Protecting Trees from Insect Damage
Be glad you’re not a male emerald ash borer out looking for a mate. If one of them could sit down next to you on a barstool and talk, he might complain about the artificiality of today’s females.“Why, it’s as if some of them were built in a lab,” he might say. The truth is, that’s because some of them were.
But more about that later.... Building fake female emerald ash borers is just one of the technologies currently being employed to help trees fight off some of their biggest little enemies: insects. Whether they’re chewing leaves, sucking sap or boring through trunks, these pests damage and kill ornamental trees by the thousands and cost homeowners, cities and states millions of dollars. They blight landscapes and decimate national forests.
The emerald ash borer isn’t the only pest out there, of course. There are gypsy moths, Asian longhorned beetles, Japanese beetles, rugose spiraling whitefly, pine bark beetles, hemlock wooly adelgids, gum lerp psyllids, erythrina gall wasps, various species of mites and many, many more.
Some, like the Asian longhorned beetle and the emerald ash borer, are illegal aliens, exotic species from foreign lands that were accidentally transported here. Most have been here for centuries.
And for just as long, arborists, landscape professionals and anyone with a tree in his yard have all wondered: How do you fight these tiny, yet highly effective killers and maimers of trees?
Knowing exactly how they hurt trees is a good start. Like so much of life, it’s all about eating. Chewing insects, such as beetles and caterpillars, munch leaves, flowers and twigs. If they eat too many of its leaves, a tree will suffer malnourishment and even death.
Sucking insects, such as aphids and mealybugs, feed on sap, a tree’s lifeblood, causing leaves to wilt and droop. Most destructive of all are the boring beetles—the ash borers, bark beetles and others. Their larvae kill by tunneling through the layers just under the bark to the phloem and the vascular cambium. This is where all the nutrients and moisture are drawn up from the ground into the tree. When they girdle the trunk, the nutrients can no longer get up into the tree and it starts to die from the top down.
You don’t have to become an arborist to learn some basic things about trees and the pests that bug them. It can only make you more valuable to your clients. Also, this could be an additional revenue stream that could be very worthwhile looking into.
Spray, soil drench or organics
There are a number of ways to treat these problems. Some insects can be stopped or controlled without chemicals.
There are barrier methods that gird tree trunks with a non-toxic glue. It simply keeps bugs that migrate up the trunks of trees, especially caterpillars, from crawling into the canopies where they feed.
There are products that use nature against itself, so to speak. Bacillus thuringiensis is a natural fungus found in soil that disrupts an insect’s digestive system when it eats leaves that have been sprayed with it. Other organic pest control methods include traps, insecticidal soaps and natural pyrethrins. You can also release a bug’s natural enemy, another bug, against it, such as using ladybugs to kill aphids.
Then we have chemical treatment. But bugs won’t die until they get poison in them or on them. Spraying has its place; it will kill many bugs (including the good ones) but it won’t touch bugs that have burrowed under bark.
“There were studies done decades ago on the effectiveness of spraying,” said Nate Dodds, president and general manager of Mauget, Inc., in Arcadia, California, a manufacturer of injectible pest and disease control products. “Those studies showed that only .1% of canopy sprays reach target pests. So you have to put a lot more material into the air. Obviously, with wind drift, you have to use a lot more pesticide to effectively cover trees with a canopy spray.” Not to mention the obvious environmental exposure issues.
Another, more direct way to stop tree-killing pests is to use a soil drench. The chemical is poured onto the root area of a tree, and is then taken up into the tree. “It’s kind of the traditional way of treating trees,” said Eric Bristol, marketing manager for Woburn, Massachusetts -based Arborjet, another provider of injectable disease and pest control products.
Soil drenches are less expensive than some of the other methods; however, with a soil drench, “You’ve got to pump a lot more chemical into the soil, because competitive plants and turf will take up some of it,” says Dodds. “You’ll also be putting it in some areas where there’s no root zone.” And the method can be slow.
The “nuclear option”—direct injection
And then there’s injection. This gets the pesticide right into the tree itself. Just as we might go to the doctor and get a shot, in this case, a “house call” is made right to a tree’s trunk. This technology was first patented in 1958 by Mauget.
