Feb 10, 2009

Codling Moth 101: Managing the New Tools and Methods

If EPA had had its way, the insecticide Guthion would be long gone by now.

But for the last decade, the fruit industry has fought to retain key uses of azinphos-methyl, that old and reliable organophosphate insecticide, especially for control of internal fruit worms in tart cherries, blueberries and apples.

But a phase-out is in progress, and by 2012 the last uses will be gone.

EPA isn’t the only force at work. Increasingly, Guthion has been losing its effectiveness. Codling moths in many areas are showing resistance, so apple growers need to find alternatives.

Across the country, land-grant university researchers have been evaluating new techniques as well as new products from the chemical industry. And EPA has registered several chemicals it calls “reduced-risk insecticides,” giving them a blessing of sorts.

Reduced-risk insecticides have low impact on humans, on the environment and non-target organisms. Unfortunately, that also means they are highly specific in how they act and often have very short residual activity. They tend to be expensive, so growers need to target their use and minimize applications.

At winter horticulture educational meetings in all the apple-producing states, the subject – controlling codling moths using reduced-risk insecticides and organophosphate alternatives – has been on the agenda regularly for about five years.

In sum, the basic outline of a Guthion-free protocol for controlling codling moth has been developed for all the apple-growing regions. Because fruit entomologists have been communicating and exchanging information, the protocol is much the same across the country.

While not as easy as it once was – a silver bullet like Guthion has not been found – growers can control codling moth. In this issue of Fruit Growers News, we’re presenting the basic approach growers across the country are learning to use.

In the article on page 14, Jay Brunner, Mike Doerr and Keith Granger from Washington State University present the basic program they have developed and are recommending to their growers in the arid climate of the West.

In this article, we’re supplementing that with material gathered from East Coast and Midwest universities – Larry Gut and the team of entomologists at Michigan State University, Dan Mahr at University of Wisconsin, Larry Hull from Penn State and Art Agnello from Cornell University in New York. Hopefully, this will help you put a modern codling moth control program to work in your orchards.

If you start this year, you should be well practiced by 2012, when Guthion may no longer be around, even as a rescue.

Integrated pest management

While growers have been using the phrase “integrated pest management” for many years, controlling codling moth will raise it to a new level.

“The keys to success of a low-risk program are monitoring, timing and rotating chemistries,” Dan Mahr told apple growers at the Wisconsin Fresh Fruit and Vegetable Conference in early January.

“For codling moth, IPM relies on pest monitoring and includes a great variety of insecticide chemistries, as well as biological control and mating disruption.”

The fruit entomologists at Michigan State University – Larry Gut, John Wise, David Epstein and Peter McGhee – have put together tables and charts that tell growers what to do when. Much of it is based on carefully counting growing degree days (GDD), because the development of insects is almost totally based on the increasing warmth that comes as spring begins.

How do you know how many growing degree days have accumulated on your farm? The most accurate way is to measure it there with your own weather station, but you can tune in to university-led programs that will give you information from places close to your farm.

“The first opportunity to control this troublesome pest is to target the adult stage using pheromone-based mating disruption,” according to the MSU team. “Pheromone products should already be in the orchard and operating when the first moths emerge from overwintering sites.”

About 200 GDD are needed to bring the moths out. How will you know moths are there? You’ll find the adult males in traps you put in your orchard, about the same time as you put out mating disruption materials.

Entomologists use the phrase “sustained moth captures” to define a date called “biofix.” Mahr defines it as “day 1 of at least two consecutive days of trap catches.” Growers use that day to reset the growing degree day accumulation count to 0 and start counting GDD. GDDs are the number of degrees accumulated each day above base of 50˚ F. The daily average temperature is calculated by adding the high and low temperature together (using 50 if the temperature reaches that or below that) and dividing by 2. Subtracting 50 gives the number of growing degree days.

Other spring orchard activities, like the early application of dormant oil sprays, should have cleaned up the trees and smothered overwintering eggs or spores and set a clean slate for the new season.

