Dr. John Palumbo’s contributions shaped our vegetable IPM program and supported countless growers and PCAs across the region. While no one can truly take John’s place, we want to reassure you that we remain committed to continuing the vital work he championed. With care and respect for the foundation he built, we are working to carry his efforts forward.

A dedicated team is in place to ensure that the needs of growers and industry partners are met for the quickly approaching 2025–26 growing season. While a permanent replacement will be hired through a formal search and selection process, the team remains fully committed and ready to maintain John’s high priority projects in the meantime.

Moving forward, members of the John Palumbo transition team will be present at future Extension and industry meetings to share trial results, program updates, and to ensure ongoing support for stakeholders. The Vegetable IPM Newsletter will remain a key outlet for sharing trial results and updates on ongoing research, as well as providing the biweekly insect trapping network results that so many rely on for timely, informed decisions. John’s information will continue to hold the top spot in the newsletter, in recognition of his leadership and as a way to keep his work front and center for our community. We also want to share that the Name the Pest competition will continue, and John’s beloved (and often legendary) hats will still be awarded as prizes. Though John’s presence can never be replaced, we can carry his spirit forward by advancing his research, keeping his traditions alive, and continuing to serve our vegetable IPM community with the same dedication he inspired in all of us.

John built this program to serve you — the growers, PCAs, and industry partners who shape and sustain it. Your letters and statements supporting a timely search and strong candidate recruitment will help keep it strong and aligned with your needs. Thank you for your dedication, your voice, and for honoring John’s legacy by continuing to move forward together.

Water is the first limiting factor in desert crop production systems, followed closely by bio-available nitrogen (N).  Nitrogen fertilizer application rates for desert vegetable crops typically range from ~ 150-300 lbs. N/acre.  This variation can be due to a lot of factors, including the residual soil N levels, crop rotations, length of the production cycle for the crop, etc.  
 
Due to the critical nature of N availability for the growth of a healthy and marketable crop with good yields in a timely manner, growers are alert to preventing a N deficiency in desert vegetable crop production.  Prices for fertilizer N are always a major factor in the crop production budget for any field and that is certainly turning out to be an important issue this year with higher fertilizer N prices.
 
Figure 1 shows the average North American fertilizer price gauge pattern from 2007-2021 with a distinct surge in 2021.  This surge in fertilizer prices is reminiscent of a similar pattern in 2008 and quite an increase in relation to average prices experienced in the past five years.  More specific to N fertilizer costs, Figure 2 shows the average weekly retail anhydrous prices in the U.S. 2019-2021 with a five-year average. 
 
The primary driving force in a higher average North American fertilizer price gauge is associated with N fertilizers.  Anhydrous ammonia is a good gauge for overall N fertilizer price since so many N fertilizers utilize anhydrous ammonia in the manufacturing process.  Nitrogen fertilizer price increases are being driven by the following major factors:
 

• Anhydrous ammonia plants in Louisiana were closed in September with Hurricane Ida’s landfall.  This resulted in supply disruptions.
• Natural gas prices have been increasing in recent months.  This is important because high demand of natural gas in the production of N fertilizers and it represents a major cost in manufacturing process
• On a national level, fertilizer prices are positively correlated with corn prices.  The use of corn in ethanol production has served to tighten the relationship between corn prices and fertilizer prices.
• Similar to many other products in the U.S. and abroad, general supply chain problems and labor issues associated with the COVID-19 has had a strong impact on all industries, including the fertilizer industry.

 
Collectively, this all translates to a more costly and perhaps challenging year for nutrient management in desert vegetable production systems.  These challenges can be dealt with by consideration of the 4R approach to plant nutrient application, consisting of:
 
 1.   Right fertilizer source at the
 2.   Right rate, at the
 3.   Right time and in the
 4.   Right place
 
The 4R nutrient stewardship approach utilizes the implementation of best management practices (BMPs) that optimize the fertilizer use efficiency by the crop. The primary objective of the 4R approach and BMPs is to match nutrient supply with crop requirements and to minimize nutrient losses from fields.  With higher fertilizer prices, this can be more important in crop production management for this year.

