Final Report for LS07-199
Field and laboratory comparisons determined that the use of kaolin and plant essential oils could be a viable management alternative for some producers to the use of conventional insecticides for the management of thrips-transmitted tomato spotted wilt virus. These materials were found to act as repellents and feeding deterrents to thrips, which help to account for reduced spread of tomato spotted wilt in the field. In replicated trials, tomato plots treated with kaolin and essential oils from lemongrass or tea tree produced yields equivalent to those treated with repeated applications of conventional insecticides.
- 1. Compare efficacy of the plant essential oils geraniol, lemongrass oil and tea tree oil, and kaolin to standard insecticides in controlling thrips and tomato spotted wilt in tomatoes.
2. Optimize use of kaolin and essential oils by determining how they affect thrips and their ability to transmit Tomato spotted wilt virus.
3. Refine use of plant essential oils and kaolin in the field based on mechanisms determined in laboratory studies of Objective 2.
4. To determine, through Cost Benefit Analysis of each field trial, the management strategies that yields the greatest financial return to the grower.
5. Demonstrate and disseminate findings to growers, commodity groups, IPM providers, and the agrochemical industry as a means to generate greater interest in developing plant essential oils as commercial products and provide baseline data on the efficacy of plant essential oils and kaolin to control thrips and tomato spotted wilt.
The purpose of this project was to develop novel sustainable programs to manage thrips and thrips-transmitted Tomato spotted wilt virus (TSWV), one of the most devastating pest complexes affecting tomato and other vegetable crops in the southern USA (Bauske 1998). We seek to integrate the use of two types of naturally occurring crop protectants, kaolin particle film coatings and plant essential oils, into a more environmentally benign and sustainable management programs for tomatoes. Our project to integrate plant essential oils and kaolin particle films for thrips and tomato spotted wilt management will help reduce the use of synthetic pesticides in tomatoes. Consequently, the results will help to enhance worker safety and environmental and food quality, without sacrificing yields and profits. Because thrips and tomato spotted wilt affect numerous vegetable and ornamental crops in addition to tomato, our findings for tomato will have broad applicability to other agricultural systems.
Tomato is the most economically important vegetable crop grown in the southern US, with a farm gate value of more than $1 billion US dollars. The southern US accounts for upwards of 60% of the fresh market production of the entire US (http://tinyurl.com/s5nlz). Tomato is an expensive crop to produce and historically has high chemical inputs (Bloem and Mizell 2004). Pesticides and pesticide application costs comprise approximately one third of total pre-harvest expenses for field grown tomatoes in Florida (Smith and Taylor 2006, University of Florida http://tinyurl.com/pzyy2). Many of the pesticides used in tomato production are restricted use materials and pose certain risks to the environment and human health. Registration for a number of these materials are now subject to cancellation because of the Food Quality and Protection Act of 1996.
Tomato spotted wilt virus is the type species of the genus Tospovirus in the family Bunyaviridae. Tomato spotted wilt disease was originally described in Australia (Brittlebank 1919), with its viral etiology established in 1930 (Samuel et al. 1930). This virus can only be transmitted to plants by adults of certain species of thrips (Sakimura 1962, Wijkamp et al. 1996, Whitfield et al. 2005, Avila et al. 2006), and only if the adult thrips acquire the virus as larvae (Wijkamp et al. 1996, Assis Filho et al. 2004). Despite the nature of this pathosystem, Tomato spotted wilt virus is one of the most polyphagous plant pathogens, with over 1,000 susceptible plant species (Parrella et al. 2003). Over the past two decades, outbreaks of tomato spotted wilt have increased greatly on a number of crops, such that TSWV is now considered one of the most important pathogens globally, with estimated losses exceeding $1 billion dollars annually. As interest in Tospoviruses has increased over the past ten years, at least 17 additional tospovirus species have been described (Whitfield et al. 2005, Campbell et al. http://tinyurl.com/lwlt8). These differ in serology, genome sequence, vector specificity, and natural host range.
With the advent of thrips-transmitted tomato spotted wilt in the southern US during the late 1980’s, tomato growers in the southern USA relied on applications of broad-spectrum insecticides on a near calendar basis. The current standard insecticide regime consists of rotations of spinosad and methamidophos, with up to 12 – 16 applications per season in attempts to control thrips and TSWV. This intensive insecticide regime has been practiced despite research showing that most losses from TSWV are the result of primary infections, which are not effectively controlled by intensive insecticide use (Puche et al. 1995). Not only is this approach costly, but it poses health risks to farm workers, and it is extremely disruptive to IPM programs for other pests.
