There are 20 essential nutrients necessary for complete plant growth and development. Not all are required for all plants, but all have been found to be essential to some. Three of the 20 (carbon, hydrogen, and oxygen) and are derived from CO2 and H2O and are not usually considered in terms of managing a plant nutrition and soil fertility program.
The remaining 17 are commonly referred to as mineral nutrients (N, P, K, Mg, Ca, S, Fe, Mn, Mo, Cu, B, Zn, Cl, Na, Co, V, and Si). Of the 17 mineral nutrients, N, P, and K are the macronutrients; Mg, Ca, and S are secondary nutrients; and Fe, Mn, Mo, Cu, B, Zn, Cl, Na, Co, V, and Si are referred to as micronutrients. The terms macro-, secondary, or micronutrients do not refer to any level of importance but rather to relative amounts required by plants.
The amount of a given nutrient found in a plant will depend on several; factors, governed in general by a broad range of plant and environmental interactions. The percentage composition of plant nutrients can vary considerably among species and locations. Since all the mineral nutrition is provided to the plant by nutrient uptake from the soil through the root system, an understanding of the soil conditions and the effects on plant nutrition are very important.
There is usually a rather poor relationship between the total amount of a given nutrient found in the soil (i.e., P or K) and the amount available to the plant for uptake and utilization. This is certainly true in Arizona where our agricultural soils are commonly rather young (geologically) alluvial soils with a high native fertility level.
Soil tests are commonly used to establish a relationship between an estimated level of a “plant-available” form of a given nutrient and its sufficiency, deficiency, or toxicity for the crop in question. The relationships between a soil test and actual crop nutrient needs are usually specific for a crop and region and a set of common soil conditions.
Developing a sound fertilization program begins with a good understanding of actual soil conditions. The collection and analyses of a good(representative) set of soil samples and then relating that information to established guidelines are the first steps toward developing a strong soil fertility and plant nutritional management program for any crop. This is important for the overall efficiency of a crop production system, including agronomic, economic, and environmental efficiency.
To maximize nutrient management efficiency, it is good to consider the 4R concept of plant nutrient management and application, consisting of:
1. Right fertilizer source at the
2. Right rate, at the
3. Right time and in the
4. Right place
The 4R nutrient stewardship approach utilizes the implementation of best management practices (BMPs) that optimize the efficient use of fertilizer by the crop. The primary objective of the 4R approach and BMPs is to match nutrient supply with crop requirements and to minimize nutrient losses from fields. Each case can vary among farms and fields, dependent on local soil and climatic conditions, crop, management conditions, and other site-specific factors.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 109Our newly constructed self-propelled steam applicator is designed to inject steam into the soil and raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (140°F for > 20 minutes). After the soil cools (< ½ day), the crop is planted into the disinfested soil. We have done some preliminary testing and are very encouraged. Results show that the machine is able to reach target temperatures at reasonable travel speeds, provide uniform temperature distribution across the bed and form nicely shaped beds suitable for subsequent planting. We still have some bugs to work out and identified improvements to make before shipping the unit to Salinas, CA where we will conduct field trials with crops this summer. If you are interested in seeing the machine operate or more information about soil steaming for soilborne pest control, please feel free to contact me.
Check out a video of the machine operating by clicking here or on the image below.
Fig. 1. Initial testing of self-propelled steam applicator video.
Acknowledgements
This project is sponsored and funded in part by the Propane Education and Research Council (PERC), Arizona Specialty Crop Block Grant Program and USDA-NIFA. We greatly appreciate their support.
As we continue to be impacted by the drought in Arizona with a reduction in the Colorado River water allocation, we need to reconsider every option for water conservation in our agricultural operations.
We know that weeds compete with our crops for water, nutrients, and space causing yield reductions. However, how much water are we loosing due to high weed infestations?
Some researchers have concluded that weeds use more water than various crops and consider them “water wasters”. Therefore, good weed control can contribute to raise available water for our crops. Transpiration of some of the most common annual weeds is approximately four times higher than crop plants. It has also been reported that weeds use up to three times the amount of water to produce a pound of dry matter.A study showed “common lambsquarters (Chenopodium album) requires 658 pounds of water to produce one pound of dry matter, common sunflower (Elianthus annus) requires 623 pounds, and common ragweed 912 pounds, compared with 349 pounds for corn and 557 pounds for wheat1.” It has been reported that increase from 0 - 8 plants / row meter of Palmer amaranth (Amaranthus palmeri) densities in corn decreased soil water available and the water use efficiency (WUE) of corn.
Uncontrolled weed growth can add direct irrigation costs of more than $50/ha while even weed densities below economic thresholds can add ~$20/ ha in production costs depending upon the cropping system and water cost (Norris,1996).
