With rain in the forecast, growers and PCAs should be alert for earlier-than-usual and rapid increases in green peach aphid (GPA) populations. Historically, rainfall events this time of year are often followed by quick aphid buildup, particularly in young lettuce.

According to observations shared by Leo Chavez, research technician in John Palumbo’s program, GPA commonly appears earlier and develops faster following rain events, likely due to favorable plant growth and aphid reproduction conditions.

Following rainfall, we recommend increasing scouting frequency, especially in younger plantings and along field edges. Early detection is critical, as GPA populations can escalate quickly under these conditions. For guidance on action thresholds and optimal treatment timing, PCAs and growers are encouraged to reference John Palumbo’s Action Thresholds for Desert Produce Crops handout.

Introduction
Soil, water, and the climate of Arizona and the desert Southwest provide the basic natural resources necessary in the development and management of productive irrigated crop production systems. Understanding the soil resources in each field and the unique characteristics are important factors in maintaining soil health and sustainable crop production systems. Soil surveys have been developed for every county in the United States by the United States Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS). Soil surveys are provided in a consistent format and have been available for many years in hardcopy through local NRCS offices. They can now be accessed online and there are phone apps (i.e., SoilWeb) that are convenient methods of obtaining soil survey information for direct field observations.

Why Soil Surveys Matter in Irrigated Crop Production Systems
Important soil properties such as texture, depth, permeability, salinity, sodicity, and organic matter content are provided for each soil type (soil series) identified in the field. Soil surveys have been conducted and field maps provided on a scale of 1:20,000 in most cases. This provides a high level of detail in identifying soil types and natural field variability.  

In my experiences working with agricultural areas across Arizona and the desert Southwest over the past 40 years, these USDA-NRCS soils are very accurate. They provide an extremely valuable resource for farm and field management. The soil survey maps can be helpful in developing irrigation systems, identifying possible internal soil drainage problems, recognizing water retention capacities of field soils, and evaluating crop variability patterns (Soil Survey Staff, 2017).

Managing Salinity and Soil Drainage
Salt accumulation is a natural consequence of irrigated desert agriculture primarily due to evapotranspiration greatly exceeding rainfall. Without proper leaching and drainage, soluble salts can accumulate, and salinity can limit crop yield and high sodium concentrations can impact soil structure. Soil survey data helps identify areas with shallow restrictive layers that can restrict internal drainage and leaching, natural saline zones, or naturally high sodium levels that require special management (Oster et al., 2012; Franzen et al., 2022).

Digital Tools
The development of the Web Soil Survey and Soil Data Access platforms provides easy access to integrate soil resource information with field implementation. Managing fields for optimal soil health begins with a good understanding of the soil types in each field and the natural variation among soil types across a field (Soil Survey Staff, 2022; USDA–NRCS, 2024).

Arizona soil surveys can be accessed through the following link to USDA-NRCS sites:

https://archive.org/details/usda-arizona?page=2

The Soil Survey of the Yuma-Wellton Area, Parts of Yuma County, Arizona, and Imperial County, California can be accessed through the following link, and pdf copies can be downloaded:

https://archive.org/details/usda-general-soil-map-of-yuma-wellton-area--parts-of-yuma-countyarizona-and-imperial-coun/page/n115/mode/2up

Conclusion
The USDA-NRCS soil surveys are valuable resources for management in irrigated desert agriculture. In the alluvial soils common across the crop production regions of Arizona, there is a high level of natural variability that is often not visible on the surface of the land.  Management practices for optimum soil health and water conservation are optimized by understanding the nature of soil variability in a field and how the soil horizons are arranged in the vertical profile, particularly in the rooting zones of crop plants.

