On behalf of the Palumbo family, we would like to extend our deepest gratitude to everyone who made Dr. John Palumbo’s Celebration of Life such a meaningful and memorable event. 

A heartfelt thank you to every amazing individual at the farm for your incredible dedication and hard work in planning and executing the celebration with such care and compassion.  We are honored that you allowed us to use the farm as the venue to gather, laugh, cry, and share memories and stories of our loved one.  We are truly grateful for the time and love that you put into honoring John.  

To the generous donors and thoughtful planning committee, we thank you for your kindness, dedication, and outpouring of support. Your generosity has helped create a beautiful space for remembrance, healing, and connection. Your heartfelt speeches touched us deeply, making us both laugh and cry as we remembered and celebrated.

We understand that the loss of John was not only that of a colleague,  but a friend and a constant presence in your daily lives.  Some absences echo louder than words can express and this is one of them.   Even in our sorrow we hold on to the memories, the love, and the moments that will forever be etched into our lives.

It meant so much for all of us to gather and celebrate a life so dearly loved. John would have been honored, and deeply moved, to know his life inspired such a beautiful tribute filled with laughter, stories, and connection.

With love,
The Palumbo Family ♥️

In the last of this UA Vegetable IPM Newsletter, I have presented a melon (Cucumis melo ‘reticulatus’ L.) crop phenology model (Figure 1; Silvertooth, 2026) based on heat unit accumulations (86/55 ºF thresholds). This model can be used for predicting and tracking crop development and identifying important stages of crop growth and development (crop phenology).  

Referring to the data from AZMET for three locations in the Yuma area, the HU accumulations from 1 January 2025 for a set of four possible 2025 planting dates are listed in Table 1. The HU accumulations from 1 January 2025 to 26 April 2026 for these sites are listed in Table 2.

The HU accumulations after planting (HUAP) for these four possible planting dates for three Yuma area locations to 26 April 2026 are shown in Table 3. The HUAP values in Table 3 are simply the difference between the values in Tables 1 and 2.  

An example for the Yuma Valley 15 January 2026 planting date is: 1540 - 95 HU = 1445 HUAP for this case.

The information in Table 3 can help serve as a reference to check for melon crop development in the field against this phenological model in Figure 1. Based on this phenology model and current HU accumulations for this season we should be able to make some projections on the current stage of growth, which we can go to the field and check.  

An interesting contrast to the information in Table 3 is that of Table 4 which provides similar information for this time last year, 30 April 2025. This clearly demonstrates the drastic differences in HU accumulations between two sequential seasons and the benefits of using HUbased information as opposed to the calendar for crop development and management. 

References:
Silvertooth, J.C. 2026. Melon (Cantaloupe) Crop Growth and Development Patterns. University of Arizona Vegetable IPM Newsletter, Volume 17, No.8, 15 April 2026. http://hdl.handle.net/10150/679979

Table 1. Heat unit accumulations (86/55 ºF thresholds) after 1 January 2026 on four possible planting dates utilizing Arizona Meteorological Network (AZMET) data for each representative site.

Yuma Valley: https://azmet.arizona.edu/application-areas/heat-units/station-level-summaries/az02

Yuma North Gila: https://azmet.arizona.edu/application-areas/heat-units/station-level-summaries/az14

Roll: https://azmet.arizona.edu/application-areas/heat-units/station-level-summaries/az24

Table 2. Heat unit accumulations (86/55 ºF thresholds) after 1 January 2026 to 26 April 2026 utilizing Arizona Meteorological Network (AZMET) data for each representative site.

 H_T = Heat Unit Total Accumulation.

Table 3. Heat unit accumulations (86/55 ºF thresholds) after planting (HUAP) from four possible 2025 planting dates and three sites in the Yuma area on 26 April 2026 utilizing Arizona Meteorological Network (AZMET) data for each representative site. Each value is rounded to the next whole number. Note: the values in Table 3 are determined by taking the difference between the HUs for each representative site and four planting dates in Tables 1 and 2.

Table 4. Heat unit accumulations (86/55 ºF thresholds) after planting (HUAP) from four possible 2025 planting dates and three sites in the Yuma area on 30 April 2025 utilizing Arizona Meteorological Network (AZMET) data for each representative site. 

Figure 1. Melon (cantaloupe) phenological development model expressed in Heat Units Accumulated After Planting (HUAP, 86/55 ^oF).

On March 30th, I shared a newsletter highlighting an increase in celery samples exhibiting symptoms consistent with black heart and black streak abiotic disorders, associated in timing with the mid-March heat wave. At that time, affected plants showed elongated necrotic pitting accompanied by pronounced horizontal cracking along the inner petioles. In more severe cases, there was complete breakdown of young tissues within the heart, including petioles and emerging leaves. Importantly, diagnostic testing on those early samples returned negative results for the common viral pathogens typically considered in the differential diagnoses fitting these symptoms. 

