Mohammad A. Bari Report

A grower managed biorational management program for artichokes on the northern central California coast.

Final Report - October 2001

Principal Investigator:
Mohammad A. Bari, Entomologist
Artichoke Research Association
US Agricultural Research Station
1636 East Alisal Street,
Salinas, CA 93905
Telephone: (831)-755-2871, Fax: (831)-755-2814
Email: mohdabari@aol.com

Project Advisor:
Sean L. Swezey, Specialist
Extension Center for Agroecology and Sustainable Food Systems, University of California
1156 High St.
Santa Cruz, CA 95064
Telephone: (831) 459-4367

Cooperator:
Reggie Knox
Central Coast Lighthouse Farm Coordinator
735 Chestnut Suite C
Santa Cruz, CA 95060
Telephone: (831) 425-8145

Location of project:
San Mateo and Monterey counties

Commodities: Artichokes

Funding:
1999-2000: $28,268

Introduction

Plume moth worm in artichoke bud

Artichoke plume moth (APM) is the primary insect pest of artichokes on the coast of California South of San Francisco to Monterey. It is a major limiting factor in the production of artichokes maintained under perennial culture (Lange 1941, 1950; Bari and Lange 1980, Bari and Kaya 1984). Along the central coast, APM undergoes 3-4 overlapping generations. The prevalence of mild weather in this region and the low developmental temperature thresholds of the various stages of APM allow it to grow incessantly throughout the yearlong (Bari and Lange 1980). For the control of this pest, conventionally artichoke growers have heavily relied on chemical insecticides. Without any control measures, the infestation of harvestable artichoke buds could reach as high as 70%. Typically, an artichoke field maintained under the perennial culture is treated 12-15 times during the annual crop cycle in an effort to keep the crop losses as low as possible. It is estimated that an annual loss of 1% of the potentially marketable buds due to the direct pest damage results in an approximate loss in revenue of $56.00 per acre from an artichoke field with an average annual yield of 450 cartons per acre.

In order to minimize the use of insecticides, other control methods such as biological control, use of sex pheromone in mating disruption and mass trapping were studied between 1980 and 1995. Goh (1980) reported several naturally occurring predators and parasites associated with APM among which the brown lacewing, Hemrobius pacificus Banks was most abundant. However, these general predators and parasitoids were found to be ineffective in suppressing APM population. Interestingly, these authors did not observe parasitism of the egg stage in the insecticide stress free fields of artichokes. Bari (unpublished) routinely found APM eggs collected from various thistles (Circium spp.) on the Northern coast parasitized by Trichogramma. Bari and Kaya (1984) studied the efficacy of the entomogenous nematode, Neoplectana carpocapase and the bacterium Bt (Bacillus thuringiensis) in the field. Of the two biological control agents, the entomogenous nematode was found to be highly effective at dosage rate of 1,000 to 2,000 nematodes per ml of spray whereas Bt was less effective than most of the commonly used insecticides. In later studies, the entomogenous nematode was also found to be highly effective in the disinfestation of worm-infested artichoke crowns used for replanting artichoke fields (Bari 1985, unpublished)

The isolation and identification of the female sex pheromone of APM as Z-11-Hexadecenal (Klune et al., 1981) presented additional options for the control of this pest. The use of pheromone-baited traps to capture adult males was extensively used to document flight phenology. These data in conjunction with the use of temperature based developmental phenology model have been helpful in making timely applications of insecticides (Ryder et al., 1983). In addition, the technique of mass trapping of adult males integrated with chemical control showed considerable potential (Ryder et al., 1983). Using the sex pheromone for mating disruption was also attempted in 1980s and 1990s. Several studies conducted in 1980s suggested that this technique applied alone for the suppression of APM without the use of insecticide was not only economically unacceptable but it was totally inefficient (Bari, unpublished). On the other hand, a large-scale 4-year study from 1991-1995 on the efficacy of the mating disruption technique integrated with chemical control indicated a gradual and significant decrease of APM infestation with a 25% reduction in the annual insecticide use (Bari, unpublished). In this strategy, rope dispensers (APM-Rope® - Shin Etsu Chemical Co.) were applied at the rate 400 ropes (28 gram of actual pheromone) per acre in the third week of July prior to the emergence of the spring generation. Insecticide was used only when the shoot infestation in weekly observations reached the treatment threshold of 2%.

Despite the demonstrable successes toward APM control with entomopathogenic nematode and pheromone-based mass trapping and mating disruption, these techniques did not gain acceptance among the artichoke growers of the central coast. This was mainly because of the significantly high cost of these techniques and/or they were more labor intensive as compared to the conventional chemical control.