Therefore, the need for less costly, safer and more sustainable management tactics for thrips and tomato spotted wilt is clear. We have developed successful alternative management tactics for control of thrips and tomato spotted wilt in tomatoes (Momol et al. 2004) and other solanaceous crops (Reitz et al. 2003). These tactics include the use of highly reflective metalized mulches to repel vector thrips, and systemic acquired resistance (SAR) promoting compounds. While these tactics have proven to be successful and have been widely adopted by southern tomato growers, they do have certain inherent drawbacks. For early plantings, black mulch is preferred because it keeps soil temperature warmer. Furthermore, metalized mulches are approximately twice the cost of standard polyethylene mulches and are more difficult to dispose of because of the combination of metal and plastics. SAR compounds are also expensive and are not approved for use in organic production.
In this project, we intend to develop effective means to integrate the use of environmentally friendly and sustainable materials to reduce the incidence of tomato spotted wilt and thrips in tomato. We propose to use environmentally safe plant essential oils as naturally occurring thrips repellents and to augment the repellent/deterrent effects of plant essential oils with kaolin based particle films. The results of this project will enhance worker safety and environmental and food quality, without sacrificing yields and profits.
Many plants produce volatile essential oils that are thought to function as defenses against pathogens and insect herbivores. These naturally occurring substances are known to have a wide range of biological activities, including toxicity and repellency to certain insect pests. Because of these toxic and/or repellent effects, certain essential oils historically have been used as pesticides against stored grain pests and biting flies (Burfield and Reekie 2005, Isman 2006). Recent work has examined the potential of essential oils to protect crops from pests such as thrips, whiteflies, aphids, caterpillars, and spider mites (e.g., Hummelbrunner and Isman 2001, Choi et al. 2003, Chiasson et al. 2004, Calmasur et al. 2006) Still, widespread commercialization of plant essential oils as crop protectants has lagged, often because critical efficacy data and optimal application methods are lacking (Isman 1997, Ujváry 2002).
Although applications of essential oils as commercial crop protectants have been limited to date, many of these essential oils are safe to humans and currently are used widely in the food and cosmetic industries. Further, with their low mammalian toxicity and low potential for other negative environmental effects (Isman 2000, Ebbon 2002), the use of essential oils as crop protectants is highly appealing. The effects of individual oils or compounds on specific target pests can differ depending on their particular mode of action (Isman, 2000). Therefore, further studies are needed to establish and optimize their use in the field and enhance their potential for commercial development for specific pests.
Another naturally derived material used as a crop protectant is kaolin. Kaolin is an aluminosilicate mineral that can be sprayed onto plants, leaving a white washable residue. Kaolin-based particle films originally were developed for horticultural applications to reduce heat stress, sunburn damage in fruit trees (Glenn et al. 2001, Glenn et al. 2002). Additional research has focused on kaolin as an environmentally benign method to suppress arthropod pests and plant diseases (Glenn et al. 1999). It has been found to reduce the abundance of sucking and chewing pests of fruit crops (Knight et al. 2000, Puterka et al. 2000, Unruh et al. 2000, Knight et al. 2001), boll weevil on cotton (Showler 2002), whitefly on melons (Liang and Liu 2002), thrips on blueberries (Spiers et al. 2004), and other pests. As with essential oils, kaolin may affect these insect herbivores in several ways. Kaolin may alter the attractiveness or host location cues of plants; it forms a physical barrier that may interfering with insect movement and feeding (see Jifon and Syvertsen 2003, Puterka et al. 2005). Mortality of certain herbivores on kaolin treated plants has been observed, but the mechanisms have not been determined. Kaolin also can increase UV reflectance (Glenn et al. 1999), which has been shown to repel Frankliniella thrips (Kirk 1984, Terry 1997, Reitz et al. 2003, Momol et al. 2004).
Our preliminary data (Reitz et al. 2006) lead us to hypothesize that kaolin and the essential oils geraniol, lemongrass oil, and tea tree oil deter thrips and can be as effective as standard insecticides in managing thrips and tomato spotted wilt in tomato crops. As described above, certain essential oils can suppress other tomato pathogens (Wilson et al. 1997, Kalemba and Kunicka 2003), and kaolin can reduce foliar pathogens in certain crops (Glenn et al. 1999, Thomas et al. 2004). Therefore, plant essential oils and kaolin used for thrips and tomato spotted wilt management may have additional benefits in tomato production. Understanding the effects of novel management tools on plant health, vigor and yield are particularly valuable when planning cost effective programs for high input crops such as tomato.
