Final Report for GS05-045

Project Type: Graduate Student
Funds awarded in 2005: $9,914.00
Projected End Date: 12/31/2006
Grant Recipient: University of Florida
Region: Southern
State: Florida
Graduate Student:
Major Professor:
Dr. Oscar Liburd
University of Florida
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Project Information

Summary:

Successful management of flower thrips in commercial blueberry plantings is determined by efficient monitoring systems and timely use of control methods. Massive releases of natural enemies as preventive or curative methods did not significantly reduce the population of flower thrips. In the evaluation of reduced risk insecticides, we found that Spinosad was the least toxic insecticide towards Orius insidiosus. However, in field studies, Spinosad was not significantly different to other treatments evaluated for control of thrips. Acetamiprid consistently reduced thrips population in field and laboratory studies but also significantly reduced the number of O. insidiosus in laboratory assays.

Introduction

Florida and southern Georgia are the only producers of early-season blueberries (April to May) in the United States, and consequently have a big advantage compared with markets from northern states. Early-season blueberries have prices that can be five to six times higher than regular season blueberries. For instance, although Florida represented only 1.18% of the national production of fresh blueberries for 2003, it collected 8.24% of the money produced from blueberries in the nation. In Florida, the total acreage has increased 21% since 2001 and the overall revenue has increased by almost 6 million dollars in the same period. (NASS and USDA 2004).
One of the key pests reported on blueberries is flower thrips from the genus Frankliniella. The main species that are repeatedly reported in Florida and southern Georgia are F. bispinosa and F. tritici. In 2003, USDA et al. reported that 40% of the losses in blueberries in Georgia were attributed to flower thrips. Two other species of flower thrips have been reported in blueberries throughout Florida and Southern Georgia. These species are F. occidentalis and F. tritici (Finn 2003). Thrips populations are known to move rapidly into blueberry fields with the help of wind currents and workers. Their life cycles are extremely short, taking only 15 days if environmental conditions are conducive for their growth and development. Their short lifecycles as well as their overlapping generations during the blueberry flowering cycle make this insect a dangerous pest that can reach economic damage levels in a very short period of time.

Project Objectives:
  • To evaluate the interaction between O. insidiosus and A. cucumeris as an alternative to pesticides in maintaining reduced populations of flower-thrips

    To evaluate reduced-risk insecticides and their interaction with Orius sp. (Heteroptera: Anthocoridae) and A. cucumeris, natural enemies of flower thrips

    To compare the effectiveness of reduced-risk insecticides with conventional insecticides for controlling flower-thrips

    To collaborate with growers, extension agents and agricultural consultants to generate and distribute new information on thrips control for early-season blueberries
    available below.

Cooperators

Click linked name(s) to expand

Research

Materials and methods:

To evaluate the interaction between O. insidiosus and A. cucumeris as an alternative to pesticides in maintaining reduced populations of flower-thrips

We used a completely randomized block design with 5 replicates and 4 treatments to investigate the effectiveness of O. insidiosus and A. cucumeris as alternative to pesticides. The study site was located at a grower’s commercial farm in north central Florida. Treatments included: 1) a plot treated with Amblyseius cucumeris alone 2) a plot with Orius insidiosus alone, 3) a treatment with the combination of both biocontrol agents, and 4) untreated control. During our first year of research, the biocontrol agents were released as a preventative tactic ~ one week before the thrips were scheduled to arrive (based on crop phenology and degree days). During the second year, biocontrol agents were released as curative agents ~ one week after thrips were detected on white sticky traps placed within the canopy of the blueberry bushes. To reduce the risk of cross contamination a reduced risk insecticide, SpinTor 2SC ([spinosad] Dow AgroScience) applied at 6 oz/acre was applied in the buffer zones between plots every two weeks. Weekly samples were taken from 5 flower clusters selected randomly in the middle of each plot, as well as white sticky traps hung within bushes. The number of thrips were counted and compared over time to evaluate differences between the treatments.

