Development and Implementation of Integrated Pest Management of Burrowing Shrimp on Washington State Commercial Oyster Beds
This project comprised primary activities towards the development of an integrated program to manage two indigenous species of burrowing shrimp on Willapa Bay and Grays Harbor oyster beds. The project comprised three primary objectives, the first of which was completed before 2006.
● Evaluate the efficacy of alternatives to carbaryl-based tactics to suppress burrowing shrimp.
○ Alternative Chemistries and Their Delivery
– Topical (Broadcast) applications Tests on plant extracts, sulfur, neonicotinoids and pyrethroids continued, but only the last two suppressed shrimp to levels below or near the accepted damage threshold of 10 burrows per m2.
– Subsurface (spikewheel) injection from a floating platform
In 2006, a 6′ wide spikewheel apparatus mounted on a pontoon boat was used to inject material subsurface during high water. Although the two techniques were never precisely compared in space and time, the topical treatments were more effective than treatments made using the barge-mounted spikeweels in 3 of 8 comparisons; differences were not significant in the other 5 comparisons. Other potential advantages of subsurface delivery of materials for burrowing shrimp control from a floating platform include: 1) an extended seasonal window for application, 2) less off-bed movement leading to 3) decreased non-target impact. These variables have yet to be tested.
● Write an IPM plan for burrowing shrimp; implement and deliver it to oyster producers….
○ The IPM Plan first written in 2003 was updated and presented in written form and at a spring growers workshop and a fall shellfish conference. Portions of the plan have been adopted into the Environmental Code of Practise for the West Coast Shellfish Industry.
This project supplemented and complemented other related activities, some of which were in place at the project’s inception. A research team with expertise in agricultural engineering, mechanical engineering, mud flat ecology, shellfish culture, and IPM development was assembled to meet the following objectives:
● Derive an economically based action threshold for burrowing shrimp control based on
○ the relationship between burrowing shrimp density and oyster yield (e.g., the damage/density relationship) and
○ an appraisal of the financial cost / benefits of burrowing shrimp control based on grower interviews and surveys.
● Evaluate the efficacy of alternatives to carbaryl-based tactics to suppress burrowing shrimp, such as sub-surface applications of registration-exempt compounds, or the mechanical crushing or shallow rototilling of shrimp burrows, within a tier of experimental designs that progress from small tightly controlled arenas, through larger microcosm studies, to field plot trials.
● Write an IPM plan for burrowing shrimp; implement and deliver it to oyster producers using workshops, newsletters and demonstration trials; to the scientific community using conferences and articles and to the public using a pre-existing website, and adopt the plan into an Environmental Code of Practice for the West Coast shellfish industry.
The first objective was addressed during the first two years of the project. Although more economic analyses are needed and will be accomplished in the near future, the bulk of the 2006 work focused on the second and third objectives.
Tactics designed to crush shrimp and/or their habitat were investigated in 2003 – 2005 and are reported on in the individual reports for those years and in the final report. None of them offered much potential to suppress burrowing shrimp to low enough levels and for sufficient time periods to warrant further consideration. Burrowing shrimp are highly adapted to their fossorial habitat and can apparently withstand large amounts of compaction and remain mobile in highly dense substrates. In related laboratory experiments, burrowing shrimp were able to construct burrows in substrates with levels of densification much higher those found in the field (Weaver 2006). Shrimp could only be crushed at stress levels found at least 1.5 m below the ground surface in association with very high surface loads.
Also in 2003 – 2005, we examined ways to design and use microcosms as experimental arenas for burrowing shrimp research and report on them in individual reports and in the final report.
As previously mentioned, carbaryl was selected as the primary pesticide for burrowing shrimp control in the early 1960s following the assessment of several compounds. Since then, pesticides with novel chemistries have been developed, implemented, and are common throughout most of American agriculture. These include “biorational” compounds with low vertebrate toxicity or compounds that selectively target pests with minimal impact to beneficial or benign organisms. Pyrethrins and pyrethrums are plant extracts with low mammalian toxicity that are certified for organic use. Some “biorational” chemistries are less selective in the marine environment where, for example, insecticides that disrupt the development of chitin in the mandibles of insect pests (e.g., diflubenzeron) would affect all crustaceans, not just burrowing shrimp. Other insect growth regulators (IGRs) like tebufenozide, methoprene, and pyriproxyfen target specific developmental hormones in some insect orders (e.g., moths, beetles or flies) but are less likely to effect only shrimp in an estuary. Compounds that disrupt mating behaviors in some insects by mimicking sex pheromones (e.g., moths) have yet to be isolated and synthesized for burrowing shrimp. Microbial control agents, though gaining importance in terrestrial systems, are less well known in aquatic systems and would be difficult to contain to local beds.
