Nitrogen (N) is the nutrient required in the largest amount by plants and the most common nutrient needed in crop fertilization. When N fertilizers are applied to a field, they are immediately subject to a myriad of possible reactions and transformations, as described as the N cycle (Figure 1).
Nitrogen is the most abundant element in the atmosphere (approximately 80-82%) as nitrogen gas (N2) but is inert and not directly usable by most organisms. Thus, atmospheric N gas is not bioavailable. In desert crop production systems, bioavailable N is the second most common limiting factor behind water.
To become bioavailable, N2 gas in the atmosphere must be converted into different mineral or inorganic forms through a process called nitrogen fixation (Figure 2), which is carried out by specific bacteria, lightning, and industrial processes such as the Haber-Bosch process in commercial fertilizer production (Nevins et al., 2020).
When N is fixed or transitioned from N2 gas into inorganic forms such as ammonia (NH3) and then into ammonium (NH4+) and nitrate (NO3-) in the soil, it can then be taken up and utilized by plants, entering the food chain and becoming available to other organisms. Nitrate-N (NO3-) is the preferred form for plant uptake (Figure 1).
Nitrogen immobilization is a process in soil systems where soil microbes consume and temporarily convert inorganic nitrogen into organic compounds, making it unavailable for plants. This occurs when decomposing plant material with a high carbon-to-nitrogen (C:N) ratio is added to the soil, as microbes consume the available mineral or inorganic N to break down the carbon-rich organic materials, such as crop residues. The process stops once the residue has decomposed, and the N cycle continues as organic forms are converted and released into the soil as inorganic forms in the soil through mineralization.
Mineralization of soil N is the process of converting organic forms of N into inorganic or mineral forms (Figure 3).
Figure 1. The nitrogen cycle. Source: Stevenson, 1982.
Figure 2. Nitrogen fixation is the conversion of dinitrogen gas (N2) to ammonia (NH3) and can be catalyzed by biotic and abiotic processes. Source: Nevins et al., 2020.
Figure 3. Nitrogen mineralization as organic N is converted or “mineralized” to
ammonium (NH4+) in the soil environment. Source: Nevins et al., 2020.
Nitrification is the process of converting ammoniacal N (NH4+) into nitrite (NO2-) and then
into nitrate (NO3-). Both steps are carried out by naturally occurring chemoautotrophic
bacterial organisms, Nitrosomonas and Nitrobacter (Figures 4 and 5).
Figure 4. Nitrification is the transformation of ammonium (NH4+) to nitrite (NO2-) and then
(NO3-) by naturally occurring soil bacterial oxidizing organisms. Source: Nevins et al.,
2020.
Figure 5. The two step process of soil nitrification shows the specific naturally occurring
soil bacterial organisms necessary for the reactions, Nitrosomonas and Nitrobacter.
Nitrogen Mineralization–Immobilization Transformation (MIT) Cycle in Soils
The nitrogen (N) mineralization–immobilization cycle represents the continuous biological transformation process between organic and inorganic forms of N in soil (Figure 6). It is driven primarily by the activity of soil microorganisms that consume mineral (inorganic) N and the those that decompose organic matter.
The MIT cycle represents the core elements of what we are trying to manage in the soils for crop production systems to optimize plant available N and produce healthy crops (Ros, et al, 2011 and Johnson et al., 2007).
Healthy soils are constantly active in these transformation processes. Thus, any inorganic or mineral source of N that is applied to the soil is immediately subject to immobilization and possibly converted into organic forms of N by soil microbes. Organic forms of N are then not available to plants for uptake and utilization until those microbes die and they are then exposed to decomposition and mineralization.
Figure 6. Mineralization – Immobilization Transformation (MIT) cycle.
The nitrogen mineralization–immobilization (MIT) cycle is a biologically mediated balance between the release of plant-available N from organic matter and the reverse reactions of sequestration in organisms and organic compounds. The continuous function of the MIT cycle is a key indicator of healthy soil, and it is central to soil fertility and plant nutrition management and efficient N fertilization.
References:
Ros, G. H., E.J.M. Temminghoff, and E. Hoffland. 2011. Nitrogen mineralization: a review and meta‐analysis of the predictive value of soil tests. European Journal of Soil Science, 62(1), 162-173.
Johnson, J.M.F., N.W. Barbour, and S.L. Weyers. 2007. Chemical composition of crop biomass impacts its decomposition. Soil Sci. Soc. Am. J. 71:155-162 doi:10.2136/sssaj2005.0419
Nevins, C.J., S.L. Strauss, and P. Inglett. 2020. Overview of key soil nitrogen cycling transformations. University of Florida IFAS Extension. SL471/SS684
Stevenson, F.J. 1982, Origin and distribution of nitrogen in soils. In: F.J. Stevenson, Ed., Nitrogen in Agricultural Soils, American Society of Agronomy, Madison, WI, pp. 1-42.