References
Franzen, D.W., D.L. Osmond, and J.J. Meisinger. 2022. Soil fertility and nutrient management in irrigated systems. In: J.L. Hatfield and T.J. Sauer, editors, Soil Management: Building a Stable Base for Agriculture, 3rd ed. ASA, CSSA, and SSSA, Madison, WI. p. 201–230. https://doi.org/10.2136/2018.soilmanagement.c11

Oster, J.D., I. Shainberg, and J. Rhoades. 2012. Salinity and sodicity management. In: R. Lal, editor, Encyclopedia of Soil Science, 2nd ed. CRC Press, Boca Raton, FL. p. 1571–1576.

Soil Survey Staff. 2014. Keys to Soil Taxonomy, 12th ed. USDA–Natural Resources Conservation Service, Washington, DC.

Soil Survey Staff. 2017. Soil Survey Manual, USDA Handbook 18. U.S. Government Publishing Office, Washington, DC.

Soil Survey Staff. 2022. Web Soil Survey. USDA–Natural Resources Conservation Service. Available at: https://websoilsurvey.nrcs.usda.gov

U.S. Department of Agriculture–Natural Resources Conservation Service (USDA–NRCS). 2024. National Soil Information System (NASIS) and Soil Data Access (SDA) User Guide. USDA–NRCS, Washington, DC.

It’s been anything but a smooth Spring melon season this year. Mild winter temperatures have contributed to the persistence of weeds and whitefly populations culminating in high viral pressure observed from the very first melon plantings onward. Through a collaborative effort between the University of California, USDA, and University of Arizona we would like to invite growers, PCAs, farm managers, researchers, and other stakeholders from the desert melon production regions in California, Arizona, and Mexicali to join us for a stakeholder meeting to discuss field observations and disease management research priorities.  

This meeting will provide an opportunity to review this season’s observations and trends across production areas, hear research and strategy updates from plant pathology specialists, and, most importantly, create space for discussion among stakeholders to better understand what is happening and give input on the disease management research priorities you want to see pursued moving forward. Topics and invited speakers include:

• Bill Wintermantel (USDA-ARS) – Overview of cucurbit viruses affecting desert melon production
• Arun Babu (UCCE Imperial)– Whitefly populations and insecticide efficacy trials in Imperial Valley
• Samuel Discua (University of Arizona, Yuma) – Whitefly populations and insecticide efficacy trials in Yuma, Arizona
• Chris Detranaltes (University of Arizona, Yuma)– Viruses and other pathogens recovered from symptomatic melon plants in Yuma, Arizona
• Ana M. Pastrana (UCCE Imperial) – Viruses and other pathogens recovered from symptomatic melon plants in Imperial Valley, California

 

Meeting details:
Where: AgWest Imperial 485 Business Pkwy, Imperial, CA 92251
When: June 2, 2026 10:30 am – 12:30 pm (lunch to follow until 1:00 pm)

Lunch will be provided. Please register here if you plan to attend so we can have an accurate food count and seating estimate: Registration Survey

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 109 

It is with mixed emotions that I write to inform you that this will be my last University of Arizona Vegetable IPM Update. The reason – I am retiring. Thank you for your support over the years. It’s been an honor and a privilege working with you and serving this ag community.

Figure 1. Automated Thinning & Weeding Technologies Field Day.
(Photo credits: Rosa Bevington)

Palmer amaranth escapes are showing up in cotton despite good early-season control. Most issues are tied to late flushes, missed timing, and heavy reliance on glyphosate programs.

Why escapes are happening

• Extended germination under irrigation and heat.
• Gaps in POST timing allowing new flushes.
• Weak residual programs or poor activation.
• Repeated use of the same mode of action (MOA), especially glyphosate (Group 9).

Glyphosate resistance in Palmer is already widespread in the Southwest, so overreliance will continue to fail.

What to do differently

• Use overlapping residuals (PRE + POST residual).
• Include 2–3 effective MOAs in every program.
• Spray small weeds (target <3 inches).
• Do not rely on glyphosate alone.