“The chemicals go directly into a tree’s vascular system,” says Dodds. “You’re getting the insecticide into a living part of a tree, and you’re assured of good distribution and commensurate control. In addition, you’re using a lot less of the chemical. A hundred percent of it goes through the tree, ‘mainlined’ into its sap system.” Injections can be done preventatively, before the fact, or therapeutically, after a tree has been infested.
Charles Boos, a certified arborist and owner of Mystic Natives Consulting Services, LLC, in Mystic, Connecticut, agrees with Dodds, at least on one point. “In my opinion, there are some distinct advantages to injectables,” said Boos. “It’s a very efficient system, because you use much less of the chemical.”
As an arborist and sustainable landscape professional, Boos doesn’t really like to kill insects. “A major portion of my business is habitat restoration and rehabilitation. Ninety-nine percent of insects don’t bother anybody, and they’re a vital component of the food chain—no bugs, no birds.”
In Pleasant Prairie, Wisconsin, Jim Sieger is maintenance account manager for Kenosha Grounds Care, a full-service landscape company. He’d been keeping an eye on the spread of the emerald ash borer until it finally appeared in Kenosha County. Last year, they showed up in a business park that the company maintains.
“We’re not a full-fledged tree service; we don’t own a chipper or a bucket truck, but we do feel a responsibility for our clients and their trees. We wanted to be able to offer our clients something that would help save their trees,” said Sieger.
The company turned to Arborjet.
Kenosha Grounds Care sent two of its licensed pesticide applicators to one of their seminars. In addition, they received onsite hands-on training from representatives of Arborjet and Midwest Arborist Supply in Grand Rapids, Michigan. In the end, they were confident that they knew how to use the product correctly.
“I make two offers to my clients,” says Sieger. “I can do a soil drench. It’s less expensive, but lasts just one year. Or, I can inject. That costs more, but lasts two years.” He gets takers for both approaches.
Once a tree starts exhibiting symptoms, it may have been infested for several years. By that time, it may be too late to save it. So, just as humans get vaccinated during flu season, Dodds suggests inoculating trees before the bugs come. “If you know that there is an impending infestation that occurs every year at a certain time on certain species, you can pre-treat the tree. We go by the old axiom, ‘An ounce of prevention is worth a pound of cure.’ In major infestations, the best performance we get or anybody gets in protecting trees is before the pests arrive.”
It’s possible that some of the things we’re doing as landscape professionals are inadvertently stressing out the trees. Try to be aware of the status of the trees while you’re working on other parts of the landscape.
“If you’re doing excavation (installing hardscape or irrigation pipes, for instance), ripping up roots under a tree, you could stress that tree and invite insects in,” said Bristol.
“Trimming too much off of a tree so that it can’t produce much carbohydrate, that’s a stressor,” said Boos. “So is someone driving over its roots—that is going to stress the hell out of a tree.”
He has some other advice for those taking care of landscapes. “Make sure the trees have enough water,” said Boos. “Fertilize them, but don’t give them too much. If you over-fertilize trees, they grow too fast and get soft and tender. They have natural defenses, but if they’re growing too quickly, they can’t develop them. They grow long, gangly shoots and may look lush, but in reality, they can’t stop themselves from growing.” Soft, tender trees…hmmm, if you were an insect, isn’t that where you’d want to dine?
If a tree has a dual diagnosis, both infested and infected, you can’t just focus on getting rid of the pest. “Diseases and insects don’t necessarily go together, but in some cases they can,” said Dodds.“If that’s the case, you may want to use two products, an insecticide along with a fungicide.” Arborjet, Mauget and other companies sell combo products that treat diseases and insect infestations at the same time.
There are many things that can stress trees, but drilling into their trunks to inject pesticide isn’t one of them. “Some people worry about drilling holes in trees,” said Bristol. “They think it hurts them, but our company has been doing this for more than ten years, and Mauget for more than 50 years. If drilling killed trees, we wouldn’t be in business.” He cites the example of the maple syrup industry. They’ve been drilling holes in maple trees—the same ones—over and over, for years. Trees do a good job of callousing over drill holes.
