This year tested the Ag Center in ways we weren’t prepared for, but it showed us how resilient we are. John’s team and the Palumbo Transition Team carried his work forward with the dedication he taught us, and Samuel and team kept the farm operating after Bert’s retirement.

And through it all, industry opened its arms to our new faculty and staff, turning what seemed like an almost impossible season into one we could navigate together.

I’m ending the year with gratitude for an IPM community that works together to keeps this program thriving.

Our next newsletter will be Jan. 7th 2026. Looking forward to what Volume 17 will bring!

To contact Macey Keith go to: maceyw@arizona.edu

The ordinary understanding among agronomists/soil scientists and plant physiologists for many years is that nitrate (NO₃^-) and ammonium (NH₄⁺) in the soil solution are the primary sources of plant-available nitrogen (N). In recent years with the increasing interest and prevalence of organic crop production systems, there has been an increasing interest in the possible uptake of organic sources of N, particularly amino acids.

In agricultural communities we sometimes encounter people who claim that organic N fertilizer sources are directly available for plant uptake. This implies that the mineralization process from organic forms to the NO₃^- and NH₄⁺ forms in the soil is not necessary for the provision of plant available forms.

In response to these claims and corresponding questions, a recent review of the literature confirms that across most terrestrial ecosystems, inorganic N forms, specifically nitrate and ammonium (NO₃^- and NH₄⁺) remain the dominant source of N taken up by plants (Figure 1).

Figure 1. The nitrogen cycle. Source: Stevenson, 1982.

Some recent research evidence demonstrates that some plants do have the ability to take up organic N compounds (e.g., amino acids). Early tracer investigations demonstrated that some plants could take up amino acids directly from soil (Kielland 1994; Näsholm et al. 1998).

Studies on this topic have shown that amino-N assimilation is particularly taking place in very cold environments and situations such as boreal forests, arctic tundra, alpine heathlands, and ericaceous (heath vegetation) shrublands. These are ecosystems where N mineralization is slow and the organic N pools are large (Schimel and Chapin 1996; Michelsen et al. 1996; Chapin et al. 2003; Näsholm et al. 2009). These are extremely different conditions than agricultural soils of the desert Southwest.

The preponderance of evidence indicates that NO₃^- and NH₄⁺ do indeed make up the majority of plant N uptake in agricultural crop production systems and most natural ecosystems (Jones et al. 2005; Schimel and Bennett 2004; Näsholm et al. 2009). In most temperate and agricultural systems, inorganic N uptake exceeds that of organic N by a huge margin.

The dominance of NO₃^- and NH₄⁺ ion uptake is primarily due to the large mineral N pools of inorganic forms that are more mobile in soil solution. In addition, plants have specific and energetically efficient transport systems for both NO₃^- and NH₄⁺ ion uptake.

Another important factor is due to the intense competition among soil microbes for organic-N, and microbes are competing with plants for mineral/inorganic N (Schimel and Bennett 2004; Inselsbacher and Näsholm 2012). Thus, bioavailable N is primarily in the form of NO₃^- and NH₄⁺ ions.

Even in the cold soils and high organic matter ecosystems where amino-acid uptake has been demonstrated, inorganic N dominates when both forms are simultaneously available at similar concentrations (Gruffman et al. 2012; Inselsbacher and Näsholm 2012).

An important pattern found in the studies of organic N uptake is that it primarily occurs with three amino acids: glycine, alanine, and glutamine. Plant uptake of amino acids is often facilitated by mycorrhizal fungi, especially ectomycorrhizal associations (Read 1991; Näsholm et al. 1998; Chapin et al. 2003; Näsholm et al. 2009).

Individual amino acid structures for Glycine, Alanine, and Glutamine:

• Glycine: The simplest amino acid, with the structure: 

• Alanine: Has a methyl group 𝐶𝐻₃ as its side chain, with the structure: 

• Glutamine: Has a side chain containing an amide H₂N-CO-CH₂-CH₂ group, with the structure:

Amino acids are the building blocks of proteins and their existence in soil solution is a product of microbial breakdown of organic materials and larger organic compounds.