To evaluate reduced-risk insecticides and their interaction with Orius sp. (Heteroptera: Anthocoridae) and A. cucumeris, natural enemies of flower thrips

Laboratory bioassays were conducted at the University of Florida, Small Fruit and Vegetable IPM laboratory to measure the toxicity of a conventional (Malathion) and 3 reduced-risk insecticides to common thrips predators (Orius sp.). These insecticides were tested at the dosages recommended by the manufacturers: Actara 25WG (thiamethoxam) at 78.80 g a.i. / ha, Assail 70WP (acetamiprid) at 112.77g a.i. / ha, Malathion 5EC (malathion) 139.8 g a.i/ ha, and SpinTor 2SC (spinosad) 105 g a.i. / ha, and an untreated control.
Natural enemies were exposed to insecticide concentrations equivalent to those in commercial blueberry operations. Ten O. insidiosus were placed in a bioassay arena that contained insecticide-treated green beans. Beans were treated using a hand-sprayer and allowed to air dry for 2 hours. The chamber was then covered with a non-thrips mesh to allow gas interchange. Data were taken at 1, 10, 12, 15, 20, and 24 hour after the release of the insects in the arenas. Data were analyzed using the one-way-ANOVA, and Least Square Difference (LSD) to establish differences among each one of the treatments

To compare the effectiveness of reduced-risk insecticides with conventional insecticides for controlling flower-thrips

Field experiments to compare reduced-risk and conventional insecticides were conducted at two commercial blueberry farms located in southern and north-central Florida, respectively.
In 2005, the trial was located in southern Florida at a highbush low-density blueberry planting. Treatments were sprayed using an airblast sprayer at manufacturer’s recommended dosages (as described above). The treatments included Malathion 5 EC at 139.8 g a.i. / ha, SpinTor 2SC (spinosad) 105 g a.i. / ha, Assail 30SG (used as TD 2480 acetamiprid- experimental insecticide) 5.4 oz/acre, Assail 70WP (acetamiprid) 112.77 g / ha, Diamond .83EC (novaluron) 145.35 g / ha, Actara 25WG (thiamethoxam) 78.80 g / ha. Treatments were applied in plots of 471 m2 with 9 m of buffer zone between treatments and 41 m between blocks of 7 treatments. Each treatment had four replicates.

In 2006, the trial was located at a southern highbush planting in north-central Florida. Treatments were during the 2006 flowering season using a CO2 sprayer calibrated at 23 PSI and using a Teejet hollow cone spray core D3 disk DC 25 (Spraying systems Co. Keystone Heights, FL). The experimental design was completely randomized extended block with four replicates per treatment. Each plot covered 219.46 m2 and buffers between treatments were 30.4 m long with 4 m between rows. The treatments included: Malathion 5 EC at 139.8 g a.i. / ha, SpinTor 2SC (spinosad) 105 g a.i. / ha, Diamond .83EC (novaluron) 145.35 g / ha, Assail 30 SG (acetamiprid) 113.48 g / ha, Actara 25WG (thiamethoxam) 78.80 g / ha, Coragen 20SC (rynaxpyr formally known as DPX-E2Y45) 98.63 g / ha, and an untreated control.
To collaborate with growers, extension agents and agricultural consultants to generate and distribute new information on thrips control for early-season blueberries
All of the trials and experiments were conducted with the assistance of blueberry growers and producers that were involved with the project. Our demonstration plots were established where other growers were able to visit and observe first hand the various monitoring and control techniques being evaluated. In addition, the results from our studies were presented at growers meetings at the Florida Blueberry fall meeting (2005) in Bartow, FL., and the spring meeting (2006) in Plant City, FL., the Southeast blueberry meeting (2006) in Savannah, GA., the annual vegetable meeting (2006) in Atlantic City. NJ. At the same time, we participated in state and national scientific meetings such as the Florida Entomological Society in 2005 and 2006, and the Entomological Society of America in 2005.

Research results and discussion:

To evaluate the interaction between O. insidiosus and A. cucumeris as an alternative to pesticides in maintaining reduced populations of flower-thrips

