With recent hot, dry conditions and temperatures in the 90s and above, spider mites can increase rapidly in melon fields, particularly watermelons. Under cooler conditions (~60°F), development can take over a month, but under warm conditions (~85–90°F), a generation can be completed in about a week, allowing populations to build quickly.

Natural enemies can suppress mites early, but under hot conditions—especially following broad-spectrum insecticide use—mite populations can outpace natural enemies. Watch for stippling and webbing on leaves. Consider treatment when webbing becomes evident and populations are increasing, and use selective materials whenever possible to preserve beneficials. Thorough coverage is essential for effective control.

These warm conditions may also accelerate development of other pests; although uncommon this early, whiteflies have already been reported in some melon fields and should be monitored closely.

BEE WARNING: If bees are present, follow all label precautions and avoid daytime applications. Apply insecticides at night when bees are not foraging.

For more information on spider mite management see: Spider Mites in Desert Melons

References:
Palumbo, J.C. 2025. Spider Mites on Spring Melons (2025). Vegetable IPM Updates, University of Arizona Extension, Vol. 16, No. 7, April 2, 2025.

A new active ingredient has recently been approved by EPA.

D. Victoria Reyes and Peter C. Ellsworth—Department of Entomology, University of Arizona

In November 2025, isocycloseram (IRAC Group 30) was registered by EPA. This new active ingredient expands the range of tools available to growers for insect management, supporting insecticide rotation and helping delay the development of resistance.

Isocycloseram has been registered for use in cotton under the product Vertento®, just in time for the 2026 cotton season in Arizona. This addition further expands the tools available for Lygus control in this crop.

For further information, please see the following publication: “Vertento® (isocycloseram) for Lygus Management in Arizona Cotton.”

At present, this active ingredient is also registered for use in multiple crops under different commercial products (see accompanying box). 

In the past several years public interest in RA has increased along with other similar designations such as sustainable agriculture, organic agriculture, etc. (Figure 1). These and similar interests tend to go in cycles, and these systems are commonly treated as new, novel, and revolutionary. There is a consistent theme and set of practices among each of these systems and they are not all new. I describe them briefly in the following sections.

Regenerative agriculture (RA) is a systems approach to crop production that emphasizes rebuilding soil health, enhancing biodiversity, and increasing the resilience of farming systems by supporting natural ecological processes. Many RA practices are grounded in old agronomic principles that predate modern conventional/chemical agriculture (CA) and remain relevant in contemporary agroecosystems (Giller, et al., 2021). 

Figure 1. The frequency of key terms in books (3-year rolling averages). Source:
Google NGram Viewer, Corpus ‘English 2019’ which includes books
predominantly in the English language published in any country (Giller et al.,
2021). 

Crop rotations and diversification
Crop rotation has long been recognized as a beneficial agronomic practice, and it is central to RA systems. Rotations disrupt pest and pathogen life cycles, improve nutrient cycling, and stabilize crop yields. The inclusion of legumes contributes to biologically fixed nitrogen and diverse root systems, which can reduce fertilizer requirements and benefit subsequent crops (Solberg, 1958; Troeh, et al., 1999; Tilman et al., 2002).

Organic residues and manures returned to soil
The incorporation of crop residues, green manures, compost, and animal manures replenishes soil organic matter (SOM) and soil organic carbon (SOC). As they decompose, they provide slow-release nutrients, and support soil biota. Returning organic materials enhances microbial activity, improves soil structure, and benefits soil waterholding capacity. Farmers have been utilizing these practices to sustain soil productivity for centuries (Lal, 2004).

Minimal or reduced tillage
Reduced tillage and no-till practices protect soil structure, reduce erosion, and support soil biological communities. Limiting physical disturbance promotes soil aggregation, porosity, and water infiltration, contributing to improved soil stability. Reduced tillage has long been a component of soil conservation and soil-building strategies for many years, particularly in the past 90 years since the Dust Bowl (Solberg, 1958; Troeh, et al., 1999).