Amino-N represents a very minor to moderate fraction of plant N supply relative to NO₃^- and NH₄⁺ on a global basis and it takes place only in very cold and wet environments (Kielland 1994; Näsholm et al. 1998; Jones et al. 2005; Näsholm et al. 2009; and Inselsbacher and Näsholm 2012).

In conclusion, organic N uptake, as amino acids and not large organic compounds, is recognized as occasionally possible in plant N uptake, but it occurs only in cold, low N mineralization environments with a limited number of plant species.

Inorganic N (NH₄⁺, NO₃^-) are the primary forms of plant-available N in agricultural crop production systems and most natural terrestrial ecosystems.

References:
Bryant, R. B. 2025. Amino acids as fertilizer for agronomic crops: The next green revolution? Agronomy Journal, 117, e70145. https://doi.org/10.1002/agj2.70145

Chapin, F. S., III, McFarland, J., McGuire, A. D., Euskirchen, E. S., Ruess, R., and Kielland, K. (2003). The changing global carbon cycle: linking plant–soil carbon dynamics to global consequences. Biogeochemistry, 60(1), 1–3.

Gruffman, L., Albrectsen, B. R., and Näsholm, T. (2012). Plant nitrogen uptake in relation to plant–soil interactions. Plant and Soil, 350, 85–94.
(Note: Paper often cited for amino-N uptake dynamics.)

Inselsbacher, E., and Näsholm, T. (2012). The below-ground perspective of forest plants: soil provides mainly organic nitrogen for plants and their associated microorganisms. Plant and Soil, 350, 25–40.

Jones, D. L., Healey, J. R., Willett, V. B., Farrar, J. F., and Hodge, A. (2005). Dissolved organic nitrogen uptake by plants—an important N uptake pathway? New Phytologist, 168(1), 3–27.

Kielland, K. (1994). Amino acid absorption by arctic plants: implications for plant nitrogen cycling. Ecology, 75(8), 2373–2383.

Michelsen, A., Schmidt, I. K., Jonasson, S., Quarmby, C., and Sleep, D. (1996). Leaf 15N abundance of subarctic plants provides field evidence that ericoid, ectomycorrhizal and non- and arbuscular mycorrhizal species access different sources of nitrogen. Oecologia, 106, 407–411.

Näsholm, T., Ekblad, A., Nordin, A., Giesler, R., Högberg, M., and Högberg, P. (1998). Boreal forest plants take up organic nitrogen. Science, 279(5347), 859–862.

Näsholm, T., Kielland, K., and Ganeteg, U. (2009). Uptake of organic nitrogen by plants. New Phytologist, 182(1), 31–48.

Read, D. J. (1991). Mycorrhizas in ecosystems. New Phytologist, 118(3), 365–375.

Schimel, J. P., and Bennett, J. (2004). Nitrogen mineralization: challenges of a changing paradigm. Ecology, 85(3), 591–602.

Schimel, J. P., and Chapin, F. S., III. (1996). Tundra plant uptake of amino acid and NH₄⁺ nitrogen in situ: Plants compete well for amino acid N. Nature, 382, 103–105.

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.

Yuma is in the full swing of downy season for lettuce. The light yellow, irregular leaf spots on the upper leaf surface with white to pale-gray fungal growth on the under leaf surface can be found popping up in fields everywhere. Damp and cool conditions are required for infection and symptom development. Sporangia of Bremia lactucae, the oomycete pathogen responsible for lettuce downy mildew (LDM), are wind disseminated and capable of germinating on the lettuce leaf surface they land on in 3 to 4 hours if free moisture is present. All across Yuma County we started reaching that leaf wetness threshold just about the last two weeks of November (See graphs below). Leaf wetness has remained especially high in Roll and South Yuma, while North and central Yuma have been drying out, although leaf wetness in central Yuma is on a rising trend as of the time of me writing this article.

Graphs retrieved from the Arizona Meteorological Network leaf wetness reports. Leaf wetness determined by electrical conductivity. Dry hours = number of hours less than or equal to 273 mV out of 24 hours in the day, transition hours = between 273 and 284 mV, and wet hours = number of hours greater than or equal to 284 mV.

