Let us (not) spray

MSU entomologist Larry Gut holds the attract-and-kill lure Matt Grieshop, Juan Huang, and he developed. (Richard Lehnert/Good Fruit Grower)

Entomologists John Wise and Matt Grieshop are in hearty agreement on one thing: There’s got to be a better way of managing pests than hauling heavy sprayers carrying hundreds of gallons of tank mix up and down orchard alleys several times each growing season, blasting away.

“Studies have shown that from 29 to 56 percent of what we spray is actually deposited on the tree,” Michigan State University entomologist Wise said during a presentation to fruit growers during the Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids in December.

That’s kind of an insult to growers’ pocketbooks as well as to the environment, when so much expensive pesticide winds up on the ground or drifts away from the target.

“Conventional airblast sprayers are inefficient delivery systems,” he said.

Wise and Grieshop did a tag team presentation, each talking about his own research to develop new ways for growers to control pests in the future.

Wise is taking some pointers from the shade tree and ornamental industry, where trunk injection is a preferred method for protecting trees in public areas like parks. Trunk injection is used when a tree owner is trying to save high-value trees from attack by invasive species like Japanese beetles, emerald ash borer, the elm bark beetle that carries Dutch elm disease, or from diseases like sudden oak death, oak wilt, apple scab, and Phytophthora root rots.

Pesticide injected into a tree’s trunk moves through its vascular system, providing protection, using greatly reduced rates of active ingredient and no exposure to the environment.

Grieshop, who heads the organic pest management program at Michigan State University, is working on a number of non-airblast-sprayer techniques, including permanent orchard irrigation-like installations known as the Solid Set Canopy Delivery System.

Grieshop and his colleagues have also developed an attract-and-kill lure for Oriental fruit moth and codling moth and are working on Japanese beetles and leafrollers. Insects are attracted by pheromones and then killed by insecticide as they contact the device trying to get to the pheromone.

Grieshop also works with waxes and other kinds of baits and with mating disruption.

As Wise looks at history, spray equipment, spray materials, and orchards evolved in harmony for about 50 years until near the end of the 20th century. “It was an amazing century,” he said. “The discovery of synthetic nerve-active materials had a huge impact on agriculture.”

Since they were relatively inexpensive and broad spectrum, and there was minimal concern about environmental impact, airblast sprayers provided good coverage. In recent years, with the use of smaller trees, sprayer nozzles and fans have been redesigned to be more efficient.

But as the 21st century approached, the playing field changed. The Endangered Species Protection Act, the Clean Water Act, and, especially, the Food Quality Protection Act resulted in many good pesticides being challenged, Wise said. The new measure wasn’t whether products were effective, but whether they were safe for workers and nontarget beneficial insects, such as honeybees.

New products that replaced old ones like Guthion (azinphos-methyl) work differently, Wise said.

While Guthion killed eggs, larvae, and adults on contact, the newer products often have no contact activity and must be ingested, or work in more subtle ways by interrupting key insect processes like molting, deterring egg laying, repelling without killing, or discouraging feeding. Some work by inducing resistance in the host plant.

Fermentation-created biopesticides, like Bt (Bacillus thuringiensis) and spinosyns and others, are exciting, Wise said. “Many of them are really good,” he added.

Some of the botanical extracts—pyrethrins, sabadilla, and neem—are being used effectively, he said.

While human medicine has been developing patches to replace needles, and row crop farmers have been using seed treatments that provide protection while reducing rates of active ingredient by 90 percent, the orchard industries have been refining the airblast sprayer but making no quantum leaps.

“What about us?” Wise asks.

Trunk injection

Wise uses tools already developed by the shade tree industry to inject fungicides or insecticides into the tree’s xylem nutrient delivery system. The modern orchard design—many smaller trees—makes the treatment process less easy than it would have been years ago. Treatment is labor intensive.

He began testing the concept in 2010, just to see if it might work, but he has worked with just a few of the many pesticides. He finds the method does well at protecting trees from insects that attack foliage. Insecticides seem to move better inside the tree than fungicides, but he reports “promising” results against apple scab.

One treatment can be effective for an entire year and sometimes even into the second year.

In his summary of strengths and weaknesses, Wise lists “slow application time” first on the list of disadvantages. Direct pests of fruit have proved hardest to control.

He’s intrigued by the potential advantages: elimination of spray drift, reduced worker exposure, reduced pesticide impact on natural enemies, reduced total pesticide use, and the ability to use this method along with other methods, such as mating disruption and attract-and-kill.

It may, in fact, contribute to resistance management. “Maybe we can do it spacially rather than temporally,” he said. Instead of alternating materials from one spray application to the next, materials could be alternated tree to tree—“a mosaic of materials in the orchard.”

If the method works, there are still hurdles—like finding effective rates and developing new product labels.

Attract and kill

Last spring, Good Fruit Grower reported that Grieshop, working with Dr. Larry Gut and postdoctoratal scientist Dr. Juan Huang, had developed an attract-and-kill device that draws Oriental fruit moths to a tiny pheromone lure contained inside an insecticide-treated pouch. When they touch the pouch, they die. (See “Attract and kill” in the March 1, 2014, issue.)

The device is moving toward a commercial release. Grieshop thinks this will be a great improvement over using pheromones for mating disruption. Using pheromones in large quantities to hide female insects inside a perfume cloud so males can’t find them is expensive, he said.

“It distracts the male for a limited time and shortens his already-short mating life,” he said. “But killing the insect uses all of his available mating life span.”

Grieshop likes the system because it requires much less pheromone to lure an insect than to hide one in a cloud, it requires much less insecticide to treat a trap than to spray a tree, and it is highly selective, targeting only those insects that are attracted to the lure.

In field tests in 2013, he found that 50 traps per acre, using one thousand times less pheromone as needed for mating disruption, were effective for Oriental fruit moth.

There are also no insecticide residues on the fruit.

To be effective, however, the insect has to be drawn to a pheromone. “You need a good attractant,” he said. That is the case with codling moths, leafrollers, Oriental fruit moths, and Japanese beetles. It may also work with brown marmorated stinkbugs, he said, and possibly spotted wing drosophila.

SSCD

Work with the solid-set canopy delivery system is continuing in Michigan, Washington, New York, and now in Italy. Dr. Alberto Dorigoni is working with Dr. Art Agnello, from Cornell, to try the system in the South Tyrol growing region.

The system consists of irrigation lines and spray nozzles permanently installed in an orchard and a pumping station where spray materials are forced into the lines with air pressure.

Grieshop heads the multi-university cooperative project. He likes it because there is less drift, there are no tractors and sprayers, weather is less limiting, and the whole orchard is sprayed rapidly, in 15 seconds or so. This allows critical sprays, like fungicides and thinners, to be applied at optimal times.

The key drawback so far is that the forced air from airblast sprayers creates a swirling effect to provide more complete coverage of the foliage. With the SSCD, a few poorly placed leaves can block the spray from a nozzle.

In tests so far, however, insect and disease control has been equal to control blocks where airblast sprayers were used, Grieshop said. •