A Space to Share, Remember, and Celebrate

We invite everyone in the veggie IPM community to use this online memorial to share
your memories, stories, or photos in honor of our beloved John. Click the link below:

John C. Palumbo | 1959 - 2025 | Online-Tribute.com

Lettuce Crop Losses Workshop— June 4th

Join us for the 2025 Lettuce Crop Losses Workshop on Wednesday, June 4 from 12:00–3:00 PM at the Yuma Agricultural Center (6425 W. 8th St., Yuma, AZ 85364). Lunch will be provided, and 3 CEUs have been approved by AZDA and CA DPR (agenda below).

This workshop is part of a long-standing effort to collect real-world data on insect losses and control costs in Arizona lettuce production. Your responses help shape research priorities, regulatory decisions, and industry guidance.

More than that — continuing this survey is a meaningful way to honor Dr. John Palumbo’s legacy. It was the PCAs behind the data that John appreciated most—your insights gave these numbers meaning. Your participation ensures that the work he championed remains impactful for seasons to come. 

RSVP by emailing Macey or call/text her directly to confirm your spot.

Also, if you're a PCA who checks lettuce and can't attend the meeting but would still like to complete the insect losses survey, email Macey to receive a copy and submit your responses remotely.

John Wesley Powell had a profound understanding of the western territories of the United States (US) and he made a strong effort to influence the geographical boundaries of territories and states that were formed in the 19^th century.  Had he been successful with those efforts, our state lines would more closely follow watershed boundaries and the nature of the negotiations for water in the west would be significantly different.
Powell was born in Mount Morris, New York in 1834.  Powell’s family moved to Ohio then Wisconsin before settling in Illinois in 1851.  From an early age he was always interested in history, literature, botany, zoology, and a broad range of natural sciences.  In 1852 he became a teacher and attended several colleges but never did receive a degree.
When the Civil War broke out in 1861, Powell enlisted in the Union Army at 27 years old, serving as a first lieutenant topographer, cartographer, and military engineer.  On 6 April 1862 at the Battle of Shiloh in Tennessee, Powell was hit with a minié ball in his right arm, and it was amputated by field surgeons at the elbow.  After recuperation, he returned to service and was promoted to the rank of Major before the end of the war (Ross, 2018 and Cope, 2019).
After the war, Powell directed much of his interested and energies to the open territories in the western U.S.  The one-armed war veteran organized his first expedition to explore the Green and Colorado Rivers that began on 24 May 1869.  The expedition was completed on 30 August 1869 when Powell and five other men climbed out of the canyon.  Powell’s second expedition on the Colorado River extended from 22 May 1871 to 7 September 1872.  The second trip offered Powell and his team an opportunity to focus on the collection of scientific data and information that included photographs, detailed maps, and observations that were later used for the development of scientific publications.
He became the second director of the United States Geological Survey (USGS) from 1881 to 1894 (Figure 1).  His experiences in the west had huge influences on Powell and he became an ardent advocate for strict water resource conservation policies for the American West’s river systems.  He saw this as particularly important at the time since most American policy makers in Washington and in the western territories did not want to accept the basic facts regarding the aridity of the west and the limitations of development due to water.
In 1869 at the Montana Constitutional Convention, Powell stated that “All the great values of this territory have ultimately to be measured to you in acre feet.”, which was not fully comprehended or incorporated into water policy.  Another good example of Powell’s prophetic opinions on the management of western water was offered in Los Angeles at the 1893 Irrigation Congress where he stated, “I tell you, gentlemen, you are piling up a heritage of conflict and litigation over water rights, for there is not sufficient water to supply these lands.” and that advice was also generally ignored.
In 1891 the USGS published its 11^th Annual Report (USGS, 1891) that contained several excellent maps.  Perhaps the most famous map from that publication is a map of the arid region of the U.S. (Figure 2) and it is commonly referred to as the John Wesley Powell Map.  This map defined the arid region of the U.S. extending west of the 100^th meridian to the Pacific Coast Range.  Working in the west today, that line is still a good demarcation opening the arid lands of the western U.S.
He resigned from his duties as the USGS Director in 1894 due to the resistance and heavy opposition to his water resource conservation efforts from western politicians.  Dealing with the water resource challenges that we have in the west today, particularly in the Colorado River basin, we can recognize the wisdom and good advice that Powell offered.  We can also see the consistency of political operators tending to ignore natural resource facts and limitations.  Some things do not change.
Now we are primarily dealing with conflicts regarding Colorado River allocations between the upper and lower basins, consisting of states defined by political boundaries and straight survey lines.  We are dealing now with many of the problems that John Wesley Powell was trying to warn people about and possibly prevent or reduce the levels of conflict.  
Thus, it is interesting to consider the Powell Map versus the state maps that we have and what those implications might have been.  We can at least appreciate his capacity to look ahead and the importance of our being able to do so today.