Under stress condition such as we experience yields can be reduced more 50% just by moisture competition. Other factors that influence water loss are weed densities, transpiration rate, other weed characteristics like root system and depth. For example, perennial weeds with a well-established root system are more drought resistant because they can explore better the soil profile.
Some report that weeds can potentially cause 34 percent of crop loss worldwide. We have seen how weeds cut the water flow in irrigation ditches and cause more evaporative loss. We believe weed control is essential for water conservation purposes and further research is needed in this matter.
A species' persistence requires the ability to adapt to the biotic and/or abiotic conditions present within its environment. This adaptation may occur through natural selection, which is the process by which organisms that are better adapted to their environment tend to survive and have better fitness. Natural selection is believed to be the motor of evolution. Evolution has occurred within all groups of organisms, including plant and animal populations.
Plants have evolved resistance in many circumstances, including resistance to pests and pathogens attacks. In response to insect herbivory attacks, plants have been using chemical defenses to resist. Consequently, to maximize their fitness, plant-feeding insects have co-evolved with plants to overcome plant defenses utilizing an array of strategies. Insects have evolved the ability to detoxify plant chemicals used for defenses and use the compounds as cues that favor the detection of the plant host. Insects have also evolved an adjusted sensory system allowing host cues detection and a nervous system that is able to integrate inputs from sensory neurons. The enhancement in the sensory and nervous systems allows the detection and avoidance of toxic plants as well as the excretion, sequestration, and degradation of plant toxins. Additionally, herbivory insects utilize target-site mutation, cuticular, humoral, and cellular defenses against plant chemical defenses. Moreover, insects have evolved to resist predation, parasitism, and pathogen attacks by means of a series of mechanisms, including cuticular adjustment, adaptive behavior, and chemical defenses.
With the intensive use of pesticides to manage agricultural pests, insect pests have evolved resistance to an array of insecticides using a variety of mechanisms. This type of evolution has been described as field-evolved resistance, which is a “genetically based decrease in susceptibility of a population to a toxin caused by exposure to the toxin in the field”. This is due to strong selection pressure that favors rapid evolution of resistance. For example, the widespread adoption of Bt crops in the U.S. has led to field-evolved resistance of corn earworm, also known as cotton bollworm, against Bt toxins. In some regions, Texas, for example, cotton bollworms being exposed to the Bt toxins in both corn and cotton throughout the year have been subjected to a high selection pressure, causing the pest to become quickly resistant to Bt toxins.
The use of beneficial arthropods to manage insects can favor a decrease in insecticide use and consequently reduce the selection pressure caused by pesticides. Although the evolution of resistance to predators and parasitoids tends to be prohibited by some factors (special and temporal refuges from enemies’ attacks, reciprocal evolution by control agents, and contrasting selection pressure from enemy species), the evolution of resistance to biological control agents has been reported for several insect pests including Argentine stem weevil, greater wax moth, and fruit fly. This is likely due to reduced plant and natural enemy diversity caused by intensive large-scale agriculture.
Several factors may play a role in the development of resistance. Large-scale homogenous agricultural systems do not allow enough refuges to sustain the susceptible strains, which would then mate with the resistant strains to dilute the resistance genes and maintain the susceptibility of the pest populations. Additionally, low biodiversity within the natural enemy population may favor the selection pressure. Coevolutionary arms races may play a significant role in that this may favor one participant in mutation and recombination rates.
Mechanisms of resistance:
Physiological resistance: Insects use physiological processes to become resistant to enemies and insecticides. In a pesticide use context, physiological resistance is defined as the capacity of an insect population to survive after being exposed to a concentration of insecticide that is known to be able to kill the totality of the population completely. However, the physiological process can also favor resistance against non-pesticide control methods. For instance, the fruit fly (Drosophila melanogaster) uses encapsulation to protect itself from koinobiont endoparasitoids. The encapsulation is a cellular immune response that follows three major stages, including the recognition of the parasitoid eggs as foreign, increasing the amount of circulating hemocytes that are produced by the lymph glands, and the lysis of the crystal cells allowing the release of prophenoloxidase which results in the melanization of the capsule surface.
Another way insects become resistant is through mutation in the target site of the toxicant. This physiological process can lead to resistance in insects against both plant defenses (toxic compounds released by the plant to protect itself from herbivory) and insecticides. This mutation can lead to target site insensitivity, meaning that even though the insect is being exposed to the toxic molecule, there will be no or reduced binding of the molecule to the target site, making the molecule ineffective. This mechanism of resistance is very common in many insecticide-resistant insect pests. Insects can also become resistant to toxic compounds from plants and to insecticides by evolving the ability to undergo detoxification of certain toxicants after exposure. This ability is also conferred by a series of mutations allowing the resistant insect to increase their enzyme production, which consequently increases their enzymatic activity and causes a rapid degradation of the toxicant into a nontoxic compound. This mechanism is also known as metabolic resistance.