Artichoke growers with smaller farm size on the northern-central coast (Santa Cruz, San Mateo counties) and San Benito county face farming problems that are quite different form those of the central coast. Among the various factors that affect their farming system, the most important ones besides APM are the poor soil fertility, shortage and high salinity of irrigation water, infestations of vertebrate pests such as rodents, rabbits, deer etc. (personal communication with Tim Hudson). Consequently, the average yield of marketable artichoke buds from these farms is significantly low (>100 cartons/acre as compared to an average of 450 cartons on the central coast). Because of the low cash flow resulting from such poor yields these farmers have little incentive to use any APM management program requiring a major capital investment. It is estimated that for the northern central artichoke growers the contracted cost of one insecticidal spray aimed at APM is approximately $ 40.00 per acre and several applications would be needed to achieve optimum control of this persistent pest. Under current situation, the secondary pests such as aphids, leaf miners, lygus bug, and proba bug do not pose a threat to these growers perhaps due to the high activity of naturally occurring predators and parasitoids. Any implementation of chemical control against APM would disrupt this delicate balance resulting in increased losses due to these secondary pests as experienced by the farmers on the central coast.

These factors suggest that the northern central coast farmers need a pest management system that would allow sustainability while being moderately effective and easy to implement. One promising technique for achieving this goal seems to be the mass trapping of APM adult males employing the sex pheromone. In several field studies it was demonstrated that this technique integrated with chemical control was very effective in suppressing APM infestation in artichoke fields under the central coast farming conditions (Bari, unpublished). By using 4 pheromone-baited traps per acre installed in a grid throughout the artichoke field, this technique allowed a 50 percent reduction in the insecticide use while managing the pest infestation at acceptable levels of 3-5%. Consep Inc. using the Z-11-Hexadecenal formulated the experimental lure used in these studies. The lure in the traps was renewed every month during the period of high activity of APM lasting from May through November. The fields were treated with chemical insecticides when the infestation exceeded 3 percent.

The Consep lure never became commercially available due to lack of market. However, several other types of APM pheromone dispensers have been available for field monitoring and mating disruption that could also be used for the mass trapping. Consep Inc. is once again developing pheromone lures for several crop pests including APM.

In this field study we evaluated the comparative attractiveness to APM adult males of various experimental lures developed by Consep (Biolure), Shin Etsu (APM-Rope) dispenser, and Trece (Trece lure). After initial evaluation and determination of the most effective lure, we evaluated the efficacy of mass trapping technique in suppressing the AMP infestation on the north central coast.

The objectives from the original proposal submitted by Sean Swezey (The project Advisor to this study) were changed to new objectives 1-3 (given below) for the following reasons.

The egg parasitoid, Trichogramma thalense is not available commercially for inundative releases. The egg parasites released in the BIORAPP fields in the previous years of this project were reared at the university facility (CASFS Insectary) under the supervision of Sean Swezey. This source of the parasitoid was no longer available after his departure from the program. Similarly, APM-Rope dispensers used for mating disruption in the Biointensive fields were no longer available locally. We could not meet the minimum order necessary to purchase the product from overseas.

Even if the egg parasitoid, Trichogramma thalense and the APM-Rope were commercially available, the estimated cost of $800.00/acre for trichogramma and $80.00/acre for APM Rope (Swezey, 1999) would be prohibitively high and beyond sustainability for the artichoke growers.

Objectives

The major goal of this study was to design and demonstrate a grower -managed Biorational pest management program in selected artichoke production sites in coastal Monterey, Santa Cruz, and San Mateo counties, in farmer led, participatory management setting.

Specific Objectives:

Evaluation of the comparative efficacy of various types of pheromone lures for trapping APM adult males in baited traps.
Evaluate the efficacy of mass trapping techniques by using the most effective trap and pheromone lure available locally for APM control by monitoring levels of pest damage in program and matched non-program controls.
Evaluate the potential economic feasibility of adopting the mass trapping technique into the existing artichoke production system.

