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:
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.
Yuma is in the full swing of downy season for lettuce. The light yellow, irregular leaf spots on the upper leaf surface with white to pale-gray fungal growth on the under leaf surface can be found popping up in fields everywhere. Damp and cool conditions are required for infection and symptom development. Sporangia of Bremia lactucae, the oomycete pathogen responsible for lettuce downy mildew (LDM), are wind disseminated and capable of germinating on the lettuce leaf surface they land on in 3 to 4 hours if free moisture is present. All across Yuma County we started reaching that leaf wetness threshold just about the last two weeks of November (See graphs below). Leaf wetness has remained especially high in Roll and South Yuma, while North and central Yuma have been drying out, although leaf wetness in central Yuma is on a rising trend as of the time of me writing this article.
Graphs retrieved from the Arizona Meteorological Network leaf wetness reports. Leaf wetness determined by electrical conductivity. Dry hours = number of hours less than or equal to 273 mV out of 24 hours in the day, transition hours = between 273 and 284 mV, and wet hours = number of hours greater than or equal to 284 mV.
There are 10 internationally recognized races of LDM reported in the United States. The naming of new races of LDM is overseen by the International Bremia Evaluation Board (IBEB), a global association of breeders, researchers, and regulatory bodies. Races are determined by inoculating varieties with known resistance genes to LDM and seeing which varieties the race can and cannot cause disease on. Per IBEB standards, all races have the prefix “Bl:” followed by a space and the race number. European isolates have the suffix “EU” and American isolates have the suffix “US”. For instance, Bl: 1US represents American race 1.
Bl: 1-6US, or American races 1-6, are no longer detected in the western US and are therefore not considered important targets for resistance breeding by IBEB. In spring of last year, five samples from a local favorite variety, ‘Boronda’, were found to be infected with downy mildew. ‘Boronda’ is marketed with genetic resistance to the US western races Bl: 5-9US. Two samples of ‘Boronda’ submitted by Dr. Stephanie Slinski, associate director of applied research & development at YCEDA, in February of last year from Yuma were evaluated by the UC Davis Bremia group led by Dr. Richard Michelmore. When inoculated on differentials, both isolates behaved like isolate VP-300, a non-IBEB-designated variant currently under evaluation to be designated as a new American race. VP-300 was identified in 2017 and is apparently capable of bypassing the genetic resistance bred into ‘Boronda’.
I have received reports of ‘Boronda’ resistance being broken again this year in South Yuma and the Wellton/Tacna/Roll area. ‘Muggins’ is reportedly showing susceptibility as well, and I am especially interested in collecting samples from this variety for additional race testing to see if this is also due to the presence of VP-300.
Take home messages for growers:
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:
Chris Detranaltes, Ph.D.
Cooperative Extension – Yuma County
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109
Useful Links:
BEB website: https://worldseed.org/our-work/disease-resistance/other-initiatives/ibeb/
UC Davis Bremia database: https://bremia.ucdavis.edu/bremia_database_main.php
AZ Meteorological Network leaf wetness reports: https://viz.datascience.arizona.edu/azmet/leaf-wetness-report/
Finger weeders are an in-row weeding tool made from flexible rubber. Pairs are centered on the seed row and overlapped slightly to remove in-row weeds. Our experience has been that finger weeders are effective at removing small weeds (< 3-4 leaf stage), but not large, well anchored weeds. A Texas A&M University colleague shared that they were able to regularly remove 3-4inch tall Palmer Amaranth with finger weeders using a cultivator configuration developed by organic cotton grower Carl Pepper. I was pretty impressed by their video. I think you will be too. Check it out by here or by clicking on the image below.
Acknowledgements
Credit and thanks are extended to Kyle R. Russell, Texas A&M University, for capturing and sharing the video.
Fig. 1. Large Palmer Amaranth being removed from the plant row by finger weeders –
slow motion video. (Video credit: Kyle R. Russel, Texas A&M University. Cultivator
configuration credit: Carl Pepper, Lubbock, TX.)
Cantaloups & Specialty Melons, Late April-Early May
Spring-planted cantaloups and specialty melons are now seeded and established across Yuma. The first 3-5 weeks after planting are the most crucial period for weed management for the entire season. Weed escapes during this window often cannot be corrected once vines begin to run.
Weeds of Concern
Most of those weeds are just emerging and are easiest to control now. Once they exceed the 2-4 leaf stage, control becomes inconsistent and costly.
Critical Period for MelonsHerbicide – Based IPM Recommendations for Melons
Pre-Plant/Burndown (Before Seeding or Transplants)
Control all winter weed escapes before seed set, especially mallow and mustards
At or Just After Planting (Pre-emergence):
Apply at planting or immediately after, then activate with irrigation.
Broadleaf + Grass Control
Residual herbicides are essential during the first 3-4 weeks.