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.
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 109References
Jay-Russell, M.T. (2013). What is the risk from wild animalsin food-borne pathogen contamination of plants?. CABI Reviews 4(8),1-16.https://doi: 10.1079/PAVSNNR20138040
Fig. 1. Bird fecal matter on romaine lettuce.
Fig. 2. Gull flying over romaine lettuce being harvested.
Fig. 3. Gulls flying over irrigation canal near lettuce field
being harvested.
Fig. 4. Bird fecal matter on lettuce harvesting equipment.
If you've been wondering whether all this talk about robotic weeders is just hype or if these machines can actually handle the real challenges we face in our desert fields, you're not alone. Many growers are asking the same question, and fortunately, we now have solid field data from right here in the Southwest to give you a straight answer.
The bottom line? Yes, these machines work—but they're not magic bullets. They need to be part of your overall weed management strategy, not a replacement for everything else you're doing.
What We're Actually Seeing in Local Fields
Over the past few years, researchers and growers in Yuma and the Imperial Valley have been putting various robotic weeding systems through their paces in lettuce, leafy greens, and other vegetable crops. The results have been pretty encouraging, though there are definitely some caveats (Smith et al., 2021; UC ANR, 2025).
These machines use cameras and artificial intelligence to distinguish crops from weeds, then either physically remove the weeds with mechanical tools or zap them with lasers. Depending on how heavy your weed pressure is and which system you're using, they can knock out anywhere from 30% to as much as 98% of your weeds (UC ANR, 2025; NIFA, 2025). That's a pretty wide range, but even at the lower end, you're talking about significant labor savings.
Here's a number that'll get your attention: trials at the UA Yuma Ag Center found that hand weeding crews were spending about 2.8 hours per acre on average. When robotic weeders were brought in first, follow-up hand weeding dropped to as little as 0.4 hours per acre in fields with moderate weed pressure (NIFA, 2025; NC State Extension, 2025). That's not just helpful—that's a potential game-changer when you can't find enough crew members during peak season.
The Good, The Bad, and The Reality Check
Let's talk about what these machines do well and where they still need work.
Where they shine:
Labor has been our biggest headache for years now, and this is where robotic weeders really prove their worth. They don't call in sick, they can work around the clock if needed, and they significantly cut down the hours your hand crews need to spend in the field (NIFA, 2025; Farmonaut, 2025; AZCentral, 2025). For many operations, that alone justifies looking into the technology.
The good news for your bottom line is that properly configured robotic weeders don't hurt your crop. Multiple studies have confirmed that lettuce stands, head size, and overall yields hold up just fine when these machines do their thing (Smith et al., 2021; UC ANR, 2025). You're not trading weed control for crop damage.
If you're farming organically or trying to cut back on herbicide use, these systems offer a way to stay on top of weeds without spraying (Carbon Robotics, 2022; Farmonaut, 2025; CORDIS, 2024). That's becoming more important as herbicide resistance continues to spread, and consumers keep pushing for reduced chemical inputs.
Where they struggle:
Here's the reality—robotic weeders aren't perfect, and anyone who tells you they'll eliminate all your hand weeding is selling you something. The biggest issue we're seeing is with "doubles"—those places where you've got two plants too close together or weeds right up against a crop plant. Most systems just can't handle those situations reliably yet (Smith et al., 2021; UC ANR, 2025; Growing Produce, 2023). You'll still need hand crews for cleanup work.
The price tag is another issue, especially for smaller operations. These aren't cheap machines, though costs are starting to come down, and some companies are offering custom services where they bring the equipment to your farm rather than you buying it outright (Smith et al., 2021; Farmonaut, 2025; Anthropocene Magazine, 2024).
And let's be honest about our Southwest conditions—rocky ground, uneven terrain, and our infamous dust storms can all throw a wrench in the works. The technology is getting better at handling these challenges, but it's something to keep in mind (HowToRobot, 2023).
Does It Make Financial Sense?
Recent economic analyses, including a case study from Western Growers, show that integrating robotic weeders can reduce your overall weeding costs while cutting herbicide expenses (UA ACIS, 2025; Anthropocene Magazine, 2024). The research suggests that getting in early—before herbicide resistance becomes a crisis in your operation—gives you the best return on investment.
Think of it this way: you're not just buying a piece of equipment, you're investing in keeping your weed management options open for the future.
Making It Work for Your Operation
If you're considering robotic weeders, here's what seems to work best based on what we're seeing in the field:
Don't try to replace your hand crews entirely. Use the robots for the bulk of the work, then have your crews come through and get the misses and the doubles. That combination gives you the cleanest fields with the least labor (UC ANR, 2025; NC State Extension, 2025).
