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Project description

Pheromone mating disruption strategies for codling moth in walnuts. (00BU014)
Program UC IPM competitive research grants program
S.C. Welter, Insect Biology, UC Berkeley
R.A. Van Steenwyk, Insect Biology, UC Berkeley
Host/habitat Walnuts
Pest Codling Moth Cydia pomonella
Discipline Entomology
Biorational Use
Start year (duration)  2000 (Three Years)
Objectives Develop alternative pheromone dispenser strategies for disrupting mating of codling moth in immature and mature walnut orchards.

Development of a means to contrast dispenser technologies rapidly.

Determine how orchard and environmental variables influence the success of the mating disruption programs.

Final report Two pheromone-dispensing technologies were evaluated. Performance of both aerosol emitters ("puffers") and sprayable formulations of pheromone looked promising, yet these face the same limitations as other pheromone programs. High-pressure codling moth situations were difficult to suppress, whereas low to moderate situations experience very low damage levels. Aerosol emitters were estimated to create a pheromone plume spread greater than 200 feet laterally and greater than 1500 feet downwind from a single puffer source. An often-significant edge effect was observed as infestation and moth capture was most commonly seen along the margins. Trials to exploit the size of a pheromone plume in large plots demonstrated successful CM control at deployment rates of one puffer per 1.5 to 3 acres in combination with supplemental insecticide or pheromone treatments of edges and "hot spots."

Sprayable formulations developed by Consep and 3M were shown to suppress traps more than 80 days following a single application in small plot trials. A relatively flat rate response was observed (5 to 150 grams per acre) relative to trap suppression. Efficacy trials demonstrated that while codling moth traps could be shut down, damage could occur as mated females may have moved from adjacent undisrupted sites. In an 18-orchard trial, low rates of sprayable in conjunction with insecticides provided enhanced suppression for moderate populations. Applications by fixed-wing plane or ground air-blast sprayers suppressed traps equally.

Protocols were developed using an electroantennogram (EAG) to estimate product performance of sprayable pheromone residues under light-exposed and shaded conditions. The EAG is in essence a biological sensor to detect active pheromone emissions. Relative stability of the shaded product measured by the EAG probably explains the relative success of sprayables in dense canopied walnut plots. However, light-exposed capsules no longer released detectable pheromone by 7 to 11 days, depending on light quality.

Overall, performance in puffer-treated plots in walnuts looked promising, yet faces the same limitations as other pheromone programs. High-pressure codling moth situations were not adequately suppressed, whereas low to moderate situations experienced very low damage levels. Potential for cost reduction using more optimally spaced dispensing units also appeared feasible under controlled experimental conditions. While the economic gain from reducing the number of dispensers from one per acre to one unit per 1.5 to three acres is significant, the current benefit may be offset in part by the documented high unit failure rate of 18%. Because of documented difficulties with the units, the number of dispensers per acre should not be decreased beyond current standards until these issues are resolved.

The sprayable pheromone technologies performed less well than expected from 2001. Codling moth traps were consistently shut down in all trials, yet damage was still observed in one walnut location (Locke). However, trap suppression was easily obtained in most locations with damage suppression generally following suite. The DA lures provided effective monitoring early in the season until ca. mid-July in the pheromone treated plots. After this point, the DA lures failed in some orchards to detect a late season flight that was indicated by pheromone traps in untreated controls. These results will need to be repeated.

Initial efforts with aerial applications of sprayable formulations looked positive with equal trap suppression of sterile moths in areas treated with fixed-wing plane or ground air-blast sprayers.

Two types of studies were used to assess the effects of aerosol emitters (puffers) on codling trap counts and damage suppression: use of highly controlled conditions using single puffer units with uniform grids of releases of sterilized codling moths or "curtains" of 3-5 puffers placed within orchards that were assessed for trap and damage suppression. Trap suppression was readily apparent for greater than 1500 feet from the puffer source when trap suppression of sterile moths was used as the test criteria. Similar results were observed with wild moths in commercial orchards but the suppression was limited to 500-750 feet because of the smaller orchard size. Residual activity was again observed to last for several days after the units were shut off presumably due to absorption on adjacent foliage or wood. Edges of orchard consistently caught moths and infestation was most commonly observed along the margins. Within one conventional orchard and one organic orchard, damage was suppressed well below the 2.0% threshold throughout the orchards, despite shifting wind conditions. However, within the smallest organic orchard, damage was uniformly distributed throughout the orchard. As observed within some pear trials, movement by mated females from the untreated upwind area appears to have resulted in high damage levels into the pheromone-treated areas. Trials in 2002 will need to move to larger orchards, establish chemical barriers between treated and untreated areas, and increase inter-plot spacing. Preliminary testing of sprayable formulations from 3M yield positive results with ca. a 66% reduction in damage from codling moth compared to an untreated control. Results were similar to the commercial program with less than 1% damage reported at harvest.

The area of influence of a codling moth pheromone plume was estimated by the release and recapture of sterilized codling moths within walnut orchards in California. The plume size and structure was determined to spread greater than 200 feet laterally and greater than 1,500 feet downwind. No clear difference was observed between 24 continuous emissions of pheromone from a single aerosol unit compared to 12-hour per day emission cycles. Highly effective trap suppression lasted up to three days after the puffer emission was terminated, suggested a residual or "ghost" effect from the pheromone. Strong edge effects were observed when the aerosol emitter was placed on the margins of the orchard. Almost complete trap suppression of a 74-acre walnut orchard was observed using six aerosol emitters placed along the perimeters of th orchard, but no data were collected for fruit damage suppression given the confounding effects of the releases of sterile codling moths. The sprayable formulations by Consep and 3M were evaluated for their ability to suppress traps using weekly releases of sterilized codling moths. Effective trap suppression was observed for greater than 80 days from a single application. A relatively flat response was observed between the rates of 5 to 150 grams per acre relative to trap suppression. The positive results for both the aerosol-based emitters and the sprayable formulations appear to warrant additional testing in 2001 using fruit damage suppression as the primary criteria for success.

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