Behavioral resistance: Many insect species have become resistant to certain host plants that use defense compounds to prevent herbivory through their plant selection and feeding behavior. For this behavior to occur, they must evolve the ability to detect toxic plants, which can be determined genetically or through a series of learning processes. Some other insects evolved the ability to deactivate or suppress the toxin produced by the plant hosts. For instance, the cotton bollworm uses its saliva, which is a gluco-oxidase, to cause a reduction in the level of nicotine produced in tobacco leaves. Other insects, when they feed on toxic plants, can excrete a significantly large amount of the accumulated toxic compound. Some insects even sequester the toxic compounds and use them for their own defense against predators and pathogens. Some insects that are hosts for parasitoids use a very effective behavioral resistant strategy by avoiding parasite contact or detection by choosing to niche away from the parasitoids or by choosing to locate themselves near a deterrent. Using this behavior, these insects are not directly resistant to the attackers but use what is present in their environment as tools to resist parasitism. Some other insects use alternative strategies, such as cryptic coloration or masquerade, to prevent their detection by predators and/or parasitoids. In this situation, they disguise themselves as something dangerous or unwanted to avoid being prayed on or parasitized.
Cuticular resistance: Insects depend heavily upon cuticular defenses to resist pathogens, parasitism, predation, and insecticides. For instance, to resist insecticide penetration, they develop a barrier in the outer layer of the cuticle either by changing the composition of the cuticle or by thickening it. This causes the toxicant to be penetrated slowly, consequently slowing the absorption of the contaminants to the insect bodies, where actions will take place.
Although the development of resistance is mostly beneficial for insects, there are some fitness costs associated with that. Physiological resistance, behavioral resistance, and cuticular resistance require the use of a large amount of energy; some energy that would have been allocated for growth, development, and reproduction is likely to be reduced, which would consequently reduce the fitness of the insect. Thus, fitness cost may cause an evolutionary constraint, which may reduce the rate or even prevent the evolution of resistance from occurring. Given that, an increase in resource availability is likely to favor the rate at which evolution occurs within a population.
In conclusion, resistance in insects can occur in a diversity of forms, and several factors may cause resistance to occur within insect populations. Additionally, while insect populations are more likely to be resistant to insecticide in large-scale agricultural systems, they can also become resistant to biological control agents, which underscores the importance of integrated pest management programs. The rate at which resistance occurs in a population closely depends on the intensity of selection pressure to which the insect populations are exposed. Thus, the more intense the selection pressure the quicker the populations will evolve resistant.
References:
1- Ali, J. G, and A. A. Agrawal. 2012. Specialist versus generalist insect herbivores and plant defense. Trends in Plant Science. 17: 293-302.
2- Balabanidou, V., L. Grigoraki, and J. Vontas. 2018. Insect cuticle: a critical determinant of insecticide resistance. Current Opinion in Insect Science 2018, 27:68–74.
3- Berenbaum, M.R. 1986. Target site insensitivity in insect-plant interactions. In: Brattsten, L.B., and S. Ahmad. (eds) Molecular aspects of insect-plant associations. Springer, Boston, MA. https://doi.org/10.1007/978-1-4613-1865-1_7
4- Boots, M. 2010. The Evolution of Resistance to a Parasite Is Determined by Resources. The American Naturalist. 178: 214-220.
5- Castagnola, A., and J. L. Jurat-Fuentes. 2016. Intestinal regeneration as an insect resistance mechanism to entomopathogenic bacteria. Current Opinion in Insect Science. 15:104–110.
6- Chareonviriyaphap, T., M. J. Bangs, W. Suwonkerd, M. Kongmee, V. Corbel, and R. Ngoen-Klan. 2013. Review of insecticide resistance and behavioral avoidance of vectors of human diseases in Thailand. Parasites & Vectors. 6: 280.
7- Dang, K., S. L. Doggett, G. V. Singham, and C-Y. Lee. 2017. Insecticide resistance and resistance mechanisms in bed bugs, Cimex spp. (Hemiptera: Cimicidae). Parasites & Vectors. 10:318, DOI 10.1186/s13071-017-2232-3
8- Després, L., D. Jean-Philippe, and C. Gallet. 2007. The evolutionary ecology of insect resistance to plant chemicals. TRENDS in Ecology and Evolution. 22: 298-307.
9- Dubovskiy, I. M., M. M. A. Whitten, O. N. Yaroslavtseva, C. Greig, V.Y. Kryukov, E. V. Grizanova, K. Mukherjee, A. Vilcinskas, V. V. Glupov, and T. M. Butt. 2013. Can insects develop resistance to insect pathogenic fungi? PLoS ONE. 8: e60248. doi:10.1371/journal.pone.0060248
10- Fellowes, M. D. E., and H. C. J. Godfray. 1999. The evolutionary ecology of resistance to parasitoids by Drosophila. Heredity. 84:1-8.