Accomplishments

Plume moth larva tunneling in the leaf petiole of artichoke

Keeping the initial goal [Establish on-farm evaluation of a biorational grower managed pest management program (BIORAPP) on artichoke production systems on the north central coast via the organization of a grower-researcher management team] intact, we met with the project cooperators in January 2000 and discussed various aspects of the project. Coastways Ranch farmed by Tim Hudson was selected to carry out the mass trapping studies. In subsequent visits with Tim Hudson we scouted the artichoke fields at Coastways Ranch to determine the APM infestation levels, which were found to be in excess of 40% with immense overlapping of all stages of the pest. After assessing his financial situation and to salvage the upcoming winter production, we advised the grower to treat his artichoke fields with one insecticide spray (Asana/Dimilin tank-mix) and consider implementing the mass trapping program in the fall of 2000. To meet our new objectives, we enrolled Dale Huss, Production Manager, Sea Mist Farms, in Monterey County. This allowed us to conduct pheromone lure evaluation trails before the commencement of mass trapping as a pest management tool on Coastways Ranch.

Objective 1. Evaluation of the comparative efficacy of various types of pheromone lures for trapping APM adult males in baited traps.

Trial 1. During January-March 2000, we evaluated Biolure, series A through E supplied by Concep Inc. all containing the APM pheromone Z-11 Hexadecenal for their efficacy in attracting APM adult males to the water-oil trap (ARA trap) developed by the Artichoke Research Association. Besides being highly effective in attracting the APM adult males, this type of trap was found to be durable, least expensive, and easy to assemble from locally available materials (Bari, unpublished). The traps were deployed at 300 ft spacing along the borders of artichoke fields at Molera Ranch (Sea Mist Farms, Castroville). One piece of each of the 5 test-lures was installed in each trap. A trap without a lure was used as control. Each lure type and the control were replicated 4 times in four different artichoke fields at the ranch. Trap catches of moths were counted at 3-4 day intervals. After each observation the lures were randomly moved to new positions within each replication. The lures were renewed three times at the 2- wk interval (Sub Trial 1-3) by installing a fresh lure in place of the old one. The trap data presented in Figs. 1-2 indicated that of the 5 test lures, Biolure E attracted significantly higher number of moths. However, this lure maintained its attraction for less than 10 days only.

Trial 2. To make the lure stable and last longer, Consep made several changes to the pheromone emission system and provided a new series of lures, Biolure F - H. In March-May 2000, we compared this series with the rubber septa type of lure made by Trece® (Trece lure). This trial was also conducted at Molera Ranch following the same experimental procedures outlined in Trial 1 with one exception. The lure in the traps was not changed during the entire period of the study.

Data presented in Fig. 2 suggested that the lures in the series Biolure F-H were also ineffective in attracting APM adult to the traps. However, Trece lure was significantly more attractive as the traps baited with this lure captured more than 5 moths per trap per night at the peak activity of the APM adults. From these data it also became evident that this lure was highly stable as it maintained its attractiveness for more than two months.

Mass Trapping Efficacy of Trece Lure:

Artichoke plume moth mass trapping

Trial 3. This trial was carried out at Neilsen Ranch, Seamist Farm, Castroville in July/August 2000 to test the mass trapping efficacy of Trece lure and APM-rope. The Trece lure comprising of red rubber septum containing 5 mg ai of the pheromone was determined to release 22.5µg per day at 20 degree C for a half-life of 222 days in a control laboratory study (McDonough, 1991). On the other hand, the pheromone emission rate from rope dispenser comprising of a 7.5-inch plastic tube containing 68 mg of the pheromone was estimated to be 290µg/day for up to 100 days of exposure to field conditions (Bari, unpublished). Each of the two lure types were installed in two separate sets of 16 ARA traps deployed in a grid with 4 rows of 4 traps each, centered at 100X100 ft spacing (=4.3 trap/acre). The two sets of traps were separated by a distance of 1000-ft and were positioned in the center of a 40-acre artichoke field. Trap catches in each of the 16 traps of each set were counted twice a week. After each reading, the lures from one set were moved to the other to account for local variation in APM density.

Data presented in Table 1 indicated that despite its very high pheromone emission rate, APM-Rope trapped an average of 1.1 moths/trap/night over the period of 17 days, which was not significantly different from the Trece lure trapping 1.2 moths/trap/night. However, the examination of individual trap catches in each set revealed that the inner 4 traps from the set baited with APM-Rope caught significantly fewer moths (0.16 moths/trap/night) than the Trece lure baited traps at the similar positions (1.05 moths/trap/night). The ratios of mean number of moths trapped in the 12 outer traps to the mean of the 4 inner traps for APM -Rope and Trece lure were 8.1:1.0 and 1.2:1.0 respectively. These values suggested that with the Trece lure, the catches were evenly distributed for all the traps with in the set irrespective of their position in the grid. Whereas, with APM-Rope, the inner 4 traps caught significantly fewer moths as compared to the outer traps in the 16-trap grid. There are two possible reasons for this observed distribution pattern of catches with APM-Rope baited traps. 1) Because of the high emission rate of APM-Rope, the individual traps were competing with each other and the adult males kept flying up wind following the pheromone trail until they reached the outer most traps of the grid. 2) The high emission rate of APM-Rope resulted in its higher concentration toward the center of the grid than near the borders that could cause sensory fatigue in male moths present near the center making them unable to orient to the traps.