The new strategies developed in this project will provide growers with more sustainable and environmentally benign tomato production practices. Users of this research will be farmers, IPM providers, extension personnel, and biorational crop protectant manufacturers. This mission-oriented project supports SARE’s long range goal of improving the sustainability of US agriculture by reducing the use of high-risk synthetic pesticide use and promoting the use of environmentally appropriate reduced-risk materials.
Project Relevance to Sustainable Agriculture
The proposed project aims to develop effective and practical tools for management of thrips and tomato spotted wilt on tomatoes, an economically important crop in the southern US. Thrips and tomato spotted wilt continue to be critical concerns for conventional growers in the southern US, and in a previous SARE funded survey project, insect and disease management were identified as the two most important issues facing organic farmers in the southern US (Boyhan 2003, LS02-142). Our project will address these concerns and contribute to more sustainable vegetable production through several mechanisms.
Management of thrips and tomato spotted wilt on tomatoes has relayed high input control measures, including extensive use of conventional synthetic pesticides. Not only do these chemicals, such as methamidophos, not provide satisfactory disease control, they also pose threats to consumers, growers, and the environment. In comparison, use of the reduced risk tactics proposed in this project will reduce these threats and will enhance the quality of life for farmers and consumers. Furthermore, the registrations for many synthetic pesticides, including methamidophos, are being cancelled because of the Food Quality and Protection Act of 1996, making the development of effective, environmentally benign crop protectants essential to meet the future needs of US agriculture. In line with that need, the plant essential oils that we propose to study are generally regarded as safe by the US FDA and EPA (GRAS under CFR 21 section 182.20), and kaolin is approved for organic farming use. Therefore, their use in place of synthetic pesticides could provide effective control of thrips and tomato spotted wilt, while improving farm worker and consumer safety, and environmental quality.
We will take a unique approach of using plant essential oils and kaolin synergistically to reduce the incidence of thrips and tomato spotted wilt. There has been increasing interest in the use of plant essential oils and other plant-derived materials as crop protectants. Although we are not aware of other SARE projects using plant essential oils to control insect vectors of plant diseases, our project would complement other SARE projects involving essential oils. One of the PI’s (M. T. Momol) is developing essential oils for control of bacterial spot and bacterial wilt on tomatoes (LS06-192). Researchers in Tennessee have examined plant-derived materials for controlling other tomato pathogens such as Phytophora and Pythium (LS03-147). A northeast SARE funded a project examined the use of plant essential oils for control of varroa mite in honeybee colonies and to improve overall hive health (LNE98-105). SARE has funded at least 17 projects involving the use of kaolin; however, none of these has examined kaolin as a method to control the vectoring of pathogens by insects. As this research evolves, there will be increasing demand for and uses for plant essential oils and kaolin in pest management. Expanding the uses of plant essential oils would complement other goals of SARE funded research in developing new markets for plant essential oil producers (see FNE01-358).
Our proposed research to look at mechanisms will help to optimize methods for using plant essential oils and kaolin in pest management programs. Determining the mechanisms by which essential oils and particle films affect insect biology and behavior is critical to deploying these materials efficiently in pest management programs for tomatoes and other crops.
Furthermore, these materials could produce multiple benefits to growers in terms of pest and disease management and crop production. Our preliminary studies show that these products deter thrips and reduce tomato spotted wilt. In addition, as described above, certain essential oils can suppress other tomato pathogens and kaolin can reduce foliar pathogens and physical damage in certain crops. Therefore, their use to suppress thrips and tomato spotted wilt would not be disruptive to overall tomato production. Rather they would enhance overall pest management in a sustainable and environmentally sound manner.
The proposed research will have immediate and longer term benefits to farmers, IPM providers and extension personnel. Our project will lead to improved use of kaolin in tomatoes and provide data to further stimulate interest in commercialization of plant essential oils as crop protectants. Therefore, this project supports the long-range goal of improving the sustainability of US agriculture by reducing use of high-risk chemicals through environmentally reduced-risk tactics.
To determine the separate and joint effects of plant essential oils and kaolin in controlling thrips and tomato spotted wilt, field trials will be arranged as factorial experiments laid out in a randomized complete block. In initial field trials, we will compare three essential oil treatments (geraniol, lemongrass oil, tea tree oil at 250 ppm, applied twice weekly) with a standard insecticide regime and an untreated control. Ethanol and a surfactant will be added to help disperse the essential oils in water. The standard insecticide regime will be a current grower practice consisting of spinosad rotated weekly with methamidophos (organophosphate), or beta-cyfluthrin (synthetic pyrethroid) and endosulfan (chlorinated hydrocarbon). These essential oil treatments will be cross classified with a kaolin treatment. Based on our preliminary data, treatments will be kaolin applied at 28 kg/ha/week (25 lbs/ac/week) (Surround WP, Engelhard, Iselin, NJ) or a no kaolin control.
