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The Oriental fruit moth (OFM) has been an occasional pest for Washington stone fruit growers for over 50 years but has now become a problem in organic apple orchards in the lower Yakima Valley.

In 2017, OFM damage showed up in several Washington orchards, most notably in organic apple and young sweet cherry orchards in and around the southeastern edge of Yakima County. Significant losses were noted in organic apples, however, the economic impact of OFM to cherries is currently unclear.

Peter Shearer

OFM was first noted as a pest in Washington in 1948 in the Sawyer district just south of Yakima (Carver, 1949). At that time, damage was limited to stone fruit.

In 1949, a trapping program was started to determine the extent of the problem and a control program based on DDT and parathion applications was recommended.

From that time on, OFM control has been a fact of life for stone fruit growers in the Yakima Valley and parts of the lower Columbia Basin.

With the introduction of mating disruption for OFM in the 1990s, pheromone-based control has been the method of choice; its effectiveness has reduced OFM damage in commercial orchards to low or non-existent levels.

Interestingly, OFM has rarely been trapped north of Interstate 90 based on surveillance programs conducted by the Washington State Department of Agriculture (WSDA).

The rarity of OFM damage in commercial stone fruit orchards doesn’t mean that the pest has disappeared. In 2016, Katie Buckley and Mike Klaus of WSDA conducted a season-long survey of stone fruit pests, placing over 600 OFM traps in commercial orchards, backyard trees, unmanaged roadside trees and abandoned orchards statewide.

Of the 4,871 OFM males caught, almost all (4,827) were caught in Yakima and Benton counties. OFM was trapped at 96 separate sites in Benton County and 45 sites in Yakima County. Thirty-four moths were caught at seven sites in Walla Walla County. In the rest of the counties where OFM was caught, the adult male numbers were in single digits.

No OFM were detected in Chelan or Okanagan counties. However, there are reports that OFM has been captured in pheromone traps this year in areas further north, including Chelan County.

If not managed properly, OFM larvae can damage fruit and growing shoots. OFM damage to apple fruit is somewhat similar to damage caused by codling moth.

Codling moth larvae tend to tunnel to the core of the apple where it often feeds on apple seeds while OFM make meandering tunnels in apple.

OFM feeding inside shoots can cause severe damage to young trees by destroying tree architecture. There are at least four OFM generations per year in Washington (Brunner and Rice: Oriental Fruit Moth).

Since OFM has only recently become a pest in organic apples, Washington-based management information is sparse. Regardless, OFM is a major pest of stone and pome fruits elsewhere, so there is a lot of information available to develop strategies to control it in Washington.

Mike Willett

Successfully managing OFM in Washington orchards requires an integrated approach.

Begin by monitoring the first adult emergence in the spring and its seasonal flight with pheromone traps, then sample for shoot and fruit damage during the growing season and apply timely, effective control measures when necessary.

Information about the precise timing for deploying pheromone traps can be found in the OFM model on the WSU Decision Aid System (DAS) website (https://decisionaid.systems/).

Although this model has not been validated for management decisions, it provides growing degree-day information and recommendations for when to put traps in the field. According to this OFM model, traps should have been deployed in orchards near Paterson, Washington, by early March and elsewhere by early mid-March.

Mating disruption for OFM works very well when deployed properly. If growers are planning on using it, then it should be deployed in the orchard soon after the first moths are captured in pheromone traps. (A good synopsis of OFM mating disruption, Gut and Haas: Manage oriental fruit moths using mating disruption, can be found at https://bit.ly/2kgvcf0).

Mating disruption is very effective against the first two generations, and a single application can provide season-long control if used properly, though it may have to be reapplied depending on when the fruit is harvested and product used.

Mating disruption should interfere with capture of male moths in pheromone traps, making it difficult to determine if it is working, thus, it’s imperative to regularly sample shoots and fruit for damage.

A word of caution for growers and fieldmen who are using the new Trécé OFM Combo Duel lure: This is an enhanced lure that is designed to catch both male and female moths in mating disrupted orchards.

These lures can demonstrate the presence of adult OFM, but that does not mean mating disruption is not working. Sampling for damage is the best way to determine whether management programs are effective.

If growers are already using mating disruptions for codling moth, then consider adding OFM mating disruption on top of a successful codling moth mating disruption program rather than using combination OFM/CM products.

Sprayable formulations of OFM mating disruption are very effective when applied at regular intervals but these are not certified for organic use. Aerosol dispensers (misters and puffers) are available for OFM, can provide season-long control and are allowed to be used in organic orchards.

Insecticides can be used against OFM alone or in combination with a mating disruption program. There are several conventional insecticides available for use (Washington State University. 2018 Crop Protection Guide for Tree Fruit: Stone Fruit [not cherry]), and these product applications should be based on specific degree-day timings.

Unfortunately, models to time applications of insecticides for OFM have not been validated in Washington. Given the lack of local information, consider using the calculated degree-day from DAS and then follow the spray timings highlighted in the UC Pest Management Guidelines for Oriental Fruit Moth Management on Peach (UC Pest Management Guidelines. Peach.

Oriental Fruit Moth). Insecticides for organic OFM management are limited. Entrust, a spinosad product, is only rated fair against OFM. Madex HP, a codling moth virus product with OFM activity, has not been thoroughly evaluated for Washington and has provided marginal OFM control in Eastern U.S. trials.

At this time, neither Madex HP nor Entrust should be relied on to control OFM under high pressure situations. It is probably best to use these products in combination with OFM mating disruption rather than as stand-alone products. •

—by Peter W. Shearer and Mike Willett

Shearer, Ph.D., is a research entomologist at the Washington State University Tree Fruit Research and Extension Center. Willett, Ph.D., is manager of the Washington Tree Fruit Research Commission.

References:

Brunner, Jay and Richard E. Rice. Oriental Fruit Moth. Washington State University Orchard Pest Management Online. http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=20.

Buckley, K.D. and M.W. Klaus. 2016 Stone Fruit Survey Report. Washington State Department of Agriculture. 15pp.

Carver, F.E. 1949. The Oriental Fruit Moth Survey and Control Program. Proceedings Forty-Fifth Annual Meeting of the Washington State Horticultural Association. 45:87-89.

Gut, Larry and Mike Haas. Manage oriental fruit moths using mating disruption. Michigan State University. http://msue.anr.msu.edu/news/manage_oriental_fruit_moths_using_mating_disruption.

UC Pest Management Guidelines. Peach. Oriental Fruit Moth. UC ANR Publication 3454 http://ipm.ucanr.edu/PMG/r602300211.html.
(Washington State University. 2018 Crop Protection Guide for Tree Fruit: Stone Fruit [not cherry])