To maximize the mass trapping efficacy, presumably there should be least competition among the individual traps so that the male moths orient to the nearest trap as soon as they become sexually active not becoming sexually fatigued due to the over dose of the pheromone. From the above results, Trece lure appeared to be more effective in accomplishing this purpose than APM-Rope.

Objective 2. Apply and monitor critical components of the management program, including mass trapping of APM adult males; monitoring pest abundance through trapping of male adults in the pheromone traps; and monitoring APM damage in program and matched non-program controls.

To achieve this objective, the experiment fields were selected on the Costways Ranch, Lots 1-4 (Fig. 3-Field Map). A replicated complete block design with two management system treatments, viz. Conventional (Lots 1-2) and BIORAPP (Lots 3-4) were established. Production practices, with the exception APM control methods, were same for both management systems. The observed period lasted from August 1, 2000 to August 24, 2001, with the harvest season occurring from September to April.

In the conventional (control) fields no attempts were made to control APM. In the BIORAPP fields mass trapping of APM adult males was initiated on October 1, 00 by installing the ARA traps. The grower under the supervision of the researchers accomplished traps' construction and their deployment in the field. Installing traps at 100 X 100-ft spacing achieved the density of 4.3 traps per acre. Trece lure (red rubber septa, each loaded with 5 mg of APM pheromone, Z-11-Hexadecenal) was used in the traps. The lures were renewed at 6-8 week interval. Adults moths caught in the traps were counted at regular intervals. At this time the traps were serviced by replenishing water and oil. APM infestation in the vegetative shoots was assessed at regular intervals by examining 100 shoots (four replications of 25 shoot each) per field. Levels of bud infestation were also determined at regular interval. However, because of severe rodent and deer damage to artichoke plants in Lots 1-3, most of the bud infestation data were collected from Lot 4 (BIORAPP) only. Nevertheless, the trend of shoot infestation in itself is considered a valid indicator of success or failure of a pest management program as it is generally directly correlated with bud infestation.

Figure 4 illustrates the overall frequency of infestation of vegetative shoots by APM larvae in the Control fields (Lots 1-2) and BBIORAPP fields (Lots 3-4). The seasonal mean shoot infestation in the BIORAPP fields Lot 3 and Lot 4 was 3.85±0.96 (SE) and 1.81±0.45 (SE) percent respectively. In Lot 1 and Lot 2 of the control fields it was 7.4±1.3 (SE) and 19.88±3.33 (SE) respectively. These differences in shoot infestation in the control and BIORAPP fields are significant. With the exception of the BIORAPP field Lot 4, all other fields had very low bud production mainly because of deer damage. The mean level of bud infestation recorded in this field during the peak production period from February to April was 6.0 percent. In a meeting held on March 19, 01 with the management team, the grower and the pest control advisor expressed their satisfaction with the above infestation levels in the BIORAPP fields.

After the releases of T. thalense in the previous season, egg parasitization was not detected during the period August 1, 00 to August 31, 2001 indicating that trichogramma did not perpetuate after their several releases in the previous seasons. The brown lacewing remained the most common generalist predator in all fields. However, it did not seem to exert any economic control of APM as also suggested by Goh and Lange (1980).

Objective 3: Evaluate the economic feasibility of field monitoring, and mass trapping of APM into the existing artichoke production procedures.

The BIORAPP production system evaluated in this study suggested that the biorational technique of mass trapping APM can contribute to the suppression of the pest damage at an acceptable level for the North Coast artichoke farmers with small farm sizes and lower crop yields. As a first step toward determining whether the BIORAPP techniques utilized in this project could become economically viable production system, we estimated the cost of the mass trapping technique employed in the above study. From the previous studies, the weekly field monitoring cost was estimated to be $20.00 per acre (Swezey, 1999). Total costs for assembling the ARA traps (parts and labor) for mass trapping on a 5-acre field was estimated to be $100.00. Depreciated over the 5-year, the total hardware cost was estimated at $20.00 per year. The recurring costs included the cost of the lure renewed 7 times during one growing season (22 traps x 7 x $2.00/lure), miscellaneous costs (oil, plastic cups, siphon, pins etc. at $5.00 per season) and trap maintenance cost ($25.00/season) making it a total of $358.00 per year ($71.60/acre). This low cost of the biorational, grower-managed mass trapping technique indicated that while being effective this technique is economically viable and totally in the realm of growers' sustainability. Apparently, the cost of APM-Rope dispenser is considerably low ($0.25/dispenser) as compared to the Trece lure, its high pheromone emission rate makes it less effective in the mass trapping technique as indicated by the results of field trials of this study. Further, this lure is not available locally and to import it, minimum order of several thousand dispensers must be met.

