the Evolution of Soft and Safer Insecticides
John C. Palumbo, Ph.D., is a professor and extension specialist in the Department of Entomology at the University of Arizona. An Arizona native, he received his BS in Agricultural Science (1982), and MS in Entomology (1985) from the University of Arizona, and a Ph.D. degree in Entomology from Oklahoma State University (1989). He joined the department in 1990 as a faculty member at the Yuma Agricultural Center where he has developed an internationally recognized extension and research program in integrated pest management for desert vegetable and melon crops.
His translational research and outreach programs are developed to provide the desert vegetable and melon industries with innovative insect management solutions. Dr. Palumbo’s research activities primarily involve addressing immediate problems in local and regional vegetable crops, as well as more basic, long-term approaches. As an Extension Specialist, Dr. Palumbo is responsible for developing a science-based outreach program that emphasizes the development, validation, and delivery of new information and technologies for managing pests in desert vegetable and melon crops that reduces grower reliance on high-risk, broadly toxic pesticides without sacrificing yield, quality and profitability. His formal teaching responsibilities include teaching ENTO 300, Insect Pest Management in Desert Cropping Systems, a 3-hour course offered as part of the College of Agriculture and Life Sciences, and Crop Production Degree offered through the UA-Yuma academic program.
Over the past 33 years, he has worked collaboratively with scientists from the University of Arizona, the University of California, USDA-ARS, and the Agrichemical Industry to develop pest management alternatives and educational programs for several invasive species in the western U.S. including sweet potato whitefly, Lettuce aphid, Bagrada bug, Diamondback moth, and Western flower thrips. These efforts have resulted in hundreds of scientific publications, book chapters, and extension bulletins. He has delivered over 700 presentations to growers, PCAs and agri-business interests during his tenure on a wide range of topics on vegetable IPM and insecticide alternatives.
As Yuma, Arizona’s 2022-2023 produce season winds down, it seems appropriate to discover from our U of A scientists what is front and center in the ongoing battle of the bugs.
Arizona Agriculture: Talk about some of the big insect ecology projects you are working on in Yuma.
Palumbo: Our big project in Yuma is currently focused on understanding the relationship between Impatiens Necrotic Spot Virus (INSV) and Western flower thrips (WFT) in desert lettuce. INSV, a virus transmitted by WFT, was first reported in Yuma in the spring of 2021. We have been developing IPM programs for WFT for many years, but we have limited knowledge of this new virus and its impact on local lettuce production. Thus began a collaborative research program with UA scientists, pest control advisors (PCAs), lettuce growers and shippers to study WFT ecology and INSV epidemiology.
We were especially curious how the virus became established in the desert and the host range of INSV and WFT. Several weed species are known to be reservoirs for both the virus and vector so we began surveys to track their abundance on weeds and crop hosts to determine if the virus can persist throughout the summer in the absence of lettuce.
To date, results indicate that weeds and other crops don’t appear to play a role in maintaining or spreading INSV in the desert even though WFT can readily be found on these hosts. Most importantly, during the summer when lettuce is not grown, INSV could not be found in the cropping landscape (weeds, alfalfa, cotton, melons). However, INSV has been detected on fall lettuce for the past three growing seasons suggesting that INSV was entering our cropping system each fall on infected transplants originating in Salinas.
A sampling of transplants entering Yuma showed that INSV-infected thrips were found infesting transplants. Concurrently, INSV-infected plants were found in transplanted lettuce fields. By the spring, INSV had spread to direct-seeded lettuce grown adjacent to or near transplanted fields.
These studies clearly indicate to us that INSV is not established in the desert, but rather immigrates back into lettuce each fall on imported transplants. We are continuing these studies for another year to confirm the epidemiology of INSV and use this information to develop management alternatives for mitigating future problems including new integrated pest management guidelines for cultural and chemical management of WFT.
Arizona Agriculture: Discuss how you believe Integrated Pest Management (IPM) programs have improved in just the last few years.
Palumbo: In leafy vegetable production, our IPM programs rely heavily on the availability of safe and effective insecticides. The evolution of soft and safer insecticides has progressively improved over time and made our IPM programs more relevant and effective.
Arizona Agriculture: What makes your efforts in Arizona, certainly Yuma, unique to the IPM world.
Palumbo: Our irrigated cropping system. I’m not aware of many agroecosystems in the world that are as diverse and productive as the Arizona desert. The ability to produce leafy vegetables during the winter overlapping with cotton, melons, alfalfa and forage crops, durum wheat, and miscellaneous specialty crops during the summer certainly makes IPM in Yuma unique. And all this surrounded by an arid desert landscape where plant abundance fluctuates seasonally with winter and monsoon rains.
