Don Thomson
Pacific Biocontrol Corporation, Vancouver, Washington 98660, USA
Key words - sex pheromone, mating disruption, integrated pest management, implementation, Cydia pomonella, Tortricidae, Lepidoptera
Introduction
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There is general agreement within and among government agencies, research institutions, industry and grower organizations that there is a need to incorporate effective and more ecologically and environmentally acceptable technologies and strategies into agricultural pest management systems and thereby reduce or eliminate the input of broad spectrum highly toxic insecticides. Pheromone-mediated mating disruption is a viable technology that is central to the development of pest management strategies that meet these criteria for several important agricultural insect pests including Oriental fruit moth, Grapholitha molesta (Rice & Kirsch 1990), pink bollworm, Pectinophora gossypiella (Carde & Minks 1995) and codling moth, Cydia pomonella (Judd & Gardiner 1991; Gut & Brunner 1994; Knight 1995). In 1991, Isomate C (Pacific Biocontrol, Vancouver, WA, USA.) was the first commercial formulation of codling moth pheromone to be registered in the United States. Total pome fruit acreage in the United States treated with Isomate C/C+ dispensers has increased from approximately 1200 ha in 1991 to over 9 000 ha in 1996 (Figure).
Figure Pome fruit acreage treated with Isomate dispensers for mating disruption of codling moth, C. pomonella, in the USA from 1991 to 1996
In 1996, Washington State with plantings of 80 000 ha of pome fruit, had approx. 5 500 ha of pome fruit treated with Isomate C+ (108 mg of E8,E10-12:OH, 60 mg of 12:OH, 12.3 mg of 14:OH) for the control of codling moth. Codling moth is the key pest of pome fruits and is widely distributed throughout Washington State. There are two complete and sometimes a partial third generation per season. Growers apply on average more than three applications of insecticide per season to control codling moth (Brunner 1989). The success of codling moth mating disruption applied to thousands of ha of pome fruit has helped create orchard environments that are able to sustain higher populations of natural enemies.
Improved biological control in codling moth mating disruption treated orchards often but not always correspond to a reduction in the number of insecticide applications needed for the control of secondary insect pests such as aphids (Aphis pomi, Dysaphis plantaginea) and leafminers (Phyllonorycter elmaella) (Gut & Brunner 1994). However, there is a strong potential for populations of other secondary pests such as pandemis leafroller, Pandemis pyrusana, and obliquebanded leafroller, Choristoneura rosaceana, to increase to economically damaging levels in the absence of codling moth cover sprays (Judd & Gardiner 1991; Gut & Brunner 1994; Knight 1995).
The ongoing biological success of codling moth mating disruption will depend in large part on the continued development of monitoring and sampling techniques in conjunction with economic thresholds to accurately assess the biological relationships between key and secondary pests and their natural enemies. The information derived will help determine the need for supplementary controls to ensure the effective management of coding moth and the various secondary pests. The approach of using mating disruption for control of codling moth in conjunction with the enhanced biological control of secondary pests is referred to as a pheromone-based IPM systems approach.
Impediments to the adoption of pheromone-based IPM
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The most important impediments to the commercial acceptance of pheromone-based IPM include the cost of the technology and its implementation, concerns over efficacy and outbreaks of secondary pests such as leafrollers.
Thirty nine people employed in the discipline of insect pest management in Washington and California were surveyed for their opinions on the cost of codling moth mating disruption technology relative to the cost of conventional insecticides (Weddle, Hansen & Associates 1993). Fifty one per cent stated that they found the cost of mating disruption technology to be high compared to conventional insecticides; 31% and 8% indicated that they found the cost of codling moth mating disruption to be very high and extremely high, respectively. Only 8% of the respondents indicated that the cost of codling moth mating disruption was reasonable.
In small plot trials conducted in pear orchards over a six-year period in California, the average cost of a pheromone-based IPM program was 40% higher than a standard insecticide program (Weddle, Hansen & Associates 1994). Two applications of mating disruption dispensers are required to control codling moth in California, thereby substantially increasing costs. A study conducted in Washington State found that the cost of a pheromone-based IPM program when adjusted for material, labour and machinery costs was $133/ha higher than a conventional insecticide program (Williamson et al. 1996). The disparity in costs provides a strong disincentive to adopt a pheromone-based IPM system approach.