Cover crops  
Cover crops planted between cash crops protect soil from erosion, scavenge nutrients, add biomass, and can suppress weeds. Living roots and added organic inputs stimulate microbial activity and promote a more diverse soil microbiome. In irrigated crop production systems this practice is more challenging and expensive due to the extra water demand and special practices for a crop with no cash value. Thus, it is impractical in most cases.

Mulching and residue management
Surface residues and organic mulches help conserve soil moisture, moderate soil temperatures, and in some cases reduce weed pressure. Mulching creates a favorable microclimate for beneficial soil organisms and contributes to soil protection (Solberg, 1958; Troeh, et al., 1999). This is also a centuries-old practice (Lal, 2004) but difficult to implement in many irrigated crop systems.

Agroforestry, hedgerows, and diversified landscapes
Some regenerative systems integrate trees, shrubs, or hedgerows with crops and livestock to enhance biodiversity and nutrient cycling and potentially diversify farm income. However, these practices are not feasible in all agricultural production systems, including irrigated crop production systems in the desert Southwest (Solberg, 1958). They have been found to be more feasible in tropical and subtropical regions.

Integrated pest management (IPM) and soil biology
Regenerative agriculture emphasizes the use of natural enemies, habitat for beneficial organisms, and reduced reliance on synthetic inputs. Most of these principles align with established IPM practices that have been successfully used for decades, including in Arizona crop production systems (Stern et al., 1959; Naranjo and Ellsworth, 2009).

Nutrient cycling and long-term soil organic matter (SOM)
Building or maintaining SOM is a primary objective of RA systems. Stable SOM improves soil structure, aeration, infiltration, and water-holding capacity. Maintaining SOM has long been recognized as a critical goal in CA systems as well (Tilman et al., 2002; Lal, 2004).

Agroecosystem management
Effective management is essential to the success of any crop production system and this is true in both RA and CA systems. Successful implementation requires integrating cropping system (agroecosystem) knowledge with careful planning, monitoring of soilplant relationships, and nutrient management to maintain yield stability and long-term sustainability.  Efforts to do this practically and effectively are central to the management of crop production systems in the desert Southwest. We have realized good progress over many decades, yet it is always good to review and consider where we can continue to improve.

References
Giller, R.E., H. Renske, J.A. Andersson, and J. Sumberg. 2021. Regenerative agriculture: an agronomic perspective. Outlook on Agriculture, Vol. 50(1) 13–25.

Lal, R. 2004. Soil carbon sequestration to mitigate climate change. Science. 304: 1623-1627.

Naranjo, S.E. and P.C. Ellsworth. 2009. Fifty years of the integrated control concept: moving the model and implementation forward in Arizona. Pest Manag Sci 2009; 65: 1267–1286

Solberg, E.D. 1958. Planning for stability in a great area. In: Yearbook of Agriculture, 1958. p 532-536. United States Department of Agriculture, Washington, D.C.

Stern, V.M., R.F. Smith, R. van den Bosch, and K.S. Hagen. 1959. The integrated control concept. Hilgardia 29:81-101.

Tilman, D.; Cassman, K.G.; Matson, P.A.; Naylor, R.; Polasky, S. 2002. Agricultural sustainability and intensive production practices. Nature. 418: 671-677.

Troeh, F.R., J.A. Hobbs, and R.L. Donohue. 1999. Soil and Water Conservation: Productivity and Environmental Protection. Prentice Hall.

We have recently seen an increase in celery samples coming into the clinic presenting with symptoms including elongated necrotic pitting with significant horizontal cracking on the inner stalks and sometimes total breakdown of the young tissues (petiole and leaf) within the heart. In these same samples, the outer stalks and leaves appear healthy and unaffected.  