During 2005, the releases of O. insidiosus or A. cucumeris, as well as the combination of both treatments as a preventive tactic did not reduce thrips populations in blueberries during the flowering period. In 2006 when curative releases of O. insidiosus, A. cucumeris, and the combination treatment of both natural enemies were conducted, we found no significant differences between the treatments of natural enemies and the control in the number of thrips caught on the sticky traps or inside the flowers. Our work indicates that inundative biological control using O. insidiosus and A. cucumeri and combination treatments (as discussed above) is not an effective strategy to suppress thrips population in blueberries. The reason for this may be related to the short period (3 weeks) during flowering when thrips are present in the field in high numbers. If biological control agents are released preventatively (before thrips are present in the field) there is insufficient hosts to support their existence. The biological control agents may then resort to feeding on other natural enemies that regulates thrips population and then die off before they build up. By the time thrips appear in the field, there is hardly any O. insidiosus or A. cucumeris, and natural enemies to regulate their population, therefore, thrips population explodes and become uncontrollable. Alternatively, when biocontrol agents are released curatively (after the pest is present) the thrips population build up rapidly (2 weeks peak) and out-competes O. insidiosus and A. cucumeris, as well as the combination treatments before these biological control agents become established; consequently, making it impossible to control thrips in blueberries.

To evaluate reduced-risk insecticides and their interaction with Orius sp. (Heteroptera: Anthocoridae) and A. cucumeris, natural enemies of flower thrips

Three of the four treatments (Actara 25WG, Assail 70WP and Malathion 5EC) evaluated killed more than 70% of the O. insidiosus used in the bioassays after 24 hours of exposure to the pesticides. SpinTor 2SC was the only insecticide that killed the lowest numbers of predators. The most lethal insecticide was Actara 25WG, which killed almost all the insects in the first 20 hours of exposure. Throughout the duration of the experiment, Actara 25WG and Assail 70WP consistently had the lowest survival rates compared with all other treatments. Neither treatment (Actara 25WG or Assail 70WP) were significantly different from each other. Both treatments were fast acting and significantly different to the control after one hour of exposure to pesticide. Ten hours later only one treatment, SpinTor 2SC, was not significantly different from the control. Interestingly, both Actara 25WG (Thiamethoxam) and Assail 70WP (Acetamiprid) are classified as reduced-risk insecticides. Apparently, these insecticides are fairly toxic to Orius sp. and A. cucumeris, despite being effective for thrips control in blueberries. If these insecticides are used for thrips management, special care such as spot spraying or border sprays would have to be implemented to reduce the negative effects on selected biological control agents.

To compare the effectiveness of reduced-risk insecticides with conventional insecticides for controlling flower-thrips

During 2005, the population of thrips was very low at the site where this trial was conducted; subsequently, we did not collect sufficient data from thrips in the flowers to do a robust analysis to show the effects of these insecticides on thrips population. However, a fairly high number of thrips were recorded on white sticky traps in all the treatments. The populations increased possibly as a result of immigration, since the number of thrips inside the flowers where they reproduce was very limited. None of treatments was significantly different from the control. When we measured population growth, Actara 25WG and Assail 70WP significantly reduced the growth of thrips when compared with the conventional insecticide Malathion.

In 2006, none of treatments was significantly different from the control when comparing the population increase for the sticky traps and inside the flowers. The value of the change in growth rate [population (r )] for the thrips captured on the sticky traps increased overtime independent of treatment application, with exception of Coragen 20SC, which was the only treatment with r < 1. Coragen 20SC had a significantly lower r value than Diamond .83EC. On the established populations collected from the flowers, the situation was similar to the situation encountered on the sticky traps; none of treatments significantly reduced thrips population growth. Our results comparing reduced-risk and conventional insecticides were conflicting. However, the following insecticides; Actara 25WG (Thiamethoxam), Assail 70WP (Acetamiprid) and Coragen 20SC (Rynaxpyr formally known as DPX-E2Y45) performed fairly well and demonstrates potential for controlling thrips. These insecticides are classified as reduced-risk and performed as well or slightly better than the conventional insecticide malathion.

To collaborate with growers, extension agents and agricultural consultants to generate and distribute new information on thrips control for early-season blueberries

Over the last two years, we have presented our work at several blueberry extension meetings including, the spring and fall 2005, and 2006 meetings. Our work was also presented at Southeastern Regional Blueberry meetings in Georgia and at the mid-Atlantic Blueberry Conference in New Jersey. Some aspects of our work were also presented in Michigan to other researchers and blueberry growers. Our project will be up-loaded to our blueberry web site at http://fruitnvegipm.ifas.ufl.edu/blueberries.htm . At the bottom of this report, we have highlighted some of our presentations, publications and extension talks.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

1….Publications.

Extension

Liburd, O. E., and H. A. Arévalo. 2005. Integrated strategies for controlling flower thrips in southern highbush blueberries. University of Florida. IFAS extension IPM-103: 4.