11- Ferré, J., and J. V. Rie. 2002. Biochemistry and genetics of insect resistance to Bacillus thuringiensis. Annual Review of Entomology. 47:501–33.
12- Heidel-Fischer, H., and H. Vogel. 2015. Molecular mechanisms of insect adaptation to plant secondary compounds. Current Opinion in Insect Science. 8: 8–14.
13- Mills, N. J. 2017. Rapid evolution of resistance to parasitism in biological control. PNAS. 114: 3792-3794.
14- Ryan, M. F., and O. Byrne. 1988. Plant-insect coevolution and inhibition of Acetylcholinesterase. Journal of Chemical Ecology. 14: 1965-1975.
15- Tabashnik, B. E. and Y. Carrière. 2010. Field-evolved resistance to Bt cotton: Helicoverpa zea in the US and pink bollworm in India. Southwest. Entomol. 35: 417–424.
16- Tomassetto, F., J. M. Tylianakisb, M. Realed, S. Wrattene, and S. L. Goldsonet. 2017. Intensified agriculture favors evolved resistance to biological control. PNAS.114: 3885–3890.Organic lettuce is a high-demand crop for organic nitrogen sources. Lettuce requires a substantial amount of nitrogen to support its growth, particularly during the heading stage when most nitrogen uptake occurs. This demand is driven by its rapid growth rate and the production of large leaf biomass. The organic iceberg lettuce production system is gaining importance both locally and nationally due to the growing demand for healthy, hygienic, and safe food, along with the need for long-term sustainability (McGrady et al, 1991; Koide & Bache, 2021).
In arid regions like Yuma, AZ, where annual precipitation is often less than 3 inches, long periods of drought and frequent heat waves create challenging conditions for soil health. Limited rainfall restricts natural moisture replenishment, leading to soil dehydration and reduced microbial activity. Prolonged drought intensifies soil compaction and salinity buildup, while extreme heat accelerates organic matter decomposition, further depleting essential nutrients. These factors collectively hinder soil fertility, making it more difficult to sustain productive organic lettuce farming without strategic soil health management practices.
Therefore, many questions arise about whether combining fertilizers with biostimulants may improve soil health, particularly soil water retention while also enhancing crop growth, development, and yield. Several studies indicate that the combination of biostimulants with organic fertilizers has a positive effect on soil structure and mitigates stress and crop yield (Rodgers et al., 2020 Li et al., 2021; Zhang et al., 2021). They enhance soil physical properties and boost crop productivity in multiple ways. The potential of biostimulant to align with sustainability policies offers promising prospects for the future of agriculture. Given the environmental challenges associated with current fertilization practices, there is a pressing need to prioritize research that optimizes plant-microbe interactions to establish more sustainable agricultural systems. Biostimulants can positively influence a plant’s response to stress and adverse environmental conditions, promoting growth by enhancing germination, root development, and the plant's ability to access water and minerals.
Thus, investigating the magnitude of the potential impacts of coupled organic fertilizer and biostimulant on soil properties (i.e., soil water retention), lettuce crop growth development and yield for local or regional conditions can result in more effective, relevant, and practical information that can aid users in making management decisions. To address the identified knowledge gaps, preliminary field experiments were conducted during the Fall 2024 growing season at the Valley Research Center, University of Arizona Yuma Agricultural Center. These experiments aimed to establish foundational data to support this proposal.
The field (Figure 1) was planted on October 29th, 2024, and the pre-sprinkler irrigation strategy was utilized to ensure germination which was noticed on November 06, 2024. On December 5, when the lettuce was about 1 inch tall, the first application of 2 quarts/acre biostimulant (FBS Organics® Zicron®) was applied via the subsurface irrigation system. A second application of 1 gallon/acre was applied on January 9, 2025.
To quantify changes in soil water retention, three types of high-tech sensors (Figure 2) were installed after crop emergence to continuously monitor soil moisture levels, along with other key parameters. Additionally, plant height (Figure 3) measurements have been taken to assess the impact of biostimulants combined with organic fertilizers on crop growth and development. Finally, yield differences will be evaluated after harvest to determine the overall effectiveness of these treatments (Figure 4). Stay tuned for the results and conclusions after harvesting.
Figure 1. Satellite image view of the organic research field in the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
Figure 2. Nitrate-N sensor and soil moisture sensor from AquaSpy and soil
moisture and salinity sensors from Sentek were installed between two healthy
plants in the organic lettuce production field at the Valley Research Center at the
University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
Figure 3. Plant height measurements in the field at the Valley Research Center at
the University of Arizona, Yuma Agricultural Center, Yuma, Arizona
Figure 4. Lettuce few weeks before harvesting in the field at the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
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.
