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Whats Eating Your Trees?

RICHARD LENTI | Tree Care

They’re a source of inspiration for all who gaze at their majesty. Poets have waxed philosophically, writers have pondered metaphorically -- artists study every bough, leaf and limb. Other than water, there is no other substance that covers the earth’s surface in as great abundance.

Yet trees are under attack. The rainforest is continually devastated by man’s greed and insatiable appetite for cheap wood. Ancient groves of redwoods fall prey to short-sighted clear-cutting practices that guarantee quick profits at the expense of long-term conservation. So the last thing we need is help from Mother Nature at destroying a resource essential to our very survival. But that’s exactly what’s happening

Insects with voracious appetites are destroying millions of trees throughout the country. A few of the pests are native to North America; many are not. Regardless of their origin, these insects can cause irreversible damage to the trees in your charge, leaving the landscape contractor with no option but to remove the infected tree. Knowing what to look for and how to effectively treat the problem before it takes hold is literally a matter of life and death for the tree.

The newest challenge
By far, the largest government quarantine of trees currently underway is of maple trees infested by the Asian longhorn beetle. According to the U.S. Department of Agriculture (USDA), if the insect becomes established in the United States, it has the potential to cause more damage than Dutch elm disease, chestnut blight and gypsy moths combined. Millions of acres of hardwood trees will be lost, including national forests and backyard trees. The potential loss to the lumber, maple syrup, nursery and tourism industries could top $41 billion.

This is such a potentially serious problem that the government is taking no chances. “What the government does with quarantines is put themselves in charge of treating the insect,” says Arnold Farran, research director of J.J. Mauget Company, in Arcadia, California. “Nobody is allowed to do any treatments other than companies under contract with the USDA, and only under their supervision.” Only two pesticides have been approved for use by the UDSA in their operational program: J.J Mauget’s Imicide and Bayer Environmental Science’s Merit.

The stakes are huge. If the Asian longhorn beetle gets out of the quarantined areas, it has a voracious appetite, feasting on all sorts of hardwood trees, including all species of maple, birch, horse chestnut, poplar, willow, elm, ash, mimosa, hackberry, sycamore, mountain ash and London plane. And since the insect has no known natural predator in the United States, the only species in its way are Homo sapiens.

The Asian longhorn beetle is believed to have hitch-hiked a ride into the U.S. inside solid wood packing material from China. It was first discovered in 1996 in the Greenpoint neighborhood of Brooklyn, New York. Within weeks, an infestation was found on Long Island, after an infested piece of wood had been moved to the area. While authorities, for the most part, have managed to contain the pest to the quarantined regions of Chicago, New York and Jersey City, New Jersey, recent discoveries have been made in a two-square-mile area near Rahway, New Jersey.

Early recognition of any pest infestation is essential to defeating the destructive little critters. In the case of the Asian longhorn beetle, after maturing, they leave behind deep, perfectly round exit holes slightly larger than the diameter of a pencil. These holes may ooze saps and deposits of frass (insect waste and sawdust). Another tell-tale sign is the unseasonable yellowing or drooping of trees.



Treatment focus
Currently, the government’s eradication plan is focusing on cutting down, then chipping or burning infested trees and replacing them with non-host species. “There is absolutely no therapy in place to save the tree. If a tree is infested, their first reaction is to get out a chain saw and cut it down,” says Dr. Terry Tatter, professor emeritus, University of Massachusetts. “They’re basically trying to kill the insect.”

Trees in the immediate area of the infested trees are then treated with the insecticide imidacloprid, which has proven to decrease beetle populations and help prevent its spread. The insecticide can be delivered through either soil or trunk injection, although in Long Island, soil injection is prohibited because of concern over groundwater contamination.

Another insect with the potential for mass devastation is the emerald ash borer. It’s mainly found in the Midwest, but is spreading to the East Coast and could possibly get loose all over the country. While federal guidelines regulating treatment are not in place, moving ash trees from infected areas is prohibited.

“As far as we know, in the U.S., the only trees that are attacked by the emerald ash borer are members of the ash group,” says Tatter. “The quarantine is to prevent movement of nursery stock ash trees or ash firewood out of the infested areas. The biggest problem is people taking firewood from one part of the state to another.”

“Because of the widespread nature of this devastation,” says Farran, “it would be difficult to contain it with government-regulated quarantines. Unlike the Asian longhorn beetle, which was detected pretty quickly, the emerald ash borer went undetected for years.” It is now firmly established in North America, putting all ash trees at risk in an area where the beetle is found.

What sets the emerald ash borer apart from other beetles is its appetite for healthy trees. While native beetles tend to attack stressed or dying trees, the emerald ash borer feasts on healthy trees, usually killing them in one to four years.

Inserting the pesticide capsule into the tree. Photo courtesy: Mauget

Trees that are heavily infested probably won’t survive even the best efforts to save them. That’s because larval feeding galleries not only prevent water and nutrients from getting to the tree, they also prevent insecticides that could save the tree from getting where they’re needed.

Efforts at stopping the spread of the emerald ash borer are being fought on three fronts: dealing with trees that can’t be saved; killing the infestation in trees that can be saved; and taking preventive measures to stop the insect from infesting healthy ash trees.

Using the same strategy
Employing a strategy similar to the battle against the Asian longhorn, removing and chipping infested trees is an important step in reducing the spread of the emerald ash borer. Experts recommend also killing the stump of a tree immediately after it’s been cut down. Products containing triclopyr, picloram, 2,4-D and glyphosate have proven effective in killing the stumps.

