In the previous edition of this publication, I described the work of Norman Borlaug and his colleagues at the International Maize and Wheat Improvement Center (CIMMYT), whose development of high-yielding wheat varieties helped launch what became known as the Green Revolution. Beginning in the 1940s, Borlaug's breeding program in Mexico produced semidwarf, disease-resistant wheat varieties. These varieties dramatically increased wheat production and improved food security in countries such as Mexico, India, and Pakistan (Britannica 2026).
Although the term Green Revolution remains widely accepted, some historians and environmentalists argue that it should also be viewed as a “Blue Revolution” because of its heavy dependence on irrigation and water resources. The new wheat varieties developed by Borlaug and his CIMMYT colleagues that responded exceptionally well to fertilizer and irrigation.
Critics contend that the productivity gains associated with Borlaug's varieties required increased use of fertilizers, pesticides, mechanization, and irrigation, particularly in arid and semi-arid regions. In areas such as the Indo-Gangetic Plains, the full benefits of the new wheat varieties could only be realized where reliable irrigation systems existed.
This perspective contends that water management was as important as plant genetics in achieving the dramatic yield increases of the Green Revolution. Some analysts therefore argue that the revolution was both “green,” because of increased plant growth, and “blue,” because of the essential role of water.
There is some validity to this interpretation. The Green Revolution greatly increased food production and is credited with helping prevent widespread famine, saving at least one million lives. But it also accelerated groundwater extraction in several major agricultural regions. Largescale irrigation projects associated with Green Revolution agriculture have been linked to declining groundwater levels and increased pressure on water resources (Britannica 2026).
From an agronomic perspective, however, crop yield reflects the interaction of genetics, environment, and management. The semi-dwarf wheat varieties developed by Borlaug and CIMMYT represented a fundamental advance in genetic yield potential and harvest index (the proportion of plant material directed into the grain versus the vegetative portions of the plant). Prior to these developments, additional water or fertilizer often produced only modest gains because traditional varieties were prone to lodging and disease. The new germplasm changed the crop’s biological capacity to convert resources into grain (improved harvest index).
Crop productivity depends on four key factors:
Water and nutrients support growth, but they do not create new yield potential by themselves. Borlaug’s breakthrough was the development of varieties that used these resources far more efficiently than previous cultivars. Without the genetic improvements, expanded irrigation and fertilizer use would have generated much smaller gains.
Irrigation and fertilizer inputs removed important constraints, allowing the improved varieties to express their genetic potential. A useful analogy is that water and nutrients provided the fuel, while the new genetics provided the engine. Neither could have achieved the same results alone, but the transformative innovation was the genetic improvement that raised the crop’s biological ceiling.
Therefore, the strongest agronomic argument identifies plant genetics as the foundational innovation of the Green Revolution. Irrigation and nitrogen fertilization were indispensable enabling factors, but they did not fundamentally alter the crop’s biological potential.
The term Green Revolution remains the most accurate description of Borlaug’s achievement, while the “Blue Revolution” interpretation serves as a reminder of the critical role of water in realizing the benefits of improved crop genetics.
References
Britannica. 2026. Green revolution. Encyclopedia Britannica. Available at: https://www.britannica.com/event/green-revolution. Accessed 29 May 2026.
Evenson, R.E., and D. Gollin. 2003. Assessing the impact of the Green Revolution, 1960 to 2000. Science 300:758–762.
Green Revolution. 2026. Wikipedia, The Free Encyclopedia. Available at: https://en.wikipedia.org/wiki/Green_Revolution. Accessed 29 May 2026.
On April 30th of this year, the U.S. Environmental Protection Agency (EPA) published document EPA-HQ-OPP-2026-2973-0002 entitled the “Draft Fungicide Strategy to Reduce Exposure of Federally Listed Endangered and Threatened Species and Designated Critical Habitats from the Use of Conventional Agricultural Fungicides”. This strategy is officially open for public comment through July 20th, and the Arizona Pest Management Center and the University of Arizona are working on formulating a cohesive response.
This latest draft strategy includes a sizable focus on potential off-site movement of fungicides through runoff associated with treated seed. The following excerpt is taken directly from the document:
“As part of the next steps, EPA is requesting stakeholder input on several aspects of the strategy including… Considerations regarding seed treatments, including seed treatment usage data, information and data on the availability of pesticides on the seed coat to runoff, prevalence of non-commercial (e.g., on-farm, on-site) seed treatments, effects of handling (e.g., loading, planting) on the quality of the pesticide coat and its availability for runoff, and relevant agronomic practices that might reduce the potential for runoff from treated seeds (e.g., seeding depths, disposal)”
Accessible as of June 2026 at https://www.regulations.gov/document/EPA-HQ-OPP-2026-29730002
While the potential route of contaminated off-site runoff from treated seed has been a minor discussion in the scientific literature, it has not been enough of a focus to warrant surveying or regulatory decisions at the federal level thus far. This request for information suggests that this may potentially change going forward. The public comment period presents the best opportunity to bring up practical considerations during early stages before regulatory decisions are made. Regulatory decisions are less likely to present unintended consequences when they are informed by real-world operational perspectives which are ultimately guided by region- and crop-specific experience.
