Final report for GS19-210
Sweetpotato whitefly, Bemisia tabaci, is a major economic pest of row crop vegetables causing widespread feeding damage and vectoring many viruses, including tomato yellow leaf curl virus (TYLCV), which leads to considerable yield loss. Growers are facing increasing challenges in controlling B. tabaci as populations during major growing seasons have become increasingly unpredictable and resistant to conventional insecticides. In an effort to develop a more sustainable integrated pest management program, alternative methods for controlling B. tabaci are being explored that take advantage of the whitefly’s natural host seeking behaviors.
Since visual stimuli play a dominant role in host searching behavior, implementing visual traps that display the most attractive wavelengths in the visual spectrum shows great potential in reducing B. tabaci infestations. In addition, many natural repellents including kaolin clay can repel whiteflies visually or mask the attractive volatiles produced by their vegetable host. Preliminary studies have already shown that kaolin clay has proven to act as a moderately successful, natural repellent of B. tabaci adults. However, little to no research has investigated the efficacy of kaolin in combination with other natural repellents and as part of a completed IPM system.
This study will highlight the potential for implementing a “push/pull” system utilizing a combination of natural repellents and visual traps to keep whiteflies below the economic threshold in row crop vegetable. Using this system will reduce the need to use conventional insecticides and lower the associated negative impacts on environmental and human health while increasing benefits for growers.
- Determine how visual attractiveness in TYLCV-infected tomato changes whitefly behavior.
- Determine how B. tabaci behavior is influenced by olfactory cues in healthy tomato vs. TYLCV-infected tomato and compare how this behavior changes when combined with the most attractive visual cues found in Objective 1.
- Determine the efficacy of several natural repellents on whitefly settling in tomato under greenhouse conditions.
- Conduct field trials to test the efficacy of kaolin clay as a natural repellent for B. tabaci nymphs and adults when applied alone and in combination with several botanic oils.
We conducted the lab work pertaining to objectives 1 and 2 in the grant proposal. Materials and methods can be obtained from the published paper mentioned in the results below. Briefly, we tested the response of whiteflies to visual and odor cues from uninfected and TYLCV-tomatoes at different stages of infection. We also compared the response of whitefly uninfected or infected with TYLCV.
In 2018, we conducted field and lab research regarding the repellency of kaolin against whitefly, Bemisia tabaci when sprayed as a particulate barrier on a vegetable host. Our results of this research showed that kaolin worked best when combined with an essential oil such as limonene. We found that kaolin and limonene had an additive effect. Kaolin is adsorbing limonene and allows for the slow release of limonene. With the potential additive effects of kaolin acting as a carrying agent for limonene, we conducted two large field trials in tomatoes in fall 2019, and fall 2020. Our four primary treatments were the untreated control, kaolin alone, limonene alone, and both kaolin and limonene combined. Data regarding adults, nymphs, TYLCV infection rate, and yield were collected.
The detailed results yielded from our lab work can be found in the following publication:
Johnston, N. and Martini, X., 2020. The Influence of Visual and Olfactory Cues in Host Selection for Bemisia tabaci Biotype B in the Presence or Absence of Tomato Yellow Leaf Curl Virus. Insects, 11(2), p.115.
This paper was recently published, and we have acknowledged the SSARE grant’s contribution to funding this research. In this paper we found that under visual stimuli only, B. tabaci exhibited a visual attraction to the color yellow, TYLCV-infected tomato leaves, and TYLCV-infected tomato volatiles. The attraction was the strongest overall when both visual and olfactory cues from TYLCV-symptomatic tomato plants were combined, as opposed to a single isolated cue. In addition, we pursued our investigations and found that TYLCV-infected whiteflies were more attracted to uninfected tomatoes as compared to uninfected whiteflies.
Regarding our field trials in tomato, we found that kaolin and limonene combined have an additive effect in repellency, were twice as effective as either product alone, and over four times more effective at reducing whitefly populations compared to the untreated control. This trend was also reflected in our tomato yield, where all tomatoes were processed and graded by industry standards. In 2019, we found that the total weight and number of large grade tomatoes from limonene-scented kaolin treatments was higher than all other treatments including control tomato plots. However; this control method is highly affected by rainfall that can decrease tremendously the efficacity of limonene scented kaolin.
The overall results of limonene-scented kaolin in our tomato field trials funded by SSARE can be found in the following article published in the journal Crop Protection:
Johnston, N., Paris, T., Paret, M., Freeman, J., Martini, X., 2022. Repelling whitefly (Bemisia tabaci) using limonene-scented kaolin: A novel pest management strategy. Crop Protection, p.105905.
