Hope you are all enjoying the summer so far and keeping busy. Although, we’re about 2 months away from the Fall produce season, it’s never too early to begin thinking of IPM strategies you will be using to battle key insects next season. This includes keeping track of their typical activity during June, July, and August. Below is a short discussion detailing individual pests. 
 
Aphids:    The major aphid species that are important in produce crops each spring include green peach aphid, foxglove aphid and lettuce aphid.  These species are considered cool season pests and are biologically most active during the winter and spring when temperature average around (55-65 F). We do not find them on summer crops as the high temperatures prohibit their activity. They essentially become extinct each summer only to reappear in the fall to infest crops in Oct-Dec migrating into the desert via N-NW winds that occur after the monsoons.
 
Diamondback Moth (DBM):  Another key pest that disappears each summer but for a different reason than for aphids. The host range of DBM is limited to only brassica crop and plants. Although brassica weeds are common during the winter, they occur during the summer due to high temperatures and dry conditions. Thus, like aphids, DBM populations from the previous spring season become “extinct” during the summer when brassica crops and weeds are absent. They reappear each fall migrating in on high winds associated with tropical storms from Mexico, or arrive into the region on infested brassica transplants from California.
 
Whiteflies:       A resident pest that occurs year-round in the desert. As a warm season pest, whiteflies are most abundant on fall produce crops, and seldom a problem during the winter and spring. Peak abundance occurs during the summer months on cotton, and again in September and October on fall brassica, leafy vegetables and fall melons.  Thus, it is important to control whiteflies in cotton prior to defoliation to prevent large migrations onto fall produce crops. In addition, whiteflies can be found on several weeds such as purslane, goosefoot, ground cherry, and sunflowers. Sanitation in and around fields being prepped for fall plantings is important. Preventatively, growers should consider applying soil, system insecticides such as imidacloprid or Verimark to Fall produce crops.

Beet Armyworm (BAW):  A warm-season pest that occurs year-round in the desert. They tend to reach peak abundance twice a year. Generally, the most important peak is in September and October when weather is ideal for their development, flight activity and oviposition. A second peak occurs in late spring. Activity is generally light during the summer, occurring primarily in alfalfa crops. Although BAW is known to migrate in from the south via monsoon and tropical storms, resident populations annually occur in alfalfa during the summer. Thus, to minimize BAW in fall produce crops, thorough management of BAW can potentially minimize their movement onto Fall produce crops.  Weeds are also a source of BAW (purslane, goosefoot, sunflower and Russian thistle) so sanitation in and around fields is important.
 
Western Flower Thrips (WFT):  Also a resident pest that can be found in the desert year round. WFT is most abundant on lettuce in the late spring, but peaks in abundance on alfalfa, melons and cotton is May and June. During the late summer numbers drop dramatically where thrips can be found on melons and alfalfa and weeds like goosefoot and purslane. WFT slowly move into lettuce again in early fall and are least abundant during the winter.  Sanitation of weeds during the summer can help reduce thrips abundance moving into the fall crops and weeds.
 
For more information see:   Keeping Track of Major Produce Pests During the Summer

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.

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum,  is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult. 
 
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields. 
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil. 
 
 Initial infection of seedlings usually occurs from chlamydospores (resting structure)  that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen. 
 
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management. 

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.

Results of pheromone and sticky trap catches can be viewed here.

 

Corn earworm: CEW moth remains light; below average for this time of season.

Beet armyworm: Moth trap counts increased in most areas, Above average for this time of the year.

Cabbage looper: Moths increased slightly in all traps in the past 2 weeks, and a little below average for this time of the season.

Diamondback moth: Adult counts decreased, but very active in N. Yuma Valley. Overall, below average for March.

Whitefly: Adult movement remains low in all areas, consistent with previous years.

Thrips: Thrips adults movement increased slightly in the past 2 weeks, most notably in Tacna and Yuma Valley. Overall activity average for March.

Aphids:  Winged aphids are still actively moving and but decreased to low numbers.  Average for March.

Leafminers: Adult activity up in some locations, below average for this time of season.