Program basics by system

All cotton systems (foundation)

• Prowl H2O or trifluralin (Group 3)
• Cotoran (Group 7) or Caparol (Group 5)
• Add Dual Magnum or Outlook (Group 15) Glyphosate-only / Roundup Ready
• POST: Glyphosate + residual
• Staple (Group 2) only where still effective
• Layby: Diuron or Caparol + residual

LibertyLink

• POST: Glufosinate (Group 10) on small weeds
• Add residual every time
• Repeat in 7–10 days if needed

XtendFlex / Enlist

• POST: Dicamba or 2,4-D choline + glyphosate + residual
• Include glufosinate where appropriate (XtendFlex)
• Always tank mix and rotate MOAs

Adjuvant reminders

• Glyphosate: AMS required.
• Glufosinate: AMS required; avoid COC/MSO; use high spray volume.
• Dicamba / 2,4-D: Only approved adjuvants.
• Residuals: Proper adjuvant + irrigation activation.

IPM reminders

• Start clean, overlap residuals.
• Control before 3–4 inches.
• Remove escapes before seed set.
• Prevent seed spread between fields.

Support for suspected resistance issues If you are seeing escapes that look suspicious, please reach out. I am available to help. As a weed specialist, I can visit fields, collect seeds, and run greenhouse bioassays to evaluate for herbicide resistance. This can help confirm what is failing and guide better program decisions moving forward. Palmer control is a season-long effort—once it sets seed, pressure increases quickly in future crops. 

Insect pests are constantly adapting to their environment. Over time, they have evolved ways to overcome control tactics. Repeated use of the same insecticides or tactics places strong selection pressure on pest populations. This allows the few individuals that can survive treatments to reproduce, leading to populations that are increasingly difficult to control, a process known as resistance.

Insects can develop resistance in several ways. Some break down insecticides more efficiently or develop changes at the target site that reduce product effectiveness. Others avoid exposure altogether by changing their feeding habits or movement patterns. In some cases, insects even develop thicker cuticles that reduce or slow down the absorption of insecticides.

Production practices can influence the rate of resistance development. Large, uniform cropping systems and repeated use of the same control tools reduce opportunities for susceptible insects to persist, accelerating resistance.

Figure 1: Chart illustrating how insecticide resistance develops when insecticides with the same mode of action (MoA) are used repeatedly.

What Should You Do to Mitigate Resistance in Insect Pests?
An integrated pest management (IPM) approach remains the best defense against resistance.

Key practices include:

• Using crop varieties that are resistant to pest attack
• Rotating insecticides with different modes of action (MoA)
• Avoiding unnecessary insecticide applications
• Preserving beneficial insects by selecting insecticides with no or minimal adverse effects on them
• Incorporating non-chemical management tools whenever possible
• Maintaining refuges to sustain susceptible pest populations
• Eliminating crop residues after harvest to remove food sources and breeding sites for pests.

No insecticide remains fully effective over the long-term if overused. Reducing selection pressure by avoiding consecutive applications of insecticides from the same IRAC group is critical. The more intensively a single tactic is used, the faster resistance will develop. Resistance can increase production costs, reduce marketable yield, and ultimately affect grower competitiveness. A diversified pest management approach helps preserve the effectiveness of available tools and supports long-term, sustainable pest control.

Additional Reading Materials

1. Calvin W., M. N. Keith, and B. McGrew. 2025. Guidelines for effective management of diamondback moth in brassica crops. University of Arizona Extension Publication. az2143. https://extension.arizona.edu/publication/guidelines-effective-management-diamondback-moth-brassica-crops
2. Ellsworth, P.C., A. Fournier, M. Keith, W. Calvin, A. Brown, W. Dixon, M. King, M. Rahr. 2025. Temporal refuges: a new tool for resistance management [IPM short]. University of Arizona Cooperative Extension, Arizona Pest Management. https://hdl.handle.net/10150/678613

The figure shows a wind rose based on daily wind direction data from the AZMet Yuma Valley station from January 1, 2021, through May 24, 2026. This figure (Figure 1) summarizes where the wind came from most often, not how fast the wind was blowing. Longer bars indicate more frequent wind direction. In this dataset, winds most frequently came from the north–northeast and south–southeast directions, while winds from the east and west occurred less frequently. 

