A big thank you to everyone who took the time to participate in this year's Vegetable Pest Losses Survey. Together, we surveyed more than 23,000 acres of head lettuce and 12,500 acres of brassicas.

The information you provide is the foundation for documenting pest pressures and yield losses while demonstrating the stewardship that helps protect the pest management tools our industry relies on. As we completed the 21st Lettuce Pest Losses Survey, it was especially meaningful to see so many of you continuing the tradition that Dr. John Palumbo started more than two decades ago.

We appreciate your time, your expertise, and your continued support of Arizona vegetable IPM.

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Regenerative agriculture (RA) crop production systems have recently been popularized in many agricultural communities. Claims are often made that RA systems are better than conventional agriculture (CA) crop production systems, which are commonly considered to be input intensive.

The definition of an RA system is highly dependent on the practitioner, and many definitions can be found. In general, RA is a principles-based approach that aims to restore and enhance soil health, biodiversity, and ecosystem services through practices such as reduced tillage, cover cropping, diverse rotations (including fallow or resting periods), crop residue retention. In some cases, it includes agroforestry and/or the integration of livestock.

Proponents of RA argue that it can increase soil organic carbon (SOC), which is a proxy measurement related to stable soil organic matter (SOM). They also contend that RA practices improve soil water-holding capacity and soil systems resilience (which is an extremely broad category).

Regenerative agriculture systems have the basic objective of increasing on-farm biodiversity and delivering long-term improvement in productivity and soil health as compared to conventional crop production systems.

Recent reviews of the literature have addressed the overall trends in field research associated with RA systems in comparison to CA crop production systems. Some studies have demonstrated some positive effects of RA systems on soil condition and soil health.

Research reviews clearly illustrate that the context of the studies is very important in interpretation and there is clear evidence of major gaps in describing and quantifying effects from RA systems (Montgomery and Biklé, 2021 and Khangura, et al., 2023).

BLUF (Bottom Line Up Front) Statement:
Regenerative systems promote crop and soil management practices that have been recognized and utilized for many years, hundreds of years in fact. Current research comparing RA and CA systems are highly variable. All asserted benefits of RA systems are highly dependent on climate conditions and the CA systems used for comparison.

Overall, RA practices generally contribute positively to soil health. However, there is no definitive evidence of RA systems being superior to CA crop production systems.

Pros – Objectives of RA systems:

• Soil carbon and structure. A meta-analysis of temperate systems found that reduced tillage and inclusion of grass-based rotation and resting/fallow periods could increased SOC relative to CA. Studies in cooler and humid climates show that RA practices can build SOC stocks over several decades (Jordan, et al., 2022). This does not transfer to other agroecosystems in drier and warmer environments.
• Soil health and resilience. Practices that increase incorporation into soil crop residues (organic material), crops with different types of root systems, and crop rotations that include legume crops can improve soil aggregate stability, infiltration, internal soil drainage, and retention has been found in some studies and reviews (Khangura, et al., 2023).
• Biodiversity and ecosystem services. Diversified crop rotations, the use of cover crops, and crop–livestock integration can increase soil biodiversity. It is also contended that crop pollination and pest-regulation (insects, weeds, and diseases) can be improved with RA systems versus CA. However, these effects are commonly poorly quantified in most studies (Sher, et al., 2024). Thus, some of these benefits are quite speculative.
• Co-benefits and livelihoods. There are some publications that conclude that RA systems can be more profitable or financially resilient for farmers. But from these studies it is only possible for RA superiority to CA systems when there are price premiums, reduced input costs, or ecosystem payment schemes that are available. Highly variable yields, the need for policy support and payment mechanisms are commonly needed to make RA systems viable at scale (Reuters, 2024).

