Oriental Fruit Moth Management in Washington Orchards

While Oriental fruit moth (OFM) has been a concern for Washington stone fruit growers for decades, infestations of this pest have only been noted in organic apple orchards in the lower Yakima Valley over the past few years. In 2017, damage from this pest showed up with a vengeance in several Washington orchards, most notably in sweet cherry and organic apple orchards in and around the south-eastern edge of Yakima County. While significant losses were noted in organic apples, the economic impact of the damage identified in cherry is currently unclear.

OFM was first noted as a pest in Washington State 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 (MD) for OFM in the 1990’s, 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, even in the absence of formal control programs in stone fruit orchards, OFM has rarely been trapped north of I-90 based on surveillance programs conducted by the Washington State Department of Agriculture (WSDA).

However, the absence 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. Statewide, over 600 OFM traps were placed in a combination of commercial orchards, dooryard trees, unmanaged roadside trees and abandoned orchards. Of the 4871 OFM males caught, almost all (4827) 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 7 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.

Orchardists with OFM problems last year should be ready to manage OFM this spring. If not managed properly, OFM larvae can damage and infest fruit. They also damage tender growing shoots by boring into and then tunneling within the shoot. Fruit damage to apple caused by OFM larvae is similar to damage caused by codling moth (CM). Larvae of both pests tunnel into the fruit. 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 in shoots can cause severe damage to young trees by destroying tree architecture after the shoots wilt and die. There are at least 4 OFM generations per year here in WA. Since OFM has only recently become a pest in organic apples, WSU-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 here in WA.

Successfully managing OFM in WA orchards will require an integrated approach. One needs to monitor the first adult OFM emergence and seasonal flight with pheromone traps, sample for shoot and fruit damage during the growing season and apply timely, effective control measures when necessary. The first thing to do is to use pheromone traps to monitor adult OFM activity to determine when the overwintering generation emerges in the spring. Traps need be placed in orchards before the moths start to fly. Information about the precise timing for deploying traps can be found in the OFM model on DAS. Although this model has not been validated for management decisions, it is primarily used for quarantine efforts as it provides degree-day (DD) information and recommendations for when to put traps in the field. According to this OFM model, traps should be set out at about 125DD from Jan 1 in advance of first OFM emergence (about 175DD). See Table 1 for the estimated date to put traps in the field. With this year’s warmer weather, we are well ahead of last year, so make sure traps are placed in orchards near Paterson by early March and elsewhere by early-mid March. Check DAS regularly for the most up-to-date degree-day forecast. Just like the weather forecast, degree-day predictions are more accurate over short time periods.

Mating disruption (MD) for OFM works very well when deployed properly. If growers are planning on using mating disruption for OFM, then it should be put out in the orchard soon after the first moths are captured in pheromone traps. A good synopsis of OFM MD can be seen by clicking on this link: Gut and Haas: Manage oriental fruit moths using mating disruption. MD is very effective against the first 2 generations and can provide season-long control if used properly. Depending on the crop and product used, MD may have to be reapplied. MD will interfere with capture of moths in pheromone traps making it difficult to determine if MD is working, thus, it’s imperative to regularly sample shoots and fruit for damage. If growers are already using MD for CM, then consider adding OFM MD on top of a successful CM MD program rather than using combination OFM/CM MD products. Sprayable formulations of OFM MD 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 applied to manage OFM either alone or in combination with MD. There are several conventional insecticides available for use (see the WSU Crop Protection Guide for Tree Fruit: Stone Fruit (not Cherry)), and these products should be applied based upon specific accumulated degree-day timings. Unfortunately, models to time applications of insecticides for OFM management have not been validated here in WA. Given the lack of local information, consider using the calculated DD 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). It is imperative to sample periodically for OFM injury to make sure the program is working. Insecticides for organic OFM management are limited. Entrust, a spinosad product, is only rated fair against OFM. Madex HP, a codling moth virus product that has OFM activity, has not been thoroughly evaluated here in WA and has provided marginal OFM control in eastern US trials. At this time, both Madex HP and Entrust should not 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.

Peter W. Shearer, Ute Chambers, Mike Willett

References:

Brunner, Jay and Richard E. Rice. Oriental Fruit Moth. Washington State University Orchard Pest Management Online. http://treefruit.wsu.edu/crop-protection/opm/oriental-fruit-moth/

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). EB0419 Online. http://cpg.treefruit.wsu.edu

Washington State University. Decision Aid System. https://www.decisionaid.systems