Two weeks ago at the Cotton Beltwide Conferences in San Antonio, I shared results from our Arizona organic cotton IPM work—and the response was immediate. Questions, follow-ups, and hallway conversations kept circling back to the same point: Arizona is different.

Arizona produces the highest-yielding cotton in the U.S. while using the lowest amount of insecticides in the Cotton Belt, the result of more than 35 years of coordinated, area-wide IPM. That same system could keep Lygus pressure low enough for organic cotton to be successful—but only if management decisions reflect organic realities.

In vegetable-focused regions like Yuma, cotton is treated as a rotational crop rather than a primary cash crop. Winter vegetables drive regional profitability and account for a significant share of Arizona’s certified organic acreage. Even so, Yuma still represented roughly 10% of the state’s cotton acreage last year, producing about 10,000 acres out of approximately 100,000 acres statewide. Cotton fits strategically as a summer rotation that benefits from the landscape-level pest suppression already in place.

Over the last 35 years, Arizona cotton IPM has evolved from an average of 11 insecticide sprays per season to fewer than two statewide, driven by decades of disciplined decision-making by growers and PCAs using selective insecticides, transgenic technologies, and conservation biological control.

Since 1996, those IPM-first choices have saved more than $700 million and prevented over 40 million pounds of insecticide active ingredient from being applied, creating the area-wide pest suppression that defines Arizona cotton today.

That foundation is what makes organic cotton feasible in this region: our field data showed limited benefit from certain OMRI-listed insecticides for Lygus, reinforcing a message shared at Beltwide that, in Arizona organic cotton, the smartest spray may be no spray at all.

Not all sunshine and cotton bolls. Important challenges remain in Arizona organic cotton IPM, and we’ll be sharing more details soon.

This work was funded in part by Western IPM Center, which also featured the project—read the story HERE.

Figure 1. The Arizona cotton IPM continuum illustrating how shifts in IPM tools and practices reduced statewide insecticide use over the past 35 years.

Click HERE to read more about our Arizona Cotton IPM Story.

Organic materials include crop residues, manures, and other organic amendments that are commonly added to the soil in a crop production system. It is the breakdown and microbial digestion process of organic materials that can contribute to stable soil organic matter (SOM). Thus, organic materials are not the same as SOM.

The decomposition of organic materials is a process that is carried out by naturally occurring soil microbes. Organic material decomposition is an important aspect of nutrient cycling, soil fertility, and soil health.

The naturally occurring soil microorganisms, that include bacteria, fungi, actinomycetes, protozoa, and soil fauna (organisms such as nematodes, mites, springtails, and earthworms) drive the biochemical transformations converting complex organic compounds in organic materials into smaller, simpler, plant-available forms (Paul 2015; Sylvia et al. 2005).  

In the initial steps of decomposition, these organisms exude extracellular enzymes that break down the large complex polymers (i.e., cellulose, hemicellulose, lignin, proteins, and lipids) in organic materials. The rate of decomposition is strongly influenced by substrate chemistry decay (Jenkinson 1981; Brady and Weil 2017).

The residues that decompose most rapidly have low carbon-to-nitrogen (C:N) ratios (higher N concentration), such as legumes or many manures. The low C:N ratio materials decompose most rapidly because microorganisms have sufficient nitrogen (N) to support biomass growth and enzyme production (Palm et al. 2001; Magdoff and van Es 2021). The microbes work hard to break down the complex organic materials, and they provide a great service in the process, but what they are seeking is N.

Organic materials with high C:N rations, such as cereal grain straw and most harvested crop residues are usually slower to decompose due to slower microbial activity. This is the result of microbes scavenging for mineral N, ammonium NH₄⁺ or nitrate NO₃⁻ to meet their metabolic demands (McGill and Cole 1981; Janzen and Kucey 1988).

When sufficient mineral N is lacking in the soil, the microbes will consume most of the available N and incorporate into their own bodies. This can cause short-term nitrogen immobilization (McGill and Cole 1981; Janzen and Kucey 1988). We often see that in the field with early crop growth immediately following a previous crop.