Arévalo, H. A., A. B. Fraulo, and O. E. Liburd. 2006. Key to the most common species of thrips found in early-season blueberry fields in Florida and Southern Georgia. University of Floida IFAS Extension.

Liburd, O. E., E. M. Sarzynski, B. J. Sampson, and G. Krewer. 2006. Blueberry gall midge: A major insect pest of blueberries in the Southeastern United States. EDIS IFAS, University of Florida, Gainesville, FL

Journal

Arévalo, H. A., and O. E. Liburd. in press. Flower thrips, oviposition and dispersion behavior in early season blueberries. J Insect Sci.

Arévalo, H. A., and O. E. Liburd. submitted. Horizontal and vertical distribution of flower
thrips in southern highbush and rabbiteye blueberry fields, With notes on a new sampling method for thrips inside the flowers. J. Econ. Entomol.

Dissertation

Arévalo, H. A. 2006. A study of the behavior, ecology, and control of flower thrips in blueberries towards the development of an integrated pest management (IPM) program in Florida and southern Georgia, pp. xiv + 153, Entomology and Nematology. University of Florida, Gainesville, FL.

2….Presentations.

Liburd, O. E. 2005. Update on blueberry insect pest management. Spring Blueberry Field Day. Windsor, Florida.

Liburd, O. E. and H. A. Arévalo. 2005. Dispersion behavior and injury caused by flower thrips in early season blueberries. Florida Blueberry Growers Association Fall Meeting. Bartow, FL.

Liburd, O. E. 2005. Dispersion behavior and injury caused by flower thrips in early season blueberries. Georgia blueberry growers association Tifton, GA

Liburd, O. E. 2006. Thrips and gall midge management in blueberries. New Jersey annual vegetable meeting. Atlantic City, NJ.

Arévalo, H. A. and O. E. Liburd 2006. Advances in understanding the relationship between flower thrips and blueberries in Florida. Florida Blueberry-Growers Association. Spring meeting. Plant City, FL.

Liburd O. E. 2006. Management of key insect pests and mites in blueberries using conventional and reduced-risk insecticides. Florida Blueberry-Growers Association. Spring meeting. Plant City, FL.

Arévalo, H. A. and O. E. Liburd 2005. Damage description and economic injury level for Frankliniella bispinosa (Thysanoptera: Thripidae) infesting rabbiteye blueberries. Entomological Society of America, ESA. Fort Lauderdale, FL.

Arévalo, H. A. and O. E. Liburd 2005. Flower Thrips, Oviposition and Dispersion Behavior in Early Season Blueberries. VIII International Symposium on Thysanoptera and Tospoviruses. Pacific Grove, CA.

Arévalo, H. A. and O. E. Liburd 2005. Dispersal behavior of flower-thrips in Highbush and Rabbiteye blueberry fields. Florida Entomological Society, FES. Fort Myers, FL.

Project Outcomes

Project outcomes:

This project gave us a better understanding of how to use natural enemies for controlling flower thrips in blueberry plantings. Briefly, we found that the traditional release of natural enemies to control flower thrips was not as efficient as previously thought. Releasing biological control agents inundatively (O. insidiosus or A. cucumeris) may not be the most economically sound practice since the cost benefit ratio was not advantageous in our studies. In addition, our studies documented that some reduced-risk insecticides have potential to control thrips; however, they may be toxic to the natural enemies that regulate thrips population in the blueberry system. Our study has direct applications for blueberry growers and is likely to change the habits of some growers particularly those that indiscriminately use conventional insecticides as well as biological control agents to manage thrips population. We speculate that the study will impact the behavior of at least 500 blueberry growers in the southeastern United States.

Farmer Adoption

Despite that our project did not include an evaluation of farmer adoption of our results we have observed that various blueberry growers are adopting some of our suggestions. Most of them from ideas collected at the field days and extension presentations. Some of the ideas including monitoring methods, insecticide selection are been used.

Recommendations:

Areas needing additional study

  • Study of alternative non-chemical forms to control flower thrips in early season blueberries in the southeastern US need to be explored.

    More reduce risk-insecticides need to be screened to find a chemistry that controls flower thrips in blueberries efficiently and at the same time have a reduce effect on non-target organisms.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.