Early black heart symptoms 


Late black heart symptoms + secondary colonization 

Black streak of celery

The YPHC has since received a new sample that changes part of that picture. This most recent submission tested positive for celery mosaic virus (CeMV). In addition to sunken discolored stalk lesions that could potentially be mistaken for early black heart or black streak, the plants in this sample exhibited severe foliar symptoms. Leaf symptoms included deformation including curling and marginal distortion. The leaves also showed distinct mosaic patterning, yellowing, and streaking, all of which are typical characteristics for viral infections. 

Sunken, discolored lesions on celery petioles 


Broad yellowing and mosaic pattern (left) and severe leaf distortion
and mild mosaic (right) on the foliage 

Mosaic, yellowing, and leaf distortion combined on the same petiole

Additional symptoms associated with CeMV can include overall plant stunting and abnormal growth habit (Greer et al. 2024). In some cases, outer petioles may distort severely and begin growing horizontally, giving the plant a flattened appearance. Symptom severity can vary depending on the strain of the virus and environmental conditions during host infection. Be on the lookout for these additional foliar symptoms if you’re seeing sunken petiole lesions as a possible indicator of viral infection. Early infections, symptoms on different varieties of celery, or symptoms caused by different viral strains of CeMV may not look identical in severity or expression as the sample photographed here. CeMV is transmitted by aphids in a non-persistent manner and may also be spread mechanically through wounds introduced during field activities (Karanfil & Randa-Zelyüt 2025). It has not been reported to be seedborne. Fungicides are not effective against plant viruses, and while insecticides may reduce aphid populations, they are generally not effective at preventing virus transmission due to the rapid transmission following the initiation of aphid feeding that occurs before the insecticide has a chance to act on the vector (Greer et al. 2024). We will continue monitoring all incoming celery samples to determine whether this represents an isolated case or a broader trend developing alongside the ongoing celery abiotic disorders.

Sources and further reading:
Greer, C., Koike, S., & Turini, T. “Celery Mosaic Virus.”  Agriculture: Celery Pest Management Guidelines. University of California Agriculture and Natural resources, 2024. URL: https://ipm.ucanr.edu/agriculture/celery/celery-mosaic-virus/#gsc.tab=0 (Accessible 4/28/2026)

Karanfil, A., & Randa-Zelyüt, F. “Celery Mosaic Virus.” Compendium of Phytopathogenic Microbes in Agro-Ecology. Springer Nature, 2025. 153–160.

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)

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

• Pigweed (Amaranthus spp., including Palmer)
• Common purslane
• Hairy fleabane
• Spurge species  
• Barnyardgrass & junglerice
• Sprangletop

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 Melons
Crop emergence —> Vine Run

• Melons are poor competitors early
• Canopy closure does not occur soon enough to suppress weeds
• Weeds pressure before vine runs directly reduces:
• o Early vine growth o Fruit set
• o Harvest efficiency

Herbicide – Based IPM Recommendations for Melons
Pre-Plant/Burndown (Before Seeding or Transplants)  

• Glyphosate – annuals and perennials (pre-plant only)
• Paraquat – fast burndown of small weeds (restricted use)
• Carfentrazone (Aim) – small broadleaf weeds

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  

• Bensulide (Prefar) – board activity on grasses and small-seeded broadleaves
• Ethalfluralin (Curbit) – excellent on pigweed and annual grasses
• Trifluralin (Treflan) – grass and pigweed control (incorporation required)

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  

• Halosulfuron (Sandea) – pigweed, purslane, spurge (size-dependent)

Grasses

• Clethodim (Select, others)
• Sethoxydim (Poast)

Effective on small grasses; timing is critical. Late POST applications after vines run reduce control and increase crop injury risk. 

Things to watch

• Prefar is a better fit when you can use overhead incorporation; it's less effective under drip or furrow irrigation
• Sandea has carryover risk, so plan crop rotation carefully  
• Poast does not control spangletop or annual bluegrass well

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. 

Cole crops (broccoli, cauliflower, cabbage, and leafy brassicas) are highly susceptible to green peach aphid and whiteflies. These pests not only reduce plant vigor but can also contaminate harvestable portions and transmit viruses, leading to direct market losses. Azadirachtin-based insecticides (neem-derived products) can be a valuable tool for early-season and rotational use in organic cole crop production.

How do Azadirachtin-Based Insecticides Work?

• Slows feeding and reduces plant damage
• Disrupts development of immature stages (aphids and whiteflies)
• Limits the buildup in protected plant areas

These effects are particularly important for whitefly management, where targeting immature stages is critical for breaking the life cycle.

Timing for Success

• Start applications early, before populations build
• Focus on early vegetative stages
• Continue monitoring through crop development

Application Tips for Cole Crops
Cole crops present unique spray challenges due to canopy structure:

• Prioritize coverage
• Use higher spray volumes to penetrate dense foliage
• Target leaf undersides and inner canopy
• Use an appropriate nozzle setup to improve coverage
• Repeat applications may be necessary (short residual)
• Avoid long spray intervals when pest pressure is building

Key Limitations

• Not a quick knockdown product
• Less effective once pests are well established inside the heads
• Requires consistent scouting and timely applications

Research-Based Evidence
Field trials conducted in Arizona demonstrate that azadirachtin-based insecticides can suppress populations of green peach aphid and whiteflies on broccoli when applied early and with good coverage.

