This has been a notable season for aphids in our desert produce crops.  Green peach aphids showed up in high numbers in early November and have only increased in abundance during our mild, dry winter so far. At the Yuma Ag Center, numbers in the past few weeks on untreated lettuce were averaging well over 40 nymphs / plant. What’s unusual about this is that dry winters generally result in light aphid pressure. Not this year.  We’ve had no rainfall and the temperatures in January and early February have been ideal for green peach aphid. What may also be playing a large role are the high winds we’re had this season.    It is well known that winged (alate) aphids migrate into desert produce from outside the area from N/NW wind currents each fall. This year was no different. But wes aw an unusually large peak in trap counts in early November (see graph below).  Furthermore, different from most years, counts show that they have been consistently moving into desert produce throughout the winter, peaking at very high numbers last week following heavy winds.  Because the desert is very dry, aphids appear to be moving directly into the valleys due to the lack of desert weeds.  This has resulted inconsistently high numbers of winged aphids found in our treated and untreated lettuce throughout the winter.

 

This constant immigration of winged aphids has also affected my insecticide trials.  In spring lettuce studies, we’ve observed less efficacy of nymphs than normal. For instance, products like Sequoia, Sivanto and Beleaf normally reduce green peach aphid nymphs by 80-90 % at 7days following application. This year we’re observing 50-60% reductions.  I don’t attribute this response to poor application, resistance or experimental error, but rather the continuous influx of winged aphids which immediately begin laying live nymphs after landing on plants. Many of these aphids have not been exposed or intoxicated by the insecticide yet giving the appearance of poor control. Reminds me of whitefly adults onfall melons when they are moving daily.  So, if you seem a bit concerned about the level of aphid control you’ve had this winter, consider that it may be mother nature working against you.

 

One last thing.  Foxglove aphids and Lettuce “Red” aphids are beginning to show up. We have found small colonies of both aphid species in our lettuce trials in the past two weeks.  I’ve also had reports of Lettuce aphid infesting lettuce in Bard/Winterhaven, Tacna and Yuma Valley.  This is later than we’ve seen in the past 2-3 years, but remember these species develop faster in warm weather. So, with daytime high temperatures forecasted to be in the 80’s next week, keep a keen eye out for these aphids. They prefer to colonize the terminals so start there on open lettuce. Foxglove aphids also attack celery, preferring to colonize in the hearts.

 

For more information on these aphids visit these links:

·       Lettuce Aphid on Desert Produce

·       Managing Foxglove Aphid on Desert Produce

·       Aphid Control Chart- 2025

Fertilizer prices have been relatively stable in 2025 and close to 2024 prices. In the last four to six weeks fertilizer prices have been increasing. Based on recent reports, prices for seven major fertilizers are now trending higher than a year ago. Price increases compared to 2024 are shown in Table 1. Recent market prices for the same seven fertilizers are listed in Table 2.

Table 1. Percent fertilizer price increases compared to 2024. Source: Quinn, 2025b.


Table 2. Recent fertilizer prices, US$/Ton. Source: Quinn, 2025b.

Anhydrous ammonia (82% nitrogen (N)) is a common measure of the fertilizer market since most N containing fertilizers are based on anhydrous ammonia in manufacturing. Price trends for anhydrous ammonia are presented in Figure 1 comparing prices for 2023-2025 with a five-year average.

Figure 1. Average weekly retail anhydrous ammonia (82% nitrogen) prices in 2023-2025
and five-year average, US$/Ton. Source: Quinn, 2025a

One concern in the fertilizer industry currently is associated with urea (46% N), which has been steadily increasing in price over the past six months (Figure 2). These concerns have recently been exacerbated by the conflict in the Middle East that has closed urea production in Iran.

Figure 2. Average weekly retail urea fertilizer prices in 2025, US$/Ton. Source: Quinn,
2025a

In 2024, Iran was the third largest global producer of urea. Annual urea export volumes from Iran have been around 4.5 million (M)tons, which is about the same as China’s urea export production. Industry experts estimate urea production of Iran to be approximately 8.9 M tons/year. Their major international clients have included Turkey, Brazil, and Argentina. The Iranians sell urea to many other countries as well (Hanrahan, 2025).

