With rain in the forecast, growers and PCAs should be alert for earlier-than-usual and rapid increases in green peach aphid (GPA) populations. Historically, rainfall events this time of year are often followed by quick aphid buildup, particularly in young lettuce.

According to observations shared by Leo Chavez, research technician in John Palumbo’s program, GPA commonly appears earlier and develops faster following rain events, likely due to favorable plant growth and aphid reproduction conditions.

Following rainfall, we recommend increasing scouting frequency, especially in younger plantings and along field edges. Early detection is critical, as GPA populations can escalate quickly under these conditions. For guidance on action thresholds and optimal treatment timing, PCAs and growers are encouraged to reference John Palumbo’s Action Thresholds for Desert Produce Crops handout.

We conducted a session at the 2026 SW Ag Summit program on Thursday, 19 February regarding the future of the Colorado River and possible management plans for water allocations that will be very important for agriculture in the lower Colorado River Valley in the next decade. The program outline included the following speakers and components:

• Introduction – Jeff Silvertooth, Moderator, University of Arizona
• Colorado River Perspectives -
• Clint Chandler, Deputy Director, Arizona Department of Water Resources
• Vineetha Kartha, Colorado River Programs Manager – Central Arizona Project
• Tina Shields, Water Manager at Imperial Irrigation District

All current conservation and operational guidelines expire in 2026. The Department of Interior (DoI) and the Bureau of Reclamation (BoR) set 11 November 2025 as a deadline for basin states (Figure 1) to come forth with an agreement and a new plan for conservation and river management. But the basin states could not come to an agreement, so the DoI extended the deadline to 14 February 2026, and the basin states failed to reach an agreement and meet that deadline.

Figure 1. Map of the Colorado River Basin and watershed. (Source: U.S. Bureau of
Reclamation).

During the SW Ag Summit session prospects for a possible agreement among the Colorado River basin states were discussed. The Lower Basin (LB) states are unified in their efforts to find a common agreement and have offered numerous plans that include substantial conservation reductions on their part, but the Upper Basin (UB) states are unified in their direct opposition to any offers made by the LB and they refuse to make any reductions in their water allocations.

In January 2026, the Bureau of Reclamation BoR published the Draft Environmental Impact Statement (DEIS), which is required in the NEPA process. The DEIS includes five alternative approaches and analyses for consideration in the development of the new operating guidelines.

The five alternative approaches are listed below in very brief terms.

1.  No Action Alternative—Included as a requirement of NEPA, this alternative reverts Colorado River operations to the decades-old operating framework that was in place prior to the adoption of the 2007 Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead.
2.  Basic Coordination Alternative—This alternative is designed to achieve protection of critical infrastructure within the Department of the Interior and Bureau of Reclamation’s current statutory authorities if no new agreements among Basin water users are adopted.
3.  Enhanced Coordination Alternative—This alternative was developed in coordination with the U.S. National Park Service and the U.S. Fish and Wildlife Service, with input from Basin Tribes and the hydropower industry. It uses an approach of distributing storage between Lake Powell and Lake Mead that enhances the reservoirs’ ability to protect critical infrastructure and support the Colorado River Basin.
4.  Maximum Operational Flexibility Alternative—This alternative was developed by a consortium of conservation organizations with the goals of stabilizing system storage, integrating stewardship and mitigation strategies for Lake Powell and Lake Mead, maintaining opportunities for binational cooperative measures, incentivizing water conservation, and designing flexible water management strategies. It uses both system storage and recent hydrology for determining annual releases from Lake Powell and Lake Mead. Additionally, it introduces the Conservation Reserve as a flexible tool for water conservation and management.
5.  Supply Driven Alternative—This alternative proposes that Lake Powell operation be based solely on historical natural flow. It incorporates concepts from the separate proposals submitted by the Upper and Lower Basin States, as well as ideas emerging from discussions with the Basin States during spring 2025. In this alternative, annual Lake Powell releases would be determined based on a set percentage of the preceding three-year average natural flow, and Lower Basin deliveries would be determined based on Lake Mead elevation.

A lot of attention at our SW Ag Summit session was directed at a review and consideration of the five alternatives presented in the DEIS. Figure 2, which describes LB and UB reductions associated with each of the DEIS alternatives plus two others (continued current strategies and supply driven pro-rata), was presented and reviewed. It is important to note the significant reductions from each alternative on the LB allocations while the UB is not subject to any reductions. 

Figure 2. Maximum shortages for the Lower and Upper Basins for a series of
possible alternatives. (source: Arizona Reconciliation Committee).

