Next Wednesday we will host a whitefly CEU meeting at YAC. Details for meeting are below.

Date: Wednesday, June 17th
Time: 7:00am-9:15am
Location: U of A Yuma Ag. Center
6425 W. 8th St., Yuma, AZ, 85364
Breakfast burritos will be provided, please email me, maceyw@arizona.edu to RSVP.

Aso, mark your calendars for Tuesday, July 14th when we will host the Vegetable Pest Losses workshop, more details to come.

Norman E. Borlaug completed his Ph.D. in plant pathology at the University of Minnesota in 1942. He worked briefly as a microbiologist for the DuPont de Nemours Foundation. In 1944 he accepted a position as a geneticist and plant pathologist and began work at the International Maize and Wheat Improvement Center (CIMMYT, Centro Internacional de Mejoramiento de Maíz y Trigo) based in Ciudad Obregón, Sonora, Mexico.  

Norman Borlaug (left) and his colleague George Harrar in a wheat field in the Yaqui Valley, Sonora, Mexico in 1944.

In joining CIMMYT, Borlaug had the responsibility of organizing and directing the Cooperative Wheat Research and Production Program in Mexico, which was a joint program with the Mexican government & Rockefeller Foundation. This program utilized scientific research in a fully integrated agronomic system utilizing genetics, plant breeding, plant pathology, entomology, soil science, and cereal technology.  

The primary objective of Borlaug and his team of colleagues was the development of semi-dwarf varieties of wheat with improved disease resistance, particularly stem rust caused by Puccinia graminis f. sp. tritici (Borlaug, 1968). In the 1940s, Mexico imported a substantial portion of its wheat because of low productivity and severe disease pressure. Within twenty years Borlaug and his team were realizing spectacular success in developing high-yielding short-strawed, diseaseresistant wheat varieties.

One of the key developments by Borlaug and his colleagues was a breeding strategy that combined shuttle breeding between contrasting environments, in this case of the Yaqui Valley of Sonora near Ciudad Obregón, Sonora and Puebla, Mexico with rigorous disease screening. This approach accelerated genetic gains and produced broadly adapted wheat cultivars with durable disease resistance.

Borlaug’s team also developed the incorporation of dwarfing genes into spring wheat varieties. Traditional wheat cultivars commonly developed long stalks and tall plants that were prone to lodging, particularly if provided sufficient water and nitrogen (N) fertilization. This lodging and vegetative growth tendency was limiting yield potential. The new semi-dwarf cultivars allocated more biomass to grain production with a higher harvest index (Pingali, 2012).  

The release of two principal varieties, Lerma Rojo 64 and Sonora 64, dramatically increased yields in Mexico and by 1963, Mexico became a net exporter of wheat. Borlaug and the CIMMYT program next directed attention to wheat production in southern Asia and between 1965 to 1970, wheat yields nearly doubled in Pakistan and India, greatly improving food security.

The collective increases in yield from these programs have been labeled the “Green Revolution”, referring to the rapid increase in global agricultural productivity that occurred between the 1940s and the 1970s through the development of improved crop varieties. These developments were especially important in Asia and Latin America, where food shortages and rapid population growth raised concerns regarding widespread famine (Evenson and Gollin, 2003).  

The Green Revolution is often credited with saving over a billion people from starvation and in 1970 Borlaug was Awarded the Nobel Peace Prize in recognition of his contributions to world peace through increasing food supply. He is the first and only agronomist to win the Nobel Peace Prize.  

The program was a systems approach that consisted of agronomic practices that included improved irrigation, fertilization, and mechanization. Although many scientists, governments, and institutions contributed to the Green Revolution, the work of Norman Borlaug was central to its success.  

The Green Revolution developments were also extended beyond wheat. Similar advances occurred in rice breeding through the development of semi-dwarf rice cultivars such as IR8 at the International Rice Research Institute. These plant breeding innovations have contributed to major increases in cereal grains and other crops across many parts of the world in the past 50 years (Khush, 2001).