Figure 1. Green peach aphid numbers on broccoli as affected by azadirachtin-based
insecticides and M-Pede. Treatments with azadirachtin reduced aphid populations
compared to the untreated control. (Yuma, AZ, Spring 2026)

Figure 2. Whitefly numbers on broccoli as affected by azadirachtin-based insecticides.
Treatments with azadirachtin reduced the number of whiteflies compared to the
untreated control. (Yuma, AZ, Fall 2025)

 

Take-Home Message for Cole Crop GrowersAzadirachtin-based insecticides are a practical option for managing the green peach aphid and whiteflies in organic cole crops. Their effectiveness depends on early application, thorough coverage, and consistent application timing.

Reference evapotranspiration, or ETo, is a daily measure of atmospheric water Reference evapotranspiration, or ETo, is a daily measure of atmospheric water demand from a well-watered reference surface. For growers in Yuma Valley, where almost every drop of water a crop receives comes from irrigation, ETo is one of the most useful numbers available for deciding when and how much to irrigate.

How ETo changes over the year
The graph shows daily ETo at the AZMET Yuma Valley station from May 2023 through early 2026 (Figure 1). The pattern repeats each year: ETo is low in winter, climbs through spring, peaks during the hot summer period, and declines again in fall. From June through August, daily ETo often rises into the 0.30 to 0.40 inch per day range, with some peak days approaching 0.44 inch per day. During December through February, daily ETo often falls below 0.10 inch per day. This seasonal swing is much more important for irrigation management than the weak downward trendline.

That is a four- to five-fold difference in daily crop water demand between the peak of summer and the depth of winter. A grower irrigating a full-canopy crop in July is managing a very different situation than the same grower irrigating in January, even if the field looks similar.

Figure 1. Daily reference evapotranspiration (ETo) at the AZMET Yuma Valley station
from May 2023 through early 2026.  

What high and low ETo numbers actually mean
Four weather factors drive ETo up or down: solar radiation, air temperature, relative humidity, and wind speed. When all four push in the same direction, bright sun, high heat, dry air, and strong wind- ETo climbs quickly and crop water demand rises with it. When conditions are mild and humid, ETo stays low, and irrigation needs ease off. The table below gives a practical guide to what different ETo ranges mean for a Yuma Valley grower and how to respond:

These ranges are general guides. The actual water use of any specific crop also depends on its growth stage and canopy cover, which is captured by the crop coefficient (Kc). A young transplant with little canopy uses far less water than a mature plant at full cover, even when ETo is the same.

Turning ETo into an irrigation target
Multiply daily ETo by the crop coefficient (Kc) for your crop and growth stage to get estimated crop water use:

Crop ET = ETo × Kc

For example, if ETo is 0.30 inches per day and your crop is at a growth stage with a Kc of 0.80, the crop is using about 0.24 inches of water that day. At a peak summer ETo of 0.40 inches per day with the same Kc, water use climbs to 0.32 inches per day. That difference adds up quickly across a field over a week. Staying current with daily ETo during high-demand periods matters more than it does in the cooler months, when ETo is low and there is more time to respond.

What this means for irrigation management
During warm, sunny, dry, and windy periods, particularly from April through September, check ETo daily and adjust irrigation accordingly. During cooler months, ETo is low enough that there is more flexibility, but it still varies with weather and should not be ignored entirely.

Current daily ETo for Yuma Valley is available from the AZMET network at ag.arizona.edu/azmet. Use the daily ETo value along with your crop’s Kc to estimate how much water to apply. Combining that number with soil moisture information and knowledge of your irrigation system’s output will give you the most reliable basis for scheduling. During peak summer demand, staying close to that daily target is one of the most effective things a grower can do to protect yield and avoid water stress. 

VegIPM Update Vol. 17, Num. 9
April 29, 2026

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW numbers remained steady at most locations over the last two weeks. CEW is active throughout the summer and high numbers are expected leading into the next produce season.

Beet armyworm:  BAW activity remained steady over the last two weeks. Historically adult BAW is collected through the summer, although numbers are lower compared to Mar-Apr seasonal highs.

Cabbage looper:  Cabbage looper moth activity remained steady over the last two weeks. Numbers are expected to decrease as temperature gets warmer.   

Diamondback moth: Adult DBM numbers continued to decrease across most locations. Based on other years data, DBM numbers are expected to continue decreasing as cole crops acres decrease.  

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

Thrips: Adult thrips activity remains steady across locations. Historically, western flower thrips numbers peak in May.  

Aphids: Winged aphid numbers continued to decrease at most sites in the last two weeks. Winged aphids disappear from our traps after April as temperatures become too hot for aphids.  

Leafminers: Adult leafminer activity decreased over the last collection. Leafminers are collected in our traps throughout the summer.