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.This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach ‘Meerkat’ was seeded, then sprinkler-irrigated to germinate seed Jan 13, 2025 on beds with 84 in. between bed centers and containing 30 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated four times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2 backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles.
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae)was first observed in plots on Mar 5 and final reading was taken on March 6 and March 7, 2025. Spray date for each treatments are listed in excel file with the results.
Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft2areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2area of bed was approximately 144. The percentage were then changed to 1-10scale, with 1 being 10% infection and 10 being 100% infection.
The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that provided most effective control against the disease include Orondis ultra, Zampro, Stargus, Cevya, Eject .Please see table for other treatments with significant disease suppression/control. No phytotoxicity was observed in any of the treatments in this trial.
The Desert Difference: A Showcase of Ag Tech Opportunities for Growing in the Desert begins TODAY Wednesday, November 13th with a Field Demo Day at the Yuma Agricultural Center. The educational workshop will feature 13 of the latest automated and robotic technologies for pest control and improved vegetable production being demonstrated in the field. Registration begins at 7:00 am and the program starts at 7:30 am (agenda below).
The Field Demo Day is part of at wo-day event. The second day will be a standard conference with keynote speakers, breakout sessions and trade booths. The event will be held Thursday, November 14th at the Yuma Civic Center. Details of the event and Conference Day (Day 2) activities can be found here.
Looking forward to seeing everyone at both events!
Fig. 1. Field Demo Day agenda (Day 1) for The Desert Difference: A Showcase of Ag
Tech Opportunities for Growing in the Desert event. More information about the event
and Conference Day activities (Day 2) can be found here.
This inquiry has been brought to us for different herbicides; How much time does this product require to safely plant lettuce?
Of course, this depends on many variables such as the management done in the crop before lettuce, texture, water applied, rate, climatic conditions presented, and many other factors.
The following table published in this Newsletter by Barry Tickes can serve as a general guideline to base Integrated Pest Management decisions and program our strategies. It’s always recommended to check the label for the product used in previous crops.
I am delighted to embark on my first produce season here in Yuma, AZ. I am looking forward to becoming acquainted with the growing region this fall as we begin identifying tools that can enhance our pest management strategies, specifically focusing on organic solutions for managing insect pests in the Desert Southwest. It is also important for me to gain a deeper understanding of the challenges and issues you are facing in the field. We are eager to evaluate both current and new biopesticides in our upcoming trials and look forward to engaging with potential collaborators.
Here is a list of our fall 2024 trials:
1- Evaluation of selected bioinsecticides against Lepidopteran pests in Brassicas
2- Evaluation of selected bioinsecticides against whiteflies in Brassicas
3- Alternative bioinsecticides for thrips management in lettuce
4- Assessing the effectiveness of beneficial insects (T. brassicae, T. pretiosum, and green lacewings) release for diamondback moth control in Brassicas
I hope everyone’s season gets off to a fantastic start. Please contact me or Macey if you have specific pest issues, biopesticides, or other organic IPM practices you would like us to evaluate. Your expertise is truly invaluable to us!
Contact Information:
• Wilfrid Calvin
Assistant Professor & Extension Specialist
Cell: (979) 709-9762
Office: (928) 782-5861
e-mail: wilfridcalvin@arizona.edu
• Macey Keith
Assistant in Extension
Cell: (928) 580-5785
e-mail: maceyw@catmail.arizona.edu
Both organic and conventional lettuce are high-demand crops for nitrogen, with organic lettuce requiring organic nitrogen and conventional lettuce requiring general 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.
Organic nitrogen/nitrogen management for lettuce production in Yuma, Arizona, is acritical aspect of efficient and sustainable agriculture. Proper nutrition(organic nitrogen or nitrogen) management can improve crop yield, reduce environmental impact, and optimize resource use. This is significantly correlated with sufficient soil moisture availability. As a result, improper or excessive water and nutrient management for both organic and conventional lettuce production systems could significantly and negatively impact growth, development, and yield quality.
Moreover, several studies have reported that proper water and nitrogen management could potentially reduce aphid attraction to lettuce, as aphids are more prevalent in lettuce with higher nitrogen content. Elevated nitrogen levels in lettuce can attract and support larger aphid populations.
There are many approaches that could be adopted for coupled water and nutrient management, or in other words, best management practices to avoid excessive or inadequate application of either element. After soil sample analysis in the pre-season, one of these approaches involves utilizing high-tech site-specific sensors, which can be installed between two healthy plants that represent the majority of the field to monitor nitrate-N levels in the soil throughout the growing season. These sensors monitor nitrate-N levels on a daily or weekly basis to evaluate nutrient levels at different soil profile depths, especially during critical lettuce growth stages. Many studies have reported that site-specific, sensor-based nutrient management increases efficiency compared to traditional methods, resulting in significant nitrogen savings.
Preliminary results from ongoing research comparing nutrient levels by utilizing AquaSpy Nitrate sensor (Figures 1. 2. And 3) with soil analysis conducted in the lab (Ward Laboratories Inc.) as part of the study on organic vs. conventional iceberg lettuce under subsurface drip irrigation at the Yuma Ag Center-Valley Research Center, suggest that the findings are comparable to a considerable extent so far. Soil moisture availability and soil temperature fluctuations significantly influence the data reflected by the sensors, particularly at varying profile depths. This is an ongoing project; however, the results are promising regarding the aforementioned objectives in organic and conventional lettuce production systems. Stay tuned for the results and conclusions after harvesting.
Figure 1. Nitrate sensor from AquaSpy was 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 2. Nitrate level in the conventional lettuce production field at the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: CEW moth counts down in all traps over the last month; about average for December.
Beet armyworm: Moth trap counts decreased in all areas in the last 2 weeks but appear to remain active in some areas, and average for this time of the year.
Cabbage looper: Moths increased in the past 2 weeks, and average for this time of the season.
Diamondback moth: Adults increased in several locations last, particularly in the Yuma Valley most traps. Below average for December.
Whitefly: Adult movement remains low in all areas, consistent with previous years
Thrips: Thrips adult movement continues to decline, overall activity below average for December.
Aphids: Winged aphids still actively moving but declined movement in the last 2 weeks. About average for December.
Leafminers: Adult activity down in most locations, below average for this time of season.
