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 a recent edition of this University of Arizona Vegetable Integrated Pest Management (UA VIPM) Newsletter, Vol. 14, No. 18, I provided a brief review of some basics related to soil physical properties and soil health.  Physical properties have strong impacts on some basic functions of healthy soil.  In irrigated agriculture one important physical feature is that of water holding capacity and the plant-available water (PAW) a soil can hold (Baver et al., 1972).
 
Soil serves as the storehouse or reservoir of water available for plant uptake.  As noted in the article regarding soil physical properties, soils vary significantly in terms of texture (relative proportions of sand, silt, and clay) and water holding capacity.  The relationship between total water in a soil and the portion of that water that is “available” to plants is shown in Figure 1 and Table 1.
 
In review of Figure 1, it is important to note several points: 1) The total amount of water that can held by a soil increases with finer textured soils.  2) The PAW held in a soil generally increases with finer textured soils but only to a certain extent with a salient bulge of maximum proportions of PAW in medium textured soils, such as loams and silt loams.  3) Soils with higher clay content, e.g. clay loams and clays, have high total water holding capacity but lesser amounts of PAW (Kirkham, 2023).  
 
Water that is held very tightly by the soil particles is referred to as “hydroscopic” water and the finer soil particles, such as clay, exert the strongest hydroscopic forces, and holding that soil-water unavailable to most plants.
 
The lower boundary of PAW shown in Figure 1 is a general line of demarcation at -1500 kilopascals (kPa) of potential energy and is referred to as the permanent wilting point (PWP).  The PWP was originally considered as a more universal limit among plant species (Briggs and Shantz, 1912).  However, the PWP as defined in Figure 1 is very general since all plant species vary considerably in their capacities to extract water from the soil.  Many native desert plant species for example can extract some hydroscopic and most crop species will suffer water stress long before soil-water content approaches the PWP line shown in Figure 1 (van Lier et al. 2023).  

Figure 1.  Soil-water holding capacity as a function of soil texture.  Source: The
COMET program.  University Corporation of atmospheric research.



Figure 2.  Soil-water relations and energy levels with soil-water content,
kilopascals (kPa) of potential energy.

Figure 2 describes a close-up view of two adjacent soil particles and the pore space between them.  Soil-water is held as a film around the soil particles leaving some air space in the pores after the gravitational water has drained away, leaving the soil at field capacity (FC).  As the soil dries the water film on the soil particles become thinner and held more strongly by the physical forces associated with the soil particles.
 
Following irrigation with the gravitational water drained away (dependent upon good internal soil drainage), which commonly takes about 24 hours, a soil will be at FC.  A crop will extract water most easily at FC and can continue to do so until the soil dries to a point where the crop plant can no longer pull water from the soil against the forces of the soil exerting holding that water.  
 
That critical point below which plants begin to encounter water stress is unique among crop plants but for most leafy green vegetable crops this limit is commonly about the 65-70% PAW level.  Other common desert crops like alfalfa, cotton, wheat, and melons can maintain adequate water levels before stressing and starting to show signs of wilting at approximately 55% PAW.
 
This means the actual range of soil-water that is available to plants is in the range from FC to the specific point of crop stress level, that is unique to each crop species, and the corresponding wilting point (WP).  Thus, PAW = FC – WP.
 
One of our challenges in managing crop production systems is identifying the WP for the crop in question and FC for the soil in that field.  In addition, with irrigation management we strive to maintain crops in a non-stressed condition and manage the fields in that range of PAW between the FC of the soil and the WP for the crop.  
 
This is a good example of a healthy soil that does not limit water availability due to physical or chemical restrictions and benefits the growth of a healthy crop.  
 
The Web Soil Survey in the following link can be used to assess soil textures dominant in a given field.  https://websoilsurvey.nrcs.usda.gov/app/

 

Texture	AWC range (in/in)	AWC range (in/ft)	Est. typical AWC (in/ft)
Coarse sand	0.01-0.03	0.1-0.4	0.25
Sand	0.01-0.03	0.1-0.4	0.25
Fine sand	0.05-0.07	0.6-0.8	0.75
Very fine sand	0.05-0.07	0.6-0.8	0.75
Loamy coarse sand	0.06-0.08	0.7-1.0	0.85
Loamy sand	0.06-0.08	0.7-1.0	0.85
Loamy fine sand	0.09-0.11	1.1-1.3	1.25
Loamy very fine sand	0.10-0.12	1.0-1.4	1.25
Coarse sandy loam	0.10-0.12	1.2-1.4	1.3
Sandy loam	0.11-0.13	1.3-1.6	1.45
Fine sandy loam	0.13-0.15	1.6-1.8	1.7
Very fine sandy loam	0.15-0.17	1.8-2.0	1.9
Loam	0.16-0.18	1.9-2.2	2
Silt loam	0.19-0.21	2.3-2.5	2.4
Silt	0.16-0.18	1.9-2.2	2
Sand clay loam	0.14-0.16	1.7-1.9	1.8
Clay loam	0.19-0.21	2.3-2.5	2.4
Silty clay loam	0.19-0.21	2.3-2.5	2.4
Sandy clay	0.15-0.17	1.8-2.0	1.9
Silty clay	0.15-0.17	1.8-2.0	1.9
Clay	0.14-0.16	1.7-1.9	1.8