Mineralization refers to the conversion of organically bound nutrients into inorganic, plant-available forms. Nitrogen mineralization involves microbial depolymerization of organic N compounds (e.g., the breakdown into amino acids and proteins) followed by the release of ammonium (NH₄⁺) (Figure 1; Stevenson and Cole 1999). 

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

Mineralization becomes dominant as the decomposition process continues. The NH₄⁺-N (N in the form of ammonium) that is produced in the first steps of mineralization is rapidly converted to NO₃⁻-N by specialized autotrophic bacteria (Nitrosomonas and Nitrobacter). These bacterial organisms are abundant in healthy soil and we commonly see clear evidence of that in our agricultural soils. This is critically important because NO₃⁻-N is the primary form of N taken up by most crop plants. (Chapman et al. 2013).  

The balance between immobilization and mineralization is central to predicting nutrient availability during crop growth. Environmental factors such as temperature, moisture, aeration, and pH regulate the rate of all of these transformations (Brady and Weil 2017; Paul 2015).  

Other essential plant nutrients follow similar mineralization pathways. For example, organic phosphorus (P) must be enzymatically cleaved by phosphatases to release inorganic orthophosphate (McGill and Cole 1981). Organic sulfur (S) compounds are transformed into sulfate (SO₄²⁻), commonly much slower than N due to their chemical composition and the activity of specific microbes (Stevenson and Cole 1999).  

Micronutrients such as zinc (Zn), copper (Cu), and iron (Fe), are released and mineralized during ligand degradation or humus (a diverse group of large, complex organic compounds) transformation, ultimately mineralizing into plant-available ions that are soluble or exchangeable in the soil (Brady and Weil 2017).

Nutrient mineralization plays a critical role in maintaining soil health and productivity. The breakdown and conversion of organic materials is important in providing essential nutrients to crops and it also contributes to SOM formation, improved soil particle aggregation and better soil structure, improved internal water movement and drainage, and overall carbon sequestration (Follett et al. 2001).  

Effective management of residues incorporated into the soil is an important feature in managing soil health. The decomposition of organic materials, as well as mineralization and immobilization processes, are indicative of healthy soil (Kaspar et al. 1990; White 1994). 

References:
Brady, N.C., and R.R. Weil. 2017. The nature and properties of soils. 15th ed. Pearson, Upper Saddle River, NJ.

Chapman, S.J., J.A. Campbell, Q. Fraser, G.C. Puri, and R. Lilly. 2013. Nitrogen mineralization and nitrification in Scottish soils: Effects of organic matter, texture, and land use. Soil Use Manag. 29: 612–621.

Drinkwater, L.E., D.K. Letourneau, F. Workneh, A. Himes, and R.A. Shennan. 1998. Fundamental differences between conventional and organic tomato agroecosystems in California. Ecol. Appl. 8: 1098–1112.

Follett, R.F., J.M. Kimble, and R. Lal (eds.). 2001. The potential of U.S. grazing lands to sequester carbon and mitigate the greenhouse effect. CRC Press, Boca Raton, FL.

Gruhn, P., F. Goletti, and M.Y. Azam. 2000. Integrated nutrient management, soil fertility, and sustainable agriculture: Current issues and future challenges. International Food Policy Research Institute, Washington, DC.

Janzen, H.H., and R.M. Kucey. 1988. C, N, and S mineralization of crop residues as influenced by crop species and nutrient regime. Plant Soil 106: 35–41.

Jenkinson, D.S. 1981. The fate of plant and animal residues in soil. In: E.A. Paul and J.N. Ladd, editors, Soil biochemistry. Vol. 5. Marcel Dekker, New York. p. 505–561.

Kaspar, T.C., D.C. Erbach, and R.M. Cruse. 1990. Corn response to seed-row residue removal. Soil Sci. Soc. Am. J. 54: 1112–1117.

Magdoff, F., and H. van Es. 2021. Building soils for better crops: Ecological management for healthy soils. 4th ed. SARE, College Park, MD.

McGill, W.B., and C.V. Cole. 1981. Comparative aspects of organic C, N, S, and P cycling through soil organic matter. Geoderma 26: 267–286.

