Every day, you walk fields, evaluate risk, and make informed pest management decisions instead of simply reacting to problems. The Vegetable Pest Losses Workshop on Tuesday, July 14 is your opportunity to help quantify that stewardship by documenting pest pressure, management practices, insecticide use, and their economic impact across Arizona's vegetable industry. While everyone interested in Arizona vegetable production is welcome to attend, we especially encourage PCAs to participate because your field experience is the foundation of this survey. Your stewardship deserves to be measured.

Food will be provided, please RSVP to maceyw@arizona.edu.

Figure 1. Agenda for the 25-26 Vegetable Pest Losses meeting 7/14 at YAC. 4 AZDA
CEUs Approved • California DPR CEUs Pending


Figure 2. Insecticide use on surveyed lettuce acres during the 2024–25 season, illustrating
a continued shift away from broadly toxic insecticides toward reduced-risk, selective
products in desert lettuce IPM programs.

Chile (Capsicum annuum) is an important crop in the desert Southwest. The Capsicum annuum species is the most common group of chiles that we encounter and these chiles are common and an important part of our southwestern cuisine. The New Mexico type chile (aka, Anaheim) is the most common type of chile crop in the portion of the desert Southwest often referred to as the “southwestern chile belt” and it includes production areas in southeastern Arizona, southern New Mexico, west Texas, and northern Chihuahua and Sonora, Mexico.

There are five domesticated species of chile peppers. 1) Capsicum annuum is probably the most common to most of us and it includes many varieties such as bell peppers, wax, cayenne, jalapeños, Thai peppers, chiltepin, and all forms of New Mexico chile. 2) Capsicum frutescens includes malagueta, tabasco, piri piri, and Malawian Kambuzi. 3) Capsicum chinense includes what many consider the hottest peppers such as the naga, habanero, Datil, and Scotch bonnet. 4) Capsicum pubescens includes the South American rocoto peppers. 5) Capsicum baccatum includes the South American aji peppers (Guzman and Bosland, 2017). Some examples are shown in Figure 1 with some other chile pepper species as well.

Figure 1. Capsicum annuum pod types include A) Asian, B) Cayenne, C) Chile de Arbol, D)
Chiltepin, E) Hungarian Paprika, F) Jalapeño, G) New Mexican, and H) Poblano.  A
Capsicum baccatum pod type is I) Aji. Capsicum chinense pod types are J) Bhut Jolokia, K)
Habanero, and L) Scorpion. A Capsicum pubescens pod type is M) Rocoto and a
Capsicum frutescens pod type is N) Tabasco.  Source: Guzman and Bosland, 2017.  

Crop Phenology
Understanding of the basic stages of plant growth in relation to time or age (crop phenology) and basic crop needs, i.e., water and nutrients, is an important part of crop management. There is a strong relationship among the phenological, morphological and physiological changes that occur with crop development. Understanding physiological function within a plant at various stages of growth and development is critical in efficiently managing crop inputs such as water and plant nutrients.  Plants respond to environmental conditions, and temperature is the primary developmental force in plant development when water is not limited. Heat units (HUs) can be used as a good measure of “thermal time” that drives plant development. Thus, HUs can be used as a management tool for predicting and identifying stages of growth and physiological needs. We can then use that information for more efficient timing of irrigation and nutrient inputs to crop and pest management strategies. Figures 2 and 3 describe the basic HU concept with upper and lower thresholds. 

Crop phenology models describe how crop growth and development are impacted by the environment, weather and climate, and provide an effective way to standardize crop growth and development among different years and across many locations (Baskerville and Emin, 1969; Brown, 1989).  

People still use days after planting to estimate stages of crop development but HUs are more accurate and reliable under irrigated conditions where water is non-limiting factor. Water stress will alter, retard, phenological plant development, and it is a major source of variation irrespective of temperature conditions. Thus, HU based methods of predicting and tracking crop growth can be more consistently and effectively used in irrigated crop production systems.

Chiles are a warm season, perennial plant with an indeterminant growth habit that we grow and manage as an annual crop. The fruiting cycle begins at the crown stage of growth (Figures 4 and 5) and continues until the plant reaches a point of “cut-out” with a hiatus in blooming as the plant works to mature the chile fruit that the crop has set and established. People familiar with cotton plant growth and development will understand similarities in this pattern.

Figure 6 describes the basic phenological baseline for New Mexico – type chile and was developed from field studies conducted in New Mexico and Arizona (Silvertooth et al., 2010 and 2011; Soto et al., 2006; and Soto and Silvertooth, 2007).  