Trials will be conducted in the spring when thrips and tomato spotted wilt are most prevalent. Horticultural practices will follow standards for field-grown tomatoes in the southern US. Transplants of FL 47, a standard commercial variety that is tomato spotted wilt susceptible, will be transplanted into black polyethylene mulch beds. Experimental plots will consist of two rows of 20 plants per row. Buffer zones of 2 m without tomato plants will be maintained between plots. Tomato plants will be staked, and tied over time.
Insect samples will be collected twice per week from one row of plants per plots. On each sample date, ten blossoms per plot will be placed in ethanol and examined for thrips. Tomato spotted wilt incidence will be determined weekly by testing symptomatic plants by ELISA (Agdia, Elkhart, IN). At harvest, fruit will be harvested from the row of plants not sampled for insects. Mature and mature green fruit will be harvested from 18 plants per plot 2 – 3 times per season, and graded to USDA standards. Weights of marketable and unmarketable yields will be determined. We will record incidence of other foliar diseases to determine if essential oils and kaolin have ancillary benefits against other pathogens (Kalemba and Kunicka 2003). Data will be analyzed by appropriate analysis of variance (ANOVA) methods.
We will conduct laboratory assays to assess the toxicity, repellency, and feeding and oviposition deterrence of different rates and combinations of the essential oils, geraniol, lemon grass oil and tea tree oil, and kaolin. Central to this objective will be determining the residual efficacy of treatments over time, and if kaolin increases the length of time that essential oils have efficacy against thrips.
Contact toxicity assays will be based on published techniques (Eger et al. 1998, Rueda and Shelton 2003). To determine if essential oils produce significant mortality in thrips, we will place newly eclosed western flower thrips (Frankliniella occidentalis) adults in microcentrifuge tubes treated with different essential oils (geraniol, lemongrass oil, tea tree oil, palmarosa oil, cineole, linalool, and thymol). Experimental materials will be mixed into a stock solution of water, 70% ethanol (1% vol:vol), and tween (0.1% vol:vol). Mortality will be assessed after 24 hours and evaluated in reference to untreated controls and an insecticide standard treatment of spinosad, applied at the labeled field rate.
We will determine the repellency/preference of essential oil and kaolin treatments to western flower thrips in still air olfactometer arenas (modified from Baez et al. 2004). Different rates and combinations of essential oils and kaolin will be tested. Solutions will be prepared as above and applied to fully expanded tomato blossoms. Blossoms will be air dried before being placed in arenas.
In choice trials, there will be two treated flowers and two control flowers. In no-choice trials, all flowers in an arena will receive the same treatment. Flowers will be added to arenas 4 or 24 hours after treatment. Addition of flowers to arenas after different time intervals will allow us to determine the residual activity of experimental treatments over time. After addition of flowers, 25 adult western flower thrips will be released into the center of each arena. The distribution of thrips after 4 hours will be determined. After determining the distribution of thrips, blossoms will be stained in acid fuchsin to reveal the presence of thrips eggs (Backus et al. 1988).
In choice trials, we will test the hypothesis that more thrips will be on control flowers than on the essential oil/kaolin treated flowers. In the no-choice trials, we will test the hypothesis that fewer thrips will be on flowers in the essential oil/kaolin treatments than in corresponding controls. Oviposition will be a proxy measure for thrips activity on flowers receiving different treatments, with the number of eggs indicative of thrips preference for different treatments. The results will show if certain treatments maintain repellency significantly longer than others do. Treatments with the greatest repellent effect will be considered for inclusion in succeeding field trials.
We will determine the effect of kaolin and essential oils on western flower thrips feeding in no-choice assays. Tomato plants will be treated with the most repellent essential oil (tea tree and lemongrass oil) and kaolin treatments as determined above, a spinosad control, or an untreated control. Leaf disks will be cut from plants 4 hours or 24 hours after treatment. Adult female thrips will be placed on leaf disks individually in agar-lined petri dishes for 24 hours. After 24 hours, thrips mortality will be assessed and thrips will be removed. Leaf disks will be scanned and the amount of feeding damage quantified through the use of image analysis software (Sigma Scan).