In recent years, the United States has not been purchasing Iranian urea. But the disruption in anhydrous ammonia and urea production from a major producer such as Iran, can be expected to create disruptions in the global fertilizer market.

This happened with N fertilizers in 2022 following the Russian invasion of Ukraine, after which global N fertilizer prices rapidly increased. After about 18 months fertilizer prices stabilized (Figures 1 and 2).

With the instability and uncertainties that are currently being experienced with Middle Eastern conflicts, it is important to watch global fertilizer markets and expect some changes.

References:
Hanrahan, R. 2025.Iran-Israel Conflict Adds Uncertainty to Fertilizer Market. University ofIllinois Farm Policy News Summary, 17 June 2025. https://farmpolicynews.illinois.edu/2025/06/iran-israel-conflict-adds-uncertainty-to-fertilizer-market/

Quinn, R. 2025a. DTNRetail Fertilizer Trends: Urea, UAN28 Lead Major Fertilizer Prices Higher.Progressive Farmer, DTN. 4 June 2025.

Quinn, R. 2025b. DTNRetail Fertilizer Trends: All Retail Fertilizers See Only Slight Price Movesfor First Time This Spring. Progressive Farmer, DTN. 18 June 2025. https://www.dtnpf.com/agriculture/web/ag/crops/article/2025/06/18/retail-fertilizers-see-slight-price

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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on October 14, 2024, on double rows 12 in. apart on beds with 42 in. between bed centers. All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned Nov 19, 2024, at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart. 

Sclerotia of Sclerotinia minor were produced in 0.25 pt glass flasks containing 15 to 20 sterilized 0.5 in. cubes of potato by seeding the potato tissue with mycelia of the fungus. After incubation for 4 to 6 wk at 68°F, mature sclerotia were separated from residual potato tissue by washing the contents of each flask in running tap water within a soil sieve. Sclerotia were air-dried at room temperature, then stored at 40°F until needed. Inoculum of Sclerotinia sclerotiorum was produced in 2 qt glass containers by seeding moist sterilized barley seeds with mycelia of the pathogen. After 2 months incubation at 68°F, abundant sclerotia were formed. The contents of each container were then removed, spread onto a clean surface and air-dried. The resultant mixture of sclerotia and infested barley seed was used as inoculum. Lettuce ‘Winter Select’ was seeded and then sprinkler-irrigation was initiated to germinate seed in double rows 12 inches apart on beds with 42 inches between bed centers. Plants were thinned Nov 19, 2024, at the 3-4 leaf stage to a 12-inch spacing. For plots infested with Sclerotinia minor, 0.13 oz (3.6 grams) of sclerotia were distributed evenly on the surface of each 25-ft-long plot between the rows of lettuce and incorporated into the top 1 inch of soil. For plots infested with Sclerotinia sclerotiorum, 0.5 pint of a dried mixture of sclerotia and infested barley grain was broadcast evenly over the surface of each 25-ft-long lettuce plot, again between the rows of lettuce on each bed, and incorporated into the

top 1-inch of soil. Treatment beds were separated by single nontreated beds. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of a 25 ft length of bed, which contained two 25 ft rows of lettuce. Control plots received sclerotia but were not treated with any fungicide.

For treatments first applied at seeding, sclerotia were introduced into plots before the first application of treatments. The first application for at seeding treatments was made on Jan 17, with an additional application on January 27, 2025. Some treatments had second application on Jan 30, 2024 (See table). For treatments first applied after thinning, sclerotia were introduced into plots after thinning before the first application of these treatments, with additional applications as noted in the data sheets. An initial sprinkler irrigation supplied water for seed germination, with subsequent furrow irrigations for crop growth. First sign of disease was observed on January 23, 2025. The final severity of disease was determined at plant maturity by recording the number of dead and dying plants in each plot due to Sclerotinia minor or Sclerotinia sclerotiorum (March 5, 2024). As a point of reference, the original stand of lettuce was thinned to about 65 plants per plot.

