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Alternatives to Organophosphate and Organocarbamate Insecticides in the Management of Thrips and Tomato Spotted Wilt Virus in Peanut

Srinivasan, Rajagopalbabu; Culbreath, Albert K; Tubbs, Ronald Scott; Kemerait, Robert C; Smith, Nathan B; Reitz, Stuart R; Hagan, Betsy A
University of Georgia
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Statement of goals/objectives/expected outputs. Thrips and Tomato spotted wilt virus (TSWV) have been a major constraint to peanut production in the southeast since the 1980s. The importance of thrips and TSWV has been emphasized in numerous management plans and in crop profiles from various states in the southeast. Management options include planting moderately resistant cultivars, in-furrow application of organophosphates and organocarbamates, and cultural tactics. None of these tactics alone can provide sufficient control in the case of a severe TSWV epidemic on a susceptible or even moderately resistant cultivar. However, together these tactics have been shown to provide reasonable level of control even under high spotted wilt pressure. Therefore, withdrawal of aldicarb and potentially phorate can disrupt the equilibrium that exists among management tactics and also negate the cumulative effect. However, the advent of next generation peanut cultivars with high levels of TSWV resistance can allow some flexibility. In such a situation, insecticides are more critical to manage thrips damage than to suppress spotted wilt incidence. The ultimate goal is to identify effective replacements and integrate the usage of the new insecticides along with the other available management tactics. This approach identifies with the first two objectives mentioned in the PMAP RFA FY 2011.

Objectives: 1.Evaluate new insecticides in the greenhouse and identify the mechanisms associated with suppression of thrips feeding and TSWV incidence in TSWV-resistant and susceptible peanut cultivars 2.Evaluate newly developed TSWV-resistant peanut cultivars and new insecticides against thrips and TSWV through field trials in multiple locations 3.Evaluate TSWV-resistant and susceptible cultivars along with selected insecticides in twin and single row planting patterns Activity Schedule. Objective 1. June 2011-December 2012, Objective 2. May 2011-October 2011, Objective 3. May 2012-October 2012, Grower oriented farm demonstration-September 2012, Extension agent training oriented workshop-September 2012, Cost benefit analyses-October 2011-April 2012; October 2012-April 2013, All other outreach related tasks-November 2012-April 2013.

Research Outputs: 1.Alternatives to organophsophate and organophophate will be identified and their usefulness to manage thrips and thrips-transmitted TSWV will be ascertained. 2. Compatibility of new insecticides with various other management tactics will be identified. 3. Mechanisms that influence suppression of thrips and thrips-transmitted TSWV will also be identified. Econometric output/ cost-benefit analyses: The feasibility of using new alternative insecticides will be examined by an economist who specializes in peanut production economics. Extension outputs: On farm demonstrations and other extension outreach efforts 1.On-farm demonstrations and workshops. 2.On-farm demonstration. 3.Oral presentations. 4.Publication of a feature article. 5.Blogs will be initiated at the grower corners in the grower oriented websites.

More information

Peanut is an important field crop. In 2010, 1.29 million acres of peanut were planted in the United States. Peanut production acreage in Georgia, Alabama, and Florida accounts to more than 70% of the total production acreage in the United States. However, peanut production is faced with numerous challenges. Thrips and thrips-transmitted Tomato spotted wilt virus (TSWV) have been the most important constraint in the last two decades. TSWV was first observed in Texas in 1971 and spread to the entire southeast in the next few years. TSWV-induced losses in Georgia peanuts from the late 1980s through 1997 were estimated to be around 12%, representing an approximate value of $40 million. TSWV was identified as a priority in several pest management strategic plans and crop profiles. In the 1980s a multidisciplinary team was formed to initiate TSWV eradication efforts (Spotted Wilt Eradication Acton Team, SWEAT). Despite its efforts, TSWV spread throughout the southeast.