Look for the signs
“The biggest mistake landscape contractors make is that they typically look at the ground,” says Dodds. “They don’t look up.” Remember that old song, I Talk To The Trees? The next line is, “But they don’t listen to me.” Well, the trees are talking, and if you’re not looking up, you’re not listening to them.
As a full-service landscape contractor, you’re already familiar with plant diseases and insect infestations. In any given region, there are a limited number of trees that people normally have in their landscapes, depending upon what growing zone you’re in, according to Dodds. “Let’s say there are about ten common species found in your area. In some places, you get a lot of conifers, in others, hardwood trees of various types. Get comfortable with those species.” Find out which insects plague them.
There are signs we can look for to see if we’ve got suckers, borers or hungry caterpillars at work. “Insect damage is generally the easiest to identify,” said Dodds. “Sooty mold or unusual or severe defoliation starts to appear. Look at the leaves and the debris on the ground.” Scalloping on leaves is a sign of caterpillars. When there are scale bugs or aphids at work on leaves, the insects excrete the sap and deposit the sticky gunk on the ground, on cars, on pool decks. That tells you you’ve got a sucking insect problem without necessarily seeing any change in the quality of foliage.
Fake females and paratroopers
The case of the emerald ash borer is a good example of just how devastating an invasive species can be. First detected in July, 2002, in southeast Michigan and neighboring parts of Ontario, Canada, this hitchhiking beetle from Asia has spread to 14 states, mostly in the Midwest. It’s killed 50 to 100 million ash trees so far, and threatens all 7.5 billion throughout North America. This bug is considered one of the most destructive nonnative insects in the United States.
It and its other wood-boring brethren cause an estimated $3.5 billion in annual damages in the U.S. alone.
Researchers are working on how to save our ash trees. One of them is Dr. Thomas C. Baker, distinguished professor of entomology at Pennsylvania State University. He says, “Back in 2006, with some funding from the Animal Plant Health Inspection Service (APHIS, part of the U.S. Department of Agriculture), I sent my graduate student Jon Lelito to Brighton, Michigan, to observe the beetles 24/7.”
Equipped with night vision goggles and ultrasonic detectors to pick up any chirping, Lelito observed that as the females sat on ash leaflets, males flying around would spot them, then drop down on them from about a meter above. He called it ‘paratrooper copulation.’ “We actually got that into the title of our first manuscript,” Baker noted with amusement.
Once they ruled out ultrasonic chirps or pheromone releases, they tested their ‘paratrooper’ theory by affixing dead male and female emerald ash borers to leaves.
They found the same phenomenon. The males dropped down and attempted to mate with the dead beetles of both sexes. Now they knew for sure that it was a visual cue the male beetles were following.
Baker then learned that another Penn State faculty member, Dr. Akhlesh Lakhtakia, professor of engineering science and mechanics, had been able to artificially replicate certain biological materials, such as fly eyes and butterfly wings. Lakhtakia and other researchers were eventually able to find the right combination of polymers and numbers of layers in order to refract light and create a color similar to the beetle’s iridescent green wings.
The decoys are easy to mass produce and less fragile than dead beetles. With stickum applied to them, the decoys can be used to trap males. “It’s an early warning system that lets you know the pests have arrived in the area,” said Baker. “That way, you can take proper measures at an early stage.”
In its native Asia, the emerald ash borer is hard to find, kept in check by several natural predators such as parasitic wasps that feed on their larvae. Researchers, of which Lelito (now a Ph.D) is one, are breeding some of these natural enemies now. They’ve already been released into areas where the beetle’s been found. It’s hoped that these biological deterrents will multiply and eventually reduce or eradicate this destructive pest.
Scientists like Dr. Baker will continue to work on the problem of pest control. And we in the green industry will keep working on maintaining landscapes, and the trees that are a part of them, healthy. Keeping trees healthy using our best practices is the best way to ensure that nasty bugs stay away. That’s good for the trees, and good for business, too.