Palm, C.A., C.N. Gachengo, R.J. Delve, G. Cadisch, and K.E. Giller. 2001. Organic inputs for soil fertility management in tropical agroecosystems: Application of an organic resource database. Agric. Ecosyst. Environ. 83: 27–42.

Paul, E.A. (ed.). 2015. Soil microbiology, ecology, and biochemistry. 4th ed. Academic Press, San Diego, CA.

Stevenson, F.J., and M.A. Cole. 1999. Cycles of soil: Carbon, nitrogen, phosphorus, sulfur, micronutrients. 2nd ed. John Wiley & Sons, New York.

Sylvia, D.M., J.J. Fuhrmann, P.G. Hartel, and D.A. Zuberer (eds.). 2005. Principles and applications of soil microbiology. 2nd ed. Pearson Prentice Hall, Upper Saddle River, NJ.

White, C.S. 1994. Monoterpenes: Their effects on ecosystem nutrient cycling. J. Chem. Ecol. 20: 1381–1406. 

To view this article as a PDF, click here and hit download.

Cladosporium leaf spot on spinach has been coming into the Yuma Plant Health Clinic in increasing numbers as of late.

Most samples have been brought in displaying early lesions which start on the upper leaf surface (adaxial side). The lesions form a sunken cavity visible under a hand lens. As the spot progresses, chlorosis can be observed on the lower leaf surface (abaxial side) corresponding to the lesions above. With disease progression, lesions on both leaf surfaces become necrotic, papery, and tan, with little to no surrounding yellowing or haloing. Early lesions are usually tan to white or yellowish and measure less than 3 mm in diameter. Under favorable environmental conditions and high leaf moisture, individual spots may coalesce into larger, irregular blotches that form dark green fuzzy growth as the fungus begins to sporulate.

Cladosporium leaf spot is caused by the fungal pathogen Cladosporium variabile and possibly other closely related Cladosporium species which have shown pathogenicity in lab assays. Disease development is favored by the high humidity and extended periods of leaf wetness Yuma has been experiencing. The pathogen can be seedborne, making the use of clean or disinfested seed especially important. However, spread between fields via wind and water is also likely contributing to the current outbreak of this disease.

Research has shown that QoI fungicides (FRAC Group 11), also referred to as the strobilurins, can be effective in managing this disease when applied preventively (Higgins 2020). However, in Arizona, these products are not labeled for control of Cladosporium leaf spot on spinach. While this year may represent an outlier associated with our atypical winter weather, repeated outbreaks in future seasons would suggest the need to re-evaluate long-term management strategies should this disease become a recurring issue. Please continue to evaluate the economic impact this disease is having on your spinach production, as documentation of yield loss, quality reductions, and increased management costs will be critical in determining the need for research support and potential registration of additional management tools.

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

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. 

1. Precision Robotic Weeding and Thinning Trial
We are approaching the final steps of our ongoing robotic weeding and thinning trial for head lettuce. As the crop approaches maturity, we will soon conduct a comprehensive comparison of lettuce marketable yield between robotic-treated and handweeded/thinned plots.

These results will provide evidence-based insights into the efficacy and viability of robotic technologies in specialty crop production. Our preliminary observations suggest promising results, and we anticipate that detailed findings will be valuable for adoption decisions across the region.

Southwest Ag Summit Presentation
Join us at the Southwest Ag Summit on February 19th for a detailed presentation of our results. This session will provide the complete analysis to support grower decision making.

Funding Acknowledgment: This research was made possible through support from the Arizona Iceberg Lettuce Research Council (AILRC).

2. Precision Chemigation Trial
In parallel with robotic thinning and weeding research, we are advancing precision chemigation through the utilization of a custom injection assembly designed to accurately deliver chemicals like herbicides and pesticides into sprinkler irrigation systems for research purposes.

The chemigation assembly enables consistent, controlled injections at different rates, allowing for optimized chemical efficacy.

The chemigation trial will evaluate the efficacy of Kerb and Prefar herbicides applied at different rates through the chemigation system for head lettuce. This research will provide weed control efficacy optimized for chemigation delivery methods. We will present details on the chemigation system and herbicide efficacy during the IPM Session at the Southwest Ag Summit.