Early Post-emergence rescue (Before Vine Run)
Target weeds at the 1-3 leaf stage
Broadleaf
Grasses
Effective on small grasses; timing is critical. Late POST applications after vines run reduce control and increase crop injury risk.
Things to watch
Non-Chemical Options Worth Combining
The herbicide list for melons is very limited, but fortunately most melon types grown in the Yuma valley grow rapidly. Non-chemical weed control practices, including cultivation and plastic mulch, can be effective.
Takeaway Message
In Yuma melon production, the most practical program is usually a preplant burndown plus a residual pre-emergence herbicide, then a carefully timed postemergence rescue like Sandea or grass herbicide if needed. The exact choice depends on whether you are growing watermelon, cantaloupe, or honeydew, and whether you use plastic mulch, drip, or furrow irrigation.
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:
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
Water conservation is becoming increasingly important for desert growers as reduced snowpack, drought, and climate variability continue to pressure irrigation water supplies. To evaluate whether PolySorb could support irrigation water savings under desert conditions, we conducted a large-field evaluation using reduced irrigation levels with and without PolySorb.
The field study included three irrigation levels: 100% full irrigation treatment (FIT), 75% FIT, and 50% FIT. The 100% FIT treatment was used as the full-irrigation standard. PolySorb was evaluated under the reduced irrigation treatments, 75% FIT and 50% FIT, and was applied at a very low rate, approximately 2 inches below the soil surface (Fig. 1).
Figure 1. Field application of PolySorb in a desert crop production system at Yuma
Valley Farm Research Center at the University of Arizona.
The full irrigation treatment, 100% FIT without PolySorb, produced 17.5 tons/ac. When irrigation was reduced to 75% FIT without PolySorb, yield declined to 14.7 tons/ac. A stronger yield reduction occurred at 50% FIT without PolySorb, where the yield was 7.8 tons/ac. Adding PolySorb improved yield under reduced irrigation. The 75% FIT + PolySorb treatment produced 16.8 tons/ac, which was very close to the 17.5 tons/ac observed under 100% FIT without PolySorb. This represents only a 0.7 tons/ac difference, or about 4% lower yield, while using 25% less irrigation water. At the 50% irrigation level, 50% FIT + PolySorb produced 12.0 tons/ac, compared with 7.8 tons/ac with 50% FIT alone. This was an increase of 4.2 tons/ac, or about 54% higher yield than the same irrigation level without PolySorb (Fig. 2)
Figure 2. Fresh yield response to irrigation level and PolySorb application. Yield was
17.5 tons/ac under 100% FIT without PolySorb, 14.7 tons/ac under 75% FIT without
PolySorb, and 7.8 tons/ac under 50% FIT without PolySorb. Adding PolySorb increased
yield under reduced irrigation, producing 16.8 tons/ac at 75% FIT + PolySorb and 12.0
tons/ac at 50% FIT + PolySorb.
These results suggest that PolySorb may help improve irrigation efficiency under desert production conditions, especially at moderate deficit irrigation. The strongest response was observed at 75% FIT + PolySorb, where yield was comparable to full irrigation. PolySorb also improved yield at 50% FIT, although yield remained lower than the 75% FIT without PolySorb treatment.
From a practical grower perspective, PolySorb should not be viewed as a stand-alone solution to water scarcity. However, it may be a useful component of an integrated water-management strategy that includes irrigation scheduling, soil moisture monitoring, crop evapotranspiration information, and efficient irrigation delivery systems. More field testing across crops, soil types, irrigation systems, and seasons is needed, but these results indicate that PolySorb could be a promising approach to help conserve irrigation water in desert agriculture.
VegIPM Update Vol. 17, Num. 7
April 1, 2026
Results of pheromone and sticky trap catches below!!
Corn earworm: CEW numbers remained high over the last two weeks; numbers remain high particularly in Welton and Tacna areas. Above average for this time of season.
Beet armyworm: BAW activity remained steady over the last two weeks. Above average for this time of the season. Historically BAW numbers are expected to continue increasing over the next few weeks.
Cabbage looper: Cabbage looper moth activity decreased over the last two weeks but remains higher than average for late-March. Based on historic data, expect to see high numbers through the end of the produce season.
Diamondback moth: Adult activity increased across most locations. High numbers seen in Yuma Valley. About average for this time of the year.
Whitefly: Adult activity increased across all locations, about average for this time of year. Expect numbers to continue increasing as temperatures warm up.
Thrips: Over the last two weeks, thrips adult activity continued to increase across locations and reached season highs. Higher than average for this time of year. Expect numbers to continue increasing as temperatures warm up
Aphids: Winged aphid numbers continue to decrease at most sites in the last two weeks. At our efficacy trials at YAC, most aphids died due to the high temperatures. below average for this time of the year.
Leafminers: Adult leafminer activity remains steady, high numbers continue to be seen in Yuma Valley, about average for this time of the season.