There are 10 internationally recognized races of LDM reported in the United States. The naming of new races of LDM is overseen by the International Bremia Evaluation Board (IBEB), a global association of breeders, researchers, and regulatory bodies. Races are determined by inoculating varieties with known resistance genes to LDM and seeing which varieties the race can and cannot cause disease on. Per IBEB standards, all races have the prefix “Bl:” followed by a space and the race number. European isolates have the suffix “EU” and American isolates have the suffix “US”. For instance, Bl: 1US represents American race 1.

Bl: 1-6US, or American races 1-6, are no longer detected in the western US and are therefore not considered important targets for resistance breeding by IBEB. In spring of last year, five samples from a local favorite variety, ‘Boronda’, were found to be infected with downy mildew. ‘Boronda’ is marketed with genetic resistance to the US western races Bl: 5-9US. Two samples of ‘Boronda’ submitted by Dr. Stephanie Slinski, associate director of applied research & development at YCEDA, in February of last year from Yuma were evaluated by the UC Davis Bremia group led by Dr. Richard Michelmore. When inoculated on differentials, both isolates behaved like isolate VP-300, a non-IBEB-designated variant currently under evaluation to be designated as a new American race. VP-300 was identified in 2017 and is apparently capable of bypassing the genetic resistance bred into ‘Boronda’.

I have received reports of ‘Boronda’ resistance being broken again this year in South Yuma and the Wellton/Tacna/Roll area. ‘Muggins’ is reportedly showing susceptibility as well, and I am especially interested in collecting samples from this variety for additional race testing to see if this is also due to the presence of VP-300.

Take home messages for growers:

• Downy mildew is active and the weather is perfect for disease development around Yuma County
• New, aggressive isolates are out there and they are breaking beloved resistant variety favorites
• Genetic resistance may be less effective this year than in previous years in certain varieties, use a full IPM approach
• You can submit samples of LDM to the Yuma Plant Health Clinic for race testing, ensure you fill out the downy mildew drop off sheet completely and leave plants in the sample fridge outside the clinic

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:

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

Useful Links:
BEB website: https://worldseed.org/our-work/disease-resistance/other-initiatives/ibeb/

UC Davis Bremia database: https://bremia.ucdavis.edu/bremia_database_main.php

AZ Meteorological Network leaf wetness reports: https://viz.datascience.arizona.edu/azmet/leaf-wetness-report/

About two weeks ago, we hosted the Automated Thinning & Weeding Technologies Round-Up at the University of Arizona’s Yuma Ag Center, Yuma, AZ (Fig. 1). The field day showcased the latest automated thinning and weeding technologies operating in the field at the commercial field scale level (> 1 acre). Participating companies thinned and/or weeded approximately one half of their respective demo plots 2-3 days prior to the event so that attendees could see the end result of the thinning/weeding “treatment”. The other half of the plot was used for live demonstrations the day of the event.

The performance of all of the thinning machines in the show was impressive, especially given the challenging conditions – intermittent patches of heavy weed pressure and roughly 2” nominal plant spacing with very poor plant spacing uniformity (i.e. a high percentage of the plants were closer than 1” apart) (Fig. 2a-c). I was also very impressed with the precision, speed and efficacy of the high precision spot sprayers and mechanical weeders (Fig. 2d).

If you missed the field day and you would like to see the demonstration plots and evaluate them for yourself, please feel free to contact me. We’ll be keeping the plots intact for the next couple of weeks.

Additionally, you are more than welcome to visit the plots with representatives from the companies that participated in the field day. Please contact me if you are interested. I’d be more than happy to make the arrangements. 

Fig. 2. Lettuce plant spacing in the 1-acre plots at the 2025 Automated Thinning &
Weeding Technologies Round-Up was a) tight (< 2”) and non-uniform. Automated
thinning and weeding machines were able to effectively (b) thin the closely spaced
lettuce plants, (c) identify and thin lettuce crop plants to the desired spacing in weedy
conditions and d) deliver herbicidal materials to target weeds precisely without injuring
crop plants. 

Why This Matters to Us
If you've been in agricultural research or extension work for any length of time, you know the drill. There's always another trial to set up, data to analyze, field work waiting, workshops to organize, and emails piling up. We push through because the work matters, and it absolutely does. But somewhere in that push, we often forget something equally important.

