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

Soil is a natural component of terrestrial ecosystems, both native and agricultural. Soils are the foundation of plant and crop production systems (Brady and Weil, 2008; Parikh and James, 2012).

In terms of soil health, a good way to consider a soil system is from the standpoint of three main categories (physics, chemistry, and biology) that are fundamentally important with healthy soil function (Figure 1).

Figure 1. Soil health factors and chemical properties.

It is estimated that soil contains at least a quarter of the biological diversity (aka biodiversity) on our planet. Soils are second only to the oceans in terms of biological diversity. Billions of earthworms, nematodes, insects, fungi, bacteria, actinomycetes, viruses, and other invertebrates exist in soil naturally. These creatures produce and consume the organic material (i.e., crop residues) found in soil as part of their basic fund and collectively work to break down the organic materials that come from their bodies and plant materials into minerals and nutrients that are cycled in the soil system and support healthy conditions in the soil environment, including plant nutrients.

During the 20th century, soil scientists began to better understand the complexity of soil biology and ecology. From that work, many drugs and vaccines have been derived soil organisms. For example, antibiotics such as penicillin have been developed. Treatments for cancer such as bleomycin have come from soil and fungal infection treatments like amphotericin have also been derived from the soil microbiome. Accordingly, the biodiversity of soil still has a huge potential to provide new drugs that can help us in combating other illnesses and dealing with pathogenic and resistant microorganisms.

This tremendous biological diversity creates the foundation for the entire soil ecosystem. Soil ecosystems impact the growth of plants and animals in natural and agricultural systems. The biological composition of soils has a very strong influence on soil health.

During the 20th century soil scientists had an appreciation for the rich biological diversity in soil but they were limited in their analytical capacities (Waksman, 1936). In the past 40-50 years, soil scientists have employed an increasing level of new analytical tools that have allowed the discovery and better understanding of the number and diversity that naturally exists in soil (Sutton and Sposito, 2005).

A good description of biological diversity and its tremendous complexity can be demonstrated by consideration of the common composition of soil and the abundance of a few classes of microorganisms in one gram of soil (Figure 2).

Figure 2. Natural abundance of bacterial, actinomycetes, and fungal organisms in one
gram of soil.

It is incredible to realize that in one gram of soil there commonly exists nearly one billion individual bacterial organisms, more than a million actinomycetes organisms, and one million fungal organisms. All these organisms naturally exist in soil and these population numbers represent just one gram of soil!

Among the approximately one billion individuals in one gram of soil, there are commonly more than 10,000 different species. Soil biologists are now working to better identify individual organisms and understand their functions individually and how they function in the complexity of the soil ecosystem. We do not know all the species. Accordingly, we do not know how all these organisms are forming and functioning as a complex ecosystem. Soil ecology is a huge and rapidly expanding area of study.

We do know that soil biology and ecology are very important aspects of soil health (Figure 1). We also know that our management in the field, agronomic stewardship, has a strong influence on soil health and accordingly crop health.

Gaining a better understanding of soil health requires a better understanding of soil biodiversity and the functioning of soil ecosystems. It would be misleading to say that we have a solid understanding of the soil ecosystem function and all the managerial relationships. However, it is important to understand that working on this frontier of soil science and agriculture is critical to our efforts to maintain sustainable and productive agricultural systems for the future.

Figure 3. Interrelationship of agronomic stewardship, soil health, and crop health.

 

At the 2025 Southwest Ag Summit Field Demo a couple of weeks ago, many of the latest technologies were demonstrated in the field. Most were related to pest control. Several of the technologies demonstrated are new to the Yuma, AZ area. The recent technologies presented included two types of high precision spot sprayers for weeding and applying beneficial pesticides (Fig. 1a, Fig. 1b) and an AI based lettuce thinner. Manufacturers stated the technologies will be getting even better/more versatile soon. Both precision spot sprayer companies are developing models for small lettuce so that the machines can also be used for lettuce thinning. Also new was that the AI lettuce thinner technology is being further developed so that the device can be used also be used as a weeder. Several “older” pest control technologies also seemed to garner a lot of interest. These included an implement designed for cultivating high density crops (Fig. 1d), a camera guided cultivator equipped with in-row weeding tools (Fig. 1e) and a field scale drone sprayer (Fig. 1f).