Cons / limitations compared to conventional cropping systems:

• Yield uncertainty and trade-offs. In most studies, RA practices do not consistently or significantly change crop yields relative to CA systems, particularly in short-term studies, anything less than a decade. Overall, review of the literature shows no consistent or general “win-win” RA situation that will reliably increase yields while increasing SOC. Yield responses are highly variable by crop, region, and the time elapsed since RA systems were adopted. In many cases, the transition years into RA systems cause yield reductions. The site-specific constraints can be quite variable it is difficult to identify consistent positive trends in RA system benefits over CA systems (Jordan, et al., 2022).
• Greenhouse gas and livestock trade-offs. RA systems that integrate livestock or increasing manure inputs can boost SOC and encourage soil biodiversity. These

types of RA systems have been shown to raise methane and nitrous oxide emissions. As a result, any net climate benefits are dependent on whole-system greenhouse-gas accounting, which is often not done or effectively included in most RA studies (Sher, et al., 2024).

• Evidence gaps and heterogeneity. Most of the cases found in the current literature on RA systems evaluation address single practices such as no-till versus conventional tillage, the use of cover crops, and animal manure application regimes. There is a substantial absence of long-term, fully integrated RA/CA systems comparisons. Accordingly, the results found in the current literature are highly variable and context dependent (soil type, climate, access to RA-friendly market benefits, etc.). As a result, generalization is extremely limited in comparing RA and CA systems (Jordan, et al., 2022).
• Adoption barriers. Moving to RA systems often requires new knowledge, increased and different levels of labor reallocation, equipment changes, and often many upfront investments to access unique markets and secure technical support. Incentive structures (i.e., subsidies) are commonly needed to make RA system transitions from CA systems and without that, adoption can be slow and highly variable (Reuters, 2024).

Regenerative systems promote crop and soil management practices that have been recognized and utilized for many years, hundreds of years in fact. Current research comparing RA and CA systems are highly variable. All asserted benefits of RA systems are highly dependent on climate conditions and the CA systems used for comparison.

There is a definite need for long-term, system-level experiments. The appropriate measurement and quantification of RA and CA system management comparisons and soil health parameters are essential priorities to help resolve the many remaining uncertainties associated with RA systems (Jordan, et al., 2022).

Overall, RA practices can potentially improve soil health. However, there is no definitive evidence of RA systems being superior to CA crop production systems.

References:
Jordon, M. W., K. J. Willis, P. C. Bürkner, N. R. Haddaway, P. Smith, & G. Petrokofsky. 2022. Temperate regenerative agriculture practices increase soil carbon but not crop yield — a meta-analysis. Environmental Research Letters 17(9):093001. doi:10.1088/1748-9326/ac8609.  

Khangura, R., D. Ferris, C. Wagg, & J. Bowyer. 2023. Regenerative agriculture—A literature review on the practices and mechanisms used to improve soil health. Sustainability 15(3):2338. doi:10.3390/su15032338.  

Montgomery, D. R., & A. Biklé. 2021. Soil health and nutrient density: Beyond organic vs. conventional farming. Frontiers in Sustainable Food Systems 5:699147. doi:10.3389/fsufs.2021.699147.  

Sher, A., H. Li, A. Ullah, Y. Hamid, B. Nasir, & J. Zhang. 2024. Importance of regenerative agriculture: Climate, soil health, biodiversity and its socioecological impact. Discover Sustainability 5:462. doi:10.1007/s43621-024-00662-z.  

Reuters. 2024. Rewarding farmers for regenerative agriculture is 'critical for decarbonising the food sector'. Reuters, June 10, 2024. (news article).  

Guardian (news). 2024. Cows help farms capture more carbon in soil, study shows. The Guardian, Sept. 28, 2024. (news article).  

Click here and hit ‘download’ for a PDF version of this article. 

First, I want to thank everyone who participated in last week's Vegetable Pest Losses Survey.  

This year's survey included the return of the lettuce disease losses section. While several diseases were present and managed last season, downy mildew accounted for the majority of disease management costs by a wide margin. This really underscores the impact that last spring's unusually rainy weather had on disease development across the Yuma lettuce production region.