Borlaug repeatedly and quite emphatically pointed out the fact that their work with the CIMMYT program was only one small step, and it was far from perfect. He consistently encouraged the next generation of agronomists and agricultural scientists to continue working diligently to address food security in the fight against what he often referred to as the “population monster” facing humanity.

Borlaug and the CIMMYT program substantially reduced hunger and demonstrated the importance of science-based agricultural innovation. Due to his contributions to global food security, Borlaug remains widely recognized as one of the most influential agronomists and plant breeders of the twentieth century.

References
Borlaug, N.E. 1968. Wheat breeding and its impact on world food supply. Proc. Third Int. Wheat Genet. Symp. 1:1–36.

Evenson, R.E., and D. Gollin. 2003. Assessing the impact of the Green Revolution, 1960 to 2000. Science 300:758–762. doi:10.1126/science.1078710.

Khush, G.S. 2001. Green revolution: The way forward. Nat. Rev. Genet. 2:815–822. doi:10.1038/35093585.

Pingali, P.L. 2012. Green Revolution: Impacts, limits, and the path ahead. Proc. Natl. Acad. Sci. USA 109:12302–12308. doi:10.1073/pnas.0912953109.

In the last edition of the Veggie IPM newsletter I advertised a collaborative incident response meeting to this year’s unprecedented spring melon virus epidemic. This meeting was made possible through a collaborative effort between the University of California’s Cooperative Extension, USDA-ARS, and the University of Arizona’s Cooperative extension, and of course through the participation of the melon growing community of the Desert Southwest. The goal of the meeting was to revisit currently available management methods and practices, discuss this year’s potential epidemiological trends and pattern observations, and, very importantly, to get a sense of the economic impact this epidemic was having as a result of this anything-but-normal season.

The community’s response to this call to action and reactionary meeting, a career first for me, was overwhelmingly encouraging in many ways. Despite limited advertising, we had excellent turnout and participation, with over 70 attendees including growers, PCAs, industry representatives, and academics filling the room and contributing valuable insights to the open forum discussion. A post-meeting survey of attendees managed to capture representation from a total of 6,825 acres of spring melon grown across Arizona, California, and Mexicali.

I thought some of the key economic, epidemiological, and entomological highlights from the community survey worth sharing were the following:

• Whitefly infestations were reported on 6313 out of 6825 surveyed acres.
• Of those infested acres about 40% of the crops were reported to have whitefly-vectored virus symptoms by the time of the meeting.
• The overall estimated yield loss attributed to whitefly and virus pressure averaged 20% and ranged from 0% in early-planted melons to 100% in late-planted melons within individual plantings.
• 100% of surveyed acres received whitefly control applications consistent with the melon IPM recommendations developed and endorsed by Dr. Palumbo.

I cannot express my gratitude enough to everyone who participated in the meeting, who added to the “debrief” discussion, and took the time to complete the economic loss survey. We never know who will be reviewing and making crucial decisions on our requests for funding or support for our applied research and for developing new IPM strategies to address these challenges. In many cases, those decision-makers are far removed from what we are experiencing here on the ground. Maybe they work in specialty crops but in a climate as different as New Jersey or they may be an expert in whitefly-vectored viruses but work only in field crops of North Dakota. When these often-anonymous gatekeepers critical to advancing our requests for support hear that the whitefly-vectored melon virus epidemic of the Desert Southwest was record-setting in 2026, we cannot afford to simply hope that they’ll grasp what that meant the way we can. We lived the reality of it, but it’s just a sentence on a piece of paper to them. The information you provided is invaluable in helping us tell that story in a way others, no matter how separated from our community they are, can understand. Your efforts and shared experience put real numbers and quantifies the impact these plant health challenges have on our industry.

