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Published: March 21, 2013
Sooner better than later – that’s the message experts are sticking too when it comes to prevention and treatment of Emerald ash borer infestation. With the disease being found at a more rapid rate in more states, arborists across the country should become familiar with the signs of infestation. “Lawn and landscape professionals should familiarize themselves with the early signs and symptoms of EAB,” says James Zwack, director of technical services with the Davey Tree Expert Co. “The earlier an infestation is discovered, the more time for local management plans to be implemented.”
As of December 2012, EAB has been found in 18 states and two provinces in Canada, Zwack says. “The most recent state where the emerald ash borer has been found is Kansas, and this discovery is over 200 miles from the closest known infestation center,” he says.
Prevention. Just like a good diet for humans will help keep you healthy, the same can be said for ash trees staving off EAB infestation. “Any cultural practices that are advantageous to tree health will result in a tree better able to fight off attack,” says Rob Gorden, director of Urban Forestry & Business Development, with Arborjet. He adds that these practices will only help keep the tree healthy and are not guaranteed to stop EAB.
“These include adequate moisture in the soil when drought occurs, mulch to protect the roots from competition with the turf, proper pruning as needed and adequate spacing from other trees in the proximity.” Zwack says there’s a chance that a tree that appears to be healthy but is located 10 miles from a known EAB infestation may actually be infested already.
“When your goal is to save a tree, risk factors for treatment failure go up the longer you wait and the closer EAB gets to you before treatments begin,” he says.
“It’s much easier to keep a healthy tree healthy than to rescue a tree already showing symptoms of EAB. I say it this way because EAB can be challenging to identify in a tree in its early stages of infestation.”
Diagnosis. Gorden, says one symptom to look for is a wood pecker high up in a tree feeding, which is a good sign the wood pecker is trying to feed off the insect.
“You should actually look for bark flaking off high up in the tree,” Gorden says. “Look at the trees in the winter because that’s when you can easily see this white flaking appearance to the tops of the trees.”
Gorden says to also look for a thinning canopy after a year or two, and new sprouts that look like a big, green ball, in the center of the tree. That’s a sign the tree is trying to save itself. Other signs of infestation, according to the Morton Arboretum website, include D-shaped exit holes (approximately 1/8 inch in diameter) on the branches and trunk, vertically split or cracked bark above the larval feeding galleries and wilting and yellowing foliage throughout the tree or limited to certain branches.
Treatment. Just because a tree is infested, doesn’t mean it’s a death sentence. But it will be if you don’t act.
“This is critically important because the perception that once it’s in the tree it’s over,” Gorden says. “The truth is this insect lives a one-year life cycle and part of that year is inside the tree. Then it flies out, lays eggs and the process starts over. So as long as a tree does not have too much decline, that tree can actually be treated, protected and saved and will be recovering. Within two years it will start to look really healthy again.”
What’s considered “too much decline” can be defined differently. Research scientists are saying that you can have as much as 40-50 percent canopy thinning and still save the tree, Gorden says. When a case has been found within 15 miles of your area, you should start treating ash trees in your area, Zwack says.
“That said, the risk tolerance of the client may influence this so that treatments begin when EAB is closer or farther away,” Zwack says. “At the present time, in the U.S., there are three active ingredients that have been proven successful in EAB management. These are imidacloprid, dinotefuran, and emamectin benzoate. Each has its advantages and limitations.”
As far a customers, Gorden says you have to get in front of them and explain the the crisis that comes with delayed treatment. “The removal and replacement even for a homeowner, is going to be north of $1,000 in any property for any size tree, where as treatment is significantly more reasonable,” he says.
Gorden says treatment normally costs about $8-$15 per inch of tree diameter, so for a 10-inch tree for two years of protection its $80-$150.
“This price reflects what a homeowner could expect to spend,” he says. “For municipalities the expenditure could be considerably less, dependent upon whether the treatment is contracted out or performed by city personnel”.
Zwack says owners also have to take into account the cost that a dying, untreated tree cost when it comes to liabilities.“Trees that are killed by this pest become brittle quickly and this presents additional safety hazards even compared to dead trees of other species,” Zwack says. While Zwack says EAB will continue to spread and continue to cost money to manage, the current body of knowledge will also expand. “New tools in the fight against this pest are being developed on various fronts – biological controls, new insecticides, new equipment – and these tools will create options for how to best manage this pest to meet the needs of the client,” Zwack says.
Pest out west
Steve Geist, plant pathologist with Swingle Lawn, Tree & Landscape Care gives an update on the mountain pine beetle.
What is the latest with the mountain pine beetle? In the Colorado Mountains, the rate of spread has decreased over the past two years. The mountain pine beetle initially attacked the lodgepole pine forest and is now targeting ponderosa pines in the Central and Northern Rockies. It is prevalent in the Rocky Mountains from Colorado all the way up into Alberta, Canada.
States with infestation are Arizona, California, Colorado, Idaho, Montana, Nebraska, Nevada, New Mexico, Oregon, South Dakota, Utah, Washington and Wyoming. In the U.S., there are some 42 million acres infested. The concern is if it continues eastward across Canada, it could reach the white pine forest and then head down into the midwest of the U.S. There it could merge with the southern pine beetle.
How does it infest the tree? Mountain pine beetle overwhelms the tree’s defenses by chewing into the wood constructing nuptial chambers, mating and laying eggs. Associated with the beetle is a complex of fungi collectively known as blue stain fungi. Previously it was thought that the fungus killed the tree. However, this is now in dispute.
What is known is the fungal infected wood is a more palatable food source for developing beetle larvae. Thus, the beetle-fungus relationship may be more synergistic. Developing larvae then tunnel beneath the bark effectively destroying the vascular system of the tree. Successfully infected trees will “fade” in the spring of the year turning a reddish brown by summer.
How can it be prevented? One trunk spray completed prior to July of the year continues to be the standard for prevention. In many locations, beetles have been found flying earlier in the year necessitating sprays to be completed in late May to early June.
Insecticides with the active ingredient carbaryl, permethrin and bifenthrin are the standard. As carbaryl at the mountain pine beetle rate – 4 gallons per 100 gallons of water – is messy and difficult to apply, most contractors are using permethrin or bifenthrin. Recently products with emamectin benzoate and dinotefuran have become labeled for use on mountain pine beetle. The emamectin benzoate is a trunk injection that is completed once every other year. Dinotefuran is a systemic lower trunk spray completed twice per year. While these are labeled for use, it is not clear if these products are as effective as the carbaryl, permethrin and bifenthrin.
How can it be treated? Mountain pine beetle in forested situations will prefer an overly dense declining pine population. Managing the pine stand, taking out old and declining individuals and encouraging young tree growth is an effective strategy. Unlike other bark beetle complexes, pine trees do have some resistance to mountain pine beetle invasion.
The trees can push the beetle out of the tree prior to mating and egg lying. These are called pitch outs and the beetle can often be found drowned in the pitch in the resulting pitch mass. If the tree is successful in pushing the beetles out, then it can still be treated with insecticides.
Once beetles are successful in colonizing the tree – no treatment is possible.