Figure 1.  John Wesley Powell at his desk in the
USGS office, ca. 1891.



Figure 2.  John Wesley Powell’s Map of the Arid Region of the United States,
published in the Eleventh Ann. USGS Report, Part II, PL LXIX, 1891.

References
Cope, M.  2019.  Major John Wesley Powell: 1834-1902.  Utah Geological Survey, September 2019.
Ross, J.F. 2018.  The Visionary John Wesley Powell Had a Plan for Developing the West, But Nobody Listened. Smithsonian, 3 July 2018. 
 
USGS.  1891.  Eleventh Annual Report, United States Geological Survey, 1891.

Yuma is in the full swing of downy season for lettuce. The light yellow, irregular leaf spots on the upper leaf surface with white to pale-gray fungal growth on the under leaf surface can be found popping up in fields everywhere. Damp and cool conditions are required for infection and symptom development. Sporangia of Bremia lactucae, the oomycete pathogen responsible for lettuce downy mildew (LDM), are wind disseminated and capable of germinating on the lettuce leaf surface they land on in 3 to 4 hours if free moisture is present. All across Yuma County we started reaching that leaf wetness threshold just about the last two weeks of November (See graphs below). Leaf wetness has remained especially high in Roll and South Yuma, while North and central Yuma have been drying out, although leaf wetness in central Yuma is on a rising trend as of the time of me writing this article.

Graphs retrieved from the Arizona Meteorological Network leaf wetness reports. Leaf wetness determined by electrical conductivity. Dry hours = number of hours less than or equal to 273 mV out of 24 hours in the day, transition hours = between 273 and 284 mV, and wet hours = number of hours greater than or equal to 284 mV.

There are 10 internationally recognized races of LDM reported in the United States. The naming of new races of LDM is overseen by the International Bremia Evaluation Board (IBEB), a global association of breeders, researchers, and regulatory bodies. Races are determined by inoculating varieties with known resistance genes to LDM and seeing which varieties the race can and cannot cause disease on. Per IBEB standards, all races have the prefix “Bl:” followed by a space and the race number. European isolates have the suffix “EU” and American isolates have the suffix “US”. For instance, Bl: 1US represents American race 1.

Bl: 1-6US, or American races 1-6, are no longer detected in the western US and are therefore not considered important targets for resistance breeding by IBEB. In spring of last year, five samples from a local favorite variety, ‘Boronda’, were found to be infected with downy mildew. ‘Boronda’ is marketed with genetic resistance to the US western races Bl: 5-9US. Two samples of ‘Boronda’ submitted by Dr. Stephanie Slinski, associate director of applied research & development at YCEDA, in February of last year from Yuma were evaluated by the UC Davis Bremia group led by Dr. Richard Michelmore. When inoculated on differentials, both isolates behaved like isolate VP-300, a non-IBEB-designated variant currently under evaluation to be designated as a new American race. VP-300 was identified in 2017 and is apparently capable of bypassing the genetic resistance bred into ‘Boronda’.

I have received reports of ‘Boronda’ resistance being broken again this year in South Yuma and the Wellton/Tacna/Roll area. ‘Muggins’ is reportedly showing susceptibility as well, and I am especially interested in collecting samples from this variety for additional race testing to see if this is also due to the presence of VP-300.

