Killing two moths with one stone

03/01/2009 02:00:00 AM

By Renee Stern
Contributing Editor

By building a multipronged attack against codling moth larvae into a single sprayable, biodegradable package, researchers hope to create a more cost-effective control.

The concept would replace cardboard traps now banded around tree trunks with a cellulose-based foam that offers similarly attractive pockets to larvae seeking protected refuges for their cocoons.

Applying foam with a sprayer cuts labor costs significantly compared with wrapping cardboard for each moth generation by hand around individual trunks, says Peter Landolt, research leader at the U.S. Agriculture Department’s Agricultural Research Service in Wapato, Wash.

The foam should last through the season but then begin to break down and wash away, Landolt says.

But labor savings are only one advantage over cardboard bands. Foam also provides a moist environment needed by entomopathogenic nematodes that attack and kill codling moth larvae, says Lerry Lacey, research entomologist at the Wapato station.

Other tactics the researchers are investigating include impregnating the foam with low doses of a pyrethroid pesticide and an aggregating pheromone that lures larvae into what has become a “death strip,” Landolt says.

Hardware store provided inspiration
Sprayable insulating foam from the hardware store triggered the idea. Easy to apply, it expands on contact and creates the desired air spaces. The problem, Landolt says, is “it’s indestructible. It’s designed to last hundreds of years.”

He and Lacey teamed up with Greg Glenn, lead scientist at ARS’ Albany, Calif., Bioproduct Chemistry and Engineering Research Unit, to develop a formulation better suited to orchard needs.

To host nematodes without harming them, the foam needs to be moist—but it also must be stable enough not to collapse. At the same time, it must be inexpensive and biodegradable.

“It’s kind of a tall order,” Glenn says.

Pulp fiber from the paper industry in a water-based slurry is the main ingredient, mixed with stabilizers, sawdust for added substance and an industrial foaming material.

Finding the right applicator turned into another challenge, he says. Too much shear as the material sprays from the nozzle can break the bubble structure.

Cost is critical to attract a wider market, Landolt says.

For organic growers, the cardboard bands now in use are a significant control method, so replacing them with a sprayable foam should produce more cost-effective results.

Adding in organic-friendly nematodes makes it even more attractive, he says.

Promising for conventional growers, too
But conventional growers have a broader range of tools to deal with codling moth. “If they’re going to use four different strategies, this can’t be expensive,” Landolt says. “It has to be mechanically applied and use a dirt-cheap material.”

He emphasizes that the foam won’t be a should add it to their arsenal as another way to reduce populations.

Initial tests in the lab and in research orchard blocks have focused on comparing foam and cardboard acceptability as a cocooning site, with suppression rate studies still to come.

Results so far are promising, Landolt says. More work is needed to refine the product. On the list for additional development is boosting the foam’s durability to better handle orchard conditions.

Surviving sprinklers
Direct blasts from under-tree sprinklers shorten the foam’s lifespan in its current formulation, he says. Without changes to the recipe, these increasingly popular sprinklers are likely to wash the water-based foam off trees before it’s done all it can against the larvae.

After application, the foam dries and forms a skin that most insects dislike, Glenn says. More field tests are needed to determine how the target larvae respond and find solutions.

High humidity also hastens the foam’s decomposition—the perfect trait for irrigated orchards in arid climates, such as Washington state and California, where humidity rises when the foam is no longer needed, Landolt says. But growers in other regions may need to time their applications more carefully.

Possible other uses
That’s a consideration when it comes to finding additional uses for the product. Lacey and Landolt see the foam potentially as a way to tackle similar pests in other tree fruit,  such as citrus.

Lacey points to cherry bark tortrix, a pest common to western Washington, and apple clearwing moth, which has turned up in British Columbia and could migrate south to Washington, as examples where the foam might work.

In both cases larvae also burrow into tree bark. More pests and crops should help attract a commercial partner when the time comes to develop a marketable product, Landolt says.

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