No one can predict exactly what this upcoming spring will bring, but there has been discussion about the possibility of a strong El Niño leading to an extended monsoon season. If that proves true, the conditions would once again support spring downy mildew development. The pathogen only needs about 3 to 4 hours of continuous leaf wetness to infect lettuce, so periods of overnight moisture, prolonged morning dew, or frequent rainfall when inoculum (spores) are present increase disease risk.

With that in mind, this seems like a good opportunity to review what is known about downy mildew and discuss strategies for its management.

Resistance in lettuce to Bremia lactucae, the causal oomycete pathogen behind downy mildew, is inherited in a gene-for-gene fashion, meaning one major gene product in the plant host interacts with one major gene product in the pathogen. When resistance is present, this leads to an incompatible interaction between plant and pathogen and results in complete immunity to infection. Resistance genes in these types of interactions most often encode a protein molecule that acts like a burglar alarm. These molecular sensors in the host bind to proteins secreted specifically by the pathogen, and when that happens a storm of defense responses is activated in the plant that excludes further infection. This is not the only mode of genetic resistance found in plants, but it is often the most drastic and effective against obligate parasites like downy mildew.

But this simple gene-for-gene interaction often puts incredible selection pressure on the pathogen populations to change such that they can get around the resistance. By losing the molecule that the plant detects in order to initiate a defense response, the pathogen becomes unrecognizable to the resistance genes a plant variety may have. Just like spraying the same mode of action over and over again leads to a pest population developing resistance to a pesticide, the same selection applies to genetic resistance. The longer a resistance gene is deployed in a region, the more likely the pathogen population is to change in response until that resistance gene is no longer effective at managing the disease.

One of the biggest challenges with lettuce downy mildew is that B. lactucae is constantly changing over time. It exists as many different races, where each race has a different reaction to the resistance genes bred into lettuce varieties. You can think of these races as different versions of the same pathogen. A lettuce variety that resists one race may still be susceptible to another.

These races are identified by testing them against a panel of lettuce varieties with known resistance genes. In the western United States, races are named by the International Bremia Evaluation Board-U.S. (IBEB-US) and are given names with a number followed by the country’s abbreviation, such as 8US, 9US, or 10US. The populations found in the western U.S. are different from those found in Europe, so each region uses its own independent naming system.

The downy mildew population has changed considerably over time. Earlier races (1US through 4US) are now rarely found in commercial lettuce production. During the 2000s and 2010s, races 5US through 8US became the most common. Race 9US was recognized after being detected repeatedly between 2015 and 2017, and the newest officially recognized race, 10US, was designated in 2025. Below is a pie chart showing the relative frequency of the races identified from 114 Yuma County downy mildew samples between 2023-2024:

Figure 1: Pathotyping results of 114 lettuce samples from Yuma County collected between 2023 and 2024. Data source: https://bremia.ucdavis.edu/bremia_database_main.php

 

The results show that much of the downy mildew population found in Yuma County is made up of novel strains of Bremia lactucae that have not yet been officially classified as a race. An official race is only recognized after it has been shown to be stable and widespread over multiple locations and growing seasons. These newer strains may disappear over time, or they may eventually become established and earn an official race designation. In the meantime, this means growers and lettuce breeders in Yuma County are often dealing with strains that can dodge the resistance in some lettuce varieties before those strains are common enough to be officially recognized. It also highlights why relying on resistance alone is not enough to manage the disease.

 

Table 1: Pathotyping and fungicide sensitivity results of samples from Yuma County collected in 2025.

This trend appears to be continuing. All of the downy mildew samples sent for race testing last season were identified as novel strains rather than known, officially designated races.

It's impossible to predict exactly how these new strains will respond to the resistance genes found in today's commercial lettuce varieties. However, because they have not been previously characterized, they are more likely to overcome existing genetic resistance than the races we already know about.