Accordingly, our cropping system often creates insect problems unique to the desert southwest. I often tell students “All IPM is local,” meaning that the principles of IPM are the same wherever you grow crops, but the strategies and tactics are unique to your growing area. Thus, when new problems arise, the IPM solutions must be generated locally. In essence, the scientific knowledge base necessary for helping growers and PCAs with local problems and implementing new IPM approaches must be developed specifically for our unique desert growing conditions in Arizona.
Arizona Agriculture: From your perspective as a scientist, what makes Yuma so special?
Palumbo: It’s the people. The growers, PCAs and local Agribusinessmen I work with are insightful and innovative, eager to work with us in understanding production problems and finding relevant solutions. Our ability to conduct high-quality research in Yuma would not be possible without their support and generosity. The state-of-the-art research labs and facilities at the Yuma Agricultural Center were essentially built by the local growers. Over the years, I’ve had the opportunity to travel and visit my Extension counterparts throughout the U.S. and have yet to see a comparable level of interaction and collaboration among Cooperative Extension, growers, and the associated Agribusinesses. Yuma is special.
Because of my relationships with Arizona growers and PCAs, I receive phone calls and text messages from them daily with IPM-related questions. I’m often asked for advice about an insect identification or a specific problem, other times I’m asked to offer my thoughts on an IPM recommendation. Sometimes they call just to see what I’ve learned lately. Often, I call them for the same reason. It’s a very synergistic working relationship.
Arizona Agriculture: What’s been the most exciting discovery, experience and even IPM advances for you?
Palumbo: In my view, the development of reduced-risk insecticides for Arizona vegetables is the most exciting advancement in IPM during my career. I’ve been fortunate to be on the leading edge of helping growers and PCAs understand these new insecticides and integrate them into their IPM programs. When I first started in Yuma, produce growers were heavily dependent on broadly toxic organochlorine, organophosphate and carbamate insecticides for insect control which raised concerns about environmental and dietary risks. The agrochemical industry responded to these issues and today produce growers have over twenty new insecticide chemistries at their disposal, that are IPM compatible, inherently less toxic to field workers, consumers, and non-target organisms, and have a low potential for groundwater contamination. Ultimately, this is how leafy vegetable growers can effectively control insect pests and produce high-quality produce while mitigating risks to human health and the environment.
Arizona Agriculture: You mention that one of your goals is to determine the relationships between insect feeding and plant injury. Talk about this and how we’ve advanced.
Palumbo: Having a thorough understanding of the relationship between insect feeding, their abundance and the associated plant damage they cause is essential for developing economic thresholds used for the proper timing of insecticides. This includes knowledge of insect biology and ecology, plant biology and market economics. In practice, an economic threshold is the level of pest abundance on plants that triggers a control measure (i.e., insecticide application) to prevent economic losses in yield and quality. As new pests appear, developing thresholds for their management has been a research priority. For example, over the years we developed thresholds for whiteflies in cantaloupes, aphids in lettuce, and most recently bagrada bug and diamondback moth in Cole crops.
Arizona Agriculture: You’re also concentrating your efforts on figuring out better monitoring and sampling of insects on vegetable crops. Share some insights.
Palumbo: There’s a saying I teach local PCAs: “When in doubt, scout!” Scouting, also known as monitoring or sampling, is the foundation of our vegetable IPM programs. Ultimately, scouting is about making sound management decisions. Scouting fields allows a PCA to determine the level of insect infestation and whether control is needed to prevent economic losses to the crop. With this information, growers can justify an insecticide application or avoid unnecessary chemical use. Most PCAs intensively scout lettuce or broccoli fields 3-4 times per week to determine if economic thresholds have been exceeded. Thus, scouting fields for insect pests plays an essential role in making informed IPM decisions. So, when there is any doubt on whether a pest has reached economic status, the best thing you can do is – scout.
Arizona Agriculture: From the perspective of an entomologist at 30,000 feet, what makes Arizona produce production so important and so special?
Palumbo: Arizona growers fill an important niche in lettuce production for American consumers. The ability of Arizona growers to produce safe, high-quality, and inexpensive leafy vegetables from November to April is not only important but uniquely special. No other domestic growing region in the country can supply the amount of produce to American consumers during the winter that desert growers do.
Arizona Agriculture: Despite water, insect, and cost management challenges, do you remain hopeful and why?
Palumbo: Absolutely. In my 33 years as an Extension entomologist working in Yuma, I’ve experienced several pest crises that threatened the economic viability of Arizona produce and melon industries. But in every crisis, the industry was able to meet these challenges and flourish.
For example, when the sweet potato whitefly invaded the desert in the 1990s, many thought that crop production in Arizona would dramatically decline due to the inability to control the pest. But, in fact, growers quickly overcame the crisis due to the collaborative efforts of university scientists, the agrochemical industry, PCAs, and growers working together to develop innovative, cost-effective solutions.