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.
Few things in Yuma County are more frustrating than watching lettuce wilt in the field. Even the best-managed fields are not immune to the many destructive soilborne pathogens capable of causing significant economic losses in lettuce production fields.
It is an unfortunate reality that Fusarium wilt, corky root, bottom rot, and lettuce drop are encountered and require management nearly every season in Yuma to produce a healthy crop. Although advances in resistant cultivars and integrated disease
management have improved our ability to reduce some of the crop losses to these diseases, management options for soilborne diseases, in general, remain severely limited and often are ineffective once symptoms progress to root or crown rot and irreversible
wilting. Strong, durable genetic resistance remains the strategic priority and most viable option when it comes to the management of these pathogens.
To select the right genetic resistance package, accurate field history and proper diagnosis of the cause of plant health challenges on that ground is critical. One of the greatest obstacles in plant disease diagnosis is that symptoms alone are rarely
what we call pathognomonic, that is, they are seldom unique enough to identify down to a single disease or environmental stressor. Temperature, soil moisture, plant age at time of infection, and varietal susceptibility all influence how diseases and
disorders develop and how symptoms are expressed in the plant as a response. As a result, the same pathogen can produce different symptoms under different conditions, while entirely different pathogens may produce nearly identical symptoms. Add to
this the complexity of the frequent occurrence of co-infections with multiple pathogens colonizing the same host at the same time and the ability to provide field diagnoses or diagnosis from pictures can quickly become confusing, overwhelming, or
downright impossible.
This known variability in symptom expression underscores the importance of confirming a diagnosis rather than relying solely on field observations, especially when the time comes for selecting resistant varieties to be planted in fields with a history
of soilborne diseases. Ideally, lettuce shouldn’t be planted on ground that is contaminated with soilborne pathogens, but this isn’t always feasible in our production systems.
Despite my obligatory warning for the difficulty and unreliability of diagnosing plant diseases and disorders from symptoms alone, I thought it would be a good chance to highlight a few key trends for two infamous diseases that we frequently observed
during last season’s atypically warm and rainy weather. I’m talking of course about Fusarium wilt and corky root. My hope is that these observations may prove helpful when scouting wilting fields, explaining your observations, and, importantly,
making it easier to document on our submission sheet what you’re seeing in the field if you choose to drop off samples to the clinic for culture testing and confirmation diagnoses. Of course, I remain happy to take a look and sample from the
symptomatic field as well. Over the 2025-2026 season the plant clinic received 20 samples culturing positive for Fusarium wilt, 16 for corky root, and 8 for a co-infection with both pathogens simultaneously.
In the field, the two diseases often appear indistinguishable from aboveground symptoms alone. Both commonly produce wilting, which may be more pronounced particularly during the heat of the day then seemingly “recover” in the evenings. Plants often lose their characteristic healthy, green waxy luster and instead develop a dull, matted appearance that is more apparent when compared with neighboring healthy plants or fields and as the wilting intensifies. As the diseases progress, the outermost leaves surrounding the crown may rot and collapse, further contributing to the appearance of a sick and declining plant. At this point, secondary microorganisms of both the bacterial and fungal kind may set in and produce signs of growth as they feed on the dead tissue, potentially appearing to be related to the cause of the disease and complicating diagnosis.
Below ground, corky root primarily affects the outermost tissues of the root system, causing feeder roots and the taproot to develop yellow to brown (sometime with specks of green) lesions that eventually crack and become roughened. To me, severely affected roots appear as if they are covered in mesquite bark. In contrast, Fusarium wilt primarily invades the plant's vascular system. Although root deterioration may occur (especially on small feeder roots), the hallmark of Fusarium wilt is vascular discoloration within the taproot and crown, where the water-conducting xylem tissues become tan to reddish-brown. These belowground differences, together with laboratory culture or other laboratory testing, provide the evidence needed to confidently distinguish between the two diseases.
Figure 1: Symptoms on a sample culturing positive for Fusarium wilt alone. Left.) outside view of the root system mostly absent of any rot symptoms, and right.) dissected root showing interior vascular discoloration. Note the bright white cortical tissue between the vascular tissue (center) and epidermis (outermost layer of cells, the “skin”) and near absence of overall rot of inner taproot tissue that is commonly observed with other soilborne diseases. The vascular system appears reddish due to the colonization with Fusarium oxysporum f. sp. lactucae.
Figure 3: Symptoms on a sample co-infected with Fusarium wilt and corky root. Left.) outside view of the root system showing significant barky lesions, and right.) dissected root shows a barky vascular dry rot towards the tip of the taproot with reddish-brown discoloration moving up towards the crown.
The images above are from some of the more diagnostically clear samples we have received in the clinic. As mentioned earlier, timing of infection, local microclimate, and varietal genetics can play a huge role in defining how a plant expresses disease
symptoms, so these observations of textbook symptomology may not be as clear in every field with wilting that you manage. For these reasons, laboratory testing remains the gold standard for disease diagnosis. Submission of symptomatic plants to the
diagnostic clinic allows for pathogen isolation and culture, providing definitive identification that can distinguish between diseases with similar symptoms. Accurate diagnosis is the foundation of effective disease management, ensuring that control
measures are directed at the true causal agent rather than its look-alikes. The Yuma Plant Health Clinic is here to help to that end.
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
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.