To better inform our response, we are seeking information from across Yuma County to help identify use patterns and current stewardship practices related to fungicide-treated seed. A brief, anonymous, five-minute survey can be found at the following link:
https://uarizona.co1.qualtrics.com/jfe/form/SV_bQpJQzNodI3c5x4
We invite growers, PCAs, seed industry professionals, and distributors to fill it out. If you do not work with treated seed as a grower or PCA, answering the first question will accordingly finish the survey. The response will still provide valuable insight into usage patterns. Thank you in advance for your time and participation.Since last season, there have been several new developments in commercial automated thinning and weeding technologies. Companies that focused primarily on weeding have developed new algorithms and/or improved precision so that the machines can now also be used for thinning lettuce. Significant enhancements have also been made to existing lettuce thinning machines including improved speed, durability and the ability to spot spray inter-row weeds. Arizona Cooperative Extension is in the process of organizing the Automated Thinner and Weeder Technologies Roundup, a field day where these technologies will be demonstrated operating in the field. NEW for this year will be that demos will be at the field scale level (> 1 acre) so attendees will have the opportunity to more fully evaluate machine performance and have time to visit with company representatives. The event will be held November 13th at the Yuma Agricultural Center in tandem with the Desert Difference Ag Connect Event. We would like to showcase as many innovative technologies as possible, so please contact me if you are interested in demoing your thinner/weeder or know someone that is. It’s an open invitation - private companies, university and government researchers are all welcome!
Fig. 1. Previous University of Arizona, Cooperative Extension AgTech Field Day Events
held at the Yuma Ag Center.
Palmer amaranth escapes are showing up in cotton despite good early-season control. Most issues are tied to late flushes, missed timing, and heavy reliance on glyphosate programs.
Why escapes are happening
Glyphosate resistance in Palmer is already widespread in the Southwest, so overreliance will continue to fail.
What to do differently
Program basics by system
All cotton systems (foundation)
LibertyLink
XtendFlex / Enlist
Adjuvant reminders
IPM reminders
The sweet potato whitefly (Bemisia tabaci) remains one of the most important insect pests affecting melon and vegetable production in the desert Southwest. In addition to causing direct feeding damage, whiteflies transmit economically important viruses, including Cucurbit Yellow Stunting Disorder Virus (CYSDV) and Cucurbit Chlorotic Yellows Virus (CCYV), which can significantly reduce melon yield and fruit quality. Unusually mild winter and abundant weed growth have led to elevated whitefly populations in spring melons and summer cotton. These conditions have allowed whiteflies and associated viruses to survive and build up earlier than typically observed in the region. Therefore, whitefly and virus pressure are also expected to be higher than normal this fall.
Whiteflies reproduce on numerous crops and weed hosts throughout the year. Cotton, alfalfa, melons, cucurbits, lettuce, and several weed species serve as important reservoirs that sustain populations between cropping cycles. As cotton and other summer hosts mature or are terminated, adult whiteflies disperse into newly planted fall melons, often bringing virus inoculum with them.
Management
Successful whitefly management requires an integrated approach that begins before planting and continues throughout the season. Relying solely on insecticides is rarely sufficient and can accelerate resistance development. Instead, effective programs combine resistant variety, crop health, sanitation, crop placement, scouting, biological control conservation, physical control, and responsible insecticide use.
Sanitation: Sanitation remains the most important management practice for reducing both whitefly populations and virus sources. Crop residues should be destroyed immediately following harvest, and volunteer melons, volunteer cotton, and weed hosts should be eliminated whenever possible. Maintaining clean field borders, canal banks, roadsides, and fallow areas helps reduce whitefly breeding sites and virus reservoirs. Area-wide cooperation among neighboring growers greatly improves the effectiveness of sanitation efforts.
Crop placement/Isolation: Field location can also influence whitefly pressure and virus incidence. Whenever possible, fall melon fields should be planted away from spring melon production areas and major whitefly sources such as cotton and alfalfa. Research conducted in Arizona has consistently shown that melon fields located near these crops are at greater risk of whitefly infestation and CYSDV infection. Isolation distances of 1.2 miles for cotton, 1.9 miles for spring melon fields with volunteers, and 0.6 mile for spring melon fields without volunteers are recommended.