At first glance, these symptoms resemble several known issues in celery, including black heart caused by calcium deficiency, black streak caused by boron deficiency, cucumber mosaic virus (CMV), and lygus feeding injury. Field observations have consistently shown low-to-absent lygus populations despite widespread incidence of severely affected celery, making insect damage an unlikely primary cause. CMV can also cause sunken, buff-colored lesions on the stalks but typically presents with additional foliar symptoms including leaf cupping and discoloration. Also, CMV doesn’t discriminate between young and old tissues, and despite testing every sample the YPHC has received thus far we have failed to detect the presence of the virus in any of the samples.  

Furthermore, I have had the chance to walk two severely affected fields in-person, from which I found two consistent observations. First, these symptoms are observed uniformly throughout large sections or the entirety of the field, a distribution pattern which is atypical of a sudden outbreak of a biotic pathogen or insect pest. Second, hosts from different plantings showed uniform severity, which indicates the issue arose at the same time across celery in the area. These two observations suggest that an abiotic culprit rather than a biotic pest is to blame for this sudden eruption of host symptoms.

So with lygus and CMV being unlikely causes and consistently negative cultures for any other bacterial or fungal causes, the last two options that fit the symptoms of these samples are both abiotic in nature. Black heart is a physiological disorder most frequently associated with calcium deficiency. The internal hearts of celery with black heart experience significant breakdown of all tissues due to insufficient calcium transport, similar to what can be observed on tomatoes with blossom end rot. Black streak, similarly, is also a physiological disorder, however, it is most often associated with boron deficiency. Black streak typically presents as elongated, sunken lesions along petioles and stems with significant crosswise cracking along the petioles. However, development of brown areas and die back in black streak cases has also been reported. 

Figure 1. Early blackheart symptoms


Figure 2. Late blackheart symptoms + secondary colonization


Figure 3. Black streak of celery

Both disorders can arise from inadequate fertilization of either calcium or boron or when rapid growth outpaces the plant’s ability to uptake enough of these nutrients from the soil. Both conditions have been linked to several causal environmental factors, but they commonly develop into severe losses when celery is grown in elevated temperatures above 90°F.  

With black streak, greenhouse studies demonstrated that susceptibility was not uniform over time and that the highest susceptibility in celery is observed during the rapid growth phase, about 4-7 weeks after transplanting (Ngouajio 2012). During this period of rapid growth and development boron demand may not be met when the growth of aboveground tissue is further stimulated by hot weather.

When celery is affected by blackheart, it often develops the most severe symptoms as plants approach maturity. This disorder is more frequently associated with rapid fluctuations in soil moisture from drought to flood conditions, excessive fertilization or soil fertility levels of nitrogen and potassium, and high soil salinity.

Of the cases submitted to the YPHC so far, both have been occurring at roughly equal frequencies. 

Sources and further reading:
Ngouajio, M.. “Hot weather requires careful management of celery to avoid black streak disorder”. Michigan State University Extension. 2010. URL: https://www.canr.msu.edu/news/hot_weather_requires_careful_management_of_celery_to_avoid_black_streak_dis

Guan, W.. “Picture of the week: Blackheart of celery”. Purdue University Extension Plant and Pest Diagnostic Lab. 2022. URL: https://ag.purdue.edu/department/btny/ppdl/potw-deptfolder/2022/blackheart-of-celery.html

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)

Identifying weeds at the seedlings stage is one of the biggest challenges in effective weed management. Yet early and accurate weed identification is the foundation of any successful weed control program.

To support this need, I am working on developing a regional Weed Garden at the Yuma Ag Center – a living, curated collection of key agricultural weed species grown under controlled conditions. This space will serve multiple purposes:

• Seed production for research and training.
• Hands-on species identification for growers, PCAs, students, and researchers.
• Herbicide demonstration and mode of action training.
• Integrated pest management (IPM) studies involving entomology and plant pathology

By maintaining a contained, year-round population of important desert vegetable weeds, we will be able to improve weed biology education, compare management tools, and support multidisciplinary applied research that reflects real-world production conditions.

In desert vegetable systems, weeds do more than just compete with crops. They often serve as reservoirs for insects and pathogens and as sources of field-level reinfestation, all of which increase production costs and management complexity.