And these numbers are what are critical for strengthening and justifying grant proposals and requests for federal dollars to research the next best management strategy, for informing regulatory and pesticide review processes who may or may not see the value in the inputs that make our industry thrive, and, perhaps most important to me and my colleagues, for advancing our understanding of regional and seasonal pest trends under unusual and atypical conditions so that we can build in more flexibility to our recommendations and strategies. Your participation helps ensure that the true scale and significance of our plant health challenges are recognized, documented, and acted upon.

From the bottom of my heart, thank you.  
-Chris

If you have any concerns regarding the health of your plants/crops please consider submitting samples to the Yuma Plant Health Clinic for diagnostic service or booking a field visit with me:

Christopher Detranaltes, Ph.D. Cooperative Extension – Yuma County
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109

It is with mixed emotions that I write to inform you that this will be my last University of Arizona Vegetable IPM Update. The reason – I am retiring. Thank you for your support over the years. It’s been an honor and a privilege working with you and serving this ag community.

Figure 1. Automated Thinning & Weeding Technologies Field Day.
(Photo credits: Rosa Bevington)

Last year, I was contacted by one of our PCAs regarding a concerning observation of escaped Palmer amaranth plants in a cotton field that may indicate potential glyphosate resistance.  

Palmer amaranth continues to be one of the most problematic weeds in row crops due to its aggressive growth habit, high seed production, and documented ability to evolve herbicide resistance.

Field Observation & Seed Collection
Following the PCA report, I visited the field and began collecting seeds from the suspected escaped Palmer amaranth plants during the 2025 cotton growing season.

Sampling collection of Palmer Amaranth, August 18th, 2025

Research Effort and Funding
In collaboration with other colleagues, we submitted a grant proposal aimed at supporting a structured study of Palmer seed collection and greenhouse bioassays to test herbicide response across Yuma and Pinal County locations to map for resistance. Unfortunately, the proposal was not funded. Despite this setback, I decided to move forward by self-funding a preliminary experiment to begin generating data and insights.

Greenhouse Bioassay Initiation
The collected Palmer amaranth seeds were planted on June 4th, 2026, in a greenhouse setting. The initial germination rate of the collected seeds was 77%

Greenhouse Bioassay Experiment Setting

Experimental Plan
The next phase of this experiment involves:

• Thinning the trays to maintain a manageable number of healthy plants per replicate
• Applying multiple rates of glyphosate, including labeled and above-label rates, to assess plant survival and response
• Monitoring plant injury, survival, and potential recovery post-application

This dose-response approach will help determine whether the population exhibits traits consistent with glyphosate resistance.

Field & Greenhouse Documentation
This study will be accompanied by images documenting the process, including:

• Early-stage germination and seedling development in the greenhouse
• Plant responses following herbicide treatment

What’s Next
The plants will continue to be carefully monitored as they develop to an appropriate stage for spraying. Once herbicide applications are completed and responses evaluated, results will be compiled and shared.

Stay tuned for updates as we assess whether this Palmer amaranth population represents a new case of glyphosate resistance in our region. If you have encountered similar escapes or suspect resistance in your fields, please feel free to reach out. Collaboration is key to staying ahead of herbicide resistance challenges

Diamondback moth (DBM), Plutella xylostella, is one of the most important insect pests of Brassica crops, including cabbage, broccoli, cauliflower, and some leafy greens. Heavy infestations can cause significant feeding damage, reduce crop quality, and increase production costs. Because DBM has a long history of developing resistance to insecticides, regular monitoring of insecticide susceptibility is essential to ensure effective management in the field. In the western United States, resistance to several key insecticide classes has been documented in field populations. For example, populations in California have shown high levels of resistance to several insecticide classes, including diamides, spinosyns, avermectins, pyrethroids, and Bacillus thuringiensis (Bt) products. More recently, outbreaks in Arizona have been associated with confirmed resistance to diamide insecticides and reports of reduced field efficacy. This highlights the importance of regular insecticide susceptibility monitoring and the implementation of resistance management strategies to maintain effective control of the pest. While field resistance and reduced efficacy reflect outcomes under production conditions, laboratory susceptibility monitoring provides a standardized approach to detect shifts in population response before or alongside observable field control issues.