In nontreated plots, about 60% of lettuce plants were dead or dying due to infection with Sclerotinia sclerotiorum and about 50 % due to S. minor, at the end of the trial. Please refer to the data tables to compare treatments of interest, using the Least Significant Difference Value listed at the bottom of each table to determine statistically significant differences among treatments. AVIV, Luna sensation, Tesaris, Elisys, Endura fb merivon and Contans (1 application at thinning), gave the best results against Sclerotinia minor. Luna Sensation, Miravis Prime and Contans (2 applications at thinning and 14 days later) gave the best control against S. sclerotiorum (see table). table).

Phytotoxicity was not observed in any of the treatments in this trial.

It is with sadness and a sense of loss that we share the news that our friend and colleague, John Palumbo passed away last weekend. John and I have been office mates so to speak, only two doors apart, for the past 17 years. What I will miss most about John is his presence. Warren Buffet said that a key to becoming a better person was to surround yourself with people that are better than you. In other words, hangout with people who had traits and characteristics that you admire and want to emulate. John was one of those people. He made you want to be a better person. We will miss you, John. RIP.

My name is Mazin Saber, and I serve as an Associate in Extension specializing in Weed Management at the School of Plant Sciences, University of Arizona/Yuma County Cooperative Extension, based at the Yuma Agricultural Center. My work focuses on developing innovative site-specific weed management strategies tailored to specialty crop systems in desert agriculture, aiming to establish effective and sustainable weed control programs. I currently lead a new weed control research initiative at the Yuma Agricultural Center.

My academic background includes a Bachelor’s degree in Agricultural Mechanization and a Master’s degree in Agronomy from the University of Basrah, Iraq. I also hold an M.E., and Ph.D. in Agricultural and Biological Engineering from the University of Florida, where my doctoral research focused on designing automated mechanical intra-row weed control system for row crops.

Previously, my research has involved quantitative assessment of crop water-use and salt balance in the Lower Colorado River region. By utilizing advanced tools such as Eddy Covariance to measure evapotranspiration across 14 major crops over multiple seasons on commercial farming, I have contributed to improving water use efficiency and enhancing the sustainability and competitiveness of desert agriculture.

As I build my weed management program, I am conducting an assessment survey to identify the most pressing weed management challenges. Your feedback is crucial to ensure this program meets your needs. Please take a few minutes to complete the survey using the link below.

https://uarizona.co1.qualtrics.com/jfe/form/SV_4Od09r4hPLThLz8

I am available for any discussions about weed issues on your farm and I am happy to arrange field visits or ride-alongs to better understand your specific challenges. Please feel free to reach out to me directly.

Email Mazin

We conducted a series of trials during Fall 2024 and Spring 2025 to evaluate the efficacy of organic-approved insecticides currently on the market. While some of the products evaluated were found to be effective, the results of our studies demonstrated that most of these marketed organic-approved insecticides had marginal to no efficacy against common insect pests that attack vegetable crops in the desert. When the insecticides were evaluated alone, the highest label rate was used; when assessed as a mixture of two products, each product was applied at half of the label rate.

Below, we list the insecticides that resulted in some level of suppression for each insect pest.

1- Brassica

Pale stripes flea beetle: Biolink (insect & bird repellent), Insect & Bird repellent mix with Pyganic, and Entrust mix with M-Pede can provide measurable suppression of pale stripe flea beetle. Multiple applications may be required to enhance seedling protection.

Whitefly: M-Pede performed best against whiteflies on brassicas, but Surround, Pyganic, and BotaniGard can also provide some marginal level of suppression. It is best to apply Surround and BotaniGard when the plants are small. Dense foliage prevents insecticide droplets from reaching the lower leaves, where most whiteflies are located on the plants.

Diamondback moth and Beet armyworms: XenTari, DiPel, Entrust, a tank mix of DiPel and Pyganic, or XenTari and Pyganic are the most effective options for controlling diamondback moth and beet armyworms. Starting with XenTari in a rotation program can lead to greater suppression of diamondback moths.