Although mating disruption has been used successfully to control codling moth in thousands of ha of pome fruits, there are still concerns about efficacy. Mating disruption will not provide commercially acceptable levels of control in orchards with high resident populations of codling moth without the application of supplemental insecticides. Other factors known to limit the efficacy of mating disruption for control of codling moth include the size of the treated area, the degree of slope, the size and unevenness of the canopy and the isolation of the orchard from external sources of codling moth. Given the above, the selection of suitable orchards is difficult and invariably every year efficacy problems occur in some ill-suited orchards. The problems are compounded by the lack of reliable monitoring techniques to monitor the level of codling moth control within season. Therefore it is essential that candidate orchards are selected carefully.
The successful deployment of codling moth mating disruption and the subsequent reduction or elimination of insecticides to control codling moth often creates orchard environments where leafroller populations can rapidly increase to economically damaging levels. In 1993, a 485-ha apple orchard in central Washington State was successfully treated in its entirety with Isomate C dispensers. Supplemental insecticides were only applied to border areas. Forty eight sex pheromone traps captured 6 748 obliquebanded leafroller males. In 1994, the orchard was again treated in its entirety with Isomate C+ and again supplemental insecticides were only applied to local border areas. Trap captures of obliquebanded leafroller increased four fold to 24 124. Increased applications of insecticides were required to prevent serious economic injury to the fruit. This example clearly illustrates how the successful use of codling moth mating disruption can increase the control problems of certain secondary pests and thus provide a disincentive to the adoption of the technology. The costs associated with the increased use of insecticides for leafroller control or the economic losses due to fruit injury can outweigh the benefits and savings derived from the biological control of other secondary pests.
The above mentioned impediments to the adoption of a pheromone-based IPM systems approach present serious obstacles to the commercial success of this technology. Yet as illustrated in Figure, codling moth mating disruption is increasingly being adopted by apple and pear growers in the western United States. There are many reasons why this is occurring but they cannot all be discussed in this paper. However, the following case study documents how one grower was able to successfully implement a pheromone-based IPM systems approach over a three-year period in a way that not only dealt with his concerns about efficacy but ultimately met his economic concerns.
Case study: economics and efficacy - the implementation of pheromone-based IPM
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In 1994, 60 ha of a 240-ha apple orchard in central Washington State were treated for the first time with Isomate C+. The table provides an analysis of some of the costs associated with the implementation of a pheromone-based IPM systems approach over a three-year period. The strategy employed by the grower was to minimize the risk from codling moth during the transition by integrating pheromones and insecticides in the most cost effective manner. The total costs per hectare were based on the number of applications times the approximate cost of materials and their application. A local distributor of agricultural chemicals and the grower provided the information on material and application costs.
Table Material and application costs associated with the implementation of a pheromone-based IPM systems approach in a 240-ha apple orchard in Washington State over three years
| 1994 | 1995 | 1996 | |||||||
| 25 ha a | 35 ha | 180 ha | 25 ha | 115 ha | 100 ha | 25 ha | 140 ha b | 75 hac | |
| Number of Applications | |||||||||
| 1 | 1 | - | 2 | 1 | - | 1.5 | 0.5 | 1 | |
| Guthion (2.2 kg/ha) | - | 1 | 3 | - | 1 | 3 | - | 1 | 1 |
| Ryania (16.8 kg/ha) | 8 | - | - | 2 | - | - | - | - | - |
| Orchex Oil (1%) | - | - | - | 6 | - | - | 6 | - | - |
| Cost ($/ha) | 1 197 | 373 | 192 | 1 136 | 373 | 192 | 760 | 218 | 373 |
| Fruit attack (%) | 20 | 0 | 0 | 0.5 | 0 | 0 | 0.25 | 0 | 0 |
aOrganic block; bCentral area of conventional orchard; cBorder area of conventional orchard;
In 1994. a 25-ha section (under organic production for three years) of the conventional orchard was treated with 1 000 dispensers/ha of Isomate C+ prior to the first flight of codling moth (biofix) and then supplemented with multiple applications of the organic insecticide, ryania. The other 35-ha section was treated with 1 000 dispensers/ha prior to biofix and then supplemented with one application of the organophosphate insecticide azinphos-methyl (Guthion®) at first cover timing. The remaining 180 ha were treated with three applications of azinphos-methyl. The control of codling moth in the azinphos-methyl treated blocks and the areas treated with the mating disruption/ azinphos-methyl program was excellent. The grower was willing to spend the extra money on Isomate C+ to treat the 35-ha area because continued codling moth control problems in this area (three applications of azinphos-methyl and 3 to 5% damage in 1993) would have prevented shipment of the 1994 harvested crop to Japan where strict quarantine regulations were in place. In the organic block, codling moth fruit injury ranged from 15 to 25%. The grower estimated that approximately $300 000 in harvestable fruit was lost due to codling moth injury. The results clearly showed the limitation of a mating disruption/ryania program to control high initial populations of codling moth.