Heat units accumulated after planting (HUAP) for any date of planting to the present date can be easily accessed in the Arizona Meteorological Network (AZMET) website.  

https://azmet.arizona.edu/

In the 2026 season, New Mexico-type chiles in southeastern Arizona and southern New Mexico experienced a good start to the season after planting. In tracking a set of New Mexico-type chile varieties, their development is tracking very closely to the HU model shown in Figure 6. For example, crown formation and first flowers have been consistently observed at approximately 1,300 – 1,450 HUAP among numerous New Mexico type varieties in southeastern Arizona this season. Many fields are progressing into peak bloom (Figure 6), which is also the growth stage of peak water and nutrient demand, particularly nitrogen.

Figure 2. Typical relationship between the rate of plant growth and development and
temperature. Growth and development cease when temperatures decline below the lower
temperature threshold (A) or increase above the upper temperature threshold (C). Growth
and development increases rapidly when temperatures fall between the lower and upper
temperature thresholds (B).


Figure 3. Heat unit calculation with the sine curve method using upper and lower
temperature thresholds (Brown, 1989).  The 86/55 ºF thresholds are used, consistent with
most warm season crops.


Figure 4. Photo of a New Mexico chile plant with crown formation and the first fruiting
branch shown withing the red circle.


Figure 5. Photo of a New Mexico chile plant with crown formation and early first fruiting
branch development. Source: Courtesy of Mr. Ed Curry, Pearce, AZ.

Figure 6. Basic phenological guideline for irrigated New Mexico-type chiles.

References:
Baskerville, G.L. and P. Emin. 1969. Rapid estimation of heat accumulation from maximum and minimum temperatures. Ecology 50:514-517.

Bosland, P.W., E.J. Votava, and E.M. Votava. 2012. Peppers: Vegetable and spice capsicums. Wallingford, U.K.: CAB Intl.

Brown, P. W. 1989. Heat units. Bull. 8915, Univ. of Arizona Cooperative Extension, College of Ag., Tucson, AZ.

Guzmán, I. and P.W. Bosland. 2017. Sensory properties of chile pepper heat - and its importance to food quality and cultural preference. Appetite, 2017 Oct 1;117:186-190. doi: 10.1016/j.appet.2017.06.026.

Silvertooth, J.C., P.W. Brown, and S. Walker. 2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum). University of Arizona Cooperative Extension Bulletin No. AZ 1529

Silvertooth, J.C., P.W. Brown and S. Walker. 2011. Crop Growth and Development for Irrigated Chile (Capsicum annuum). New Mexico Chile Association, Report 32. New Mexico State University, College of Agriculture, Consumer and Environmental Science.

Soto-Ortiz, Roberto, J.C. Silvertooth, and A. Galadima. 2006.  Crop Phenology for Irrigated Chiles (Capsicum annuum L.) in Arizona and New Mexico. Vegetable Report, College of Agriculture and Life Sciences Report Series P-144, November, University of Arizona.

Soto-Ortiz, R. and J.C. Silvertooth. 2007. A Crop Phenology Model for Irrigated New Mexico Chile (Capsicum annuum L.) The 2007 Vegetable Report. Jan 08:104-122.

Fall melon season is approaching, and one recurring question I've been hearing is: Will viruses be as bad this fall as they were in the spring?

The incidence and severity of melon viruses this past spring were unprecedented across Yuma County, Imperial County, and northern Mexico. This is supported by the volume of feedback we received from growers, PCAs, and industry representatives who attended the June 2nd melon virus incident response meeting. As a result, predicting what we can expect is going to happen this fall is difficult. We have no recent, if any, experience with virus pressure at this scale in spring melon to guide our expectations for the upcoming fall season. At this point, predictions are more of an educated guess without the guidance of past observations.

To quickly recap, the three main viruses that affected cucurbits this spring were cucurbit yellow stunting disorder virus (CYSDV), cucurbit chlorotic yellows virus (CCYV), and watermelon chlorotic stunt virus (WmCSV). All three are transmitted by the Biotype B whitefly (Bemisia tabaci), whose populations overwintered at unusually high levels between 2025 and 2026. Between melon seasons, these viruses persist in a wide range of crop and weed hosts, many of which show few or no visible symptoms of infection. Unfortunately, these asymptomatic plants can still serve as reservoirs, allowing both the viruses and their whitefly vectors to bridge the melon-free gap between cropping seasons and provide a source of inoculum for newly planted fields. It is an unfortunate reality that neither the whitefly vectors nor many of the alternate host plants (weeds) show symptoms or suffer ill effects while carrying these viruses. As a result, they can stealthily maintain virus populations between melon seasons and serve as a source of infection for newly planted fields.