 
Table 1.  Available Water Capacity (AWC), range, and typical levels for various soil textures. Source: Chapter 2 “Soils”, Irrigation Guide, Natural Resources Conservation Service- National Engineering Handbook.
 

 
References 
Baver, L.D., Gardner, W.H., and Gardner, W.R. 1972. Soil Physics. 4th ed. Wiley: New York.
 
Briggs, L.J., and Shantz, H.L. 1912. The wilting coefficient for different plants and its indi-rect determination. USDA Bur Plant Industry Bull No. 230. U.S. Dept. Agr: Washington, DC.
 
Kirkham, M.B. 2023.  Field capacity, wilting point, available water, and the non-limiting water Range. Ch. 8. In: Principles of Soil-Plant-Water Relations. 2023 Elsevier Ltd.
 
“Soils”, Irrigation Guide, Natural Resources Conservation Service- National Engineering Handbook.https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17837.wba
 
van Lier, Q. J., S.D. Logsdon, E. A. Rodrigues, and P.I. Gubianid,  Plant-Available Water.  Ch. 12.  In: Principles of Soil-Plant-Water Relations. 2023 Elsevier Ltd.

The Yuma Plant Health Clinic (YPHC) is receiving an increasing number of black rot cases, confirmed with molecular diagnostics, affecting Brassica/cruciferous crops across Yuma County. This bacterial disease, caused by Xanthomonas campestris pv. campestris (Xcc), is causing severe wilt and necrosis with the help of our recently sunny and warm weather.

The conventional understanding of this pathogen’s transmission is that it is thought to be seed-borne. This mode of transmission was first conclusively demonstrated in a paper published in Phytopathology in 1952 by John Charles Walker, one of the founding fathers of modern plant pathology and author of several of the first comprehensive textbooks on the subject (Cook et al., 1952). He put the Walker in Walker’s Plant Pathology.

Thus, it is true that initial sources for a black rot epidemic can include contaminated seed and infected transplants grown from wherever Xcc is already present. Xcc is globally distributed, meaning sources of inoculum are in no short supply. Worldwide, black rot is one of the leading biotic causes of crop loss in Brassicas. While it isn’t wrong to say that black rot is distributed on seeds and transplants, it’s not the full story either…

Xcc has been shown to survive for extensive amounts of time on crop debris. In 2011, researchers at Wageningen University demonstrated that Xcc could survive on whole Brussels sprouts stalks, either left on the surface or buried in the soil up to 20 cm, for at least 2 years (the total duration of their study) (Köhl et al. 2011). As far back as 1990 Kritzman & Ben-Yephet reported survival times of at least 22 months in cauliflower residue (Kritzman & Ben-Yephet 1990). It is important to note these studies did not look at Xcc survival for longer than two years, so while the survival is known to be up to 2 years, it’s unknown if this is the upper limit of survival on residues. Field studies like these are difficult to perform for more than a few years due to funding constraints, cropping practices, and land availability.

And while Walker famously demonstrated Xcc’s transmission via the seed, he also demonstrated that the bacteria could enter healthy roots from soil inoculum alone (Cook et al., 1952). Subsequently, Alvarez and Cho achieved 90% disease incidence in treated, disease-free cabbage transplants after infesting a clean tenth-of-an-acre field with 14 lbs of infested and minced cabbage stumps and wrapper leaves (1978). Of note, in that same study, only 1 out of every 20,500 commercial cabbage seeds was found to be contaminated with Xcc.

So, couple the long-term survival of Xcc on crop residues with wind or flowing surface waters, natural or via irrigation, and you have a vector for spreading the bacteria whether a Brassica crop is present or only its residue alone.

A further complication surrounding Xcc’s initial origins within and subsequent spread throughout fields is the fact that it can also survive and be transmitted via infected cruciferous weeds (Dubrow et al. 2022). The host range of Xcc includes many, if not all, species in the Brassica genus and several closely related genera. A quick search of SEINET’s flora of Arizona database reveals at least 148 species from the family Brassicaceae widely distributed in the state. A cursory glance reveals even more familiar species that are absent from the herbarium’s list. Shepherd’s purse, camelina, and wild mustard are just three of the common AZ weeds that could potentially be acting as reservoirs with wild mustard confirmed in at least one study (Dubrow et al. 2022).