The possible impacts from the DEIS alternatives being considered are both interesting and puzzling considering the contrasting UB and LB facts (Figure 3). Some of the basic facts associated with the economic impact of the use of the Colorado River water include:

• 75% of economic productivity from the river is associated with the lower basin.
• 75% of the 40 M people supported by the waters of the Colorado River reside in the LB as well as 74% of the jobs.
• 78% of the total crop sales derived from the irrigation with Colorado River water is from the LB.
• Agriculture in the LB is substantially more efficient, economically (based on agricultural sales) and agronomically (crop yields and productivity per unit of water utilized), than the UB.

The UB states have never utilized their complete allocation of 7.5 MAF of Colorado River water while the LB has consistently utilized their 7.5 MAF and put it to good work (Figure 3). Yet the UB states have been insistent on not making reductions on their part and insisting that all future reductions come the LB.

A huge amount of infrastructure has been developed in the LB in the past 100 years to facilitate the development and productivity described in Figure 3, all in partnership with the United States via the DoI and BoR, Good examples include: the Boulder, Glen Canyon, Parker, Davis, Palo Verde Diversion, and the Imperial Dams as well as the Colorado River Aqueduct and the Central Arizona Project. In review of the DEIS, the proposed alternatives do not seem consistent with the historical precedent established by the DoI and BoR in recognizing the value of the Colorado River in the LB.

Figure 3. Some basic Colorado River basin facts. (Source: Coalition for Protecting
Arizona’s Lifeline, Colorado River Facts.
https://protectingarizonaslifeline.com/members/)

Public input is critical to shape long-term water management for Lake Mead and Lake Powell. Comments have been openly solicited from citizens on the DoI DEIS for Post-2026 Colorado River operations via email to crbpost2026@usbr.gov The deadline was 2 March 2026. However, most of the deadlines imposed by the DoI and BoR for proposals from the basin states have passed without consequence, so perhaps they will extend the period for public comments as well.

The DEIS proposed alternatives can be accessed at the Bureau of Reclamation website. Also, a Web Tool has been developed to help explore and understand different operational strategies: Post-2026 Operations Exploration Web Tool .

Given an opportunity, it is also important to attend meetings hosted by the BoR, which are designed to provide information and collect public input.

Fusarium wilt of lettuce, caused by Fusarium oxysporum f. sp. lactucae (Fol), continues to be one of the most economically significant soilborne diseases affecting lettuce production. To date the most successful strategy for disease management, outside of preventing the introduction of the pathogen into new fields, has been the development and deployment of Fol resistant lettuce varieties. Resistant varieties carry genes which allow the lettuce to impede or respond to the pathogenic invasion through a defense response. The result of this interaction is often tolerance to the presence of the Fol, meaning genetically resistant varieties are still capable of getting infected but show less damage, form marketable heads more often, and may even slow the reproduction of the pathogen in the field.

Unfortunately, one size does not fit all. Each Fol resistance gene is not expected to be effective at defending against every isolate of Fol. When a new resistance gene is introduced into crop varieties, it imposes a strong selection pressure on Fol populations, favoring isolates that can overcome or evade the host’s genetic resistance. Put simply, isolates that are controlled by the resistance don’t reproduce, while random changes can allow other isolates to avoid detection and reproduce a lot. In some cases, change in just a single gene in the pathogen can cause a breakdown in varietal resistance and since fungi can mutate and reproduce much faster than we can breed new lettuce varieties, we are often on the losing end of this “arms race”. The progeny of isolates that overcome the resistance increase in frequency and eventually become predominant in the local pathogen population, ultimately resulting in declining performance of the resistant variety in the field.

For plant pathologists, geneticists, and breeders we need to have a way to describe and report this variation in response to different resistance genes. Hence breaking pathogens into “races” (also referred to as physiological races or pathotypes) is the practical way we capture the biologically meaningful variation within a single species of pathogen with regards to their ability to infect different varieties. A race is typically defined by what specific varieties it is able to cause disease on, and the panel of varieties with known resistance we use to determine races of a pathogen are called differentials. These differentials are a product of academic and industry breeding efforts to try to capture the most relevant patterns of disease susceptibility and pathogenicity that exists across commercial production environments.

Four races of Fol (designated 1, 2, 3, and 4) have been identified globally based on the ability to infect seven varieties. Race 1 was the first to be characterized and has been reported in the major lettuce-producing regions of Japan, Taiwan, the United States, and parts of Europe. It is as of yet the only race to have been reported in the United States. Resistance to race 1 has been successfully incorporated into many commercial lettuce varieties, and for years this provided control in affected areas.