Many priority weeds, such as Amaranthus (Amaranth/Pigweed), Portulaca (Purslane), Malva (Mallow), Solanum (Nightshade), and various Brassicaceae species (Wild Mustard, Shepherd's Purse), lack readily available, hands-on resources for early-season identification or demonstration of management concepts. Currently, there is no consistent local supply of live weed material for extension events, student instruction, or cross-disciplinary IPM demonstrations.

A dedicated Weed Garden would fill this gap by providing a stable, long-term platform for:

• Live plant identification workshops
• Seedstock maintenance and research needs
• Herbicide and non-chemical IPM demonstrations
• Collaboration among weed science, entomology, pathology and precision ag teams

Here is an example of this type of project:

Figure 1. Source: Beck, L., & Patton, A. J. (2015). Weed Garden: An Effective Tool
for Extension Education. Journal of Extension, 53(4), Article 15.
https://doi.org/10.34068/joe.53.04.15

Growers and PCAs: Your Input Is Needed
As we begin planning this Weed Garden, I would greatly appreciate your input:

• What weed species would you like to see?
• Which species are most challenging for early ID in your fields?
• What demonstration, training topics, or research activities would be most valuable to you?
• Any additional ideas that could make this project more useful for your farm operation?

Your feedback will help ensure this Weed Garden becomes a practical, relevant resource for our desert vegetable industry. 

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 or movement behavior. In some cases, insects even develop thicker cuticles that slow 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?
An integrated pest management (IPM) approach remains the best defense against resistance.  

Key practices include:

• Rotating insecticides with different modes of action  
• Avoiding unnecessary applications  
• Preserving beneficial insects  
• Incorporating non-chemical tools when possible  
• Maintaining refuges to sustain susceptible pest populations  

Reducing selection pressure is critical. The more intensively a single tactic is used, the faster resistance will develop. A diversified management approach will help extend the life of available tools and improve long-term pest control. 

Daytime and nighttime temperatures have risen well above the recent norm, with important implications for crop development, irrigation demand, and pest management.

Yuma Valley has experienced an unusually warm spring pattern since late February 2026. Based on AZMET Yuma Valley station data, daily maximum and minimum air temperatures from January through March 29, 2026, diverged markedly from the 2020–2025 pattern, with the greatest separation occurring during March. In the most recent period, daytime temperatures repeatedly rose into the mid-90s and above 100°F (Figure 1), while nighttime temperatures frequently remained near or above 60°F (Figure 2). Relative to the recent historical pattern, both daytime and nighttime conditions have remained consistently warmer than expected for this point in the production season.

This warming trend is agronomically important because crops respond not only to extreme temperatures but to cumulative thermal exposure over time. When both maximum and minimum temperatures remain elevated for prolonged periods, crop development accelerates, the growing season becomes compressed, and management schedules can shift quickly. In several vegetable production systems, this season’s heat pattern appears to be advancing crop maturity and harvest readiness by as much as three weeks. While earlier harvests may appear favorable at first, such rapid progression often reduces the amount of time the crop has to accumulate biomass and achieve full yield potential.

In desert vegetable systems, crop growth and maturity are strongly linked to heat-unit accumulation. Under warmer-than-normal conditions, crops move more quickly through vegetative development, canopy expansion, and market maturity. However, earlier maturity is not necessarily equivalent to better productivity. Yield depends not only on developmental timing, but also on the duration of active growth. Crops need adequate time to intercept sunlight, expand leaf area, produce carbohydrates, and partition assimilates into the harvestable portion of the plant. When the season is shortened by sustained heat, plants may reach harvest stage before fully developing the biomass needed for optimum size, weight, or quality. The result can be smaller plants, lighter fresh weight, reduced head development, and lower total marketable yield.