Spraying the trunk and foliage of an elm with insecticides like cyfluthrin and bifenthrin are an effective preventive measure, but timing is crucial. The goal is twofold: to kill female beetles before they lay eggs; and to kill larvae before they bore their way back into the tree. Since adult beetles can lay eggs from mid-May through mid-August, at least two applications of spray insecticide will be needed to protect the tree throughout the summer.

Once the tree is infested, a systemic insecticide like imidacloprid is needed. Because it is either absorbed through the tree roots or injected into its trunk, the insecticide is translocated throughout the tree, attacking the larvae as they feed under the bark. Imidacloprid takes at least four weeks to move through a large tree and should be injected into the soil by mid-April, or injected into the trunk by early May.

Western threat
Out west, the lerp psyllid has been wrecking havoc on eucalyptus trees. “It started in 1998,” says Farran. “There’s no federal quarantine on this, but it’s been a huge pest. The lerp psyllid came from Australia; it hitch-hiked a ride to this country and occurs anywhere there’s eucalyptus. California was significantly affected, but it has spread to Arizona, Nevada, Utah and Texas. We’ve even gotten reports as far as Mexico.”

Unlike the insects we’ve mentioned, the lerp psyllid is not a boring insect. It kills the tree from the outside attacking its leaves. By gorging on plant phloem sap and sucking the very life out of the host tree, it is unable to photosynthesize, getting weaker and weaker until the tree finally dies.

“When the insect reaches a high level of infestation, a tree becomes defoliated,” says Tatter. “The tree will recover and grow new leaves, but it needs to be treated before the next infestation. If it gets infested and defoliated again, it will start to weaken and run out of energy. If that happens several times, the tree will die.”

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Asian beetle larva. Photo courtesy: USDA, Peggy Greb

Because of the protective covering the lerp (a solidified honeydew shelter) provides for the insect, spray application of pesticides has not proven effective. Plus, there are no selective insecticides that specifically target the psyllid. Biological controls involving predatory insects like wasps have met with limited success.

Cal Poly Pomona entomologist Dr. Lester Young achieved the greatest success by attacking the problem with a systemic insecticide. Psyllid populations were monitored for 15 months. The first week following the initial treatment significantly reduced their numbers. Imicide-treated trees sustained up to eight months of protection, while trees injected with Inject-A-Cide MSR showed results for up to two months. The combination of both products also proved effective.

“The Imicide has an advantage,” says Tatter, “because it’s more stable over a long period of time. The lerp psyllids reproduce over several generations. If you use an insecticide that only has to treat one generation, then some of the short-lived materials will be effective. But when you’re combating insects that are multi-generational, you want to have materials that are stable and will last in the tree for a long period of time.”

A native threat
Another tree under constant attack is the pine. There are several species of bark beetles and they are specific to pine trees. Unlike the other pests we’ve discussed, bark beetles are native to this country. They attack weakened trees that are under stress for various reasons, the most common being drought.


Top: Emerald ash borer. Bottom: Ash tree with 60% die back.
Photo courtesy: David Cappaert

“There’s no one effective control for pine bark beetles,” says Farran. “They have to be put into a management program to have any degree of success. You have to deal with what’s causing the underlying stress. You’ve got to protect the tree from invasion, and then you’ve got to clean the trees from the inside where the larva are feeding.”

The pine bark beetle is found wherever pines exist. Whether it’s called the southern, western, black turpentine or ips engraver, they’re all pine bark beetles and they function in a similar manner. Although they may feast on different parts of the tree, their method of attack is the same: they tunnel and feed within the soft inner bark of pine trees

Once pine beetles begin to attack, they are difficult to control. Identifying the infestation early involves recognizing what are called pitch tubes on the lower trunk of the tree. When the beetle begins burrowing into the tree, a reddish colored pitch (resin) will ooze from the hole. A healthy tree will use the pitch to protect itself and expel the invader. A tree with a few pitch tubes can possibly be saved. But once the tree is weakened or attacked repeatedly, it becomes overwhelmed.

Because pines hold on to their needles longer than hardwoods or broadleaf non- coniferous trees, by the time a pine tree starts changing colors to a brown and straw yellow, it’s too late. The insects have already done their damage; the sap flow has been cut off by the beetle and the tree is drying out.

The way to begin breaking that cycle is by preventing any healthy trees from becoming infected. That’s achieved by spraying the bark of the pine tree with an insecticide that establishes a protective barrier. Cypermethrin is among those used for that purpose. It not only creates a barrier, but also repels bark beetles. One application can last a month or more.

But spraying trees is only part of the program. You can’t ignore the stress-related issues that are attracting the pine bark beetles in the first place. And once a tree is infested there’s the issue of how to deal with treating what’s going on inside that tree. If a tree can’t be saved, it’s advisable to remove it as quickly as possible to avoid letting the beetles infect nearby trees.

In an effort to save trees that aren’t beyond redemption, soil and tree injections of insecticides formulated with imidacloprid have proven successful. When injecting a tree, either high-pressure or micro-injection methods can be used. High pressure injections immediately deliver the insecticide into the tree; micro-injections use the tree’s vascular system to deliver the product. Soil injection involves delivering the insecticide to the tree through its roots.

An ounce of prevention
In the long run, protecting the trees in your care begins with keeping a watchful eye on them, and noting any unusual changes in appearance. If you’re not sure of how to deal with a problem, consult an expert. Knowing what to look for and how to deal with it is half the battle.

“If you don’t get enough insecticide into the root zone, then soil injection is not going to be effective,” says Farran. “And if you don’t know how to properly micro-inject a tree and get it into the wrong area, it’s not going to be effective. You really have to know what you’re doing.”

 
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