New strains develop naturally over time. They can arise when different strains exchange genetics (i.e. intermate) or through random mutations. When growers plant varieties with similar resistance packages over large areas, the pathogen population is placed under strong selection pressure. Any strain that happens to acquire the ability to infect those resistant varieties gains a major advantage and gets to reproduce without competition where other strains cannot. Over just a few disease cycles, those successful strains can become much more common in the population until they are the predominant strain overall.

An important point to remember is that the resistance bred into commercial lettuce varieties is not wearing out or becoming weaker over time. The genetics in the lettuce remain just as effective as when the variety was released. What changes is the pathogen. As the downy mildew population evolves new strains emerge that can bypass resistance genes that previously worked very well.

That means that varieties carrying resistance to races 5US through 10US are still doing exactly what they were designed to do. They continue to suppress those known races and help prevent them from becoming widespread in commercial fields. So, if you experience significant downy mildew in a field planted with a variety that has a strong resistance package, the culprit is most likely one of these newer, uncharacterized strains rather than a failure of the variety itself.

Unfortunately, Bremia lactucae can evolve much faster than scientists can identify new races and breeders can develop and release resistant varieties. That's why no resistance package should be viewed as a stand-alone solution.

This is also why extension, researchers, and the seed and crop protection industries place so much emphasis on the integrated pest management (IPM) concept. Genetic resistance is an essential tool, but it works best and remains the most sustainable when combined with other management practices. For novel strains that can slip past host resistance, timely fungicide applications and other disease management strategies become especially important for maintaining control.

Below are the results from last season's downy mildew fungicide efficacy trial, where we compared 12 fungicide programs under Yuma growing conditions.

 

Figure 2: Mean disease severity by treatment. Disease severity was determined by rating 10 plants within each of the five replicate plots per treatment using the following rating system: 0 = no downy mildew present; 1 = downy mildew present on bottom leaves of plant; 2 = downy mildew present on bottom leaves and lower wrapper leaves; 3 = downy mildew present on bottom leaves and all wrapper leaves; 4 = downy mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = downy mildew present on entire plant. Disease severity is displayed as the mean of five replicates across all three lettuce varieties and bars show a 95% confidence interval around the mean calculated from individual treatment data. Compact letter display (CLD) above boxes show significantly different treatments (Kruskal-Wallis ANOVA and Dunn’s test). Boxes sharing the same letter(s) are not significantly different from one another. Fb = “followed by” in the rotation. Not all products are registered yet for use in lettuce. The inclusion of specific fungicide products or formulations in these trials does not constitute an endorsement or recommendation over other labeled products.

 

The most effective way to manage lettuce downy mildew is to use an integrated approach. Plant varieties with a strong resistance package against races 5US through 10US, and pair that resistance with timely, full-label-rate fungicide applications when environmental conditions favor disease. This combination provides the broadest and most reliable protection against both known races and the novel strains that continue to emerge in Yuma County.

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

At the 2025 Southwest Ag Summit Field Demo a couple of weeks ago, many of the latest technologies were demonstrated in the field. Most were related to pest control. Several of the technologies demonstrated are new to the Yuma, AZ area. The recent technologies presented included two types of high precision spot sprayers for weeding and applying beneficial pesticides (Fig. 1a, Fig. 1b) and an AI based lettuce thinner. Manufacturers stated the technologies will be getting even better/more versatile soon. Both precision spot sprayer companies are developing models for small lettuce so that the machines can also be used for lettuce thinning. Also new was that the AI lettuce thinner technology is being further developed so that the device can be used also be used as a weeder. Several “older” pest control technologies also seemed to garner a lot of interest. These included an implement designed for cultivating high density crops (Fig. 1d), a camera guided cultivator equipped with in-row weeding tools (Fig. 1e) and a field scale drone sprayer (Fig. 1f).