We will compare transmission rates of tomato spotted wilt by western flower thrips in relation to essential oils and kaolin treatments in another bioassay. To produce viruliferous thrips, tomatoes will be mechanically inoculated with a local isolate of tomato spotted wilt virus and then western flower thrips females from our colony will be placed on plants to oviposit. Virus free tomato plants will be treated with the most repellent essential oil and kaolin treatments as determined above, a spinosad control, or an untreated control. Leaf disks will be cut from plants 4 hours or 24 hours after treatment. Putative viruliferous thrips will be placed on leaf disks individually in agar-lined petri dishes for 24 hours. After 24 hours, thrips mortality will be assessed and thrips will be removed. Leaf disks will be incubated for 5 days and then tested by ELISA for the presence of Tomato spotted wilt virus. These results will help us determine if there are differences in transmission rates of Tomato spotted wilt virus according treatments. By using different time intervals, we will be able to establish what the effective time frame for treatments is.
The results of these preceding experiments will be used to determine how best to optimize applications of essential oils and kaolin for in field trials. We will have information on the most effective rates of essential oils and kaolin and the length of their residual effects.
The University of Florida and University of Georgia Extension Services will be actively involved throughout to help disseminate information in print and electronically. Results will be incorporated in Florida Plant Disease Management Guide and Vegetable Production Handbook. We will present research at the North Florida Research & Education Center’s Horticultural Field Day and commodity group meetings.
Research demonstrations will be presented in conjunction with the annual field day, and will include a tour of the project plots. Previous research has shown the usefulness of the reduced-risk tactics for thrips and Tomato spotted wilt virus (Reitz et al. 2003, Momol et al. 2004), and growers in US are rapidly adopting the tactics. Implementation will increase with the demonstrated results for pest management and increased yield and economic returns. Specific concerns of producers concerning cost of implementation, quality of materials used, and safety of products can be addressed most effectively with grower and integrated pest management workshops and visits to on-farm trials.
Treatment effects on incidence of TSW in Field Trials. Although high levels of TSW were recorded in year 1, even higher levels occurred in year 2 (Fig. 1). In year 1, disease incidence increased substantially over time, with treatment differences evident by the third disease assessment date (May 23) (Fig. 1A-1B). There was no significant interaction between the essential oil treatments and kaolin. For the essential oil main effect, there were significant differences among the five treatments, with grower standard having the lowest level of TSW. Kaolin led to a significant reduction in TSW incidence. Although there was not a significant interaction between the essential oil treatments and kaolin, the addition of kaolin led to significantly lower incidence of TSW for all of the essential oil treatments (P < 0.05 LSMeans t-tests) except for the grower standard.
The analysis of AUDPC gave similar results as the final disease incidence analyses. Overall, AUDPC was >30% lower with kaolin than without kaolin. Lemongrass oil and tea tree oil had significantly lower AUDPC’s when applied with kaolin than without kaolin (P < 0.05). Those combined treatments performed as well as the grower standard, suggesting that these materials do have beneficial properties for TSW management.
Although disease pressure was much higher in year 2 than in year 1, similar patterns emerged (Fig. 1). On all disease assessment dates in year 2, TSW was lower for treatments with kaolin than for treatments without kaolin (Fig. 1C-D). There were significant differences among the essential oil treatments, with the tea tree oil and grower standard having the lowest levels of TSW. Overall, the lowest levels of TSW were in the tea tree oil plus kaolin and the two grower standard treatments (i.e., with and without kaolin). AUDPC was approximately 25% lower overall with kaolin than without kaolin, and each of the 5 essential oil treatments had significantly lower AUDPC with kaolin than the corresponding treatment without kaolin (P < 0.05).
Treatment effects on thrips populations. Thrips populations differed in overall abundance, composition, and timing of peak abundance between years. Based on overall means in the control plots adult thrips were more abundant in year 1 (66.1 +/- 10.2 per sample) than in year 2 (53.2 +/- 8.4). In both years, Frankliniella tritici was the dominant species, but that species changed from comprising over 94% of the adults collected in year 1 to comprising just 80% in year 2. The three species capable of vectoring TSWV (F. occidentalis, F. fusca, F. bispinosa) were more abundant in year 2, the season with more TSW, with a total mean of 8.9 +/- 0.9 across all control samples, than in year 1 when there was a mean of 2.8 +/- 0.4 per control sample. Adult populations of these thrips species also peaked 1 – 2 weeks earlier in year 2 than in year 1 (Figs. 2 and 3). More importantly, each of the four Frankliniella spp. showed species specific responses to the different essential oil and kaolin treatments.
