Pheromone-based IMP in Washington

J. F. Brunner
Washington State University
Tree Fruit Research & Extension Center

Washington state is located in the very northern portion of the United States. The state is characterized by having two very distinct climates, a moist cool climate west of the Cascade Mountains and a hot dry climate east of the Cascade Mountains.

The majority of commercial fruit production is located in eastern Washington, primarily associated with major river systems of the Columbia, Wenatchee, Okanogan and Yakima. Irrigation is critical to the production of pome and stone fruits with each acre receiving 30 to 40 inches of supplemental water each year.

Codling moth, Cydia pomonella L., is the KEY pest of the apple in Washington. Control of codling moth has been achieved with organophosphate insecticides for the past thirty years. Dr. Stan Hoyt developed integrated mite management which coupled the biological control of Tetranychid mites, McDaniel spider mite and the European Red mite, and chemical control of codling moth.

Integrated mite management was possible because Dr. Hoyt discovered that the predatory mite, Typhlodromus occidentalis, had developed tolerance to certain organophospate insecticides, especially azinphosmethyl and phosmet. This program has provided Washington apple growers a stable and economical pest control program for many years. Most Washington apple growers have not applied a specific miticide since the late 1960s.

The use of organophosphates for codling moth control resulted in the disruption of biological control of a wide range of other secondary pests, such as aphids, leafhopper and leafminer. These secondary pests also developed resistance to the most commonly used insecticides. And as a result additional insecticides were required to control them.

In the early 1980s the western tentiform leafminer, Phyllonorycter elmaella, developed populations resistant to most organophosphate insecticides and many carbamate insecticides. Control can be achieved with oxamyl (Vydate) but this product often results in the suppression of predatory mites, a rapid increase in phytophagous mite populations and the subsequent need to apply specific miticides.

Dr. Bruce Barrett and Dr. Jay Brunner demonstrated that in a majority of situations a parasitic wasp, Pnigalio flavipes, could keep leafminer densities below damaging levels if interactions were allowed to occur. P. flavipes was also shown to be tolerance of many of the same organophosphate insecticides that T. occidentalis was tolerant to. The prophilactic use of oxamyl has declined substantially as growers have learned how to rely upon P. flavipes for control of leafminer.

In 1989 an average of three insecticides, mostly azinphosmethyl, were applied to control codling moth. Aphids, mainly Aphid pomi, the green apple aphid, and leafrollers, Pandemis pyrusana and Choristoneura rosaceana were the pests for which the majority of other insecticides were applied.

By 1993 the average number of insecticides applied to control codling moth had increased to 3.3 per year and the rates had also increased. Some growers reported levels of codling moth injured fruit much higher than expected even with 4 to 6 applications per year. By 1993 leafrollers had become the most important secondary pest based on insecticide use and they were often identified as causing more fruit injury than codling moth.

The trend of increasing insecticide applications was very troubling, especially with reports of codling moth resistant populations from California. While the protection of fruit is still possible in California the cost of control programs is high. In Washington codling moth resistance levels have not been as high as those detected in California, however, coupled with leafroller resistance problems Washington growers are facing tremendous challenges in maintaining a cost-effective stable pest management system.

The development of codling moth populations resistant to many organophosphate insecticides is troubling but the potential for this resistance to be expressed as resistance to other insecticides is even more alarming. Cross-resistance of OP resistant codling moth to carbamate insecticide was expected since the mode-of-action is similar. Cross-resistance to insect growth regulators was not anticipated and these products were expected to provide a new line of chemical defense against codling moth. However, research in California has indicated that OP resistant codling moth are also tolerant of some insect growth regulators. Additionally in Europe codling moth has developed resistance to insect growth regulators where they have been used as the primary means of control for several years.

A scenario that is too often played out in Washington apple orchards has its basis in the disruption of natural controls by organophosphate insecticides used to control leafrollers and the resistance to these products in several pest species. Leafrollers cannot be controlled with insecticides commonly used to control codling moth. Thus, growers must rely upon additional insecticides, such as, chlorpyriphos (Lorsban) or encapsulated methylparathion (Penncap-M) to achieve adequate control. These insecticides are highly toxic to P. flavipes, the parasite providing biological control of leafminer. Released from natural controls leafminer populations increase and growers are must use oxamyl (Vydate) to achieve control. Oxamyl is toxic to predatory mites and McDaniel or European Red mite populations often increase to damaging levels requiring the use of specific miticides. Few miticides are currently registered on apple that the potential to select for mite resistant populations is high under these conditions.

Codling moth and leafroller resistance, higher levels of fruit injury by insects, concerns for farm worker safety and environmental stewardship and increased costs of pest control has promoted efforts to find alternative pest management approaches that would be safe, stable as well as economical.

Since 1991 there has been as active research program conducted by Washington State University on the use of pheromones, i.e. mating disruption, as a control of codling moth. Under normal conditions the female moth emits a sex pheromone, i.e. calls the male, which attracts the male from long distance so that mating can occur.