Figure 1. Wind rose showing the frequency distribution of daily wind direction at the AZMet Yuma Valley station from January 1, 2021, through May 25, 2026. Longer bars indicate more frequent wind directions. Dominant winds were primarily from the north–northeast and southsoutheast directions. Data source: Arizona Meteorological Network (AZMET) – University of Arizona

Wind direction is important because it indicates the likely origin and pathway of air moving into crop fields. Depending on surrounding land use and regional weather conditions, air moving from different directions may be warmer, cooler, drier, more humid, or dustier. For example, air passing over irrigated agricultural areas may carry relatively more humidity, while air moving across desert, fallow ground, or dry soil surfaces may be hotter, drier, and dustier. Therefore, wind direction can influence field microclimate, soil moisture loss, crop stress, pest movement, and spray drift pathways.

For irrigation management, prevailing wind direction can help growers interpret field variability. In flood or furrow irrigation, wind direction may influence surface drying after irrigation, especially along exposed beds, field borders, and tail-end areas. Wind moving across hot, dry ground can accelerate evaporation from wetted furrow surfaces and contribute to soil crusting. This may affect seedling emergence, salinity accumulation near the bed surface, and the timing of the next irrigation. In sprinkler-irrigated fields, wind direction during irrigation can influence water distribution patterns. In drip-irrigated vegetables, wind direction may help explain recurring dry zones, edge effects, or uneven crop vigor when combined with soil moisture, ET, and field observations.

Wind direction can also affect crop growth and development by modifying canopy microclimate. Air movement from different directions may influence canopy temperature, humidity, dust movement, and drying conditions. Young vegetable seedlings are especially sensitive to windblown soil particles, which can cause abrasion, stand injury, and delayed early growth. Leafy vegetables may also show reduced market quality when exposed to repeated dust or sand movement. This figure does not directly measure crop stress, but it helps identify the directions from which wind-related exposure is most likely to occur.

The wind rose should not be interpreted as direct evidence of yield loss. It only shows the dominant wind direction. However, yield and quality can be affected when prevailing wind direction interacts with high wind speed, dry air, poor irrigation uniformity, soil moisture stress, or physical crop injury. Long-term wind direction information can help growers evaluate whether certain field margins, bed orientations, or crop rows are repeatedly exposed to incoming air movement and associated stress factors.

Wind direction is also important for IPM because it influences the movement of insects, pathogens, dust, and pesticide droplets. Aphids, whiteflies, thrips, leafhoppers, and some airborne pathogens may move with prevailing air currents. Knowing the common upwind directions can help growers identify potential pest-source areas and improve scouting strategies. Wind direction is also important for pesticide applications because it determines the likely pathway of spray drift and off-target movement.

Overall, wind rose information provides a practical decision-support tool for understanding dominant airflow pathways in Yuma vegetable production. This figure should be used together with real-time wind speed, wind direction, pesticide label restrictions, droplet size, boom height, irrigation records, soil moisture monitoring, ET data, and field scouting. When combined with these additional data, wind direction can support better irrigation planning, crop stress interpretation, yield protection, and IPM decision-making.

References: Arizona Meteorological Network (AZMet) https://azmet.arizona.edu/ 

VegIPM Update Vol. 17, Num. 11
May 27, 2026

Results of sticky trap catches below!!

Whitefly: Adult activity continues to increase across locations, yet these numbers do not reflect what we are seeing in the field on melon insecticide efficacy trials at YAC, numbers for untreated plots and melon virus incidence are well above what we have seen in other years. Historically whitefly numbers peak in July.

Thrips: Adult thrips activity remained steady across locations over the last two weeks. Historically, western flower thrips numbers peak in May.