Lynn Sosnoskie, an Assistant Professor at Cornell University working in weed science, posted something on LinkedIn that really stayed with me: "My friend, your science is important. So is your health. Take care of yourself so you can take care of others."  

It's straightforward advice, but it's worth sitting with for a moment. Because she's right

The Real Talk on Health
When it comes to wellness, there's something important to acknowledge upfront: not everyone can take care of their health in the same way. Some people don't have the same resources, financial or otherwise, to exercise like others do. Some people face real barriers to time, accessibility, and capability that make wellness look different from person to person. And that's okay.

The point isn't to shame anyone into exercise routines or perfect eating habits. The point is to recognize that when we invest in our own well-being, however that looks for us personally, we're building resilience. We're improving our mental and physical capacity to handle the demands we face. We're investing in our ability to do the research better, mentor our colleagues better, and serve our communities better.

When we do find ways to take care of ourselves, moving regularly, eating real food instead of grabbing whatever's convenient, our thinking is clearer. Our problem-solving improves. We're genuinely better at what we do. But that wellness journey is personal, and it looks different for everyone.

As we head into Thanksgiving week, that feels particularly relevant. Taking care of yourself during the holidays—and being thoughtful about it—isn't about restriction or missing out. It's about showing up for yourself in ways that let you enjoy the season without derailing the health habits you've built.

Simple Moves Make a Real Difference
Remember: wellness doesn't have to be complicated. Simple physical activity can go a long way. Something as basic as tapping your body—literally tapping different areas of your body—can increase your energy and reduce the stress that builds up from sitting at a desk for hours. The point is this: wellness doesn't have to be complicated. It doesn't have to cost money. It doesn't have to take up your whole day. Sometimes it's just about recognizing what your body needs in the moment and giving it that, whether that's movement, a break from the screen, or a few minutes to breathe.

An Unexpected Connection: Weeds and Wellness
Here's something interesting that bridges weed science with personal wellness, some of the weeds we deal with in the field actually have real nutritional value.

Take Purslane, for instance. Most of us have seen it popping up where it shouldn't be, especially with the recent rain events. But in fact, this common weed is packed with antioxidants, vitamins A and C, and actually contains plant-based omega-3 fatty acids. Research suggests it may help with blood pressure, diabetes management, and even bone health. It's not a miracle plant, but it's legitimate food.

In many cultures around the world, purslane, or Barbeen (bar-BEEN)/Barbeer (bar-BEER) as it's called in Arabic, is very common. Used for its tangy and slightly tart flavor, often used in Middle Eastern cuisine to add zing to rice dishes. It's not exotic or special; it's just food that's nourishing and readily available. What's fascinating is that traditional food knowledge aligns with what modern nutrition science validates: the omega-3 fatty acids, the heart-healthy properties, the minerals, it all checks out.

Back when Marco Peña was in this position, he created a video called "If you can't beat em, eat em!" that explores this exact idea. The title's catchy, but the concept is real understanding that the plants we work with can have dimensions beyond our immediate management concerns. Also, check the article from the UC Master Gardener Program of Alameda County. Sometimes it's educational, sometimes it's practical, and sometimes it just reminds us that nature's more complex than we give it credit for.

Resources We Can Count On
We're fortunate to have our Associate in Extension, Maria Doten. She works as a Family, Consumer, and Health Science (FCHS), basically helping people navigate the real-world stuff that matters, nutrition, family health, financial wellness, that kind of thing. She's not just spouting theory; she's focused on what actually improves people's quality of life in our communities. Check out her posts on the Yuma County Cooperative Extension Facebook webpage.

If you're looking for solid, research-based guidance on nutrition, stress management, or just practical strategies for balancing work with taking care of yourself, that's who you reach out to. She gets that extension work is about serving real people with real challenges.

The Bottom Line
The bottom line is this: you can't pour from an empty cup. We all know that phrase by now, probably because it's true. When we invest in our own health and wellbeing, in whatever way works for us, we're not being selfish. We're building the foundation to do everything else better.

Your science matters. Your health matters too. And so does self-worth. Taking care of yourself isn't about perfection or doing it exactly like someone else. It's about recognizing that you deserve that investment and doing what you can with what you have.