Figure 1.  North American fertilizer prices.


Figure 2. Average weekly retail anhydrous prices. Source: Progressive Farmer, 10 November 2021.

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach ‘Meerkat’ was seeded, then sprinkler-irrigated to germinate seed Jan 13, 2025 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂ backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles.

Downy mildew (caused by Peronospora farinosa f. sp. spinaciae)was first observed in plots on Mar 5 and final reading was taken on March 6 and March 7, 2025. Spray date for each treatments are listed in excel file with the results.

Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft²areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft²area of bed was approximately 144. The percentage were then changed to 1-10scale, with 1 being 10% infection and 10 being 100% infection.

The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that provided most effective control against the disease include Orondis ultra, Zampro, Stargus, Cevya, Eject .Please see table for other treatments with significant disease suppression/control.  No phytotoxicity was observed in any of the treatments in this trial.

Yesterday, we initiated our first trial of the season examining the use of band-steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes.

In our multi-year study, we are using a 35 BHP steam generator mounted on a custom designed elongated bed shaper to inject steam in the soil (Fig. 1). Trials conducted last fall show the technique holds promise. Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph travel speed and 53 in the 0.5 mph travel speed treatments, respectively (Fig. 2).

Fusarium load at the site where this week’s trial was conducted is reportedly high and we’re looking forward to obtaining good results. We’re also planning a second trial later this month at the Yuma Ag Center that is also focused on Fusarium wilt of lettuce control.

Stay tuned for results of all our trials examining the efficacy of using steam heat to control Fusarium wilt of lettuce, sclerotinia lettuce drop, pythium and weeds.

As always, if you are interested in seeing the machine operate or would like more information, please contact me.

Acknowledgements
This project is sponsored by USDA-NIFA and the Arizona Specialty Crop Block Grant Program. We greatly appreciate their support. A special thank you is extended to Larry Ott and Gila Valley Farms for allowing us to conduct this research on their farm. Fig. 1. Prototype band-steam applicator/bed shaper operating in Wellton, AZ. Fig. 2. Effect of band-steam applied at two travel speeds on Fusarium colony forming units (CFU) in the soil.

Fig. 1. Prototype band-steam applicator/bed shaper operating in Wellton, AZ.


Fig. 2. Effect of band-steam applied at two travel speeds on Fusarium colony
forming units (CFU) in the soil.

Malva (malva parviflora) is one of the oldest and most pervasive weeds that that we deal with here. It is also known as little mallow or cheeseweed and is in the same family as cotton, okra and hibiscus. It is often classified as a winter annual but survives all year in this region. It has a deep taproot and can grow in compacted clay or sand and in freezing conditions and high temperatures It provides a refuge for insects and diseases that can damage several crops.

Malva is easy to identify both as a seedling and mature plant. The seedlings are distinctively  heart shaped and the mature plant is broad and palm shaped. It is very vegetative and can grow to 6 ft.

The deep tap root of this weed makes it difficult to cut out after it is established. Its response to herbicides id somewhat unusual. It is very sensitive to contact herbicides that do not move into the plant. These include Goal, Sharpen Gramoxone , Rely,Aim and others. However, it is not sensitive to systemic herbicides like 2,4-D and Glyphosate. It reproduces from seed and can be controlled preemergence with many of the same preemergence herbicides used in cotton like Prowl or Treflan. The seed pods are wheel shaped which is where the name cheeseweed comes from. Each seed pod contains 10 to 12 seeds

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 17, Aug 21, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts decreased areawide; about average to previous years.
 
Beet armyworm:         
BAW moth counts are up in south Yuma valley and Dome valley; about average for August

Cabbage looper:           
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:      
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                      
Adult movement continues to decrease, average for this time of the year.
 
Thrips:                          
Thrips adult activity continues to decline, average for August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity declining and average for August.