Below is a compilation of reported host plants for CYSDV, CCYV, and WmCSV. This list reflects the viruses’ confirmed hosts identified to date but is unlikely to be exhaustive. Additional weed and crop species may also be capable of serving as reservoirs for these viruses but have yet to be discovered or reported. Note that many of these plants may grow throughout the region as weeds, native vegetation, commercial crops, or in backyard gardens:

Table 1: Primary and alternate hosts of CYSDV, CCYV, and WmCSV reported to date.

I can see this upcoming melon season unfolding in one of two ways. On one hand, the most intuitive prediction is that the high virus inoculum and abundant whitefly populations present during the spring melon season will carry over into the fall, resulting in early and significant virus pressure. On the other hand, the intensive whitefly management programs implemented throughout the spring may have suppressed vector populations to provide knockdown to pre-winter 2025 levels, resulting in lower virus incidence early in the season than at the start of spring.

Regardless of which scenario plays out, proactive and preventative management of both whiteflies and weed reservoirs remains the most effective strategy for minimizing virus pressure in fall melons. This approach targets two critical stages of the disease cycle by reducing the initial sources of virus inoculum and limiting the whitefly vectors responsible for further virus spread.

Dr. Palumbo developed a management guide for whiteflies and CYSDV in fall melons in 2024. The recommendations are based on research findings from two key publications and provide practical guidance for reducing virus risk throughout the season, from planting through netted fruit (Castle 2017a and 2017b).

Table  2: Insecticide Use Guidelines for Whitefly /CYSDV Management in Fall Melons

Source: https://vegetableipmupdates.arizona.edu/sites/default/files/2024-07/2024%20Whitefly%20CYSDV%20Guidelines.pdf

The earlier melons become infected with one or more of these viruses, the greater the impact on plant growth, fruit development, and ultimately yield. Even when infection cannot be completely prevented, delaying virus establishment can substantially reduce losses in both yield and fruit quality. Protecting young plants from early whitefly feeding, and virus infection, is therefore one of the most important management objectives to reducing losses.

In field trials comparing at-plant soil applications of flupyradifurone (trade name Sivanto), dinotefuran (Venom), imidacloprid (Admire Pro), and cyantraniliprole (Verimark), Dr. Palumbo and colleagues found that flupyradifurone and dinotefuran provided the greatest protection against both whiteflies and lowest final incidence of CYSDV (Castle et al. 2017b). All products were applied as a single soil shank injection at planting, allowing systemic uptake and protection during crop establishment.

Across both spring and fall trials, flupyradifurone consistently produced the lowest whitefly densities and the lowest incidence of CYSDV. Dinotefuran was the second most effective treatment, significantly reducing both whitefly populations and CYSDV incidence, although its performance was somewhat less consistent than flupyradifurone. In contrast, at-planting treatment with imidacloprid and cyantraniliprole did not consistently reduce CYSDV incidence.

Further reading:
Castle, S., Palumbo, J., Merten, P., Cowden, C. and Prabhaker, N. (2017a), Effects of foliar and systemic insecticides on whitefly transmission and incidence of cucurbit yellow stunting disorder virus. Pest. Manag. Sci., 73: 1462-1472. https://doi.org/10.1002/ps.4478

Castle, S.J., Palumbo, J.P., Merten, P. (2017b), Field evaluation of cucurbit yellow stunting disorder virus transmission by Bemisia tabaci. Virus Res., 241:220-227. doi: https://doi.org/10.1016/j.virusres.2017.03.017

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)

Last year, I was contacted by one of our PCAs regarding a concerning observation of escaped Palmer amaranth plants in a cotton field that may indicate potential glyphosate resistance.  

Palmer amaranth continues to be one of the most problematic weeds in row crops due to its aggressive growth habit, high seed production, and documented ability to evolve herbicide resistance.

Field Observation & Seed Collection
Following the PCA report, I visited the field and began collecting seeds from the suspected escaped Palmer amaranth plants during the 2025 cotton growing season.

Sampling collection of Palmer Amaranth, August 18th, 2025

Research Effort and Funding
In collaboration with other colleagues, we submitted a grant proposal aimed at supporting a structured study of Palmer seed collection and greenhouse bioassays to test herbicide response across Yuma and Pinal County locations to map for resistance. Unfortunately, the proposal was not funded. Despite this setback, I decided to move forward by self-funding a preliminary experiment to begin generating data and insights.