In addition to the class of pesticide, the method of application can affect efficacy, selectivity, ease of use, and cost. The current application method, aerial application using helicopters, is by far the most cost effective and quickest, but is limited to specific application dates as determined by the tides, weather, and the season of salmon migration. Subsurface injection of pesticides is becoming a common technique to directly target subterranean pests with little contamination or exposure to surface organisms (Khalilian et al. 2000, Mann et. al. 1999, Ressler et. al. 1997). The amount and distribution of injected material can be varied according to depth and spacing of the injectors and the speed of the vehicle. Burrowing shrimp that are not directly killed by pesticides may be entombed, stressed, or forced to reconstruct burrows and so contact more pesticide. Subsurface injection may reduce pesticide exposure to surface dwelling non-target organisms and offsite impacts due to drift. Alternative chemistries were applied either to the bed surface using a CO2 powered backpack sprayer or subsurface delivery from land based vehicles or from boats or barges. Water volumes for backpack applications were 10, 20, 30 or 40 gal/ac to approximate the water volume used in the standard applications of Sevin by helicopter (10 gal/ac). Subsurface injections featured much larger water volumes (100 – 400 gal/ac).
All compounds were applied under Washington State Experimental Use Permits issued by WSDA, which limited total acreage applied per year to less than 1.0 ac for some compounds and less than 0.1 ac for others. Plot sizes were therefore frequently small (i.e., 10×10m, 10×30m, 30×30m) and minimally replicated (3 or 4 plots per application).
Trials featureing 25b list and other eaily registered compounds were conducted during the first two years of the project and are presented in the final report. Here we report on materials and applicatin methods investigated during 2006.
Pyrethroids, Pyrethrums, and IGRs
These compounds, applied by broadcast, were compared to one another and the standard material, carbaryl (Sevin) in a single large plot in 2006. Results were very similar at both 13 and 102 days after treatment. Carbaryl was among the most effective, even at the relatively very low application rate of 2 lb a.i. per ac. Aside from Deltaguard (Bayer Corp.), the pyrethroids were also quite effective, especially Mustang (FMC). The pyrethrin compound, (Pyganic; MGK), was somewhat effective compared to the untreated check, especially at the higher rate, but number of burrows remained above 10 per ac. Pyrethrum (Evergreen; MGK) showed greater efficacy at 102 compared to 13 DAT, but also failed to pass the 10 burrow/ac threshold. The IGR, pyriproxyfen (Esteem; Valent) was ineffective. An ancillary trial showed the pyrethrin Pyganic to be intermediate in efficacy compared to carbaryl at 60 days after treatment.
Trials in 2003 also included the neonicotinoid, acetamiprid (Assail®; Cerexagri, Inc) in comparison with the standard carbaryl (Sevin 80WP®) and an untreated check. Assail was generally ineffective in these trials. However, the 2004 broadcast trials showed the neonicotinoid, clothiniadin (Poncho®; Bayer Corp.), to be more effective than carbaryl, although the latter was applied at less than the standard rate (8 lb a.i./ac).
Both Cerexagri and Bayer indicated that they were not willing to participate in a registration process for their products’ use on Washington state commercial shellfish grounds, but the patent for the neonicotinoid imidacloprid (Admire, Pravado; Bayer Corp.) was scheduled to expire in 2006, so trials were initiated for that material with generally acceptable results. Imidacloprid was effective at a range of rates.
Several adjuvants were compared for the ability to increase the efficacy of carbaryl, but had little affect. A trial conducted in 2006 showed that the adjuvant, Sinker®, slightly but not significantly enhanced efficacy of carbaryl.
Results of another trial conducted in 2006 were more encouraging. Burrow densities were lower in plots treated with Pyganic in combination with Li700 than in plots treated with Pyganic alone, but the difference was not significant (t-test; P = 0.05).