Currently, efforts are directed towards management of TSWV rather than eradication by the same team (Spotted Wilt Action Team, SWAT). It should be noted that there is no single management tactic that can be sufficient for thrips and TSWV management. As a result growers often use an integrated approach. The main management tactics regularly adopted by growers include planting TSWV-resistant peanut cultivars, insecticide applications (phorate and aldicarb) at the time of planting, and cultural tactics such as planting date adjustments, planting in various row patterns, and fertilization practices. Applications of Aldicarb and Phorate can lead to undesirable environmental and non-target effects. The non-target effects are so undesirable that a recent risk assessment study conducted by the US Environmental Production Agency (EPA) indicated that the carbamate insecticide (aldicarb) no longer meets agencies rigorous food safety standards. Recently, US EPA and Bayer Crop Science have agreed to withdraw the use of aldicarb (Temik). Withdrawal of aldicarb and potentially phorate can disrupt the equilibrium that exists among management tactics and also negate the cumulative effect. However, the advent of next generation peanut cultivars with high levels of TSWV resistance can allow some flexibility. In such a situation, insecticides are more critical to manage thrips damage than to suppress spotted wilt incidence. The ultimate goal of this proposal is to identify softer insecticides with high thrips activity and integrate them into the existing integrated management programs. A number of new insecticides that are more environmentally friendly and have relatively low non-target effects are available. In order to address this issue, a multistate transdisciplinary team has been formed. Efficacy of alternative chemical insecticides and an insight on the mechanisms through which they suppress thrips feeding and affect TSWV incidence will be studied in detail. Results of these studies will be disseminated to peanut growers in all three participating states and in the southeast through numerous outreach efforts.

Objective 1. Evaluate the effect new alternative insecticides on thrips feeding injury, thrips reproduction, TSWV acquisition, and TSWV inoculation. New insecticides will be selected for this purpose, including thiamethoxam (Cruiser), acetamiprid (Assail), cyantraniliprole (Cyazypyr), spinosad (SpinTor and/or Entrust), spirotetramat (Movento), azadirachtin (Azatin), and lambda-cyhalothrin (Karate). One TSWV-resistant cultivar (GA-06G) and a susceptible check (Georgia Green) will be evaluated. a. Effect of new insecticides on thrips injury and reproduction. New insecticides will be applied as seed treatments, soil drenches, or as sprays near the time of emergence of peanut plants. Thrips will be released on sprayed plants. Thrips on each treatment will be counted. Proc GLM in SAS will be used to evaluate treatment effects. b. Effect of new insecticides on TSWV inoculation by thrips. All new insecticides will be applied as explained in subsection a. Viruliferous thrips will be released in each cage and TSWV-infection in each treatment will be evaluated by using DAS-ELISA. Differences in infection status among treatments will be evaluated by Proc GENMOD in SAS. c. Effect of new insecticides on TSWV acquisition by thrips. This experiment will be conducted in Munger cells, two leaflets from TSWV-infected peanut plants treated with new insecticides and an unsprayed leaf will be placed in Munger cells. Ten non-viruliferous thrips will be released into each cell. If the next generation adults are recovered, their infection status will be tested. d. Effect of new insecticides on TSWV titer accumulation. This experiment will utilize foliage from TSWV-infected plants in subsection b of objective 1. Plants that tested positive by ELISA will be subjected to quantification using Real Time-Reverse Transcriptase Polymerase Chain Reaction (RT-RT-PCR).

Objective 2 Field trials will be conducted to evaluate the effect of new insecticides on thrips and TSWV incidence in TSWV-resistant (GA-06G) and susceptible (Georgia Green) cultivars in 2011. Three field trials will be conducted in all three participating states (Alabama, Georgia, and Florida). Insecticides, imidcaloprid, thiamethoxam, acetamiprid, cyantraniliprole, spirotetramat, spinosad, and lambda-cyhalothrin will be evaluated. Thrips feeding injury will also be visually graded using an arbitrary scale. Spotted wilt rating will also be conducted through visual ratings using a similar scale. Spotted wilt rating will be performed at least three times during the growing season. Differences in peanut yield will be identified by conducting ANOVA by using Proc GLM in SAS after suitably transforming the data. Cultivar-insecticide interaction, if any, will also be evaluated.

Objective 3 Insecticide treatments will be selected based on the previous trial and evaluated under different planting scenarios. In all the locations the same runner type cultivars will be planted. Thrips populations and feeding injury will be monitored throughout the course of the experiment. Yield estimates and statistical analyses of data will also be conducted as indicated in objective 2.