Fig. 1. Newer pest control technologies demonstrated at the 2025 Southwest Ag Summit
Field Demo included a) Ecorobotix1 Ara high precision spot sprayer, b) Verdant Robotics
Sharp Shooter, c) Niqo Robotics AI based lettuce thinner, d) Oliver high density
cultivator, e) Steketee IC Light camera guided cultivator and f) DJI Agras T50 drone
sprayer.

An Economic Reality Check for Small-Scale Arizona Lettuce Producers

As precision robotic weeding and thinning technologies become more accessible, Arizona's small-scale lettuce growers increasingly ask: Does the investment in robotic systems make economic sense for my operation? With labor challenges intensifying across the state and wage pressures mounting, our recently completed trial provides a timely economic analysis specific to Arizona's growing conditions and regional labor markets.

The Economics of Labor vs. Technology in Arizona

Traditional lettuce hand weeding and thinning costs in Arizona:

• Labor represents one of the largest operational expenses in Arizona lettuce production
• Arizona minimum wage continues to rise, now exceeding $16 per hour in many regions
• Seasonal worker availability has become increasingly unpredictable, with competition from other industries and reduced cross-border workforce mobility
• In Arizona's major growing regions like Yuma, manual hand thinning and weeding costs range from $100 to $454 per acre, depending on field conditions, weed density, and bed width
• Inexperienced crews may cause crop damage, reducing marketable yield and compounding labor costs
• Hand operations require supervisory oversight to maintain quality standards

Precision robotic weeding/thinning system costs:

• Outright purchase: $250,000–$1.2 million+, depending on system sophistication
• Rental/lease options: $5,000–$15,000 per season (varying by availability in Arizona and neighboring states)
• Service-based models (Robotics-as-a-Service): $166–$304 per acre
• Monthly lease: ~$25,000 per month for large operations
• Operating costs: Fuel, maintenance, software updates, and technical support
• Learning curve: Training and implementation time

 

Key Economic Factors to Consider for Arizona Operations

Farm Size Threshold
In Arizona, robotic systems become economically viable for farms where weeding and thinning labor costs exceed $8,000–$12,000 per season. Small operations (under 20 acres of lettuce) may find rental or shared-equipment arrangements more cost-effective than outright purchase. Service-based models (RaaS) have emerged as a practical entry point, particularly for farms in Yuma County and other Arizona production regions where labor scarcity is acute.

Labor Availability Crisis in Arizona
Arizona's desert lettuce production regions face acute labor constraints. In regions where reliable labor is scarce or increasingly expensive, a reality across Arizona's major growing areas, precision robotic systems provide operational predictability while reducing damage risk. One precision robotic system operating consistently may replace 3–5 seasonal hand workers, improving both economics and quality control. Arizona growers who have struggled with labor availability during critical thinning and weeding windows recognize the operational value of robotic consistency.

Marketable Yield
Arizona's intensive production system and specialized lettuce varieties demand precision crop management. Many Arizona growers report hand labor costs ranging from $161 to $454 per acre, depending on specific field conditions, weed density, and bed width. Even modest yield improvements of 5% from reduced crop damage can offset system costs, particularly when inexperienced hand crews are the alternative. Given Arizona's premium lettuce market positioning, yield quality and consistency provide additional value beyond simple volume.

Operational Flexibility and Regional Equipment Availability
Renting or leasing robotic weeding/thinning systems allows Arizona small farms to avoid large capital expenditures while testing technology fit. Equipment providers now offer season-specific rental arrangements suitable for small-scale Arizona operations. Robotics-as-a-Service (RaaS) models, where growers pay per acre or per hour rather than owning hardware, have emerged as a game-changer for Arizona small operations, with several providers now establishing regional service capabilities in Yuma and surrounding areas.