Greenhouse Bioassay Initiation
The collected Palmer amaranth seeds were planted on June 4th, 2026, in a greenhouse setting. The initial germination rate of the collected seeds was 77%

Greenhouse Bioassay Experiment Setting

Experimental Plan
The next phase of this experiment involves:

• Thinning the trays to maintain a manageable number of healthy plants per replicate
• Applying multiple rates of glyphosate, including labeled and above-label rates, to assess plant survival and response
• Monitoring plant injury, survival, and potential recovery post-application

This dose-response approach will help determine whether the population exhibits traits consistent with glyphosate resistance.

Field & Greenhouse Documentation
This study will be accompanied by images documenting the process, including:

• Early-stage germination and seedling development in the greenhouse
• Plant responses following herbicide treatment

What’s Next
The plants will continue to be carefully monitored as they develop to an appropriate stage for spraying. Once herbicide applications are completed and responses evaluated, results will be compiled and shared.

Stay tuned for updates as we assess whether this Palmer amaranth population represents a new case of glyphosate resistance in our region. If you have encountered similar escapes or suspect resistance in your fields, please feel free to reach out. Collaboration is key to staying ahead of herbicide resistance challenges

Whiteflies are among the most important insect pests of broccoli, cauliflower, cabbage, and other cole crops grown in Arizona. Whitefly feeding reduces plant vigor and contaminates harvestable portions with honeydew and sooty mold. With the unusually high whitefly abundance this spring and summer, it is crucial to be vigilant as you are planning for the fall growing season. As always, IPM approaches are the most effective way to manage the pest, regardless of the crop.

Resistant variety: Although highly resistant brassica varieties are limited, growers should select varieties with available tolerance whenever possible. These varieties can reduce pest damage, lower production costs, and minimize environmental impacts associated with insecticide use.

Sanitation: Crop residues should be destroyed immediately following harvest. Maintaining weedfree field borders, canal banks, roadsides, and fallow areas helps reduce breeding sites for whiteflies.  

Figure 1. Immediate disking of crop residues after harvest reduces whitefly carryover
compared with leaving crop residues on the soil surface.

Crop placement: Whenever possible, avoid planting your brassica crops directly adjacent to or downwind of significant whitefly hosts like cotton, alfalfa, and melon. Delaying planting until after adjacent whitefly host crops are harvested and terminated can play a significant role in reducing whitefly pressure in your brassica crops.

Crop health: Maintaining healthy, vigorously growing crops can help reduce the impact of whitefly feeding. Proper irrigation management, balanced fertility programs, and avoidance of excessive nitrogen applications can reduce plant stress and improve crop tolerance. Excessive nitrogen promotes lush vegetative growth that may increase the crop's attractiveness to whiteflies.

Scouting: Regular scouting is essential for timely management decision-making. Fields should be monitored beginning at crop emergence and inspected at least weekly throughout the season. Scouting twice weekly during head formation is encouraged. Placing yellow sticky traps in your fields may help monitor flight activity and population increases. Particular attention should be given to fields located near cotton, alfalfa, melon, or recently harvested crops where whitefly movement is likely. Monitoring should include assessments of adults, eggs, nymphs, and beneficial insect activity.

Figure 2. The whitefly Bemisia tabaci. A) Male (smaller) and female adults feeding on a
leaf; B) circular pattern of eggs laid by B. tabaci; C) exuvia of Bemisia that is left after adult
emergence; D) Bemisia life cycle.

Conservation of natural enemies: Natural enemies can help suppress whitefly populations and should be conserved. Predators such as lacewings, lady beetles, minute pirate bugs, and big-eyed bugs, along with some parasitoid wasps, help suppress whitefly populations. Although natural enemies alone may not prevent economic damage during heavy infestations, preserving beneficial insects can reduce whitefly pressure and improve overall pest management.

Figure 3. A minute pirate bug feeding on whitefly eggs and nymphs.

Management with organic insecticides: Organic insecticides, including Pyganic, neem-based products, insecticidal soaps, microbial products containing Beauveria bassiana (e.g., BotaniGard), and Kaolin clay (Surround), can provide whitefly suppression when applied early and with thorough coverage. Multiple applications at short intervals are often necessary because most organic insecticides have limited residual activity and primarily target exposed life stages. Thorough coverage of the undersides of leaves is essential for effective suppression, as whiteflies are concentrated on the lower leaf surfaces.

Organic insecticides should be viewed as population suppression tools rather than rescue treatments. Once heavy infestations become established, satisfactory control is difficult to achieve with any currently available organic product.