At about 100 GDD after biofix, codling moths that have mated start laying eggs. By 250 GDD, eggs begin to hatch. An ovicidal spray should be applied about 230-250 GDD, to catch those eggs before they hatch.

The chart and the two tables with this article, supplied by the MSU entomologists, give you three kinds of information:

1. Table 1 tells you what action to take at certain critical points in the life cycle of the codling moth.
2. The chart gives basically the same information in a graphic form, showing the critical points to aim at.
3. Table 2 tells you what insecticides are available, what life stage of the codling moth it acts on and what the best timing is for the application of the spray.

Mating disruption

Not all the materials available for control are insecticides.

Mating disruption, for example, is a key step in stopping eggs from ever being produced. If codling moth males can’t find females, females will not lay fertilized eggs.

In a few areas, entomologists and growers have worked together to form area-wide mating disruption programs, which have been highly effective in reducing populations of codling moth. Mating disruption is less effective in small blocks of trees because there are plenty of breeding sites in the natural world surrounding orchards.

Granulosis virus

Another biological tool is a virus that attacks codling moth larvae and kills them quickly enough to prevent internal damage in apples.

“Growers should not overlook including granulosis virus in the codling moth management program,” according to the MSU entomologists.

Larry Hull at Penn State has evaluated this naturally occurring virus extensively.

There are two products – Cyd-X and Carpovirusine – available for use, he said. The virus is highly lethal -– only a few need to be ingested to kill a larvae – but the products are short-lived in the orchard. The virus must be ingested by codling moth larvae to kill them.

This naturally occurring virus should be applied after eggs are laid and before they hatch. Mahr notes that codling moth larvae often eat their own eggshells after they hatch, so a strategy that puts granulosis products over unhatched eggs prevents damage. If the larvae eat nothing until they reach a developing apple, feeding injury, called a sting, may result.

Usually, apples with shallow stings will heal, or they may be lost during June drop.

Because so few virus occlusion bodies are needed to kill a larva, Hull and other entomologists recommend low rates and frequent applications during the egg-laying period up to the time larvae would penetrate into fruit. And, if making a choice, apply it against the first generation, Hull said, because the effects linger and can greatly reduce the size of the summer generation of codling moths.

Hull recommends the first application at the beginning of egg hatch (230-250 DD after biofix), or use an ovicidal insecticide at 75-150 DD and then apply the virus at 300-350 DD. Use a higher rate for the first application and repeat applications every seven to nine days, or 125-150 DD.

The material can be tank mixed with insecticides and other crop protection chemicals, but not with copper or lime sulfur. Use a buffer if needed to keep the spray mix above pH 5 and below pH 9. Larry Gut at MSU notes that neonicotinoid insecticides have some anti-feeding activity on larvae and should not be used at the same time.

Rotating chemistries

Entomologists all recommend rotation of chemistries from generation to generation.

“Treat different generations with materials of different chemical classes,” said Cornell’s Art Agnello. “Good insecticide stewardship means applying only when necessary, using correct dosages, obtaining adequate coverage and using optimal timing.”

The materials listed in Table 2 are identified by class so you can make those choices.

Web sites

Many of the recommendations and protocols for codling moth management can be found at Web sites of the land-grant universities in the various states. The following Web sites are useful:

For information in Washington and the Northwest, go to the Washington State University Tree Fruit Research and Extension Center Pest Management Transition Project Web site, http://pmtp.wsu.edu, to www.tfrec.wsu.edu or to http://weather.wsu.edu for weather-related data upon which to make decisions.

For Michigan weather information, go to www.envioweather.msu.edu. MSU Web sites contain good codling moth control information that can be tracked down by going to http://web1.msue.msu.edu/fruit or www.ipm.msu.edu/fruit-cat.htm.

For New York information, go to www.hort.cals.edu or www.nysipm.cornell.edu.

In Pennsylvania, visit www.ento.psu.edu or http://frec.cas.psu.edu.