Mechanical Barriers:
Is There a Place for them in 21st Pest Control?

By Becke Davis

Gypsy moth. Cankerworm. Across North American, they are the modern day equivalent of a plague of locusts. No one talks about eradicating these pests; the best we can hope for is to control the damage. Pesticides are being used on a large scale because the number of infested trees is so enormous. Municipalities, parks, commercial sites and residential lots face the same problems but, because they are working on a smaller scale, they may have other options.

With the current focus on non-chemical controls, arborists are looking at mechanical barriers - everything from duct tape to burlap barriers to Tanglefoot to BugBarrier Tree Band - as viable options. Even if the population is reduced, will that protect the affected trees from defoliation?

First, let's take a look at the best known branded products. The Tanglefoot Company, based in Grand Rapids, Mich, has been in business for well over 100 years. Back in the 1880s, the company produced a sticky paper to trap flies. Today, Tanglefoot is still all about "sticky." Tree Tanglefoot Pest Barrier, Tangle Guard Tree Banding Material, Tanglefoot Pre-coated Sticky Tree Bands and Tanglefoot Paper Tree Wrap are all used to block crawling insects from the upper branches of trees.

Joe Skendzel, president of Tanglefoot, says, "Everything we do is sticky." Tanglefoot Pest Barrier, which has been in production since about 1900, is made from natural ingredients, primarily castor oil, wax and resins, he explains. "It's gooey and sticky, but it does the trick," says Skendzel. "Our products provide a physical or mechanical barrier, a form of interference to insects who crawl up to deposit their eggs. It remains sticky in all weather, and is not affected by moisture, heat or cold."

Skendzel concedes that sheer numbers of these crawling pests can overwhelm even the stickiest barrier by forming a bridge. "The important thing about Tanglefoot is that it stays sticky. It never comes off. You can apply it directly to the tree - there's nothing toxic in it - but over time it can cause damage. We recommend using waterproof paper to protect young trees."

Another mechanical product on the market today is the BugBarrier Tree Band produced by Envirometrics Systems, Inc. in London, Ontario, Canada. This product has been tested for use with emerald ash borer as well as gypsy moth, spring and fall cankerworm and winter moth. The product is described as "a dense, flexible, fiber barrier" that is wrapped around the trunk of the tree, filling in crevices and blocking the pests from escaping. A film barrier is installed over the fiber, the adhesive side next to the tree.

Brian Pancoast is the sales manager for this product and Duane Pancoast, CEO of The Pancoast Concern, Ltd., in Victor, N.Y., is communications director for the BugBarrier Tree Band. Duane Pancoast notes that the inventor of this product came from Winnipeg, Manitoba, where there was a terrific cankerworm problem.

"The inventor didn't like spraying," says Pancoast, "and he didn't like the messiness of (other available products). Working with an entomologist at the University of Toronto, a team of designers put it together. Denis Crane, president of Envirometrics, was the entrepreneur who made it a viable product and put it all together."

The main focus of the patented BugBarrier is residential and commercial markets, Pancoast explains. "Entomologists don't look at eradicating this pest as much as controlling it. This product helps to manage the problem, but I don't think you'll ever wipe out a population with anything. BugBarrier has a fiber that is put around the tree, acting as a barrier to keep bugs from getting into the crevices. The stickiness is facing the tree but doesn't touch the tree - the pests get stuck on the adhesive. It's easy to apply - one person can do it."

Patrick George is the owner of long-time TCIA member Heartwood Tree Care in Charlotte, N.C., a region that has had severe cankerworm infestations. He has used BugBarrier in the past and found it effective, but says the problem in his area has gone too far for mechanical barriers at this point. "Cankerworms have reached plague proportions; it means the barriers need to be cleared every couple of days during the height of the movement of the females, about a month long period. Since labor is money, that becomes expensive."

In residential situations, George thinks the barriers might provide a benefit simply because the barriers need to be maintained on a regular basis - it makes the homeowners more aware of the problem. "It raises the profile of the tree care industry," he says. "Everyone loves trees but they don't realize it requires some investment to maintain them - kind of like your hair when you're in your 20s!"
Arborist Dave Story is a local manager at the Northbrook, Ill., office of Bartlett Tree Experts. He tries to address the problem earlier through spraying. "We use helicopter spraying for municipalities and ground spraying from a truck."

The problem in Lake Forest is so bad, Story says, that the city forester "literally goes around with a super soaker brigade" to spray the trees. "He's pretty happy with the results," Story adds.
When it comes to pesticides, Story says that choices have greatly improved. "The aerial people tend to use an improved strain of Bt (Bacillus thuringiensis) but it's slower acting and the residual effect is not as long," Story observes. "There are some nice choices for naturally derived materials, such as ConsERV™, which has really low mammalian toxicities. It's a pretty big improvement. Both Bt and ConsERV are pretty good."