To evaluate current insecticide susceptibility levels in DBM populations across Arizona's major Brassica-growing regions and some California populations, DBM larvae were collected from multiple locations in Arizona and California. DBM populations were reared in the laboratory, and their progenies were tested under controlled laboratory conditions.

In the laboratory, larvae were exposed to insecticides at the highest labeled field rate using a leafdip bioassay. The insecticides evaluated included Exirel®, Coragen®, Harvanta®, Radiant®, Baythroid® XL, Proclaim®, Torac®, DiPel®, and XenTari®, representing commonly used conventional and organic management options, as well as IncipioTM, which was recently registered. These laboratory bioassays measure relative susceptibility under controlled conditions using field-collected populations reared in the laboratory. Results represent mortality at the maximum labeled rate under leaf-dip assay conditions and may not directly reflect field performance, where environmental conditions, application timing, coverage, larval stage, and population dynamics influence control. These data are intended to monitor susceptibility trends and help inform resistance management decisions. Accordingly, extrapolation to field performance should be made cautiously, recognizing both the constraints of laboratory bioassays and the mosaic of susceptibility that may exist within and among field populations.

Several Insecticides Showed High Laboratory Mortality Across Field-Collected Populations

Several of the insecticides evaluated caused high mortality of DBM larvae in laboratory assays across field populations. Proclaim, Incipio, Radiant, DiPel, and XenTari caused high mortality, indicating laboratory susceptibility across the tested populations. These products remain promising options for managing DBM in Brassica crops based on current laboratory susceptibility data. In contrast, Coragen, Exirel, and Baythroid XL resulted in lower mortality in laboratory assays than the other insecticides (Figure 1).  

Figure 1. Mean mortality (%) of DBM larvae exposed to the maximum label rate of
insecticides, combined across 10 field populations from California and Arizona.

DBM Mortality by Collection Location, with Some Population-Level Variability
The levels of larval mortality caused by each evaluated insecticide were generally consistent across populations. For DBM populations collected during fall 2025, Proclaim, Incipio, Radiant, DiPel, and XenTari resulted in high larval mortality under laboratory assay conditions for most DBM populations tested (Figure 2). However, slight reductions in larval mortality were observed in specific populations. For example, DiPel resulted in approximately 70% larval mortality in the Coachella Valley, CA population # 4, and Radiant caused approximately 55% larval mortality in the Coachella Valley, CA population #2. Despite this variability, these insecticides generally resulted in high mortality of DBM larvae across geographic locations under laboratory assay conditions (see Figure 1). In contrast, Coragen, Exirel, and Baythroid XL consistently resulted in low DBM larvae mortality in the field-collected populations from Salinas Valley, CA; Coachella Valley, CA; and Gila Valley, AZ (Figure 2).  

We observed similar mortality trends among populations collected during winter/spring 2026 for the evaluated insecticides except for DBM mortality caused by Dipel, which declined in many populations (Figures 3 and 4). Harvanta was evaluated for two populations (Imperial Valley, CA and Somerton, AZ), which exhibited similar reduced larval mortality to that of the other diamides. Torac was also evaluated for the Imperial Valley, CA, population, resulting in a high level of DBM mortality (Figure 4). We also tested a population collected from the Yuma Ag Center, which resulted in susceptibility levels very similar to those of the susceptible laboratory colony (Figure 3). Previous DBM monitoring studies performed by Dr. Palumbo over several years also showed that while populations collected from commercial fields showed very low susceptibility to diamides, populations collected at the Yuma Ag Center remained highly susceptible. This indicates that transplant sources and/or field-specific DBM management practices are also affecting DBM susceptibility and control across Arizona’s brassica-growing regions.  