Fig. 1. Newer pest control technologies demonstrated at the 2025 Southwest Ag Summit
Field Demo included a) Ecorobotix1 Ara high precision spot sprayer, b) Verdant Robotics
Sharp Shooter, c) Niqo Robotics AI based lettuce thinner, d) Oliver high density
cultivator, e) Steketee IC Light camera guided cultivator and f) DJI Agras T50 drone
sprayer.

Thank You

In 2010 we started publishing the Arizona Vegetable IPM Updates to a small number of friends. It was embraced by the community because of contributions from Mike Matheron, John Palumbo and Barry Tickes in the Plant Pathology, Entomology and Weed Science areas. Mike, John and Barry are the original IPM dudes. 

I was honored to be part of the team editing and sending the Newsletter for almost
16 years. 


This is my last update, and I would like to thank the UA team and the agricultural community for the opportunity to work with you. 

Aphids are considered the most difficult to control insect pests in organic vegetables due to the lack of effective bioinsecticides as well as their ability to hide within plant structures. For instance, lettuce aphids normally hide in the head or heart of lettuce, making them difficult to reach by insecticide treatment or natural enemies. It is important to adopt other methods, such as nitrogen and water management, for additional aphid suppression.

As sap-sucking insects, aphids depend on the nutritional content of the sap ingested from the plant hosts for proper growth and development. Nitrogen availability is one of the most important factors in the development of aphid populations. Thus, limiting your nitrogen application to the optimum amount required for your crops is good practice for maintaining your aphid population below damaging level. Additionally, the use of slow-release (minimizing the risk of nutrient deficiency or excess) nitrogen fertilizer can be beneficial for aphid control. On the other hand, excess of nitrogen will make your crops a superfood for aphids. This accelerates the growth, development, and reproduction of the pests, reduces their generation time, and results in an increase in the number of generations and density during the cropping season. Excess of nitrogen particularly affects aphids on host crops such as lettuce, wheat, and sorghum. In some situations, high nitrogen levels in plant tissue can decrease resistance and increase susceptibility to aphids’ attacks. Applying the optimum amount of nitrogen fertilizer can tremendously help to manage aphids. In addition to pest management, effective fertilizer usage can also result in economic and environmental benefits.

Selected References:
1- Altieri, M. A., C. I. Nicholls, and M. A. Fritz. Manage insects on your farm: a guide to ecology strategies. SARE. https://www.sare.org/resources/manage-insects-on-your-farm/

2- Aqueel, M. A., and S. R. Leather. 2011. Effect of nitrogen fertilizer on the growth and survival of Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Homoptera: Aphididae) on different wheat cultivars. Crop Protection. 30:216-221.

3- Bal, R., M. Groshok, and Y. Jama. 2024. Effects of nitrogen and potassium-based fertilizers on green peach aphid and abundance and arugula condition and growth. The Scientist. 6:1. https://journals.mcmaster.ca/iScientist/article/view/2931

4- Sinha, R., B. Singh, P. K. Rai, A. Kumar, S. Jamwal, and B. K. Sinha. 2018. Soil fertility management and its impact on mustard aphid, Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae). Cogent Food & Agriculture. 4: 145094.

5- Xia, C., W. Xue, Z. Li, J. Shi, G. Yu, and Y. Zhang. 2023. Presenting the Secrets: exploring endogenous defense mechanisms in chrysanthemums against aphids. Horticulturae. 9: 937. https://doi.org/10.3390/horticulturae9080937

Supplying the optimum amount of water to your crop is also very important for effective pest control. Water availability around plant roots increases nitrogen absorption. Additionally, with high water availability, there is an increase in phloem pressure, making food more accessible to sap-sucking insect pests. Supplying the required amount of water using appropriate irrigation methods and irrigation scheduling can be beneficial for pest management. Although these practices will not completely prevent infestation of aphids, they can surely play a role in reducing the density of aphid populations on your crops.