Run the numbers carefully for your specific situation. How much are you spending on hand labor now? How hard is it to find crews when you need them? What are your weed pressure levels like? The answers to these questions will tell you whether the investment makes sense (Smith et al., 2021; Anthropocene Magazine, 2024).
Look into custom services or equipment-sharing arrangements if buying your own machine seems like too big a leap. The technology is evolving fast enough that you might not want to own it outright anyway.
See for Yourself
We're going to have several different robotic weeding and thinning machines running live demonstrations at our AgTech Field Day on November 13-14, 2025, at the UA Yuma Agricultural Center (6425 W. 8th Street). This is your chance to see these machines working large-scale in real desert conditions and ask the manufacturers all your tough questions (Desert Ag Solutions, 2024; Western Growers, 2024; Desert Ag Solutions FarmTech, 2024).
We'll kick things off on November 13 at 7:00 AM with field demonstrations running until noon. You'll see robotic weeders, automated thinners, and precision sprayers all operating in actual field conditions—not some perfect demo plot. After lunch, you'll have time to talk with the equipment reps and other growers about their experiences. On November 14, we've got expert panels discussing where this technology is headed and what it means for desert agriculture (Desert Ag Solutions FarmTech, 2024).
Bring your questions, bring your skepticism, and come see for yourself whether this technology has a place in your operation.
Where Do We Go From Here?
Look, robotic weeders aren't going to solve every weed problem we face in the desert Southwest. But they're proving to be a valuable tool that can significantly reduce labor demands, cut costs, and help us stay ahead of herbicide resistance (Smith et al., 2021; UC ANR, 2025; NIFA, 2025). The key is figuring out how they fit into your overall management program.
The technology keeps getting better—the AI is getting smarter, the machines are becoming more rugged, and the costs are gradually coming down (NC State Extension, 2025; PMC, 2024; UA ACIS, 2025). Whether you jump in now or wait another season or two, it's worth staying informed about what these systems can and can't do. Come out to the field day in November and see the technology in action. Talk to other growers who are using it. Kick the tires, ask the hard questions, and decide for yourself whether robotic weeders have a place in your operation. We'll see you there.
Don't Miss Out! Register by October 31 to take advantage of the FREE Early Bird Registration. Starting November 1, a registration fee of $75 (plus fees) will be charged. Please Register Here
References
Anthropocene Magazine. (2024, November 28). Are robotic weeders a cost effective part of sustainable farming? Retrieved from https://www.anthropocenemagazine.org/2024/11/are-robotic-weeders-a-cost-effective-part-of-a-sustainable-farming-future/
AZCentral. (2025, May 12). Arizona farmers experiment with AI to improve crop harvests. Retrieved from https://www.azcentral.com/story/news/local/arizona/2025/05/12/arizona-farmers-experiment-ai-to-improve-crop-harvests/76899659007/
Carbon Robotics. (2022, November 10). AI Autonomous Weeder By Carbon Robotics. Telecom Hall Forum. Retrieved from https://www.telecomhall.net/t/ai-autonomous-weeder-by-carbon-robotics/18431
CORDIS. (2024, June 2). A fully autonomous solar-powered lightweight weeding robot, using advanced AI and computer vision. Retrieved from https://cordis.europa.eu/project/id/101166300
Desert Ag Solutions. (2024, November 6). The Desert Difference: A Showcase of AgTech Opportunities for Growing in the Desert. Retrieved from https://desertagsolutions.org/events/desert-difference-showcase-agtech-opportunities-growing-desert
Desert Ag Solutions FarmTech. (2024, December 31). The Desert Difference: FarmTech Connect. Retrieved from https://desertagsolutions.org/events/desert-difference-farmtech-connect
Farmonaut. (2025, June 17). Automated Deserts: Transforming Desert Agriculture In Arizona. Retrieved from https://farmonaut.com/usa/smart-farming-tech-7-ways-it-transforms-arizona-agriculture
Growing Produce. (2023, October 3). Laser Weed Control in the Farm Field: Why Growers Need To Give It Time. Retrieved from https://www.growingproduce.com/vegetables/laser-weed-control-in-the-farm-field-why-growers-need-to-give-it-time/
HowToRobot. (2023, July 16). Weeding robots: redefining sustainability in agriculture. Retrieved from https://howtorobot.com/expert-insight/weeding-robots-redefining-sustainability-agriculture
NC State Extension. (2025, October 27). Artificial Intelligence (AI)-enabled Robotic Weeders in Precision Agriculture. Retrieved from https://content.ces.ncsu.edu/artificial-intelligence-ai-enabled-robotic-weeders-in-precision-agriculture
NIFA. (2025). Automated Machine for Simultaneous Thinning, Weeding and Spot Spraying Lettuce. USDA National Institute of Food and Agriculture. Retrieved from https://portal.nifa.usda.gov/web/crisprojectpages/1000315-automated-machine-for-simultaneous-thinning-weeding-and-spot-spraying-lettuce.html