Financial Decision Framework for Arizona Growers
Consider purchasing/owning robotic weeding/thinning systems if:

• Your operation has 30+ acres of lettuce requiring annual weeding and thinning
• You can achieve 80+ operational hours per season to justify equipment investment
• Local labor costs exceed $18–$22 per hour (now the reality across much of Arizona)
• You prioritize operational consistency and yield protection over capital flexibility
• You have 200+ acres and can achieve a 2–3 year ROI

Consider service-based (RaaS) or rental/leasing robotic systems if:

• Your operation has 10–30 acres of lettuce
• You want to test technology fit before major capital investment
• Labor availability is seasonal and unpredictable (increasingly common in Arizona)
• You prefer to minimize equipment ownership and maintenance responsibilities
• You want to access the latest technology without capital expenditure
• You want to pilot robotic systems during your most labor-intensive seasons

Stick with traditional hand operations if:

• Your farm is under 10 acres of lettuce requiring intensive management
• Local labor is readily available at competitive rates (increasingly rare in Arizona)
• You have experienced, retained crews who consistently perform high-quality work
• Your capital budget is constrained

Return on Investment (ROI) for Arizona Operations

The primary driver for adoption is the economic disparity between robotic costs and manual labor, a gap that has widened significantly in Arizona.

Labor Cost Baseline for Arizona: In Arizona's major growing regions like Yuma, manual hand thinning and weeding costs range from $100 to $454 per acre, with an average of $250–$350 per acre for experienced crews during peak seasons.

Payback Period: Most robotic systems aim for a break-even point within 2–3 years. For Arizona operations relying on expensive seasonal labor or facing acute worker shortages, ROI can sometimes be achieved within a single season, particularly if labor costs exceed $300 per acre.

Secondary Benefits: Beyond labor savings, precision robotic systems can increase yields by approximately 5% through reduced crop damage compared to manual crews and better weed control. For Arizona's premium lettuce market, quality improvements and consistency may provide additional market premiums.

Arizona-Specific Considerations:

• Desert soil conditions and shallow-rooted lettuce make mechanical damage from conventional cultivation particularly costly
• Water efficiency gains from precision robotic systems align with Arizona's water sustainability priorities
• Extended growing season in southern Arizona may allow higher utilization rates, improving equipment ROI

Key Takeaway for Arizona Growers

Precision robotic weeding and thinning technology is no longer exclusively for large-scale operations. For Arizona's small-scale lettuce growers facing mounting labor costs, unpredictable seasonal workforce availability, and premium market positioning, the economics increasingly favor at least exploring service-based, rental, or shared-equipment options. Arizona's unique labor market dynamics and growing season characteristics make robotic technology particularly relevant. The decision hinges on your specific operation: farm size, local labor costs, available capital, and risk tolerance for new technology.

Interested in Field Trials?
If you have any questions or are interested in doing a trial, please reach out to weed specialist Mazin Saber at the University of Arizona Yuma County Cooperative Extension. Dr. Saber leads research initiatives comparing manual labor to commercially available robotic weeding technologies to establish sustainable weed control programs for Arizona desert agriculture.

Organic vegetable production in the desert Southwest requires a different mindset for insect management. Our insecticide options are more limited, and results can be more variable, so success depends on using these tools thoughtfully within an IPM framework. In my Southwest Ag Summit talk, I focus on how organic materials perform under desert conditions.


Session details below:
AFTERNOON BREAKOUT SESSION
Thursday, February 19, 2026 | 1:30 PM – 3:30 PM

Vegetable IPM

Dr. Palumbo Veg IPM Insecticide Program: 2025–2026 Efficacy trials — Dr. Samuel Discua Duarte, Yuma Ag Center
Insecticide Options for Insect Pest Management in Organic Vegetable Production — Dr. Wilfrid Calvin, UofA
Area Wide Trapping Network: Program Update and Expansion — Macey Keith, UofA
Advances in Vegetable Weed Management: Herbicides and Chemigation Strategies — Dr. Mazin Saber, UofA

Relative humidity (RH) is a microclimate variable that strongly shapes crop water relations, canopy wetness duration, and the “comfort zone” for many pests and pathogens. In leafy greens, RH influences transpiration rate, stomatal behavior, and leaf-surface wetness, which are tightly linked to crop stress and disease favorability. Using the AZMET Yuma Valley station annual summaries (1987–2025), our figures show that maximum, minimum, and average RH have declined over time, even though year-to-year variability remains evident.