The underlying premise of mating disruption is that high concentrations of the codling moth sex pheromone, codelmone, are dispensed into the orchard thus preventing male moths from locating females and mating. The exact mechanism by which this is achieved is not totally understood but in Washington the approach has worked well.

In the three year study of the transition of apple orchards to a pheromone-based codling moth control program pheromones (Isomate-C) provided control as good as the growers standard method (Gut and Brunner 1994). In one orchard codling moth densities exceeded levels that could be controlled using pheromone alone.

In experiments conducted in over 200 orchards over the last five years different pheromone dispensers systems (Isomate-C, Checkmate-CM, TNO) have been directly compared. In these tests Isomate-C has provided the most consistent and highest level of codling moth control. Collective experience indicates that mating disruption can provide codling moth control when low densities are present but may require supplemental applications of insecticides under moderate densities. Under high codling moth densities mating disruption alone will not provide adequate control of codling moth and almost always must be supplemented with insecticides.

A consistent problem associated with the use of mating disruption is the disproportional amount of fruit injury on orchard borders. Over three years in the study of transitioning of orchards to a pheromone-based codling moth control program two to three times more fruit damage was detected on the border compared to the orchard interior.

Leafrollers have been the most important pest problem occurring in codling moth mating disrupted orchards. In the first or second year of codling moth mating disruption leafroller populations have increased to damaging levels. Leafroller may be the Achilles' heal of codling moth mating disruption. Unless they can be controlled using "soft" insecticides, such as, Bacillus thuringiensis (Bt) and insect growth regulators or biological control agents it will be necessary to use broadspectrum insecticides, greatly reducing or eliminating most of the economic and environmental advantages of codling moth mating disruption.

The potential to use mating disruption over large contiguous area was part of a proposal to the USDA-ARS for management of codling moth in the western US. The goal of this proposal is to reduce broad-spectrum insecticide use by 80% in five years by demonstrating the utility of implementing mating disruption as a control for codling moth.

Five implementation sites in three western states (Washington-3, Oregon-1, California-1) were selected. Sites in California and Oregon are primarily pear production areas while Washington sites were primarily apple areas. The size of the pheromone treated area at each site varied as did the number of growers and crop consultants involved.

One site established in Washington was at the Howard Flat growing area near Chelan. This is a fairly isolated production area of about 1,200 acres. Apple is the predominant fruit crop produced though pear and cherry are also grown. Thirty-six (36) growers farm at Howard Flat and they pack fruit at four cooperative warehouses and 16 crop consultants provide advice on pest control and horticultural practices.

In 1994 a grass-roots effort of crop consultants and interested growers attempted to initiate an areawide codling moth control program. Only about 300 acres were treated with pheromone and results were mixed. Grower education meetings were held to explain how best to use mating disruption and to show why higher than expected injury occurred in some orchards.

This did not deter interest in the approach and in the fall of 1994 meetings were held to explore the idea of organizing the entire Howard Flat area as an Codling moth Areawide Management Project (CAMP). Growers and crop consultants established a CAMP Board consisting of five consultants and three growers. In cooperation with a Howard Flat Technical Advisory Committee a proposal was submitted to the USDA-ARS Fruit Research Laboratory in Yakima to be a site to receive funding to help implement an areawide codling moth management pilot project in the western US.

The proposal was funded and $105,000 was allotted to Howard Flat in 1995. The funding provided a salary for a full-time coordinator, supplies, and operations. Over half of the funding, $55,000, was used to subsidize the cost of the pheromone to the growers at a rate of $50 per acre. The cost of the pheromone used, Isomate-C+, was $110 per acre so the grower was paying out of pocket $60 per acre, this in addition to insecticides that he would need to apply.

Organization meetings with growers were held prior to the season and only two of 36 decided not to participate in the project. A total of 1,135 acres were treated with Isomate-C+ in April. Some growers applied the pheromone dispensers themselves while about half decided to pay the project $15 per acre to apply the dispensers. Pheromone was attached to large plastic clips prior to the time of hanging. It was placed high in the tree canopy, within the upper two feet, using long poles, avoiding the need for ladders and greatly speeding the application.

To monitor codling moth activity in orchards pheromone traps, (Pherocon 1CP, Trécé Inc) and a high load lure (red septum with 10 mg of codelmone) were place in every 2 to 2.5 acres, a total of 448 traps were used. Traps were place at mid-canopy, ca. 8 feet average, monitored weekly and lures changed every three weeks (first flight) or two weeks (second flight).

The use of high load lures to monitor codling moth activity in mating disruption orchards and the need to apply pheromone high in the tree canopy has been established by research conducted by Larry Gut and Jay Brunner (WSU) and Alan Knight (USDA-ARS), respectively.

Leafroller moths were also monitored at Howard Flat. Fifty-six traps of P. pyrusana and C. rosaceana were distributed uniformly throughout the area and checked weekly. Other pests monitored in 15 pre-selected blocks included aphids, leafhopper, mites, leafminer and the mullen plant bug, Campylomma verbasci. Common natural enemies associated with these pests were also monitored. The intent of monitoring this group of secondary pests and their natural enemies was to follow changes in their populations and compare these to similar pest and natural enemy populations in conventional orchards within the area but not at Howard Flat.