Key Take-Home Messages

• Destroy crop residues immediately after harvest.
• Scout fields weekly, beginning at crop emergence.
• Conserve natural enemies.
• Apply organic insecticides early before populations become established.
• Ensure thorough spray coverage.

Yuma agriculture is often described by its winter vegetable production numbers, but the deeper story is the management system behind those numbers. The Yuma region produces roughly 90% of the leafy greens grown in the United States during the winter season, and according to the U.S. Department of Agriculture Economic Research Service, from mid-November through early April, most lettuce sold in the country is sourced from the irrigated desert valleys of the Yuma area and California’s Imperial County (USDA ERS, 2023). That success is not because the desert is easy. It is because Yuma growers farm with precision in a place where rainfall is limited, sunlight is abundant, and irrigation management carries the crop. In this environment, water is not used only to meet crop demand; it also governs the movement of salts, nutrients, and moisture through the bed and root zone. This makes salinity management one of the background forces shaping almost every production decision in desert vegetable systems.

Water and salts must be managed together because they move through the soil as one system. Irrigation water commonly contains dissolved salts, and because evapotranspiration removes water while leaving those salts behind, repeated irrigation can concentrate salts in the root zone when they are not moved below it. Salinization is a long-recognized constraint on irrigated agriculture, particularly in arid and semi-arid regions where rainfall is not sufficient to flush salts from the soil profile. In desert vegetable fields, some irrigation beyond crop water use is therefore needed to move salts below the active root zone, but that water must be managed carefully. Too little leaching allows salts to concentrate near roots and reduce water uptake; too much irrigation wastes a limited supply and can carry nutrients below the root zone. The leaching requirement defines this balance: it is the minimum fraction of applied water that must drain below the root zone to keep soil salinity from reducing crop yield.

General salinity management starts with knowing where the salts are and what kind of salt problem exists. Soil and irrigation-water testing should track electrical conductivity, sodium adsorption ratio, pH, chloride, bicarbonate, calcium, magnesium, and sodium. If the problem is mainly soluble salts, the primary approach is controlled leaching with adequate drainage to move salts below the active root zone. If the problem is sodicity, in which sodium degrades soil structure and reduces water infiltration, calcium-based amendments such as gypsum may be needed to replace sodium on the soil exchange complex before leaching.

Soil structure is itself part of salinity management. High exchangeable sodium can disperse soil particles, reduce pore space, limit oxygen movement, and restrict water infiltration. This dispersion and aggregate breakdown can lower oxygen availability in the root zone and constrain plant productivity. Calcium amendments can improve aggregation and water movement where sodicity is present, but amendments alone do not remove salts. The displaced sodium and accompanying soluble salts still require water movement and drainage to leave the crop root zone. This is why desert farming is, at its core, root-zone management. The goal is not simply to apply more water, but to apply the right amount at the right time to support crop growth, maintain uniform moisture, protect nutrient availability, and prevent damaging salt accumulation. In Yuma, every irrigation decision is also a salinity decision. It affects where salts move, where roots grow, how nutrients remain available, and how uniformly the crop develops across the field.

Salinity also connects to IPM. Salts are not insects, weeds, or pathogens, but salinity is an abiotic stress that can weaken the crop. High root-zone salinity can reduce root growth, water uptake, nutrient balance, and plant vigor. A crop under this kind of stress may be less able to tolerate insect feeding, disease pressure, or weed competition, although the strength of that relationship varies with crop, pest, and growing conditions. In this sense, salinity management becomes part of preventive IPM: a healthy root zone gives the crop more capacity to withstand pest pressure.

Salinity management is not a single irrigation, amendment, or corrective action. It is a continuous production strategy that links irrigation scheduling, drainage, soil testing, nutrient management, and crop monitoring. In Yuma’s desert vegetable systems, managing salts before they become a visible crop problem helps protect stand uniformity, root function, water-use efficiency, and long-term soil productivity. Every irrigation moves water, but it also moves salts; understanding that movement is central to farming successfully in the desert.

VegIPM Update Vol. 17, Num. 14

July 8, 2026

Results of trap catches below!!

 

Whitefly: Adult activity remains steady across locations; above average for this time of the year. Historically, whitefly numbers peak in July.  

Thrips: Adult thrips activity decreased over the last two weeks. About average for this time of the year. Historically, thrips numbers remain low until Sept-Oct.  

Diamondback Moth: No diamondback moths have been collected in the traps since May 19th.  Based on the past six years summer collection data, no DBM is collected in the traps in the summer months (Jun-Aug) until September.