In 2006, the spikewheel apparatus was carried on a 10×16′ pontoon raft. A 16′ aluminum boat equipped with a 40 hp outboard engine pushed rather than pulled the raft over the bed, to minimize effects of the engine’s propellor. The spikewheels were mounted on a bracket that could be raised or lowered to a maximum depth of 12′ using a hand powered winch. The bracket initially carried 6 spikewheels, but after the first few trials, the number was reduced to 4, each spaced 19″ apart, to treat a 6′ wide strip. The spikewheels were mounted and rotated independently from each other, but calibration tests showed that they remained well synchronized. Another, non-spiked drive wheel placed in front the Spikewheels rotated at the same speed and regulated injection timing via a chain-drive belt connected to a roller pump, which pumped material through the injector-spikes precisely when they reached the bottom of each spikewheel revolution; speed did not influence the amount of material injected. The pump delivered 48 gal/acre at a line pressure of 15 psi with the boat motor running 2900 rpm and land speed was 1.8 mph. Material was delivered to the pump from one of two 50 gal plastic tanks via a manually operated “Y” valve. Each spikewheel held 12 4″ long spikes. As in the land-based system, material was injected through a pore ⅛” in diameter located on the right side of the spike just above the tip. Preliminary tests using dyes, as well as observation using scuba, showed that material was injected to a depth of ~7″.
Most treatment plots in 2006 comprised one or more 6×150′ strips (900 ft2 ≡ 1 gal material). Strip borders were marked by PVC pipes as visual cues for alignment during applications at high water. Injectors were checked prior to each trial and two calibration passes were made using water as material on areas next to the target strip. Plots were not treated when wave height was more than 2′ or wind gusted more than 15 mph. Applications were made on both in-coming and out-going tides, but only in the direction of the tidal current; not cross-current. The spikewheel assembly was lowered as the barge crossed the beginning of the strip, causing the drive wheel to contact the substrate and engage the pump. The assembly and drive wheel was lifted as the barge crossed the end of the strip, disengaging the pump and halting injection. Treatments were checked for uniformity on the next day’s low tide by examining the spikewheel paths in the sand. Efficacy was assessed at one or more post application intervals by counting the number of shrimp burrows. Results were analyzed using analysis of variance or t-tests when appropriate. In some instances, results from trials involving separate application dates were compared by computing each treatment’s percentage (proportion) of the untreated check. Percentages were transformed to the arcsin for statistical analysis.
Preliminary trials with carbaryl
Carbaryl (Sevin 80SP) was used in preliminary trials to both test the operation of of the floating barge / spikewheel system and to provide comparisons for other alternative materials. Burrow density was significantly lower in all carbaryl treated plots than in untreated plots at both 6 and 49 days after treatment, but were either higher in the treated than in the untreated plots at 20 and 256 days after treatment. The lack of significant differences among treatments at the longest interval was likely due to shrimp moving into the narrow (6′ wide) plots as well as poor long-term efficacy.
Elemental sulfur (Kumulus 80DF, Microflo Co.) was tested in 3 separate trials. Results of each trial were assessed at different post application intervals and compared to appropriate untreated check. In most cases, burrow density was significantly lower in plots treated with sulfur than in untreated checks, but burrow density remained above 10 per m2.
Efficacy of different rates of habanjero extract were poor to moderate, whether injected with oil or water, but plots were examined at only 4 days after treatment; efficacy might have been greater at a longer post application interval. Extracts of lilly (Veratran®) and powdered chrysanthemums (Ecozone®) also showed moderate to poor efficacy at 17 days after treatment.
Efficacy of pyrethrins (Pyganic®) varied among trials. In a trial where burrow densities were initially low, pyrethrins showed excellent efficacy (burrow density was reduced to nearly 10 per m2) at 6 days after treatment (Table 26). Overall burrow density was higher in another trial conducted 10 days later. Burrow density was lower in plots treated with Pyganic compared to untreated plots, densities were ultimately substantially higher than 10 burrows per m2.
The insect juvenile hormone analogue (JHA) methoprene showed moderate efficacy at 13 days after treatment, but burrow counts at longer post application intervals were substantially higher.
Three pyrethroids were applied in 3 separate trials: 1) Belay®, 2) Mustang® at 0.01 lb a.i./ac, and 3) Mustang at 0.005 lb a.i./ac and Capture® at 0.01 lb a.i./ac. The separate applications complicated direct comparison, but most treatments were moderately effective, judging by comparisons between each treatment and its appropriate untreated control plot. Surprisingly, the higher rate of Mustang was less effective than the lower rate.
The neonicotinoid pesticide, imidacloprid (Admire®; Bayer Corp.), was tested multiple times at various rates and locations. Usually, efficacy of imidacloprid was greater (final burrow density was lower) at higher rates, but the response was not always linear. At a test area near Nahcotta, where substrates were primarily sandy, burrow density were substantially, if not significantly, higher at rates less than 0.2 lb a.i./ac. This was especially true at longer post application intervals (e.g., 42 or 50 days after treatment). Efficacy was not necessarily greater in plots treated with imidacloprid at rates greater than 0.2 lb a.i./ac. Burrow density was also significantly lower in plots treated with 2.0 lb a.i./ac imidacloprid than in plots treated with 3.0 lb a.i./ac carbaryl.