However, in response to reports from Californian lettuce growers regarding abnormal disease patterns, namely increased susceptibility in race 1-resistant cultivars and reduced severity in susceptible cultivars, researchers also identified additional novel variant samples of Fol from California lettuce fields. Among them was the variant designated CR4 (named for its inability to cause disease on the differential variety ‘Costa Rica 4’) which was consistently able to exhibit a strong and unique pathogenicity pattern on the seven resistance differentials not matching any of the four previously known races. The researchers who discovered and characterized this new CR4 variant are now in the process of fulfilling the criteria necessary to have it internationally recognized as a new race. Until then, it is being referred to as a variant. Initially this variant was isolated from samples from coastal lettuce fields, however, occurrences across multiple fields and two non-adjoining counties (Monterey and Santa Barbara) indicated that it may have already spread across the major lettuce production regions of California and even Arizona as well. Since its discovery, CR4 was confirmed to be present in lettuce samples from Arizona by the same group who initially discovered it in California.

This lettuce season we’ve received some feedback concerning the possibility of race 1 resistance breakdown in lettuce in Arizona lettuce fields. It is not yet known in all of these cases if the infection of race 1-resistant material is due to CR4 variants that are evading race-1 resistance or if the abnormally warm and wet lettuce season made race-1 resistance look less effective than in past years, both of which are possible explanations this season. Determining this answer is made complicated by the pathotyping processes currently used to determine an Fol isolate’s race. It requires the precise inoculation of several different varieties under tightly controlled environmental conditions to see on which varieties the strain can and cannot induce disease. With Fol, this is further complicated by the need to designate intermediate reactions between complete susceptibility and resistance, which symptomatically can be difficult to reliably distinguish across pathotyping experiments.

However, researchers at the University of California led by Dr. Alexander Putman and in collaboration with the USDA-ARS are working on developing a DNA-based test that will be able to rapidly detect the Fol CR4 variant. The process bypasses the need for artificial inoculations and can be achieved much faster and more reliably than through inoculation-based methods. Updates on this exciting work will be featured in the plant pathology breakout session during this year’s Southwest Ag Summit. Be sure to drop by room AS112 on February 19th, from 1:30 – 3:30 pm to hear all about it!

Until then, while the CR4 variant does show the ability to evade the race 1 resistance bred into some varieties, it does not appear to be able to infect all lettuce varieties equally. In fact, it appears some varieties that have historically been susceptible to race 1 show increased resistance to the new variant, which is a promising sign that genetic resistance will remain available despite this pathogen’s shifting nature. The development of this DNA-based test will allow us to gauge the relative populations of each race across Yuma County and to tailor varietal recommendations depending on which race or variant is predominant in the field.

 

Recommended reading:

Nayak, Santosh et al. “Detection of Novel Pathogenic Variants of Fusarium Oxysporum f. Sp. Lactucae in California.” Plant pathology 74.2 (2025): 295–307.

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

Founded in 2016, FarmWise has been at the forefront of AI based weeding technologies for nearly a decade. Over this time, the company has raised over $65 million in capital. In 2023, the company launched their flagship machine, Vulcan - a 21’ wide automated in-row smart cultivator for vegetable crops, priced at $645,000 (Fig. 1). In a surprising announcement just two weeks ago, FarmWise stated that the company was going through a business restructuring and will cease operations in the coming weeks. The bottom line for the decision was that despite having a field-tested automated weeding machine that reduces hand weeding labor costs, the company has not been able to reach profitability with the resources on hand. Moving forward, the company says that they are actively pursuing strategic opportunities including acquisition, partnerships and technology transfer to ensure the Vulcan technology lives on. During the transition, their number one priority is supporting current customers.

For insightful details on the need for restructuring and FarmWise’s plans going forward, you can refer to articles from The Packer and AgFunderNews.

Fig. 1. FarmWise’s automated in-row smart cultivator, the Vulcan, operating in Salinas,
CA. (Photo credit: FarmWise, Santa Clara, CA)

Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable

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.

Area-Wide Insect Trapping Network—SUMMER EDITION

As something new this season, we will continue sharing thrips and whitefly counts throughout the summer months. Since these data are already being collected as part of our ongoing monitoring efforts, we felt it would be valuable to provide this information to stakeholders managing summer crops in the region.

VegIPM Update Vol. 17, Num. 10
May 13, 2026

Results of sticky trap catches below!!

Whitefly: Adult activity continues to increase across locations, about average for this time of year. Expect numbers to continue increasing as temperatures warm up.

Thrips: Adult thrips activity increased across locations over the last two weeks. Historically, western flower thrips numbers peak in May.