing tree injections for many years, indicated that most of the EAB treatments were injections into the base of the tree, and in his experience, ash trees are especially difficult to treat, because they do not take up the chemicals very rapidly. Our dry soils add to the problem, so watering a tree prior to treatment might be helpful. Pfeiffer likes to use soil injections of nutritional materials and beneficial mycorrhizae and bacteria to help support tree health.
Robert Brudenell, certified arborist, with The Natural Way believes that watering the trees will not only help with injections, but will help keep the trees healthy which will improve the trees’ ability to survive the damage done by the beetle even with treatment. He says EAB will attack even healthy trees and believes that without treatment, ash trees will die. He will be using TreeAzin, a neem derivative, but believes Tree-age is more effective and will be using this too.
Fred Berkelhammer, President of Berkelhammer Tree Experts, is wary of a pesticide over-reaction to the Emerald Ash Borer. He says that as valuable as our trees are, it is the overall health of the earth that we must keep in mind. He is concerned that Merit and other neonicotinoid pesticides that are recommended for EAB are very toxic to bees. He is planning to use TreeAzin (after flowering) because it will not harm bees and because it biodegrades quickly.
Kathleen Alexander, city forester for the city of Boulder, says that the effect of Emerald Ash Borer could be very bad, but that it is good that it was discovered before it had spread very far. Now she and the whole state of Colorado are starting to prepare. Once the state entomologist’s report is completed, she will have a clearer direction for what to do. She said that since this is an invasive species, there are no natural predators and if an ash tree is not treated, it will die. It is best for home-owners to evaluate the worth of their ash trees, and start planting replacement trees for those that will not be treated.
Carol O’Meara, horticultural entomologist with CSU Extension in Boulder County, told me “I’ve gotten to be a pretty good stripper.” She and a group of professionals have been stripping the bark from 766 samples of ash trees to determine how far EAB has spread. They have determined so far that the beetle is within a four mile area. She said that the Emerald Ash Borer is far worse than the Lilac-Ash Borer a pest that has bothered our ash trees for decades. It multiplies very rapidly and the sheer numbers of beetles will girdle and kill a tree within 3 or 4 years. Unfortunately the only way to save a tree is with pesticides. She is unclear whether bees visit ash flowers and might be harmed by the pesticides. She is very impressed by the level of support to Colorado from other states that have experience dealing with this pest.
A USDA report stated that insecticides “…will need to be applied on a regular basis, possibly several times within one growing season, and even then might not completely prevent the EAB from attacking an ash tree.” The most effective insecticides for EAB seem to be tree trunk injections. The reports I read said that one injection of Imidacloprid per year or one injection of Tree-age every two years were recommended. TreeAzin, a bio-pesticide made from Neem, is also injected into the trunk. All give “varying degrees of EAB control”. Soil drenches and soil injections are believed to have “too many unintended consequences.” If treatments are applied as a soil drench under an ash tree, any flowering plants under that tree could carry the poison and harm honey bees and other pollinators. Other pesticides are used as trunk sprays and leaf sprays.
Most of the pesticides registered for EAB are systemic, which means the poison travels through all parts of the tree so it kills the beetle (and anything else) wherever it may be feeding. If the object is to kill, this sounds good, but what about the collateral damage to bees, ladybugs and woodpeckers? And what happens to the poison that falls from the ash trees as pollen, seeds and leaves?
Imidacloprid (in products like Merit, Adonis, CoreTect and Bayer Advanced Shrub and Tree Control) is a neonicotinoid pesticide which acts on the central nervous system of insects “with much lower toxicity to mammals.” Currently it is the most widely used insecticide in the world. The European Food Safety Authority has stated that “neonicotinoids pose an unacceptably high risk to bees.” And their use has been somewhat restricted in Europe. Ladybugs that eat aphids from plants treated with imidacloprid “showed reduced survival and reproduction.” The chemical can last for months or years in the soil where it is “acutely toxic to earthworms” and very toxic to beneficial insects. (from the National Pesticide Information Center). Even if ash flowers are not very attractive to bees, the copious pollen will blow all over and as pollen is nutritious could be eaten by many beings.
One of the most effective and long lasting treatments for EAB is Tree-age. This is the insecticide Emamectin benzoate. “While emamectin benzoate is more toxic to invertebrates (like insects) than to mammals, the underlying mechanism of action…is common to both groups of organisms. Neurotoxicity is clearly the primary and critical effect…including neurodegenerative changes in the brain, spinal cord, peripheral nerves and sensory nerves…changes in body weight…reproductive effects…” It is “…over 600 times more toxic to bees than to the most sensitive mammalian species…” (USDA Forest Service Report).
These are just two of chemical treatments for EAB. Space does not permit further discussion about these chemicals, but it seems there are ample reasons for us to question their use. I was an arborist for 30 years and spent much of my life in trees and caring for trees, but I have to ask: Are our ash trees worth poisoning our environment by treating thousands of trees in our communities? Are these poisons going to get into our water supply? Will they kill our soil life? Will they reduce our beneficial insects causing more pest problems? Will we have to keep ash leaves out of our composts and veggie gardens? Perhaps the bio-pesticide TreeAzin will give adequate control if begun before the beetle damage has gone very far. We need to learn more and really think this through.
In the meantime, as many of those I interviewed suggested, we can start to plant replacement trees. I am including a list of shade trees in a publication done by the Colorado Nursery and Greenhouse Association. Hundreds of trees were rated “A through F”. Here is the list of trees over 30’ that were rated “A”:
Big Tooth Maple; Common Horsechestnut (Buckeye); Western Catalpa; Honeylocusts-Imperial, Shademaster and Skyline; Kentucky Coffeetree; Western Hackberry; Callery Pears: Aristocrat, Cleveland Select, Redspire; Bur Oak; English Oak; Chinkapin Oak; Lindens: Legend, American Sentry, Redmond, Greenspire; Colorado Blue Spruce; Austrian Pine; Southwestern White Pine.
It is also useful to consider whether you actually need a shade tree to replace an ash. Trees on the north and east sides of a building are usually not that necessary for shade. Big trees are more expensive to maintain and take the sun from flowering plants and many grasses. Greater value may be gained by planting smaller ornamental or fruit trees.
Losing thousands of ash trees will have a big impact on our community and will be very painful, but treating thousands of ash trees with nerve toxins could also have a big impact on our community of humans and other beings. Please consider the big picture in your responses to this crisis.
If you suspect Emerald Ash Borer contact 1-866-322-4512