The reduced and variable levels of larval mortality observed in laboratory assays across multiple field populations for some tested insecticides highlight the importance of routine susceptibility monitoring to better understand resistance dynamics and to support informed field-level decisions regarding product selection and rotation.  

Figure 2. Mortality (%) of DBM larvae from field populations collected from Arizona
and California as affected by maximum label rates of 8 insecticides, Fall 2025.


Figure 3. Mortality (%) of DBM larvae from a susceptible lab colony and field
populations collected from Arizona as affected by maximum label rates of 8
insecticides, Winter/Spring 2026.

Figure 4. Mortality (%) of DBM larvae from two field populations collected from
Arizona and California as affected by maximum label rates of ten insecticides, Spring 2026.

Key Laboratory Findings

• Several products resulted in consistently high larval mortality under laboratory assay conditions across field-collected populations.
• Some products resulted in comparatively lower larval mortality in laboratory assays across multiple field-collected populations.
• Mortality levels varied among certain DBM populations, suggesting differences in susceptibility.

Implications for Resistance Monitoring and Field Decision-Making

• Continued susceptibility monitoring is important for detecting shifts in population response before widespread field control issues emerge.
• Product rotation among different modes of action remains an important tactic to slow resistance development.

Laboratory monitoring informs our understanding of resistance trends, but field scouting remains essential to evaluate how populations respond under production conditions. As always, when in doubt, scout!

Additional Reading Materials

1. Calvin W., M. N. Keith, and B. McGrew. 2025. Guidelines for Effective Management of Diamondback Moth in Brassica Crops. University of Arizona Extension Publication. az2143. https://extension.arizona.edu/publication/guidelines-effective-management-diamondbackmoth-brassica-crops
2. Calvin, W. and J. C. Palumbo. 2024. Chlorantraniliprole Resistance Associated with Diamondback Moth (Lepidoptera: Plutellidae) Outbreaks in Arizona Brassica Crops. Journal of Economic Entomology. toae212, https://doi.org/10.1093/jee/toae212.

If you have ever watched a well-irrigated field show signs of stress during a hot, dry afternoon, you have seen the effects of Vapor Pressure Deficit (VPD) in action. While growers often focus on temperature, humidity, evapotranspiration (ET), and soil moisture when making irrigation decisions, VPD provides another valuable piece of information: how strongly the atmosphere is pulling water from the crop.

What Is VPD?
Vapor Pressure Deficit (VPD) is the difference between the amount of moisture the air can hold when fully saturated and the amount of moisture actually present in the air. In simple terms, VPD measures the atmosphere's demand for water. VPD is determined by both air temperature and relative humidity. As temperatures rise and humidity decreases, VPD increases. Conversely, cooler temperatures and higher humidity result in lower VPD values. Because VPD integrates the effects of both temperature and humidity, it often provides a better indication of crop water demand than either variable alone. Two days with the same air temperature can place very different demands on a crop if humidity levels differ substantially.

Why VPD Matters for Irrigation Management
Among its many applications, VPD is particularly valuable for irrigation management. Higher VPD values increase transpiration, causing crops to lose water more rapidly through their leaves. As atmospheric demand increases, crops require greater water uptake from the root zone to maintain normal physiological functions. For this reason, VPD can help explain why crop water requirements may change from day to day, even when temperatures appear similar. Monitoring VPD alongside ET estimates and soil moisture measurements can improve irrigation scheduling and help growers maintain adequate soil moisture during periods of elevated atmospheric demand. When VPD remains high for several consecutive days, crops may experience substantial increases in water use. Understanding these conditions can help growers anticipate periods of increased irrigation demand and make more informed water management decisions.