Over the entire year 1 season, there was a significant essential oil treatment x kaolin treatment interaction on the abundance of F. tritici. This interaction indicates that the response of F. tritici populations to the 5 essential oil treatments changed according to whether kaolin was applied or not. The interaction was primarily a result of the grower standard having an opposite response than the essential oils and untreated control. For those 4 treatments, the addition of kaolin resulted in significantly lower F. tritici abundance (P < 0.005 for each pairwise comparison). The reduction in F. tritici ranged from 31 to 50% in each treatment. In contrast, F. tritici populations were significantly higher in the grower standard insecticide treatment with kaolin (57.6 +/- 2.3, averaged over all sample dates) than without kaolin (36.8 +/- 1.9, P < 0.0001). This represents a 58% increase in abundance of F. tritici with kaolin in the grower standard. This increase in F. tritici abundance in the grower standard with kaolin also meant that the essential oils with kaolin preformed as well or better than the grower standard with kaolin in terms of managing F. tritici (Fig. 2). In year 2, kaolin by itself (comparing control vs. control + kaolin), or with insecticides (grower standard vs. grower standard + kaolin) did not have an effect F. tritici populations (P > 0.05). However, for each of the essential oils, the presence of kaolin significantly reduced the numbers of F. tritici adults (P < 0.05 for each pairwise comparison).
Frankliniella occidentalis was the most abundant TSWV vector species in both year 1 and year 2. It comprised 67% of the vector species adults collected in year 1 and 89% in year 2 (Figs. 2 and 3). In year 1, the essential oil and kaolin treatments did not significantly affect F. occidentalis populations (Fig. 2). However in year 2, there were significant differences among the essential oil treatments (Fig. 3). The lowest F. occidentalis populations were found in the grower standard treatments but these were not significantly lower than populations in the tea tree oil treatments.
Frankliniella bispinosa populations showed significant differences among the essential oil treatments in both years of the study (Figs. 2 and 3). The overall abundance of F. bispinosa was about 60% higher in year 2 than in year 1. In year 1, the lowest levels of F. bispinosa were in the control, although these levels were not significantly different from those found in the geraniol, lemongrass and tea tree oil treatments. In contrast, the grower standard had significantly higher levels of F. bispinosa than the control. In year 2, the pattern differed among the essential oil treatments, with the grower standard and tea tree oil treatments having significantly lower levels of F. bispinosa compared with the three other treatments. Populations of F. bispinosa were not affected by kaolin treatments in either year.
Treatment effects on tomato yield. In year 1, total marketable yield was significantly affected both by the essential oil and kaolin treatments. The grower standard treatments had the highest yields on a per hectare basis, but these were not significantly greater than the tea tree oil plus kaolin treatment (Fig. 4). Overall, kaolin significantly improved yield. Neither the essential oil or kaolin treatments affected the yield per plant, (P > 0.05 for all tests), indicating that differences in total yield on an area basis were largely from treatments affecting the number of healthy, harvestable plants rather than the treatments affecting individual plant physiology. Because of the high levels of disease for all treatments in year 2, yield determinations could not be made.
Toxicity of Essential Oils to Western Flower Thrips
The seven tested essential oils and constituents varied in their toxicity to adult western flower thrips. The field rate of spinosad produced 99 – 100% mortality in all trials (Fig. 5). Thymol had the greatest residual toxicity to western flower thrips (Fig. 5). All of the tested concentrations of thymol resulted in significantly higher mortality compared with the control, and the two highest concentrations of thymol gave mortality equivalent to that of the field rate of spinosad (Fig. 5). The highest concentration of geraniol (3200 ppm) was the only other treatment that produced mortality similar to that of spinosad. Linalool resulted in significant mortality at all tested concentrations; however the increase in mortality from 100 ppm to 3200 ppm was less than for thymol, the only other material that produced mortality at all tested concentrations. 1,8-cineole was the least toxic material tested. Only the two highest concentrations of cineole produced mortality significantly greater than the control (Fig. 5) and based on the nonoverlap of fiducial limits the LC25 value for 1,8-cineole was significantly higher than for any of the other materials.
The complete essential oils from lemongrass, palmarosa and tea tree were intermediate in toxicity and did not show consistent linear dose dependent responses over the concentrations tested. Although lemongrass oil had an LC25 near 800ppm, the estimated LC50 would have been in excess of 3200 ppm. Palmarosa and tea tree oils induced significant levels of mortality at concentrations of 400 ppm and greater. However, their LC50s were significantly greater than LC50s for linalool or thymol.