PROGRESS: 2011/09 TO 2012/08

Activities: The overall goal of this project is to identify new insecticides with reduced non-target effects to replace insecticides with broad-spectrum toxicity, such as aldicarb and phorate in peanut production. In 2011, one insecticide trial was conducted in Tifton, GA. Seven to nine insecticides were tested for their efficacy in reducing thrips populations and suppressing spotted wilt incidence. The trials were conducted using a Tomato spotted wilt virus (TSWV)-resistant cultivar (GA-06G) and a susceptible cultivar (Georgia Green). GA-06G is known to exhibit field resistance. Treatments typically were applied at cracking or as foliar applications. Thrips counts were taken from foliar and bloom samples at two-week intervals. TSWV incidence was assessed prior to harvest and harvest data was collected. In 2012, peanuts were planted in late April in GA, AL, and FL. The trial evaluating insecticide efficacy in comparison with aldicarb and phorate was conducted in all three states as explained above. Another trial was conducted in the Attapulgus Peanut Research Center, GA. This trial included single and twin rows and resistant and susceptible cultivars, once each. Three insecticides based on previous trials (imidacloprid, thiamethoxam, and spinetoram) along with phorate were evaluated. Thrips counts were taken from foliar and bloom samples. TSWV incidence and yield estimates were obtained. In 2012, greenhouse experiments were conducted in Tifton to evaluate the efficacy of four insecticides (imidacloprid, thiamethoxam, spinetoram, and cyantraniliprole) in suppressing thrips feeding and TSWV transmission. Feeding and transmission assays were conducted in thrips-proof enclosures following previously established protocols. Thrips feeding damage index was calculated to assess feeding suppression and percent TSWV infection was assessed with respect to insecticide treatments. Events: Georgia Peanut Tour- The importance of finding alternatives to aldicarb and phorate was addressed on at least two occasions during the 26th Annual Georgia Peanut Tour, September 2012. Hundreds of people from 15 states and three countries attended this tour. Co-PI Dr. Kemerait's presentation on peanut disease management emphasized the importance identifying alternatives to aldicarb and phorate as part of the HOT TOPICS session. A field demonstration was also included in the tour, during which the PI discussed the importance of TSWV in peanut and the overall goal of this research project. A county extension agent-training workshop is scheduled for January 2013. Consulting: The extension specialist who is a Co-PI in this grant, Dr. Kemerait, is regularly involved in consulting for growers and training county extension agents. Products and dissemination: A peanut pointer will soon be published on alternatives to aldicarb and phorate usage in peanut. The alternatives will be included in the Peanut Risk Index. The risk index is a tool that is currently used by growers before planting to calculate associated risks. Addition of alternatives will make the tool more robust and will require no substantial special efforts from growers.

Drs. Srinivasan, Culbreath, and Tubbs (UGA) were involved in designing and conducting the insecticide trials in 2011 and 2012, respectively. Personnel from Dr. Srinivasan's lab (including postdoctoral associate) were involved in sample collection, TSWV rating, and collection of harvest data. Drs. Srinivasan, Culbreath, and Tubbs were involved in data analyses and interpretation. Dr. Kemerait (UGA) primarily was involved in extension activities conducted until now and has other events planned for 2013. Dr. Srinivasan's postdoctoral associate and his graduate student were involved in conducting all the greenhouse experiments and in data analysis. Dr. Nathan Smith (economist) is currently working on econometric analysis to evaluate the feasibility of using newer insecticide compounds as replacements to aldicarb and phorate. Dr. Smith's graduate student is also taking part in the econometric analysis. Dr. Austin Hagan, Auburn University, AL was involved in designing and conducting all the experiments at Alabama. His thrips samples were sent to Dr. Srinivasan's lab for identification. Dr. Hagan and his research associate have been involved in sample collection, TSWV evaluations, and harvest. Dr. Stuart Reitz, USDA ARS, FL was involved in designing and conducting all experiments at FL. His research technician was also involved in collecting samples, TSWV rating, thrips identification, and harvest. The PI and the Co-PIs will meet in the next two weeks to revise the peanut risk index for 2013 peanut reason. They will also be conducting a county extension agent training workshop and preparing an extension publication in spring 2013. TARGET AUDIENCES: More than 80% of the peanut production occurs in GA, FL, and AL. Thrips-transmitted Tomato spotted wilt virus still remains as the most important production constraint to peanut growers in the southeast. Our main target audience comprises peanut growers of the southeastern USA. We will be using the events organized by the Georgia Peanut Commission and their websites to emphasize how growers can switch to newer insecticides and replace aldicarb and phorate in peanut production without compromising yields. Our training workshops will target county extension agents and growers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

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Nat'l. Inst. of Food and Agriculture
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