Results of a trial conducted on sandy/silty substrates were confounded somewhat by heavy growths of eel grass (primarily invasive Zostera japonica, but also Z. marinera), which slowed tidal drainage, left standing water on the bed, and obscured burrow counts.
Another trial, conducted at the Willapa Bay Fish and Wildlife Refuge, featured applications of imidacloprid (0.2 lb a.i./ac) on four different types of substrate. Burrows were counted in four 1 m2 quadrants within and in a single 1 m2 plot adjacent to each treatment plot. Shrimp burrow density was significantly lower in all treated compared to untreated plots ( ± SE, 52.2 ± 15.7 burrows/m2; LSD, P=0.05), but was significantly higher in a plot of silty hummocks than in plots of other substrate types.
Theoretically, pesticides could be injected to greater depths and with more precision using a harrow than a spikewheel. In 2005, McGregor Company (Pasco, WA) designed, with the help of Jim Durfey, and constructed a large iron harrow with skids that could be adjusted to different lengths. Pressured lines secured to the back of each of six curved tines (12″ apart) delivered material to injectors. Unfortunately, the unit was so heavy that it was difficult to pull. It also was difficult to keep level while harrowing. It easily became entangled in eel grass and other immovable objects. The unit was modified in 2006 by removing the skids, allowing the tines to better settle into the substrate. Still, the unit could not be adequately controlled.
Also in 2006, J. Durfey and McGregor Co. designed and constructed a much lighter flexi-coil spring harrow equipped with 18 straight tines arranged in a 4×4 ft square. The leading row (6 tines) carried material through pressurized lines to injector ports located near the bottom of each tine (Figure 30). The model proved too light and merely skimmed the surface. The addition of weights (Figure 31) allowed suitable penetration.
Results of trials using the flexi-coil spring harrow were generally satisfactory (Figure 32), but the system was still difficult to operate and the amount of material delivered was difficult to control.
A preliminary framework for the development of “A comprehensive plan towards the development of an integrated program for burrowing shrimp management on commercial oyster beds” was submitted to Washington Department of Ecology in March 2003 and was updated to much greater detail in 2007. The plan included sections on 1) IPM Definitions & Concepts, 2) IPM Plan Goals, 3) Principle Authorities, 4) Principle Policies, 5) IPM Elements (Funding, Research & Development, Implementation, and Evaluation / Regulatory Compliance) and 6) References (Appendix A). The Research & Development component of the plan was enhanced substantially in 2004 through the influx of a special Washington State proviso of $200,000 per year. The 2007 Plan also includes a detailed summary of all research projects completed since 2003.
The IPM Plan, as well as all other progress reported here, was presented at a spring grower workshop held in Long Beach, WA and at the Annual Pacific Coast Shellfish Growers Association / National Shellfish Association Conference held in the fall in Vancouver, WA. Fewer growers, but more scientists, including those from outside the Pacific Northwest, attended a special Burrowing Shrimp session. The session usually included wide ranging discussions of research progress and priorities.
The IPM Plan is referenced in the West Coast Shellfish Research and Education 2015 Goals and Priorities as Goal 5.1 (Pacific Shellfish Institute, 2006). The Plan is briefly described as part of the rationale to manage burrowing shrimp and the major elements of the plan are listed as high priority goals. The IPM Plan is also currently included in the upcoming revision of the Pacific Coast Shellfish Growers’ Association Environmental Codes of Practice.
Impacts and Contributions/Outcomes
Several alternatives to aerial applications of carbaryl were evaluated. Mechanical techniques to crush burrowing shrimp proved not to be feasible. Efficacy of alternative compounds ranged from highly ineffective (e.g., those on the 25b list) to highly effective (neonicotinoids and pyrethroids). Most effective compounds are not candidates for registration due to concerns regarding non-target effects or lack of corporate support. Imidacloprid, recently released from patent, could be registered given the support of another producer and if it were to meet federal and state requirements. Although sub-surface delivery of alternative compounds does not appear to greatly improve efficacy, it may reduce off-site movement and thus help lower non-target impacts. These hypotheses have yet to be tested.
The IPM plan developed in association with these WSARE funds has become an important informational document. Although specific steps towards an integrated plan still depend on research results, the general pathway is more apparent than it was three years ago. The document itself, like this one, is comprehensive, detailed, and targets the scientific and academic audience. The associated newsletters and workshops both informed the shellfish farmers themselves and also increased program visibility. All these efforts ultimately helped fund other grants and initiatives.
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