Funding Acknowledgment: This project was funded in part by the USDA National Institute of Food and Agriculture through the Western Integrated Pest Management Center.

Both projects represent important steps forward in the adoption of precision agriculture technologies for sustainable crop production. Results from both trials will be presented at the Southwest Ag Summit on February 19th.

Western flower thrips (Frankliniella occidentalis) is one of the most economically important insect pests affecting vegetable production in Arizona’s vegetable-growing regions. This species is particularly problematic in head, leaf, romaine, and baby-leaf lettuces, as well as cabbage and spinach. Feeding injury results in cosmetic leaf scarring and contamination of harvested plant parts, reducing marketability and crop value. Western flower thrips are present throughout the growing season in leafy vegetable crops, but typically reach their highest population levels during the spring as temperatures increase.

Bean thrips (Caliothrips fasciatus) emerged as a significant pest in Arizona vegetable production in the fall of 2017, especially in fall lettuce. Populations often migrate into vegetable fields from nearby cotton and alfalfa. Bean thrips have a broad host range that includes many vegetable crops such as asparagus, beans, beets, cabbage, cantaloupes, carrots, cauliflower, fennel, kale, leeks, lettuce, melons, peas, peppers, radishes, Swiss chard, tomatoes, and turnips. Several common weeds also serve as hosts, including field bindweed, milkweed, mallows, mulleins, redroot pigweed, sowthistle, and prickly lettuce. Similar to western flower thrips, bean thrips cause cosmetic leaf scarring and contamination of harvested plant parts, leading to quality losses and reduced market acceptance.

Fall 2025 Insecticide Efficacy Results
Results from the fall 2025 trial demonstrate that a mixture of Entrust at 2 fl oz/ac and M-Pede provided the most effective control (>70%) of western flower thrips, outperforming Entrust applied alone. Entrust at 2 fl oz/ac, when mixed with Des X, provided approximately 50% thrips suppression, similar to that of Entrust applied alone at 4 fl oz/ac. This indicates that insecticidal soap can improve Entrust efficacy against citrus thrips. Entrapment and M-Pede alone provided only limited suppression (~35%) of western flower thrips (Fig. 3).

Similarly, insecticidal soaps significantly improved Entrust performance against bean thrips. Tank mixes of Entrust at 2 fl oz/ac with either M-Pede or Des X resulted in the greatest reductions (≈80%), exceeding control achieved with Entrust applied alone at 4 fl oz/ac (63%). In contrast, Entrust at 2 fl oz/ac mixed with Captiva Prime provided moderate suppression (56%), and the remaining products evaluated were ineffective (Fig 4). Overall, these findings highlight the value of integrating insecticidal soaps with Entrust to enhance thrips control and improve management efficiency in organic production systems.

Figure 3. Seasonal western flower thrips numbers per 5 Romaine lettuce plants as
affected by selected organic insecticide applications. Insecticides were applied once a
week for 3 weeks. Kenetic (0.25% v/v) was used in all insecticide treatments except
Entrapment, where Ampersand (0.25% v/v) was used.


Figure 4. Seasonal bean thrips numbers per 5 Romaine lettuce plants as affected by
selected organic insecticide applications. Insecticides were applied once a week for 3
weeks. Kenetic (0.25% v/v) was used in all insecticide treatments except Entrapment,
where Ampersand (0.25% v/v) was used.

Between November 15 and November 25, 2025, the Yuma Valley station recorded 1.81 inches of rainfall. In many places, that amount would read like a simple win. In the Yuma winter lettuce season, it can land very differently, because timing is everything and water is usually something you control.

Most years, the region’s advantage is not just that it is dry. It is that it is predictable. When the skies stay clear, field crews can move in a steady sequence, and managers can keep crop development on pace. Irrigation is not only a way to keep plants alive. It is part of how growth is regulated. You add water, you accelerate; you hold back, you slow down. The schedule works because the system is designed for control.

Then the storm arrives, and control shifts.
The part of lettuce production most people never see.

