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.
Galls observed on the stems of begonias submitted to the clinic
Recently, we received a submission of begonias to the Yuma Plant Health Clinic that immediately presented a diagnostic challenge. At first glance, the symptoms seemed to point toward a familiar set of suspects. The plants had developed severe swelling of the stems, symptoms characteristic of physiological oedema or bacterial Agrobacterium-associated crown gall. But, as is often the case in plant diagnostics, appearances can be deceiving.
The begonias had been grown indoors in high-humidity terrariums and planter boxes. The symptoms were not associated with a particular begonia variety, nor were they consistently expressed across all plantings or cuttings. When the plants were removed from their planting substrate, however, another clue emerged: additional small galls were scattered throughout the root systems of those plants also showing the stem swellings. That observation changed the diagnostic picture considerably.
Galls observed on the roots of begonias submitted to the clinic
Dissection of both the swollen stem tissue and the roots revealed an abundance of eggs, juveniles, mature female nematodes, and giant cells, a classic signature of root-knot nematode (RKN) infection. Root-knot nematodes belong to the genus Meloidogyne, a group of microscopic roundworms that are among the most important plant-parasitic nematodes worldwide. Their typical symptom is familiar to many resulting in the formation of characteristic galls on roots.
These galls are not simply a physical wound created by the nematodes. Rather, RKNs actively manipulate their host. During infection, the nematodes secrete salivary compounds that alter plant growth and development, effectively hijacking normal cellular processes and redirecting them toward the formation of specialized feeding structures known as giant cells.
These giant cells become a nutrient-rich feeding site for the developing and mature nematodes. In doing so, the nematode establishes a sustained drain on the plant's resources. As infection progresses, the resulting disruption to the root system can interfere with nutrient acquisition and water uptake. Aboveground, this typically translates into stunted growth, declining foliage, wilting, and, in severe infestations, plant death. With more than 3,000 plant species reported as hosts to different root-knot nematode species worldwide, including many field and vegetable crops, the annual impact of these pathogens is enormous. Much research has been done on RKN in various crops, and reports of stem swellings occurring naturally is almost non-existent.
Yet the begonia case raises an especially interesting question: Why did a pathogen best known for producing root galls appear to be responsible for such dramatic swelling in the stems? This is where the environment becomes an essential part of the diagnosis.
The symptom is not the pathogen. It is a reaction of the plant to the presence of a pathogen. One of the most important principles in plant pathological diagnostics is that the same pathogen does not necessarily produce the same symptom under every set of environmental conditions. Likewise, similar symptoms can arise from entirely different causes.
Temperature, humidity, water availability, substrate conditions, light, nutrition, plant age, and even the way a plant is cultivated can all influence how a disease develops and how its symptoms are expressed. In other words, the symptom we see is the product of an interaction between the host, the pathogen, and the environment. Change any one of those components, and the resulting disease can change dramatically. This recent begonia case is a particularly useful reminder of this principle.
Root-knot nematodes are well known for their belowground symptoms, but reports of rare and isolated cases of infections on aerial plant tissues, including stems, leaves, and flowers, are reported in only one publicly available extension bulletin from 1985. These symptoms remain unusual and have rarely been observed unless aerial tissues are artificially inoculated, and they have only been documented in a limited number of hosts.
So, when confronted with the unusual stem symptoms in a begonia, it would be easy to focus exclusively on the appearance of the tissue and pursue diagnoses such as oedema or crown gall. These plants were being cultivated in enclosed, high-humidity conditions, where moisture levels around the plant were substantially different from those experienced by a plant growing in a more open environment. Such conditions can alter transpiration rates, water movement, tissue hydration, pathogen development, and the plant's own physiological responses. They also give rise to the wet, humid conditions necessary for oedema to develop or crown gall bacteria to thrive.
The small root galls were an important clue. Microscopic examination then provided the confirmation: eggs, juveniles, mature females, and the characteristic giant cells associated with root-knot nematode feeding. These signs of RKN were found in both the root and stem swellings. Understanding the environment in which the hosts were being grown, with its high moisture conditions, then provided supporting evidence that the nematodes had favorable environmental conditions to migrate into much higher foliar tissues than is typically seen in RKN infestations and produce an unusual symptom. Swollen galls on the stem told us that something was wrong, and if we relied on the most common culprits associated with this symptom alone, namely oedema or crown gall, we would have gotten the diagnosis wrong.
The begonia case is a fascinating example of how flexible disease expression can be. A pathogen with a reputation for being almost exclusively soilborne and producing galling symptoms on root tissues, under particular host and environmental circumstances, can be associated with symptoms in tissues where we do not ordinarily expect to find them.
Ultimately, environment is not simply a backdrop against which plant disease occurs. It is one of the determinants of how disease develops, how severe it becomes, and critically for anyone trying to ID the pathogenic cause, what it looks like.
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.