Future Workplan

The interim one-year goals of this project have been successfully accomplished. A 12-month insecticide free period was achieved in the BIORAPP fields (August 2000-August 2001) with acceptable levels of APM infestation. In the control fields, which were also insecticide stress free, the pest infestation was significantly high.

It is highly desirable to apply this grower managed biorational pest management system to the entire Coastways Ranch and other adjoining small farms including the only organic artichoke field at Swanton Ranch. It appears that the ARA traps employed in this study were not compatible with organic culture because of the petroleum-based oil used in the traps. Studies could be made to find out if there are other effective alternatives to the petroleum based oil that would be compatible with the organic production system. Vegetable oils used in previous studies were found to lower the trap efficacy because of their rapid deterioration (Bari, unpublished). Use of Sticky traps is a viable alternative.

Summary

Several types of commercially available pheromone lure containing the artichoke plume moth (Platyptilia carduidactyla) pheromone, Z-11-Hexadecenal were evaluated for their relative efficacy in trapping maximum number of APM male adults into water-oil traps during 1999-2000. Mass trapping of artichoke plume moth using four traps per acre baited with Trece lure was attempted in two out of four 5-acre artichoke fields on the northern Santa Cruz/San Mateo County coast. This grower-managed BIORAPP was used from October 2000 to August 2001. The efficacy of the program was measured by monitoring plume moth infestation by a pest management team consisting of one grower and the researchers from the Artichoke Research Association.

The impact of mass trapping of the male adults on the pest suppression was measured by recording infestation level of APM larvae in the vegetative shoots at regular intervals. These shoot infestation data were compared with those recorded in control fields where no plume moth control of any sort was attempted. Because of severe crop damage resulting from the infestation of the vertebrate pests (mainly deer, meadow mouse, and gopher), bud infestation data could be collected only from one of the two BIORAPP fields from February, 2001-April 2001. The bud infestation levels recorded during the peak production period were quite acceptable to the grower.

Estimated costs for installing and maintaining the pheromone traps for mass trapping are presented in this report.

References

Bari, M. A., and W. H. Lange, 1980. Influence of the temperature on the development, fecundity, and longevity of the artichoke plume moth. Environ. Entomol. 9: 673-676.

Bari, M. A., and H. K. Kaya, 1984. Evaluation of the entomogenous nematode Neoplectana carpocapsae (=Steinernema feltiae) Weiser (Rhabditida: Steinernematidae) and the bacterium Bacillus thuringiensis Berliner var. kurstaki for suppression of the artichoke plume moth (Lepidoptera: Pterophoridae). J. Econ. Entomol. 77: 225-229.

Goh, K. S. and W. H. Lange, 1980. Spatial distribution pattern and sampling plans for immature stages of the artichoke plume moth. J. Econ. Entomol. 73: 113-116.

Goh, K. S. and W. H. Lange, 1980. Life tables for the artichoke plume moth in California. J. Econ. Entomol. 73: 151-158.

Klune, J. A., K. F. Haynes, B. A. Bierl-Leonhardt, M. C. Birch, and J. R. Plimmer. 1981. Sex pheromones of the artichoke plume moth, Platyptilia carduidactyla. Environ. Entomol. 10 (5): 763-765.

Lange, W. H., Jr. 1941. The artichoke plume moth and other pests injurious to the globe artichoke. Calif. Agr. Sta. Bull. 653. 71 pp.

Lange, W. H., Jr. 1950. Biology and systematics of plume moths of the genus Platyptilia in California. Hilgardia 19: 561-668.

McDonough, L. M. 1991. Control release of Insect Sex Pheromone from Natural Rubber Substrate. ACS Symposium Series 449 (Naturally Occurring Pest Bioregulators).

Ryder, E. J., N. E. De Vos, and M. A. Bari. 1983. The globe artichoke (Cynara scolymus) L. HortScience 18: 646-653.

Swezey, S. 1999. A grower-managed biorational pest management program for artichokes on the northern central California coast. Progress Report. University of California, Sustainable Agriculture Research and Education Project.