Codling moth monitoring indicated high populations in many orchards. More than 3,000 moths were captured in 270 of the 448 traps (60%) during the first 3 weeks of monitoring. The high level of codling moth pressure in many orchards was anticipated based on fruit injury reports from 1994 and histories of pest problems in certain areas on Howard Flat. All growers were advised by crop consultants to apply a well-timed first cover spray for codling moth control; this was in addition to suppression expected by the pheromone. Following the beginning of the first cover applications, codling moth captures in traps dropped dramatically. Twenty-one percent of traps captured zero moths during the first codling moth generation, and 57% of the traps captured four or fewer moths, a level suggested as a treatment threshold in orchards using mating disruption.

The dramatic drop in moth captures on Howard Flat following the initiation of codling moth cover sprays suggested that moths in the region were not resistant to organophosphate insecticides. Bioassays were conducted to determine the level of resistance in codling moth adults at four separate locations within Howard Flat and at the Tree Fruit Research and Extension Center in Wenatchee. Dose-mortality curves generated from the bioassays indicated that only a low level of resistance was present within codling moth populations at Howard Flat.

Capture of codling moth was much lower during the second generation. Sixty-five percent of traps captured zero moths during the first codling moth generation, and 93% of the traps captured four or fewer moths. Cover sprays to control codling moth were planned in high pressure orchards during the second generation. However, additional controls were not applied to most pheromone treated blocks because of the high level of fruit damage caused by a hailstorm that hit the region on July 9.

Approximately 70% of the orchards on Howard Flat were affected in some way by the hailstorm, and in many orchards such a high percentage of fruit was damaged that it could only be harvested for the processing market. Mating disruption alone provided adequate codling moth suppression in the second generation for most orchards, even those which were damaged by hail.

In 1994, 5,006 codling moths were captured in 155 traps at Howard Flat, an average of 32.3 moths per trap. In 1995, 3,929 codling moths were captured in 448 traps, an average of 8.8 per trap. These data cannot be used to compare years but serve to show the high pressure from codling moth on Howard Flat prior to the initiation of the project.

Fruit injury by codling moth was determined following the first generation in selected blocks by visually examining 1,000 fruits per block. Fruit injury by codling moth was between 0 and 0.3%. The combination of the pheromone and insecticide applied first generation was very effective.

Bin samples were taken to assess codling moth injury to fruit from as many blocks as possible during the harvest period. A minimum of 25 bins per variety, 100 fruit per bin, was monitored from each block. A total of 1,726 bins (172,600 fruits) was sampled from 46 blocks. The overall average fruit injury in blocks from Howard Flat sampled was 0.55%. There was more damage in Golden Delicious (0.9%) compared to Delicious (0.4%). The highest levels of fruit damage occurred in blocks near the airport where traditionally there had been high pressure from codling moth. Without hail damage, some growers would have responded to pheromone trap captures in their blocks and applied a control spray in the second codling moth generation.

Fruit packout records from Howard Flat orchards indicated an average level of codling moth fruit injury of 0.8%, this despite the application of an average of 2.87 insecticides specifically to control codling moth. In 1995 the average number of insecticides applied for codling moth control was 1.7.

Capture of P. pyrusana was concentrated in the northwest section of Howard Flat, most in just a few traps. In the second flight P. pyrusana moths were again concentrated in the northern portion of Howard Flat but higher counts were recorded in more orchards. Capture of C. rosaceana was lower than that of P. pyrusana in the first flight period but was again concentrated more in the northern section of Howard Flat. There was an increase in the number of traps capturing C. rosaceana in the second flight. Howard Flat has not had a historical problem with leafrollers, however, reductions in organophosphate insecticides because of mating disruption of codling moth coupled with the level of moth captures in 1995 should be sufficient warning to growers. Leafrollers should be monitored carefully and the need for controls in 1996 anticipated.

Monitoring aphids, leafminer, leafhoppers, leafroller and the mullen plant bug in 15 selected blocks revealed very little about these insects or their natural enemies. Aphids, leafminer, leafhopper and mite densities were very low throughout the summer as were natural enemies commonly associated with them. Leafroller densities were also low in all blocks except one that was not treated with pheromone but managed with conventional insecticides. It is too early in the project to determine how much influence the use of pheromones had on reducing problems with secondary pests in most orchards.

The potential of using codling moth mating disruption to radically alter pest management in apple orchards of Washington and other western states is only just beginning to by understood. It appears to hold great promise for reducing reliance on broadspectrum insecticides as the first line of defense against codling moth and other pests. A pheromone-based pest management system for apple and pear would allow growers to take greater advantage of biological controls for many pests, rely on "soft" chemical controls to suppress pests when needed and reserve the BIG weapons, the fast acting broadspectrum insecticides to stop pests that cannot be controlled with other means. This should lead to a stable, safe, environmentally friendly and hopefully economical pest management system.