As conventional systems rely mostly on insecticides, these new methods of combining kaolin and repellents offer growers a potentially novel, organic method for controlling one of the most destructive agricultural pests in Florida.
Educational & Outreach Activities
On October 1st 2021, we held a 50th anniversary for our work building where farmers and the general public were given field and lab tours. During this event, we were able to conduct demonstrations of our research with kaolin clay repelling whiteflies to dozens of people.
On October 21st, 2021, we organized a sustainable vegetable production workshop using SSARE grant funds. During this event, we had several keynote speakers talk about research outlined in this grant and garnered awareness from many local growers and farmers. 40 attendees
On December 9, 2021, the research regarding kaolin clay and limonene as whitefly repellents was presented at the Gadsden County tomato grower field day. Quincy, FL. 80 attendees.
On January 25, 2022, the research regarding kaolin clay and limonene as whitefly repellents was presented at the TriState Cucurbit and Emerging vegetables conference. Marianna, FL. 50 attendees.
We had one press release on this research by UF/IFAS
Romaguera K. (2022) Study: White clay spray mix repels major crop pest. https://blogs.ifas.ufl.edu/news/2022/01/25/study-white-clay-spray-mix-repels-major-crop-pest/
We had the following presentations at scientific conferences from this grant:
Martini X., Paris T., Johnston N. Symposium. Use of kaolin, semiochemicals and visual cues to develop control strategies against Bemisia tabaci in vegetable crops. Southeastern Branch of the Entomological Society of America. March 26-30, 2022, San Juan, PR.
Johnston N, Martini X. Controlling silverleaf whitefly (Bemisia tabacibiotype B) using limonene-scented kaolin: A non-insecticidal approach. Annual meeting of the Entomological Society of America, October 31, November 3, 2021, Denver, CO.
Johnston N, Martini X. Symposium. The influence of visual and olfactory cues in host selection for Bemisia tabaci Biotype B in the presence or absence of tomato leaf curl virus. Annual Meeting of the Entomological Society of America. November 11- 24 2020. Online meeting.
Johnston N, Martini X. Controlling sweet potato whitefly (Bemisia tabaci) using kaolin: an integrated IPM approach. Annual Meeting of the Southeastern Branch of the Entomological Society of America. March 3-6, 2019, Mobile, AL.
Johnston Ng, Martini X. Changes in plant visual and volatile cues caused by Tomato yellow leaf curl virus influence Bemisia tabaci, MEAM 1, Host Selection over Time. Southeastern Branch Meeting of the Entomological Society of America. March 26-29 2022, San Juan PR.
The following Extension articles have been published:
Johnston N, Paret M, Martini X. (2019) Using Kaolin to Manage Whiteflies: A Novel Approach. Panhandle AG e-news. http://nwdistrict.ifas.ufl.edu/phag/2019/03/01/using-kaolin-to-manage-whiteflies-a-novel-approach/
Overall, this project did much to promote awareness for alternative whitefly management practices other than heavy insecticide use. Implementation of these methods will greatly reduce environmental contamination and negative impact on beneficial organisms such as plant pollinators. Once limonene scented kaolin becomes widely distributed as a commercial product available to growers (making it more affordable), this research will greatly benefit sustainable agriculture by providing an organic whitefly control method comparable to insecticidal control. We have worked to promote interest in the research funded by SSARE and have already conducted a successful commercial field trial using the methods described in the grant proposal. We hope that continued success with our developed product will continue to garner interest from local growers and eventually become adopted on a larger scale in the future.
By working directly with growers we found that limonene scented kaolin could replace at least 50 % of the conventional insecticide applications without losing control against whitefly. This new technology has already been adopted by several growers and we will continue to promote it among our clientele.
We gained an increased understanding of how to manage field scale projects in conjunction with other researchers. There is always a learning experience to be gained when realizing that sustainable agricultural practices are easy to theorize but difficult to implement. For my part, it is humbling to realize that my area of expertise (entomology) is only one aspect of all the problems that growers must face. For example, even if whitefly populations are controlled, crops might still have difficulty growing due to poor soil quality, mismanagement of water resources, or even a fungal infection (which happened in our watermelon). These problems have shown me the importance of collaboration between scientists with diverse areas of agricultural expertise.
We will continue to explore new avenues for improving the use of kaolin on vegetable crops. Notably, we are investigating the use of dye to color kaolin clay in blue or red, that is colors that are less attractive to whiteflies. The major area of research is t be able to decrease the cost of limonene-scented kaolin at a level that will make it competitive with most conventional insecticides used in vegetable production.
- Using Kaolin to Manage Whiteflies: A Novel Approach (Fact Sheet)