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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Development of Weather-based Regression Models for Predicting Flights of Tobacco Thrips and Spread of Tomato Spotted Wilt Virus

Project Directors (PDs): George G. Kennedy [1] James W. Moyer [2]

Lead State: NC Lead Organization: North Carolina State University

Research Funding: $97,424

Start Date: Sep-01-2005 End Date: Aug-31-2008

Summary: TSWV is now well established in weeds that commonly grow in and around agricultural fields in NC and can be expected to continue to cause severe losses to pepper, peanut and tomato in eastern NC, as it has in the past. Because the incidence of TSWV varies greatly from year depending on populations of its thrips vectors, growers frequently implement costly and complex control measures when they are not needed and fail to implement them when they are needed. it is difficult and costly to manage. The proposed project seeks funding to develop the basis for predicting spring flights of tobacco thrips, Frankliniella fusca, and outbreaks of tomato spotted wilt virus based on winter and early spring rainfall and temperatures. This will be accomplished through on-farm monitoring of the spring flights of tobacco thrips and spread of TSWV from winter weeds in spring, and through controlled field experiments to validate the relationship between winter and spring growth of tobacco thrips populations, increase of TSWV inoculum in weed hosts and the spread of TSWV to crops in spring. The specific objectives to be addressed are: 1. Validate and refine the relationship between temperature and rainfall, development of tobacco thrips populations on winter weeds, and spread of TSWV among winter weeds during late winter and early spring. 2. Validate and refine the relationship between the size and timing of the dispersing population of F. fusca in spring, and winter and spring temperatures and rainfall. 3. Describe the relationship between the amount and timing of TSWV spread in spring, and winter and spring temperatures and rainfall. This project builds on our preliminary findings that the growth of tobacco thrips populations and the spread of TSWV among winter annual weeds during early spring is directly and significantly related to winter temperatures and rainfall. The relationships between weather parameters, tobacco thrips flights and spread of TSWV elucidated under this project will be used to develop a user-friendly, web-based system for predicting annual risk from tobacco thrips and TSWV. Such a system will prove of great value to producers in deciding the most economical and appropriate thrips and TSWV management measures to implement each year. Objectives: 1. Validate and refine the relationship between temperature and rainfall, development of tobacco thrips populations on winter weeds, and spread of TSWV among winter weeds during late winter and early spring. 2. Validate and refine the relationship between the size and timing of the dispersing population of tobacco thrips in spring, and winter and spring temperatures and rainfall. 3. Describe the relationship between the amount and timing of TSWV spread in spring, and winter and spring temperatures and rainfall.

Final Report:

Results PROGRESS: 2005/09 TO 2008/08 OUTPUTS: The goal of this project was to develop weather based regression models to predict spring flights of tobacco thrips, Frankliniella fusca, the primary early season vector of tomato spotted wilt virus (TSWV) in eastern and central North Carolina, based on winter and early spring temperatures and rainfall. Models were developed, which describe the relationship between temperature, amount of rain and number of days with rain during defined periods in late winter and spring and the magnitude and timing of spring flights of the tobacco thrips. Separate models were developed to describe the magnitude of tobacco thrips dispersal during each of the following intervals: April 1-15, April 16-30, May 1-15, and May 16 through 30. These intervals represent periods when susceptible crops are transplanted and are most susceptible to early season thrips damage and to infection by TSWV. In field trials over two years, these models characterized the need for and the most effective timing to apply Acibenzolar-S-methyl, an activator of plant resistance to TSWV, to reduce final incidence of TSWV. Results were presented to growers during 2 field days, and at annual meetings of the NC Tomato Growers Association, the Southern Agricultural Leadership Council, and the North Carolina Crop Consultants Association. Additional presentations were made at two annual meetings of the Entomological Society of America. During 2007, email advisories based on these models were sent to County Extension Agents in areas of North Carolina where TSWV is particularly problematic. PARTICIPANTS: Refer to outputs & outcomes in termination report TARGET AUDIENCES: Refer to outputs & outcomes in termination report PROJECT MODIFICATIONS: Refer to outputs and outcomes in termination report IMPACT: 2005/09 TO 2008/08 Work under this project demonstrated that rainfall timing, amount and duration dramatically influenced tobacco thrips populations and TSWV spread within patches of winter annual weeds. Tobacco thrips flights and spread of TSWV during late winter and spring at 15 field locations during 2005-2007 were monitored using yellow sticky traps and sentinel plants. The resulting data revealed a strong and highly significant relationship between the timing and magnitude of F. fusca flights and TSWV spread. Spread of TSWV into crops was also shown to be primarily by the second and third generation adults dispersing from winter annual weeds. Regression analyses of tobacco thrips spring flight data collected over 44 field site-years produced models that indicated late-March rainfall had a strong negative relationship with the number of tobacco thrips caught on traps during April 1-15, April 16-30, and May 1-15, presumably because it killed larvae present during late March. Late April rainfall had a strong negative relationship on number of adults caught during the same period, presumably reflecting the ability of rainfall to suppress adult flight. Late April rainfall was also negatively related to the number of tobacco thrips caught on traps during May 1-15, and May 16-30, presumably reflecting rain-induced larval mortality during late April. Early May rainfall had a positive relationship to the number of tobacco thrips caught during late May, presumably because it delayed senescence of the winter weed host plants of the thrips. Finally, late May rainfall was negatively related to the number of tobacco thrips caught during late May, presumably because it suppressed thrips flights. Degree-day (DD) accumulations from November 1 were positively related to the number of tobacco thrips caught during each trapping interval, but the influence of DD was less for the late May interval than the earlier interval because host plant senescence in late May caused tobacco thrips populations to peak and decline despite the continued accumulation of DD. Although there are numerous factors unrelated to weather that also influence the timing and magnitude of thrips dispersal, discrete intervals of rainfall and cumulative DD consistently explained the majority of variation observed in spring tobacco flights. Thrips transmitted tomato spotted wilt virus (TSWV) causes losses to peanut, pepper, tomato, and tobacco that exceed $100 million annually in the southeastern US. Procedures to reduce losses are both complex and expensive, and must be implemented before the crop is infected. These models are being tested to determine their ability to predict tobacco flights and the risk of TSWV outbreaks on an area-wide basis. If these are successful, the resulting prediction system could enable growers of susceptible crops to make informed decisions regarding the need for costly and complex TSWV management procedures. PUBLICATIONS (not previously reported): 2005/09 TO 2008/08 1. Morsello, S.C. 2007 The Role of Temperature and Precipitation on Thrips Populations in Relation to the Epidemiology of Tomato Spotted Wilt Virus. PhD Thesis, North Carolina State University, Raleigh, NC October 30, 2007. 2. Morsello, S.C., R.L. Groves, B.A. Nault and G.G. Kennedy. 2008. Temperature and precipitation affect seasonal patterns of dispersing tobacco thrips, Frankliniella fusca, and onion thrips, Thrips tabaci (Thysanoptera : Thripidae) caught on sticky traps. Environmental Entomology 37: 79-86. 3. Morsello, S. R.L. and G.G. Kennedy. 2008. Spring temperature and precipitation affect tobacco thrips, Frankliniella fusca (Thysanoptera: Thripidae) population growth and Tomato Spotted Wilt Virus within patches of the winter weed Stellaria media. Entomologia Experimentalis et Applicata (accepted). 4. Morsello, S.C., R.L. Groves, B.A. Nault and G.G. Kennedy. 2008. Weather-based regression models explain temporal variation in the number of tobacco thrips, Frankliniella fusca (Thysanoptera: Thripidae), captured on sticky traps during spring in North Carolina and Virginia, USA. Entomologia Experimentalis et Applicata (pending).

Outcomes N/A

Impacts FROM REPORT BY THE PI TO usda cris REPORT SYSTEM Work under this project demonstrated that rainfall timing, amount and duration dramatically influenced tobacco thrips populations and TSWV spread within patches of winter annual weeds. Tobacco thrips flights and spread of TSWV during late winter and spring at 15 field locations during 2005-2007 were monitored using yellow sticky traps and sentinel plants. The resulting data revealed a strong and highly significant relationship between the timing and magnitude of F. fusca flights and TSWV spread. Spread of TSWV into crops was also shown to be primarily by the second and third generation adults dispersing from winter annual weeds. Regression analyses of tobacco thrips spring flight data collected over 44 field site-years produced models that indicated late-March rainfall had a strong negative relationship with the number of tobacco thrips caught on traps during April 1-15, April 16-30, and May 1-15, presumably because it killed larvae present during late March. Late April rainfall had a strong negative relationship on number of adults caught during the same period, presumably reflecting the ability of rainfall to suppress adult flight. Late April rainfall was also negatively related to the number of tobacco thrips caught on traps during May 1-15, and May 16-30, presumably reflecting rain-induced larval mortality during late April. Early May rainfall had a positive relationship to the number of tobacco thrips caught during late May, presumably because it delayed senescence of the winter weed host plants of the thrips. Finally, late May rainfall was negatively related to the number of tobacco thrips caught during late May, presumably because it suppressed thrips flights. Degree-day (DD) accumulations from November 1 were positively related to the number of tobacco thrips caught during each trapping interval, but the influence of DD was less for the late May interval than the earlier interval because host plant senescence in late May caused tobacco thrips populations to peak and decline despite the continued accumulation of DD. Although there are numerous factors unrelated to weather that also influence the timing and magnitude of thrips dispersal, discrete intervals of rainfall and cumulative DD consistently explained the majority of variation observed in spring tobacco flights. Thrips transmitted tomato spotted wilt virus (TSWV) causes losses to peanut, pepper, tomato, and tobacco that exceed $100 million annually in the southeastern US. Procedures to reduce losses are both complex and expensive, and must be implemented before the crop is infected. These models are being tested to determine their ability to predict tobacco flights and the risk of TSWV outbreaks on an area-wide basis. If these are successful, the resulting prediction system could enable growers of susceptible crops to make informed decisions regarding the need for costly and complex TSWV management procedures.

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