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Biobased Pest Management

Predatory Mites Benefit Apple Growers in Pennsylvania

Pennsylvania tree fruit growers could potentially save up to one million dollars per year in pesticide applications, reduce their pesticide usage by almost one ton of active ingredient, as well as receive federal conservation payments, thanks to a predatory mite recently discovered by a Penn State researcher.

Tree fruit is a $69 million a year industry in Pennsylvania. At one time, the state was internationally known as a model system for the biological control of mites from the black lady beetle, Stethorus punctum, which was resistant to organophosphate insecticides. Conservation of Stethorus as a biological control agent reduced miticide use by 50 percent (an estimated 2.2 million pounds) over a 15 year period, saving growers an estimated $20 million. However, the introduction of new classes of synthetic insecticides and miticides used to control orchard pests decimated populations of the black lady beetle and other predatory mites.

The use of biological controls, such as predatory mites, is one component of a grower's integrated pest management (IPM) program. IPM aims to manage pests—such as insects, diseases, weeds and animals—by combining physical, biological and chemical tactics that are safe, profitable and environmentally compatible.

According to Dr. David Biddinger, biocontrol specialist at the Penn State Fruit Research & Extension in Biglerville, Pa., it was a surprise to find high numbers of the predatory mite Typhlodromus pyri (T. pyri) in a commercial apple orchard in Adams county. "With the implementation of the Food Quality Protection Act, growers can no longer use some of the more toxic compounds in their orchards to control pests and more selective pesticides are being developed and applied," explains Dr. Biddinger. "As a result, we are starting to see new beneficial insects and mites in the orchard."

Before the introduction of synthetic pesticides just before World War II, pest mites such as European red mites and the two-spotted spider mites were kept under control by predatory mites such as T. pyri. According to Dr. Biddinger, it is very important to keep these pests at bay, because they feed on the leaves of apple trees, which can reduce fruit quality and yield. As broad-spectrum insecticides were introduced to control insect pests, naturally occurring mite predators were also killed. This necessitated the use of pesticides to control the pest mites (miticides). "Miticides are expensive and mites quickly developed resistance (immunity) to them, forcing the pesticide companies to produce new products and pass related costs onto the grower," he says.

Armed with the observation that T. pyri were emerging and a grant from the Pennsylvania Apple Marketing Board in 2004, Dr. Biddinger surveyed approximately 20 apple orchards for the presence of the predator, usually only detected in orchards in New York and New England. T. pyri has never been detected in Pennsylvania or other mid-Atlantic states before. He found that about three-quarters of all surveyed orchards contained populations of the predatory mite. "The survey confirmed what we already suspected, that T. pyri is capable of tolerating the hotter summers of Pennsylvania and can exist in multiple sites," says Dr. Biddinger.

A 4-year USDA Risk Avoidance and Mitigation Program (RAMP) grant is allowing Dr. Biddinger and other researchers to work with seven apple growers and four peach growers in Adams, Bedford, and Centre counties using only reduced risk insecticides to manage pests. Many of these new insecticides, such as the insect growth regulators, are not broad-spectrum in activity, meaning that they target only specific pests and are not harmful to predatory mites. "Unlike other predatory mite species, T. pyri never leaves the tree, even when pest mite populations decline. They are able to subsist on pollen and fungal spores until the pest mites return," Dr. Biddinger explains. "This close association with fruit trees allows them to respond to pest mite populations before the pests can cause injury, but makes them very susceptible to pesticides. Just one spray of a toxic compound can affect predatory mites for the following three growing seasons."

In addition, a 3-year Pennsylvania Department of Agriculture grant is allowing Dr. Biddinger and other researchers at Biglerville to work specifically with fruit growers throughout the state to conserve or introduce T. pyri into apple orchards. "During the first year of the project, we started the process of transplanting T. pyri into new orchards. Researchers either transfer flower clusters and shoots from a T. pyri orchard in the spring and summer to a new one, or in the fall place burlap bands around trunks of trees to collect overwintering T. pyri and then transfer the bands to trees in new areas in the spring," Dr. Biddinger says. "We've been having great results so far; the predatory mites seem to adapt well and are building up quickly in new orchards."

Dr. Biddinger is also working with growers to conserve T. pyri in sites where it already exists and advising them as they transition to beneficial organisms. Since it can take 2 to 3 years for the predator population to become abundant enough to regulate pest mites without the need for any miticides, other measures may be needed to keep the pest mites under control. "We are advising growers to use non-toxic oil sprays to augment mite control and to avoid using toxic insecticides such as pyrethroids to control other pests. We visit the orchards bimonthly to help growers monitor mite populations and give advice," Dr. Biddinger reports. In addition, the researchers are presenting information at grower field days and also providing online updates in Penn State's Fruit Times Newsletter.

Not only do growers benefit from reduced pesticides and production costs, but they may also receive government payments as an incentive for adopting these practices. Dr. Biddinger encourages interested growers to participate in this incentive program aimed at supporting this transition to environmentally friendly pest management and pesticide handling tactics. The program, Agriculture Management Assistance (AMA), is administered by the USDA's Environmental Quality Incentives Program (EQIP) through National Resources Conservation Service (NRCS). The program partially reimburses growers for introduction of various conservation practices into their farm operations, including biological controls in an IPM program.

According to Barry Frantz, assistant state conservationist for programs with the USDA in Pennsylvania, NRCS, the AMA provides cost-share assistance to agricultural producers to voluntarily address issues such as water management, water quality, and erosion control by incorporating conservation into their farming operations. "Producers may construct or improve water management structures or irrigation structures, plant trees for windbreaks or to improve water quality, mitigate risk through production diversification or resource conservation practices, adopt integrated pest management tactics, or transition to organic farming," Frantz explains.

Applicants may request AMA assistance by submitting an application to the local NRCS office. Questions about the program may be directed to Frantz at (717) 237-2216, or e-mail at barry.frantz@pa.usda.gov.

Currently, Dr. Biddinger says they are testing new low-toxicity pesticides to see how they will affect T. pyri and are looking to expand the program to other areas of the state. For more information on the project, contact Dr. David Biddinger at (717) 677-6116 or by e-mail at djb134@psu.edu.

The Pennsylvania IPM program is a collaboration between the Pennsylvania State University and the Pennsylvania Department of Agriculture aimed at promoting integrated pest management in both agricultural and nonagricultural situations. For more information, contact the program at (814) 865-2839. Also, you may view archived program news releases.


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