In regions like Yuma, AZ, extensive farming practices, irrigation and nitrogen (N) fertilizer management should be considered simultaneously due to the important fact that N moves in the soil with water and both variables should be managed together to enhance production efficiency. Coupled irrigation and N management strategies with the efficient irrigation method can lead to a critical approach to increase irrigation and nitrogen use efficiency (NUE) while maintaining crop yield and soil productivity and minimizing the potential for N leaching or losing. The mass of leached N during the growing season may be reduced by improved irrigation efficiency that can reduce drainage volume. For example, the surface/furrow irrigation system has greater irrigation depths and lower NUE than sprinkler irrigation systems. Moreover, the methodology of N application through split/timing applications can increase the NUE, especially when utilizing micro-irrigation and sprinkler irrigation systems. One of the primary objectives of the irrigation systems is to maximize the water storage in the root zone through uniform irrigation application and distribution and in the meantime to minimize water losses through deep percolation and surface run-off. In addition, irrigation systems have been utilized to apply fertilizers (fertigation) throughout the season. Generally, these systems provide a way to supply adequate N (allows small dosage application) to the crop in-season and those systems can deliver the desired nutrition amount to the crop at any crop stage with a high efficiency and distribution uniformity. In other words, a given irrigation system has the potential to reduce the fertilizer inputs and the production costs, reduce foliar disease, and minimize leaf wetness as well as reduce the weeds.

The three most commonly used irrigation methods/systems are (i) surface (gravity), (ii) sprinkler (including center pivot), and (iii) micro-irrigation. For each of the methods, there a different management processes and the uniformity of water applications as well as infiltration dynamics, which influence the efficiency of the system as well as the efficiency of N applications. Worldwide, low NUE is one of the most important challenges for researchers, farmers, and agencies, and it is on average quite low in both organic and conventional agricultural systems, including in developed nations. It is reported that globally, pre-plant N is most commonly applied, which may lead to poor synchrony between N and crop demand, contributing to low NUE. Applying N at a uniform rate is another factor of low NUE, because the available N level for crop uptake may vary between the fields and within a given field due to the spatial variability in soil characteristics and temporal characteristics due to environmental factors.

Timing nitrogen applications for lettuce is key to maximizing nutrient management efficiency, though it can be challenging if growers are constrained by time. To minimize nutrient loss, it's best to avoid pre-plant nitrogen applications, especially in the fall. At planting, apply a starter fertilizer, positioning it below and to the side of the seed row. The first sidedress application should occur after thinning at the 2-4 leaf stage, but only if soil nitrate-nitrogen is below the critical level. A second application is recommended a few weeks later at the cupping stage, contingent on soil nitrate levels. These applications should be carefully timed and adapted based on soil conditions to ensure effectiveness. Aligning nitrogen applications with the crop’s demand not only enhances nitrogen use efficiency but also helps in managing tight schedules, reduces environmental impacts, and optimizes lettuce yield and quality (Figure 1).

Figure 1: Harvesting in the Organic/Conventional Lettuce Production Field at the Valley
Research Center, University of Arizona Yuma Agricultural Center, Yuma, Arizona.

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 23, Nov 17, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts continued to decline over the past 2 weeks across all locations and about average for this time of the season. 
 
Beet armyworm:         
Trap counts decreased in most locations, but well below average for late-October. Most activity in Yuma, dome and Gila Valleys.
 
Cabbage looper:          
Cabbage looper trap counts declined in most areas but increased in the Bard and Yuma Valley. Activity below average for early November.
 
Diamondback moth:     
Adults peaked in Gila and Yuma Valleys and above average in all locations for this time of year. Traps located adjacent to cauliflower and broccoli transplants had the highest trap captures 
 
Whitefly:                     
Adults remains active in Dome Valley, Wellton, and Roll consistent with melon crops completing harvest, but below average movement for this time of season. 
 
Thrips:                          
Thrips adult movement increased in most locations last week,  particularly in Dome Valley, Wellton, and Tacna. Activity about average for early November.
 
Aphids:                        
Aphid movement increased sharply in Bard, N. Yuma Valley and N. Gila Valleys over the past 2 weeks. Activity average for this time of year.
 
Leafminers:                  
Adult activity increased sharply in the Gila Valley, Roll and Wellton; about average for this time of season.