PMC. (2024, October 29). A novel mechanical-laser collaborative intra-row weeding prototype. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC11557383/
Smith, R. et al. (2021, February 9). Autonomous Weeders Showing Promise in Lettuce Fields. AgNet West. Retrieved from https://agnetwest.com/autonomous-weeders-showing-promise-in-lettuce-fields/
UC ANR. (2025, March 30). 2020-2021 Evaluations of Automated Weeders in Lettuce Production. University of California Agriculture and Natural Resources, Salinas Valley Agriculture Blog. Retrieved from https://ucanr.edu/blog/salinas-valley-agriculture/article/2020-2021-evaluations-automated-weeders-lettuce-production
UA ACIS. (2025, September 30). Western Growers Case Study – Carbon Robotics LaserWeeder. University of Arizona Agricultural Climate Information Service. Retrieved from https://acis.cals.arizona.edu/agricultural-ipm/vegetables/vipm-archive/western-growers-case-study-carbon-robotics-laserweeder
Western Growers. (2024, September 29). 2024 Desert Difference AgTech Conference. Retrieved from https://www.wga.com/news/2024-desert-difference-agtech-conference/While late instar larvae of beet armyworm (BAW), diamondback moth (DBM), and cabbage looper (CL) can usually be distinguished without difficulty, identifying their eggs and early instars can be challenging, especially when these species occur together on the same hosts, such as the Brassicas. The following descriptions summarize key diagnostic features that can help to accurately identify the eggs and young larvae of these pest species in the field.
Figure 1: Diamondback moth eggs (A) and early instar larva (B).
Figure 2: Cabbage looper eggs (A) and early instar larva (B).
Figure 3: Small cluster of beet armyworm eggs (A),
newly hatched larvae (B), and 3rd instar larva (C).
To view this article as a PDF, click here and hit download.
Water conservation continues to be one of the biggest challenges for vegetable growers in the Lower Colorado River Basin, especially as irrigation supplies tighten and desert conditions push crops toward high evaporative demand. In recent years, many growers have asked whether organic production can contribute to real water savings, or whether its benefits are limited mostly to soil health. Our recent field study at the University of Arizona Yuma Agricultural Center provides new evidence that helps answer this question, and the findings suggest that organic lettuce can, in fact, reduce crop water use in measurable ways.
Throughout the 2024–2025 season, we compared organic and conventional iceberg lettuce fields managed under both traditional grower-timed irrigation and soil-moisture–sensor scheduling. Using subsurface drip irrigation combined with continuous soil moisture monitoring, we tracked the actual crop evapotranspiration (ETc) from emergence to harvest. What stood out clearly in the data was that the organic lettuce consistently used less water than the conventional lettuce across all irrigation strategies. Seasonal ETc values ranged from 217 to 261 mm (fig. 1), and the lowest crop water use occurred in the organic sensor-based treatments. This means the organic crop–soil system lost less water overall, even though both systems were irrigated using the same thresholds.
Figure 1. Seasonal crop evapotranspiration (AKA: crop water use) for each treatment
under organic and conventional cropping systems at the Valley Research Center,
University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
One of the main reasons for this reduction is the improved water-holding capacity of the organic soil. The organic field, which received chicken pellets and organic fertilizer inputs more like contributed to retaining moisture relatively longer. As a result, soil evaporation was lower and the root zone stayed wetter between irrigation events, allowing plants to access water more efficiently. This also meant that the organic plots required slightly less irrigation water to stay within the optimal moisture range, even though both systems were managed using the same depletion thresholds.
Another contributing factor was the difference in crop growth patterns. Because organic nutrients release more slowly in cool early-season conditions, the organic lettuce canopy developed a bit more gradually. This led to slightly lower transpiration during the first half of the season, which reduced overall ETc without compromising the final crop maturity. As the season progressed, the growth curves of the organic and conventional crops became more similar, but the early-season advantage still resulted in lower total water use by the end of the cycle.
Overall, the study shows that organic lettuce production can act as a genuine water-saving strategy—not only because of soil health improvements, but because it reduces actual crop water use. When paired with soil-moisture sensors, the water savings become even more substantial. The full Extension publication is available here: https://extension.arizona.edu/publication/cropevapotranspiration-organic-lettuce-production-water-saving-strategy-under-sensor
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.