Take home messages for growers:

• Downy mildew is active and the weather is perfect for disease development around Yuma County
• New, aggressive isolates are out there and they are breaking beloved resistant variety favorites
• Genetic resistance may be less effective this year than in previous years in certain varieties, use a full IPM approach
• You can submit samples of LDM to the Yuma Plant Health Clinic for race testing, ensure you fill out the downy mildew drop off sheet completely and leave plants in the sample fridge outside the clinic

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

Useful Links:
BEB website: https://worldseed.org/our-work/disease-resistance/other-initiatives/ibeb/

UC Davis Bremia database: https://bremia.ucdavis.edu/bremia_database_main.php

AZ Meteorological Network leaf wetness reports: https://viz.datascience.arizona.edu/azmet/leaf-wetness-report/

Our newly constructed self-propelled steam applicator is designed to inject steam into the soil and raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (140°F for > 20 minutes). After the soil cools (< ½ day), the crop is planted into the disinfested soil. We have done some preliminary testing and are very encouraged. Results show that the machine is able to reach target temperatures at reasonable travel speeds, provide uniform temperature distribution across the bed and form nicely shaped beds suitable for subsequent planting. We still have some bugs to work out and identified improvements to make before shipping the unit to Salinas, CA where we will conduct field trials with crops this summer. If you are interested in seeing the machine operate or more information about soil steaming for soilborne pest control, please feel free to contact me.
Check out a video of the machine operating by clicking here or on the image below.

Fig. 1. Initial testing of self-propelled steam applicator video.

Acknowledgements
This project is sponsored and funded in part by the Propane Education and Research Council (PERC), Arizona Specialty Crop Block Grant Program and USDA-NIFA. We greatly appreciate their support.

These types of herbicides are also called contact herbicides. PPO inhibitor means they slow down the production of the protoporphyrinogen oxidase (PPO) enzyme, which is used in chlorophill production. This inhibition also results in the formation of highly reactive molecules that attack and destroy lipids and protein membranes which ultimately affect cell membranes. This result in leaky cells and disintegration of the tissue.

Goal (Oxyfluorfen) is one of the earliest registered of these products (1980) but has only been used widely over the about the last 16 years. This is the only one of these that has problems with “lift off” or codistillation with water. ⁽¹⁾
According to University of CA IPM “In dry bulb onions, GoalTender may be tank-mixed with other pesticides such as bromoxynil, but tank mixes must only be used on older onions with well-developed cuticles to avoid unacceptable crop injury. Unacceptable injury may occur if applied to small onions without adequate cuticle development, and in conditions such as after cloudy or rainy weather. Follow the label closely to avoid crop injury when tank mixing.
Oxyfluorfen has some residual soil activity after application. It controls small broadleaf weeds, some grasses, and nightshade, and controls little mallow (cheeseweed) well ”. ⁽¹⁾

Other PPO herbicides are: Aim or Shark, Chateau, Sharpen or Treevix, ET, and Spartan. They work as contact herbicides and do not move through the plant.
Most of these products don’t have preemergence activity but when used at higher rates Goal and Chateau do.⁽²⁾ As the plant emerges from the soil and contacts the herbicide it dies, so it is recommended to avoid disturbing soil after the application of these products.
 
This week in Yuma oxyfluorfen uses:

1. Directed application in broccoli for goosefoot, lambsquarter, and cheeseweed control.
2. Broadcast application in onions for goosefoot, grasses and lambsqurter

 
References

1. https://cales.arizona.edu/crop/vegetables/advisories/more/weed173.html
2. https://ipm.ucanr.edu/agriculture/onion-and-garlic/integrated-weed-management/

Dec. 10, 2025

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW moth counts down in most traps over the last two weeks; about average for early December.

Beet armyworm: BAW counts decreased across all locations over the last two weeks; but activity remains in most areas. Above average for December.

Cabbage looper: Cabbage looper trap counts decreased across locations except for East Gila. Activity remains at all locations and above average for early December.

Diamondback moth: Adult activity continues to increase across most locations. About average for early December. Historically DBM adult numbers peak around Dec-Jan and remain high until the end of the produce season.

Whitefly: Adult activity decreased across all locations, about average for early December. Expect numbers to remain low as temperatures continue to fall. Historically, whitefly numbers typically peak in October and then again in July-Aug.

Thrips: Thrips adult activity continues to decrease across locations, about average for this time of year. Historically, thrips numbers start picking up again until mid to late January.

Aphids: Winged aphid counts were low across all sites; below average for early December.

Leafminers: Adult leafminer activity remains low in all areas, about average for this time of season.