VPD and Crop Performance
VPD directly influences crop growth, productivity, and physiological performance. Under favorable conditions, plants maintain open stomata that allow carbon dioxide to enter the leaf for photosynthesis while water vapor exits through transpiration. This process supports plant cooling, nutrient transport, and biomass production. However, when VPD becomes excessively high, plants often respond by partially closing their stomata to reduce water loss. Although this protective mechanism conserves water, it also limits carbon dioxide uptake and photosynthesis. Prolonged exposure to high VPD conditions can reduce growth rates, decrease biomass accumulation, and negatively affect yield and crop quality.Conversely, extremely low VPD conditions can suppress transpiration and reduce nutrient movement within the plant. As a result, both excessively low and excessively high VPD conditions can influence crop performance.

VPD and Integrated Pest Management (IPM)
VPD can also provide useful insight into environmental conditions that influence pest and disease development. Low VPD conditions are typically associated with higher humidity and longer periods of leaf wetness. These conditions may favor the development of fungal and bacterial diseases in susceptible crops. High VPD conditions, on the other hand, can increase plant stress and influence crop susceptibility to certain insect pests and other environmental stresses. While VPD alone does not predict pest outbreaks, it helps explain environmental conditions that affect crop health and pest dynamics. Integrating VPD information into crop monitoring programs can therefore support both irrigation and IPM decision-making.

Seasonal VPD Patterns in Yuma
To better understand VPD conditions in the lower Colorado River region, daily weather data from the Yuma Valley AZMet station were analyzed from January 2020 through May 2026. The analysis revealed a remarkably consistent seasonal pattern (Figure 1). The 2020–2025 monthly mean VPD ranged from a low of 0.91 kPa during January and December to a peak of 3.78 kPa in July.

Atmospheric demand increased steadily during spring, rising from 1.33 kPa in March to 2.50 kPa in May. The highest VPD values occurred during the summer months, with June through August averaging between 3.41 and 3.78 kPa.

For practical purposes, these seasonal patterns can be grouped into four production periods (Table 1). Winter months experience relatively low atmospheric demand, while summer months are characterized by extremely high evaporative demand. The difference in atmospheric demand between winter lettuce production and summer crop production is more than three-fold.

March 2026 provides an example of why monitoring current conditions remains important. The monthly average VPD reached 2.39 kPa, approximately 80% above the long-term March average of 1.33 kPa. Growers relying solely on historical expectations would have underestimated crop water demand during that period.

Table 1. Seasonal VPD Conditions in Yuma

Figure 1. Monthly mean vapor pressure deficit (VPD; kPa) at the Yuma Valley AZMet station from January 2020 through May 2026. Colored lines represent individual years, while the dashed black line indicates the 2020–2025 monthly mean. Higher VPD values indicate greater atmospheric demand for water and increased crop transpiration. June 2026 was excluded because only 8 of 30 days were available. 

The Success of Yuma Growers
Perhaps the most remarkable aspect of these findings is not the magnitude of VPD itself, but the ability of Yuma growers to consistently produce high-quality crops under some of the most challenging atmospheric conditions for agriculture in North America. Summer VPD values in Yuma routinely approach 4 kPa, reflecting an environment where the atmosphere exerts an intense demand for water. Despite these conditions, Yuma growers continue to achieve exceptional productivity through efficient irrigation systems, precise water management, and decades of agronomic expertise. Their success demonstrates that agricultural productivity and water conservation can go hand in hand. Through innovation, adoption of advanced irrigation technologies, careful scheduling, and science-based management practices, Yuma growers continue to produce more crop per drop while maintaining the region's position as one of the most productive agricultural areas in the nation.

Data source: Arizona Meteorological Network (AZMet), Yuma Valley station, University of Arizona Cooperative Extension (azmet.arizona.edu).

VegIPM Update Vol. 17, Num. 12
June 10, 2026

Results of sticky trap catches below!!

Whitefly: Adult activity remains steady across locations; above average for this time of the year. Historically, whitefly numbers peak in July.  

Thrips: Adult thrips activity decreased across locations over the last two weeks. About average for this time of the year. Historically, western flower thrips numbers peak in May.