Repellency. Repellency did not correspond with toxicity. Although thymol and linalool induced significant mortality (>20%) at 100 and 200ppm, these concentrations were not repellent to adult western flower thrips (Fig. 6). Four of the materials that were tested did show significant repellency to western flower thrips at concentrations of 100 and 200 ppm (Fig. 5).
The complete oils of lemongrass, palmarosa, and tea tree, and the monoterpenoid geraniol were highly repellent to western flower thrips, when applied to tomato flowers at 100 ppm and 200 ppm (Fig. 6). Based on the overlap of 95% confidence intervals, there was no increase in repellency with concentration.
Based on these tests, we examined the effects of kaolin and three of the essential oils: lemongrass oil, tea tree oil and geraniol on thrips behavior. Western flower thrips adults were less likely to be found in tomato flowers treated with the plant essential oils and kaolin (Fig. 7). The results indicate there were also synergistic interactions where mixtures of kaolin and oils further increased repellency to western flower thrips. The repellency to adult thrips also resulted in lower oviposition by females (Fig. 8).
In laboratory tests, treating tomato foliage with kaolin reduced western flower thrips feeding by an average of over 80% compared with feeding on foliage not receiving kaolin. Interestingly, feeding was not affected, either negatively or positively by the presence of plant essential oils.
Although feeding was suppressed by kaolin, virus transmission in laboratory tests was not reduced by kaolin. This is because transmission trials conducted to date have been no choice trials, and virus transmission to leaf disks can occur even with very little feeding. Currently, we are using different protocols to ascertain how kaolin and essential oils lead to reduced transmission of tomato spotted wilt virus in the field.
- Figure 1. Disease progress curves for tomato spotted wilt as affected by different plant essential oil and kaolin treatments in year 1 (A and B) and in year 2 (C and D). Note the different scale between years.
- Figure 2. Seasonal abundance of adults of Frankliniella spp. thrips in tomato flowers during year 1 field trials, as affected by plant essential oil and kaolin treatments.
- Figure 3. Seasonal abundance of adults of Frankliniella spp. thrips in tomato flowers during year 2 field trials, as affected by plant essential oil and kaolin treatments.
- Figure 4. Yield per acre (expressed in 25 lb cartons) for tomato plots receiving different plant essential oil and kaolin treatments for the first year field trial. High disease pressure in the second year across all plots precluded collection of yield data.
- Figure 5. Toxicity of plant essential oils to adult western flower thrips at different concentrations.
- Figure 8. Oviposition selection by adult western flower thrips as affected by kaolin and plant essential oil treatments applied to tomato flowers. Thrips were exposed to treated flower for 4 hours, either immediately after application or 24 hours after application.
- Figure 6. Repellency of plant essential oils to adult western flower thrips at different concentrations, as determined in choice tests between treated and untreated tomato flowers.
- Figure 7. Host selection by adult western flower thrips as affected by kaolin and plant essential oil treatments applied to tomato flowers. Thrips were exposed to treated flower for 4 hours, either immediately after application or 24 hours after application.
Educational & Outreach Activities
Reitz, S. R., G. Maiorino, S. Olson, R. Sprenkel, A. Crescenzi, M.T. Momol. 2008. The effects of plant essential oils and particle films on tomato spotted wilt and thrips in tomatoes. Plant Disease. 92: 878-886.
Reitz, S. R., Maiorino, G., Crescenzi, A., and Momol, M. T. Repellency and toxicity of plant essential oils to the western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae). In preparation.
Reitz, S. R., Maiorino, G., Crescenzi, A., and Momol, M. T. Interaction of plant essential oils with kaolin as pepellents to the western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae). In preparation.
Reitz, S. R., Maiorino, G., Crescenzi, A., and Momol, M. T. Transmission of tomato spotted wilt virus by Frankliniella occidentalis as influenced by kaolin and plant essential oils. In preparation.
S. Reitz, G. Maiorino, L. Ritchie, S. Olson, R. Sprenkel, A. Crescenzi, M.T. Momol. 2007. The effects of plant essential oils and particle films on tomato spotted wilt and thrips in tomatoes. American Phytopathological Society, San Diego, CA. Phytopathology 97:S98
S. Reitz, G. Maiorino, L. Ritchie, S. Olson, R. Sprenkel, A. Crescenzi, M.T. Momol. year 2. Plant Essential Oils and Particle Films for the Management of Tomato Spotted Wilt on Tomatoes. American Phytopathological Society, Quebec, QC. Phytopathology 96: S97
S. Reitz. Tomato Pest Management. Gadsden County Tomato Forum. Quincy, FL. December 2010.
S. Reitz. A new look at some old foes: Thrips and tomato spotted wilt virus, and implications for their management. Symposium on Vector-Virus Interactions in Agro Ecosystems: Approaches, Advancements, and Limitations, Annual Meeting of the Entomological Society of America. San Diego, CA. December 2010.