Dr. Michael J. Raupp, professor of entomology and extension specialist at the University of Maryland in College Park, says that when it comes to the issue of mechanical barriers in relation to gypsy moths and cankerworms, "We're not really sure. Their impact is questionable, especially with a high density population, but it is a way for homeowners to be actively involved. There is some good data out of the Pacific Northwest and Canada for issues with cankerworm, but that is quite a different organism than gypsy moth. With gypsy moths, we are trying to prevent the larvae from migrating up into the tree.
"In theory, mechanical barriers can reduce the population, but whether that has a measurable impact on defoliation is unclear. Using mechanical barriers falls into the category of things homeowners can do, but while these are not a detriment, their benefits are unclear," he observes.

Raupp has reservations about the use of burlap or hiding bands: "Burlap provides a daytime hiding place," he explains. "You have to go out every day and collect the caterpillars under the band. If you put up burlap bands and don't go out and remove the caterpillars you will be exacerbating the problem. By creating a perfect place to hide them from predators, you've increased their survival. In Bethesda, Md., I saw two magnificent white oak trees with their foliage totally stripped because they didn't go out and regularly kill the immatures."

Daniel A. Herms, associate professor of entomology and associate chair of the Department of Entomology at the Ohio Agricultural Research and Development Center of The Ohio State University at Wooster, Ohio, says mechanical barriers, for gypsy moth anyway, "don't prevent defoliation."
"The primary dispersal is after the first instar," Herms explains. "They blow in the wind and lay in the upper canopy above the barriers. A lot of those caterpillars stay in the upper canopy. If there is an isolated residential tree, the barriers prevent migrating caterpillars, but what's the risk - where are they going to come from? If the neighbors have trees they aren't treating, the barriers become overwhelmed - you see the sides of houses covered with the caterpillars. Tanglefoot becomes saturated very quickly, and there may be more than a thousand a day captured in burlap. The mechanical barriers are recommended as a sampling tool when populations are high enough that trees are going to get defoliated. When the populations are low, you can get away without doing anything.

"People are hungry for alternatives to pesticides, but they get very upset when the mechanical barriers don't work," Dr. Herms observes. "They have the false impression that every caterpillar vacates the tree at night, but in reality tons of them stay up in the tree. Bt is recommended because of its selectivity in its caterpillars and it doesn't harm birds or other insects," he says. "Bt is registered as an organic; it lasts only five to seven days, so there is a narrow window."

Rex Bastian, who has a Ph.D. in entomology and is vice president of Field Education and Development for The Care of Trees, uses mechanical barriers in certain circumstances, noting that "they are not perfect, but they are an option." He explains that if he was to suggest this option to a client, he would be sure to "set out the parameters to avoid setting them up for disappointment." While he is aware that some entomologists have concerns about these products, he observes, "Entomologists don't always have the same concerns as we in the industry do."

Bastian does not advise that Tanglefoot be applied to trees directly: "Sometimes Tanglefoot will leave a mark on the trees," he says. "You can still see the marks on trees from cankerworm infestations 20 years ago. While this doesn't really hurt the tree, you can see the remnants of the applications many, many years later, so there is this visual reminder. Gypsy moth in large numbers are starting to move through the Chicago area, and we used BugBarrier Tree Bands at the home of a client who had a large group of oaks right near their house. The clients were so accepting of it they've asked us to do it again.
"With cankerworms, the female moths are flightless and they get stuck in the BugBarrier band very easily, so the product may be more effect with them than with gypsy moths. Gypsy moths are a little different. The caterpillars are pretty spiny. The fiber of the BugBarrier band holds it away from the trunk a little. When the caterpillars get larger they don't get as good contact as cankerworm, but it can form a physical barrier to them.

"This particular homeowner was interested enough that he would go out and destroy the caterpillars that got stuck underneath the barrier. I certainly wouldn't claim that this is going to stop defoliation on your trees if there are extremely high population levels, but this client didn't want sprays done. We gave the BugBarrier a try and they worked to the client's satisfaction. They don't leave any residue - sometimes a little batting, but no discoloration.

"In a low level infestation, gypsy moths tend to feed at night, and in the day they will crawl down the trunk. That's how the barriers work. When the caterpillars are getting larger and feeding on the foliage, under very high populations they often don't have that migratory behavior. None of the banding type approaches will work then - with Tanglefoot, they get stuck on it and others crawl over them. With burlap, you have to remove the caterpillars or you're really just giving them a place to hide in the folds. You have to go out and pick them off every day or they will climb again, and the spines can cause skin irritations or asthma if you touch them."

The benefit of the mechanical barriers, Bastian says, is that they provide "a way of trying to do something as opposed to doing nothing if spraying is not acceptable." He explains, "These aren't perfect and they may not prevent damage, but they may trap enough caterpillars to be deemed a partial success. We have to respect the opinions of our clients when we determine which option is the best for their peace of mind, as long as we set the proper expectations. We have to look at these as an option that may be worth considering."

While there does not seem to be one definitive answer as to the effectiveness of mechanical barriers, one common thread seems to be that if these products or methods are to be considered as an option, it is important that you don't oversell the likely results. Make sure that the appropriate level of expectation is clear when describing this option.