Crop health: Maintaining healthy, vigorously growing crops can help reduce the impact of whitefly feeding and virus infection. Proper irrigation management, balanced fertility programs, and avoidance of excessive nitrogen applications can reduce plant stress and improve crop tolerance. Excessive vegetative growth resulting from over-fertilization may increase crop attractiveness to whiteflies.
Physical control: Row covers can provide effective protection against early-season whitefly infestations and virus transmission in melon production. Covers should be installed before crop emergence and removed before flowering to allow pollination. In areas with high migration pressure, an insecticide application following row-cover removal may be warranted.
Scouting: Regular scouting is essential for timely management decisions. Fields should be monitored beginning at crop emergence and inspected at least weekly throughout the season. Particular attention should be given to fields located near cotton, alfalfa, or recently harvested crops where whitefly movement is likely. Monitoring should include assessments of adult whiteflies, immature stages, virus symptoms, and beneficial insect activity.
Conservation of natural enemies: Natural enemies can contribute to whitefly suppression and should be conserved whenever possible. Predators such as lacewings, lady beetles, minute pirate bugs, and big-eyed bugs, along with some parasitoid wasps, help suppress whitefly populations. Although biological control alone may not prevent economic damage during heavy infestations, preserving beneficial insects can reduce whitefly pressure and improve overall pest management.
Insecticide control (conventional): In conventional production systems, whitefly management should begin at planting with systemic insecticides that protect young seedlings during the critical establishment period when plants are most vulnerable to virus infection. Products such as Verimark, Sivanto, Venom, Scorpion, and imidacloprid-based materials can provide early protection. During crop development, foliar products including PQZ, Sefina, Sivanto, Assail, Exirel, and Beleaf can be used to suppress migrating adults. Effective rotation among modes of action is essential for preserving product performance.
Insecticide control (organic): Organic production systems rely heavily on resistant varieties and preventative measures such as sanitation, crop isolation, weed management, and conservation of beneficial insects. Organic insecticides, including Pyganic, neem-based products, insecticidal soaps, and microbial products containing Beauveria bassiana (BotaniGard) or Isaria fumosorosea (PFR-97), can provide suppression when applied early and with thorough coverage. However, these products generally have limited residual activity and are most effective when used before populations become established.
Pollinator protection: Pollinator protection should remain a priority in melon production. Honeybees are essential for fruit set and yield. Whenever possible, insecticide applications should be avoided during bloom. If treatments are necessary, applications should be made during evening or nighttime hours when bees are not actively foraging.
Insecticide resistance management: Because whiteflies readily develop resistance to insecticides, resistance management should be incorporated into every control program. Insecticides should be rotated among different IRAC mode of action (MoA) groups, and repeated applications of products with the same MoA should be avoided. Treatment decisions should be based on field scouting and pest pressure rather than calendar schedules.
Conclusion
Given the elevated whitefly populations and virus incidence observed this spring, growers should anticipate increased whitefly and virus pressure during the upcoming fall season. Implementing an integrated management program that emphasizes resistant varieties, crop health, sanitation, crop placement, scouting, conservation of biological controls, physical controls, and responsible insecticide use will provide the best opportunity to minimize economic losses and protect crop productivity.
Additional Documents for More Detailed Information and Control Options
Palumbo J.C. 2020. Cultural Practices Key to Whitefly and Virus Management in Fall Melons.http://hdl.handle.net/10150/677934
Palumbo J.C. 2024. 2024 Guidelines for Whitefly / CYSDV Management on Fall Melons. http://hdl.handle.net/10150/677911If 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. 7
April 1, 2026
Results of pheromone and sticky trap catches below!!
Corn earworm: CEW numbers remained high over the last two weeks; numbers remain high particularly in Welton and Tacna areas. Above average for this time of season.
Beet armyworm: BAW activity remained steady over the last two weeks. Above average for this time of the season. Historically BAW numbers are expected to continue increasing over the next few weeks.
Cabbage looper: Cabbage looper moth activity decreased over the last two weeks but remains higher than average for late-March. Based on historic data, expect to see high numbers through the end of the produce season.
Diamondback moth: Adult activity increased across most locations. High numbers seen in Yuma Valley. About average for this time of the year.
Whitefly: Adult activity increased across all locations, about average for this time of year. Expect numbers to continue increasing as temperatures warm up.
Thrips: Over the last two weeks, thrips adult activity continued to increase across locations and reached season highs. Higher than average for this time of year. Expect numbers to continue increasing as temperatures warm up
Aphids: Winged aphid numbers continue to decrease at most sites in the last two weeks. At our efficacy trials at YAC, most aphids died due to the high temperatures. below average for this time of the year.
Leafminers: Adult leafminer activity remains steady, high numbers continue to be seen in Yuma Valley, about average for this time of the season.