As we head into the holidays, give yourself permission to enjoy the season. Eat the food that brings you joy. Spend time with family. And then, when the holidays are over, get back to the practices that help you feel your best—moving your body, eating real food, getting rest, and being kind to yourself in the process.

Taking care of yourself isn't about perfection. It's about recognizing that you deserve that investment, and doing what you can with what you have.

Take the time to move your body in ways that feel good. Eat actual food when you can. Talk to someone if you're struggling. Get outside. Rest when you need it. And remember, sometimes the simplest things, a few taps on your shoulders, a walk around the building, a moment to breathe, are exactly what you need in that moment.

Bagrada bug (Bagrada hilaris) is an invasive stink bug recently established in the desert Southwest of the U.S. It has become a major economic pest of many cruciferous vegetable crops cultivated in fall and winter in the agricultural valleys of Arizona and southern California. Crop injury caused by Bagrada bug feeding has resulted in major economic losses. Depending on the crop species, Bagrada bugs may cause yield losses of 15-35%. Effective options for controlling Bagrada bug infestations in organic crops are limited, creating a significant challenge for organic growers. The objective of this study was to evaluate selective organic-approved insecticides to identify new tools that organic vegetable producers in the desert can use to manage Bagrada bugs effectively.

This fall growing season, we conducted a field trial to evaluate several organic-approved insecticides against the Bagrada bug in broccoli. The results of our trial show that M-Pede and a tank mix of M-Pede and Entrust can provide approximately a 60% reduction in Bagrada bugs relative to the untreated check. Captiva Prime and Neemix also resulted in a nearly 50% reduction in Bagrada bug numbers. Aza-Direct, Entrust alone, and Botanigard each resulted in about a 30% reduction in Bagrada bugs relative to the untreated check (Fig. 1). Our observations indicate that the insecticides evaluated are unlikely to provide quick knockdown. Tank mix of M-Pede and Entrust, Neemix, and Captiva Prime resulted in 39, 35, and 34% reduction in damage caused by Bagrada bug feeding. Entrust alone and M-Pede resulted in Bagrada bug feeding damage reductions approaching 25% (Fig. 2). Previous research trials conducted in Yuma also show that mixture of Entrust and M-Pede, Entrust alone, Aza-Direct, and Pyganic can fairly suppress the pest (Palumbo 2022).

Figure 1. Number of Bagrada bugs per 10 broccoli plants as affected by biological
insecticide applications, Fall 2025. All insecticide treatments included Nu-Film
P at 1 pt./ac.

Figure 2. Percentage of broccoli plants with damage caused by Bagrada bug
feeding, Fall 2025. All insecticide treatments included Nu-Film P at 1 pt./ac.

Additional Reading Material:
Palumbo, J.C. 2024. Bagrada Bug Management Tips - 2024. Veg IPM Newsletter, Vol. 15, No. 18 University of Arizona, Department of Entomology. http://hdl.handle.net/10150/676902

Keith, M., & Calvin, W. 2025. The Evolution of Bagrada Bug Management in Desert Cole Crops: The Legacy of John C. Palumbo (2010–2025). Veg IPM Newsletter, Vol. 16, No. 21. University of Arizona, Department of Entomology. http://hdl.handle.net/10150/678668

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  

Dec. 10, 2025

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW moth counts down in most traps over the last two weeks; about average for early December.

Beet armyworm: BAW counts decreased across all locations over the last two weeks; but activity remains in most areas. Above average for December.

Cabbage looper: Cabbage looper trap counts decreased across locations except for East Gila. Activity remains at all locations and above average for early December.

Diamondback moth: Adult activity continues to increase across most locations. About average for early December. Historically DBM adult numbers peak around Dec-Jan and remain high until the end of the produce season.

Whitefly: Adult activity decreased across all locations, about average for early December. Expect numbers to remain low as temperatures continue to fall. Historically, whitefly numbers typically peak in October and then again in July-Aug.

Thrips: Thrips adult activity continues to decrease across locations, about average for this time of year. Historically, thrips numbers start picking up again until mid to late January.

Aphids: Winged aphid counts were low across all sites; below average for early December.

Leafminers: Adult leafminer activity remains low in all areas, about average for this time of season.