S. Reitz. 2010. Particle Films as an IPM Tool. W-1008 Thrips and Iris Yellow Spot Virus Research Project Meeting. Reno, NV. December 2010.
S. Reitz. Tomato Pest Management. Gadsden County Tomato Forum. Quincy, FL. December 2008.
S. Reitz. New Approaches for the Management of Thrips and Tomato Spotted Wilt. Gadsden County Tomato Forum, Quincy, FL. November 2007.
S. Reitz, G. Maiorino, L. Ritchie, S. Olson, R. Sprenkel, A. Crescenzi, M.T. Momol. year 2. New Approaches for the Management of Tomato Spotted Wilt on tomatoes with Plant Essential Oils and Particle Films. 37th International Symposium of Essential Oils, September 10 – 13, year 2. Grasse, France. P96
Field Day Presentations:
S. Reitz. Particle films for insect pest management. Florida A&M Grape and Biocontrol Harvest Festival Day. 2009.
S. Reitz. Update on New Approaches for the Management of Tomato Spotted Wilt on tomatoes with Plant Essential Oils and Particle Films. North Florida Horticultural Field Day. 2008.
S. Reitz. Particle films for insect pest management. Florida A&M Grape and Biocontrol Field Day. 2008.
S. Reitz. New Approaches for the Management of Tomato Spotted Wilt on tomatoes with Plant Essential Oils and Particle Films. North Florida Horticultural Field Day. 2007.
Jan Suszkiw. Researchers Testing “One-Two Punch” Against Disease-Spreading Thrips. USDA-ARS. Agricultural Research http://www.ars.usda.gov/is/pr/2009/090615.htm. Published: 06/15/2009. Subsequently reprinted in numerous industry magazines.
Growers recognize that thrips-transmitted tomato spotted wilt is a major constraint on tomato production in the southern USA. In response, growers have relied on intensive insecticide applications, which can be expensive and pose long-term risks to sustainability from the development of insecticide resistance and secondary pest resurgence. Replicated field trials have shown that kaolin particle films and at least two plant essential oils (lemongrass and tea tree oil) can interact synergistically to reduce the incidence of thrips-transmitted tomato spotted wilt virus in tomato. Kaolin and plant essential oils are relatively inexpensive and environmentally benign management tactics that can reduce disease incidence as well or better than standard insecticides without the long-term risks to sustainability. Complementary laboratory studies have shown limitations of the use of these materials, which will provide guidance on future research to improve the effectiveness of using plant essential oils and particle films as part of sustainable vegetable production.
This SARE funded project provided the basis for an additional project, entitled “State-wide Implementation of Novel Push-Pull Strategies for IPM of Thrips,” funded by the Florida Dept. of Agricultural and Consumer Services. This new project will help refine the use of kaolin particle films as a component of overall IPM practices for southern vegetable producers.
Results of this project were presented at four grower forums and field days that were open to the general public. There were over 20 farmers, crop consultants, and extension personnel at each of these events. Several farmers attending these events have expressed an interest in using these techniques, and we have offered to provide technical assistance as needed. The materials are relatively inexpensive and are commercially available and can be applied through standard equipment.
Areas needing additional study
Clearly there is no one solution for management of thrips and tomato spotted wilt in tomato production. Although we have shown that particle films and plant essential oils can be used as management tools, additional research is needed to determine if residual effects of plant essential oils can be maintained over longer time periods by using alternative application methods or formulations. Other research on plant essential oils and particle films has demonstrated that these materials have other benefits in crops production (e.g., foliar disease management, reduced sunburn damage, etc.). The scope of our project did not allow us to document other possible effects of plant essential oils and particle films in tomato production. However, these aspects are critical for grower adoption. Therefore, overall effects of these materials as part of a sustainable crop production program should still be addressed. Our findings show that the greatest effect of plant essential oils and particle films on pest thrips results from altering pest behavior rather than from inducing mortality. We still need to work closely with growers to demonstrate that altering pest behavior can be an effective management strategy, and may be a more sustainable approach than reliance on insecticides to kill thrips. Some of these issues will be addressed on continuing studies based on this SARE funded project.
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