Green peach aphid: Aza-Direct can provide measurable (greater than 50% reduction) green peach aphid suppression on broccoli. Because Aza-Direct works as a growth regulator, it is recommended to apply it early in the season to allow the product sufficient time to work and enhance its efficacy.

2- Lettuce

Green peach aphid: Aza-Direct and M-Pede exhibited variable performance when applied to broccoli or lettuce. Aza-Direct performed better at controlling green peach aphid in broccoli, but M-Pede provided the greatest (>50% suppression) green peach aphid suppression in lettuce.

Thrips: Entrust can provide excellent (>90%) control of thrips nymphs and adults. In our studies, other bioinsecticides, such as Gargoil and Aza-Direct, also resulted in thrips suppression of approximately 40% and 50%, respectively. In a rotation program, Aza-Direct and/or Gargoil can be applied at the beginning of the season when thrips populations are low, and thrips injuries are less problematic.

Bioinsecticides and their active ingredients

Improving crop yields through sustainable practices remains a key goal for agricultural research, particularly in regions facing environmental constraints like desert conditions. Biostimulants, products known to enhance plant growth, nutrient uptake, and resilience against environmental stress, offer potential benefits for organic agriculture, especially when integrated with precision irrigation techniques. This study, conducted at the Yuma Agricultural Center (University of Arizona) during the Fall 2024–Spring 2025 growing seasons, evaluated the effects of biostimulant combined with sensor-based irrigation scheduling on iceberg lettuce production under organic and conventional systems. The experimental design included four treatments each for organic and conventional systems, which combined traditional irrigation, sensor-based irrigation, and biostimulant applications.

Results indicated clear distinctions between organic and conventional lettuce systems in response to biostimulant treatments. In organic fields, the integration of biostimulant with sensor-based irrigation (OSB) achieved the highest yield, approximately 16.7 tons per acre. This represented a 20% improvement over organic treatments without sensor-based scheduling (OTI and OTB, 13.9 tons per acre) and an 8.4% increase over sensor-based irrigation without biostimulant (OSI, 15.4 tons per acre). These yield differences highlight the synergistic effect of combining biostimulant with precise irrigation water management techniques in an organic lettuce production system, potentially due to enhanced soil nutrient availability, improved root growth, and optimized water uptake. Conversely, conventional treatments yielded consistently high production across all variations, averaging around 27 tons per acre, with no measurable yield enhancement from adding biostimulant. This may indicate that conventional systems already operating at optimal nutrient and irrigation levels have limited potential for further yield improvement through biostimulant use.

These findings emphasize that biostimulant suggestively enhanced yield in organic lettuce production only when combined with sensor-based irrigation management but offered negligible benefits under conventional farming conditions. The outcomes suggest potential economic and environmental benefits for organic producers adopting integrated management practices involving biostimulant and sensor-based irrigation. Figure 1 provides detailed comparisons of yields across treatments, emphasizing the advantage of coupling biostimulant with sensor-based irrigation in organic systems at the Yuma Agricultural Center.

Figure 1. Lettuce yield: Organic Field: Organic sensor-based irrigation + biostimulant
(OSB), Organic traditional-based irrigation (OTI), Organic traditional-based irrigation +
biostimulant (OTB), and Organic sensor-based irrigation (OSI); Conventional Field:
Conventional sensor based irrigation + biostimulant (CSB), Conventional traditional-based
irrigation (CTI), Conventional traditional-based irrigation + biostimulant (CTB), and
Conventional sensor-based irrigation (CSI) at the Valley Research Center, 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 most traps over the last week; about average for early October.

Beet armyworm: Trap counts increased in several areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts increased in most locations, but still below average for this time of the season.

Diamondback moth: Adult activity spiked 2 weeks ago, particularly in the Yuma and Dome Valleys, but down over the past week. Average for this time of season.

Whitefly: Adult movement increasing Tacna consistent with melon harvests; overall about average for early October.

Thrips: Thrips adult movement peaked 2 weeks ago but down ovr the past week, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; below average for October.

Leafminers: Adult activity increased significantly last week in several locations, above average for this time of season.