From the road, a lettuce field looks uniform early on, but the planting strategy behind it is not as simple as putting down one seed for one head. In practice, stands are often established with more seed than the final harvest population. It is a practical hedge against uneven emergence. Wind, small differences in seed placement, and moisture variability can all create skips. If a field were planted exactly to the final stand, those skips would translate directly into lost yield.

So the field starts a little crowded on purpose. Later, that crowding is corrected by thinning, removing extra plants so the remaining lettuce can grow into consistent, marketable heads.

The important point is that thinning is not a task you can do whenever you get around to it. It lives inside a narrow window. Plants need to be big enough to identify and strong enough to tolerate disturbance, but not so far along that removal becomes damaging or ineffective. The window is short, and in a normal season, it is manageable because the field pace is steady.

In Yuma Valley, soil moisture is more than a field condition. It is the clock that sets the tempo of operations. With irrigation, that clock is adjustable. With rainfall, it is not.

During the November 15 to 25 period, the 1.81 inches of precipitation did two things at once. It provided a flush of water that pushed plants forward quickly, and it narrowed the timing for field access. When the crop advanced faster than expected, the thinning window tightened. When the ground conditions shifted, the ability to run mechanized operations on schedule tightened too.

That combination is what makes rain at the wrong time so disruptive. It is not only that the crop grows faster. It is that the step needed to manage that growth becomes harder to execute.

In a smooth season, mechanized thinning is one of the pieces that keeps the whole system efficient. When that timing is missed, the work does not go away. It simply changes form.

Manual thinning with crews becomes the fallback. It is slower, more variable, and harder to schedule at scale. The cost rises immediately, but the hidden cost is time. The longer the thinning takes, the more the crop continues to move forward, and the more likely variability shows up later as uneven head size.

As soils dry, the surface can set into a firm crust. Under those conditions, any corrective work that disturbs the surface can become more aggressive than intended. Instead of a clean adjustment, thinning can carry a higher risk of nicking or bruising plants that are supposed to remain. At that point, the field is not only managing spacing. It is managing injury risk, variability risk, and timing risk at the same time.

Rain in the mountains and river basins supports water supply stability. That is water that can be stored and delivered when needed. Rain on the active lettuce ground is different. It arrives without a schedule, and it arrives during operations that depend on narrow windows. It can be beneficial in the long run and disruptive in the moment, all in the same event.

What does this event suggest for next season
The lesson from this November rain is not that storms are bad. The lesson is that systems built on precision need contingency plans that activate early.

One practical approach is to treat the days leading into thinning as a high-sensitivity period. When the forecast shows meaningful rainfall in the next few days and fields are close to the thinning stage, the decision point should come sooner rather than later: thin early if it is safe, or prepare the alternate plan immediately so the first workable day after the storm is productive.

The second takeaway is that after rain, monitoring needs to tighten. Not because growers do not already scout, but because crop speed changes quickly when moisture status changes. A few days of accelerated growth can close an operational window faster than expected.

Takeaway
The November 15 to 25, 2025 rainfall in Yuma Valley, 1.81 inches, was not just a weather note. It was a reminder that desert lettuce is as much about execution as agronomy. When water arrives outside the plan, it can accelerate the crop and compress the operations that keep it uniform. In Yuma Valley, sunshine keeps the system predictable. Rain can still be welcome, but when it arrives at the wrong time, it rewrites the week.

VegIPM Update Vol. 17, Num. 2

Jan. 21, 2026

Results of pheromone and sticky trap catches below!!

Corn earworm:  Few CEW moths were found in traps over the last two weeks; about average for mid-January.

Beet armyworm: BAW were collected across all locations over the last two weeks; and activity slightly increased in most areas. Above average for mid-January.

Cabbage looper:  Cabbage looper moth activity remains at all locations and above average for mid-January.

Diamondback moth: Adult activity slightly decreased across most locations. About average for mid-January.  

Whitefly: Adult activity remains low across all locations, about average for this time of year.

Thrips: Thrips adult activity remains low across locations, about average for this time of year.

Aphids: Winged aphid numbers increased over the last two weeks; below average for mid-January.

Leafminers: Adult leafminer activity remained low over the last two weeks, about average for this time of season.