In 1995, the grower expanded the mating disruption/azinphos-methyl program from 35 to 115 ha. The organic block was treated with two applications of Isomate C+ at 1 000 dispensers/ha and supplemented with 2 and 6 applications of ryania and Orchex® horticultural oil, respectively. The remaining area was treated with a standard convention program. At harvest, the level of codling moth injury was non-detectable in the azinphos-methyl and mating disruption/azinphos-methyl treated blocks, and below 0.5% in the organic block. As a result the overwintering populations of codling moth in the orchard were substantially reduced.
In 1996, almost the entire orchard was treated with Isomate C+. However, as codling moth populations had been substantially reduced, Isomate C+ was applied to the middle 140 ha at 500 dispensers/ha and supplemented with one application of azinphos-methyl. The border areas (75 ha) were treated with one application of Isomate C+ at 1 000 dispensers/ha and supplemented with one application of azinphos-methyl. The organic block was treated with 1 applications of Isomate C+ at 1 000 dispensers/ha prior to biofix and a half rate of Isomate C+ prior to the start of the second flight and supplemented with six applications of horticultural oil. At harvest, codling moth damage was almost non-detectable in all areas.
This case study illustrates how a grower implemented a pheromone-based IPM program over the course of a three-year period. By the third year, the growers was able to substantially reduce costs by reducing the application rate of Isomate C+. The supplemental application of one azinphos-methyl spray at first cover timing ensured a high level of codling moth control and additionally helped to keep leafroller populations under control. The overall reduction in the input of azinphos-methyl over the three years helped to enhance biological control of secondary pests although no attempt to quantify the cost savings is presented in this analysis. In addition, by adopting pheromone-based IPM other benefits often difficult to quantify were derived such as decrease potential for insecticide resistance, less expense associated with the implementation and administration of worker protection regulations and reduced costs associated with the management of the daily activities of orchard employees. At the end of the third year the grower felt that the cost and performance of a pheromone-based IPM systems approach had considerable advantages over the standard program. In 1997, the grower intends to further reduce rates of Isomate C+ in the middle of the orchard and to eliminate the supplemental use of azinphos-methyl wherever possible so as to enhance biological control of secondary pests while further reducing costs.
Conclusion
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The adoption by growers of a pheromone-based IPM systems approach in pome fruit will depend upon how well the system can meet grower concerns about efficacy and cost. More research is needed into the mechanisms of mating disruption to make codling moth control more robust and reliable. The development of monitoring and sampling techniques in conjunction with economic thresholds are essential in order to accurately assess the biological relationships between key and secondary insects and their natural enemies and to apply supplementary controls if required. Pheromone-based IPM should be presented to growers as a long-term approach and commitment to pest management. Growers should be encouraged to define yearly objectives and then identify the strategies and tactics needed to achieve those objectives with a focus on optimizing efficacy and keeping costs reasonable.
References
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Brunner JF (1989) Apple pesticide use survey - 1989. Washington State Report, Washington State University, Wenatchee
Carde RT, Minks AK (1995) Control of moth pests by mating disruption: Successes and constraints. Annu Rev Entomol 40, 559-485
Gut LJ, Brunner JF (1994) Pheromone-mediated control of codling moth in Washington apple orchards. Good Fruit Grower 45
Judd GJR, Gardiner MGT (1991) Large-scale commercial trials of pheromone-mediated mating disruption for control of codling moth in British Columbia apple and pear orchards. Research Report. Agriculture Canada, Summerland, British Columbia
Knight AL (1995) The impact of codling moth (Lepidoptera: Tortricidae) mating disruption on apple pest management in Yakima Valley, Washington. J Entom Soc Brit Columbia 92, 29-38
Rice RE, Kirsch P (1990) Mating disruption of oriental fruit moth in the United States, pp. 193-211 in Ridgeway RL, Silverstein RM, Inscoe MN (eds.) Behavior-modifying chemicals for insect management. Applications of pheromones and other attractants. Marcel Dekker, New York
Weddle, Hansen & Associates (1993) Barriers to the implementation of mating disruption for the control of codling moth. Research Reports for California Bartlett Pears. California Pear Advisory/Pear Pest Management Research Fund
Weddle, Hansen & Associates (1994) Management of codling moth in Bartlett Pears in California: A preliminary analysis of the relative costs of insecticide- and pheromone-based IPM strategies. Research Reports for California Bartlett Pears. California Pear Advisory/Pear Pest Management Research Fund
Williamson ER, Folwell RJ, Knigth AL, Howell JF (1996) Economics of employing pheromones for mating disruption of the codling moth, Carpocapsa pomonella. Crop Prot 15, 473-477
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