“Great Chris, so what should I do?” you might ask. Well, one thing that seems to have worked in reducing the chance of Xcc coming from residue is finely chopping infected crops and burying the residue where it has the best chance at decomposing. In another study out of Wageningen Xcc infested cabbage was chopped to a maximum of 15.5 in2 and resulting plant debris was tilled into the soil at a depth of at least 4 inches (Kocks et al. 1998). Eradication of the pathogen occurred at temperatures above 68 °F and, in the Netherlands, could occur between cropping seasons without rotation. How important soil moisture and microbiome differences may play in the decomposition process and subsequent eradication of Xcc is unknown. Subsequent control of cruciferous weeds in fields intended for future Brassica crops is then critical, even in the off-season.

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:

 

Chris Detranaltes, Ph.D.
Cooperative Extension – Yuma County
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109

 

Sources:
To access SEINET’s database, use the following link (accessed 11/10/2025):
https://swbiodiversity.org/seinet/

Alvarez, A. M., Cho, J.J.. “Black Rot of Cabbage in Hawaii: Inoculum Source and Disease Incidence.” Phytopathology 68.10 (1978): 1456. Web.

Cook, A., Larson, R. H., and Walker, J. C.. Relation of the black rot pathogen to Cabbage seed. Phytopathology, 42(6), 316-320 (1952).

Dubrow, Zoë E et al.. Cruciferous Weed Isolates of Xanthomonas Campestris Yield Insight into Pathovar Genomic Relationships and Genetic Determinants of Host and Tissue Specificity. Molecular plant-microbe interactions, 35(9), 791–802. (2022).

Kocks, C.G. et al.. Survival and Extinction of Xanthomonas Campestris Pv. Campestris in Soil.”European journal of plant pathology, 104(9), 911–923 (1998).

Köhl, J et al.. Survival of Pathogens of Brussels Sprouts (Brassica Oleracea Gemmifera Group) in Crop Residues. Plant pathology, 60(4), 661–670, (2011).

Kritzman, G., Ben-yephet, Y.. Control by metham-sodium of Xanthomonas campestris pv. campestris and the pathogen’s survival in soil. Phytoparasitica 18, 217–227 (1990). https://doi.org/10.1007/BF02980991

Please watch a demonstration of a spray assembly delivering herbicidal spray (blue dye) to spot spray targeted weeds. The device will be integrated with an imaging system for precision, automated / robotic weed control. Weed targets and crop plants are indicated on paper by green and yellow squares respectively. The same targeting pattern is used for simulated weeds (small plastic plants) and crop plants (white roses). Off target spray on paper is due to liquid splashing on a hard surface and is not observed on plastic weed targets. The travel speed is 2 mph and nozzle height - 5".
Click on the following demonstration link or the picture area:

Thank you for attending the Weed Control breakout session at the Southwest Agricultural Summit last week. Dr. Jesse Richardson presented the historical perspective on how the methods of applying Pronamide have been developed. Some of this information can be found in the following links:
https://cals.arizona.edu/crop/counties/yuma/farmnotes/2003/fn0803kerblettuce.html
 
https://live-azs-vegetableipmupdates.pantheonsite.io/sites/default/files/2023-03/Kerb%20Word%20slides.pdf
 
   Also Dr. Samuel Discua presented an update on the Survey of Weeds as Reservoirs of INSV in Yuma County and the presentation can be found here: 
 
https://live-azs-vegetableipmupdates.pantheonsite.io/sites/default/files/2023-03/SWAG%202023%20Weeds%20Survey%20Update%20.pdf
 
Dr. Jose Carvalho shared with us results from his research program at the Maricopa Agricultural Center including evaluations with the “King of Weeds” Palmer amaranth.
 
Additionally, some information was presented on Prefar Chemigation as well as the effect on spinach plantings if planted too early. The trials were done this season at the Yuma Agricultural Center and The Arizona Cooperative Extension will make videos of these presentations available soon.

Results of pheromone and sticky trap catches can be viewed here.

 

Corn earworm: CEW moth remains light; below average for this time of season.

Beet armyworm: Moth trap counts increased in most areas, Above average for this time of the year.

Cabbage looper: Moths decrease slightly in all traps in the past 2 weeks, and a little below average for this time of the season.

Diamondback moth: Adults about remain the same, but very active in N. Yuma Valley. Overall, average for February.

Whitefly: Adult movement remains low in all areas, consistent with previous years.

Thrips: Thrips adults movement increased slightly in the past 2 weeks, most notably in Tacna and Yuma Valley. Overall activity average for February.

Aphids:  Winged aphids are still actively moving and reached seasonal highs in the past two weeks, particularly active in N. Gila Valley. Well above average for late-February.

Leafminers: Adult activity down in most locations, below average for this time of season.