In Figure 1 (maximum RH), the trendline equation is y = −0.099x + 27.1 with R² = 0.11. The negative slope indicates a gradual decline in annual maximum RH at approximately −0.099 percentage points per year (about −0.99% per decade). The yellow dotted line represents the long-term mean for the series, providing a visual reference for how many years fall above or below the multi-decadal baseline.

In Figure 2 (minimum RH), the trendline equation is y = −0.12x + 24.9 with R² = 0.33. This is the strongest RH signal among the three metrics, indicating that annual minimum RH has decreased at roughly −0.12 percentage points per year (about −1.2% per decade). The higher R² value suggests that the drying signal is more consistently expressed in the minimum RH metric, which is often closely tied to the driest parts of the diurnal cycle and evaporative demand.

In Figure 3 (average RH), the trendline is y = −0.13x + 28.2 with R² = 0.21, indicating a decline in annual average RH of about −0.13 percentage points per year (approximately −1.3% per decade). As in the other figures, the yellow dotted line marks the long-term mean, illustrating that recent years more frequently sit at or below the historical baseline.

What this means for leafy greens agronomy
A gradual decline in RH generally implies higher atmospheric demand for water (a drier air mass), which can increase crop transpiration and intensify the need for precise irrigation management. For leafy greens, this can translate into:

• Faster canopy water loss during warm, dry periods and greater sensitivity to irrigation timing.
• Potential for physiological stress when high temperature coincides with low RH, particularly during rapid canopy expansion.
• More rapid drying of leaf surfaces after irrigation events, which can influence how long a “wet canopy” persists.

What this means for IPM
Declining ambient relative humidity in the AZMET Yuma Valley record suggests the background atmosphere is gradually becoming drier, which typically corresponds to higher evaporative demand. For IPM in leafy greens, this should be interpreted cautiously: many foliar diseases are favored by extended leaf wetness and high canopy humidity, so fewer naturally humid periods may slightly reduce baseline favorability. However, in irrigated systems the conditions that matter most for infection—irrigation method and timing, canopy density, and short-term weather events—can still create localized humid microclimates and wet leaves even when ambient RH is trending downward. Likewise, lower RH combined with warm conditions can increase the likelihood of transient crop water stress if irrigation is not well aligned with demand, which can indirectly affect pest dynamics and tighten scouting and management windows. Overall, the long-term RH decline is best viewed as a shift toward greater atmospheric drying power, while day-to-day IPM risk remains primarily governed by crop stage, irrigation practices, canopy microclimate, and episodic weather rather than the trend alone.

Figure 1. Distribution and long-term trend in annual maximum relative humidity
(RHmax) at the AZMET Yuma Valley station (Yuma Valley, AZ) for 1987–2025; the
dashed line shows the linear trend and the yellow dotted line indicates the long-term
mean.


Figure 2. Distribution and long-term trend in annual minimum relative humidity
(RHmin) at the AZMET Yuma Valley station (Yuma Valley, AZ) for 1987–2025; the
dashed line shows the linear trend and the yellow dotted line indicates the long-term
mean.


Figure 3. Distribution and long-term trend in annual average relative humidity
(RHavg) at the AZMET Yuma Valley station (Yuma Valley, AZ) for 1987–2025; the
dashed line shows the linear trend and the yellow dotted line indicates the long-term
mean.

VegIPM Update Vol. 17, Num. 15

July 22, 2026

Results of trap catches below!!

 

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

Thrips: Adult thrips activity remained low over the last two weeks. About average for this time of the year. Historically, thrips numbers remain low until Sept-Oct.  

Diamondback Moth: No diamondback moths have been collected in the traps since May 19th.  Based on the past six years summer collection data, no DBM is collected in the traps in the summer months (Jun-Aug) until September.