Warm nighttime temperatures may be especially important in explaining this response. Plants photosynthesize during the day, but they respire continuously, including throughout the night. When nights remain warm, respiration rates increase, and a larger proportion of the carbohydrates produced during the day is consumed for maintenance rather than retained for growth and yield formation. This reduces carbon-use efficiency and limits dry matter accumulation. In practical terms, the crop may mature earlier while simultaneously losing some of its ability to build harvestable biomass. Warm nights also reduce the recovery period plants normally experience after hot daytime conditions, creating sustained thermal stress across the full 24-hour cycle.

The recent heat pattern is also likely increasing crop water demand. High daytime temperatures elevate evapotranspiration, and warm nights can prolong plant metabolic activity and maintain greater atmospheric demand. As a result, irrigation requirements may now be higher than expected for late March. Fields managed under fixed irrigation intervals may begin to experience short-term moisture deficits if irrigation is not adjusted to current weather conditions and crop demand. Even brief periods of water stress during rapid growth can reduce cell expansion, canopy development, and final yield. At the same time, excessive irrigation in response to heat can create additional problems, including nutrient leaching, fluctuating root-zone aeration, and reduced fertilizer-use efficiency. Under these conditions, irrigation decisions should be based on crop stage, soil moisture status, and weather-based demand rather than on calendar assumptions alone.

From an IPM perspective, abnormal warming may also alter pest pressure and the timing of management decisions. Higher temperatures can accelerate insect development, shorten generation times, and increase the rate of population growth. At the same time, crop phenology is also advancing more quickly, which narrows the window for scouting, threshold-based treatment decisions, and timely intervention. In effect, both the crop and the pest may be moving ahead of schedule. Heat-stressed plants may also be less tolerant of pest injury because they are already operating under shortened growth duration and higher respiratory demand. Under these conditions, pest damage that might otherwise have been manageable under normal spring temperatures could become more economically significant.

Other agronomic practices may also need adjustment. Nutrient demand can shift when crop development accelerates, and fertilizer programs designed around the normal seasonal calendar may no longer align well with actual crop uptake. Harvest logistics may also be affected if multiple planting blocks mature earlier than expected. Labor scheduling, harvest sequencing, cooling, and market timing can all become more difficult when crop development is compressed. Thus, the current warming pattern should be viewed not only as a temperature anomaly but as a whole-system production issue affecting physiology, water management, pest pressure, and field operations.

Bottom line
The abnormal warming pattern that developed in Yuma Valley from late February through March 2026 may be substantially shortening the vegetable production window. Although earlier maturity may move harvest ahead of schedule, the physiological and agronomic costs can be considerable. A compressed season reduces the time available for biomass accumulation, while elevated nighttime temperatures increase respiration and reduce carbon retention. Together, these conditions may lower yield potential, increase irrigation demand, intensify pest management pressure, and complicate agronomic decision-making across the production system.

Figure 1. Daily maximum air temperature recorded at the AZMET Yuma Valley
station from January 1 through March 29, 2026, compared with the 2020–2025
temperature pattern. 



Figure 2. Daily minimum air temperature recorded at the AZMET Yuma Valley
station from January 1 through March 29, 2026, compared with the 2020–2025
temperature pattern. 

VegIPM Update Vol. 17, Num. 5

March 4, 2026

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW moth activity seen in some areas, but numbers have been low; About average for this time of season.

Beet armyworm: BAW numbers decreased across most locations since last collection. Above average  for this time of the season. Historically BAW numbers peak in March/April.

Cabbage looper:  Cabbage  looper moth activity decreased across most sites since last collection, but  remains higher than average for late-February. Historically cabbage looper moth  numbers peak in March/April. 

Diamondback moth: Adult activity remains steady across most locations. About average for this time of the year. 

Whitefly: Adult activity remains low across all locations, about average for this time of year.  

Thrips:  Thrips adult activity remains steady across locations, about average for this time of year. Expect numbers to continue increasing as temperatures warm up.

Aphids:  Winged aphid numbers decreased at most sites since last collection; below average for this time of the year.

Leafminers: Adult leafminer activity remains steady, high numbers seen in Yuma Valley, about average for this time of the season.