Over the past 2 weeks, whitefly adult numbers on fall melons have been extremely high in trials conducted at the Yuma Ag Center. In fact, based on numbers sampled from our untreated checks, adult numbers thus far have been almost 10-fold greater than what we've observed in the past several yea (see graph below). Furthermore, whitefly pressure has been exceptionally high in the Roll/Tacna area where our sampling has shown numbers in excess of 150 per leaf on pre-blooming plants in numerous fields. This high whitefly abundance can be attributed to some extent to the crop landscape in these areas. Crops planted near or adjacent to cotton and alfalfa are clearly more heavily infested. In addition, our monsoon conditions this year may be playing a role where total rainfall and average relative humidity during July and August have been higher this year than in the previous 10 years. Interestingly, these monsoon conditions were also very high in 2005 where, if you recall we had very heavy whitefly that year. Given that whitefly pressure does not appears to be letting up, PCAs should pay particular attention to early whitefly control on their newly planted produce crops. It is important that PCAs prevent prolonged feeding by high numbers of adults on seedling lettuce plants which can result in stunted growth. If you observe honeydew on leaves in the absence of nymphs then there are way too many adults on the seedling plants. Furthermore, allowing adults to remain on plants unchecked generally results in the development of large nymph populations which can cause significant growth/yield reductions in all produce crops. It is strongly recommended that growers apply a soil neonicotinoid on lettuce and cole crops throughout September and early October. Local research has shown that imidacloprid applied at 0.25 lbs AI/ac (e.g.,  Alias 2F-16 oz, Wrangler 4F-8 oz; Admire Pro- 7 oz) at planting provides less residual control of nymphs today than it did 10-12 years ago. Given the current economics of imidacloprid, cost-effective whitefly control can be achieved by using higher rates of imidacloprid to extend residual control ( e.g.,  Alias-24 oz,  Wrangler- 12 oz or  Admire Pro- 10.4 oz). Once plants get larger, products like Movento, Venom, Scorpion, Assail, Knack and Courier can provide effective control of nymphs. With the loss of endosulfan, growers have few options for effective adult control, but good knockdown can be achieved on lettuce and cole crops with combinations of bifenthrin (e.g. Brigade, Sniper, Discipline, etc) or Danitol tank-mixed with Orthene, Lannate, Lorsban, Venom, Scorpion, and Assail. For more information on whitefly biology, management and insecticide alternatives see Insect Management on Desert Vegetables and Melons: Whiteflies and Whitefly Management in Leafy Vegetables, Cole Crops and Melons

For those of us living in the desert, particularly working in agriculture, we commonly use rather affectionate terms to describe water.  Water is often referred to as the “life blood” of the desert and we know that “water is life” and it is the most critical limiting factor in any desert crop production system.  It is important for everyone in Arizona agriculture to be aware of our water supplies and the prospects for the future.  
 
As the population has grown in the desert Southwest, the demands on our water resources have increased substantially.  This has been exacerbated by two decades of drought and increasing average temperatures.  As a result, Arizona water supplies have become increasingly critical in terms of both short and long-term capacities. 
 
Continual reviews are being conducted by the Arizona Department of Water Resources (ADWR) and the Central Arizona Project (CAP) and other Arizona agriculture groups regarding Arizona water supplies, specifically from the Colorado River, which supports, at least in part, more than 80% of the Arizona population. The system-wide effort to stabilize the Lake Mead water supply with the 2019 Drought Contingency Plan (DCP) seems to be working as intended to help forestall drops in the reservoir’s levels.  However, it does not remove all risk of continually lowering water supplies in Lake Mead. 
 
The DCP for the lower basin of the Colorado River, below Lake Powell, is a set of shortage-sharing agreements among the Lower Basin States of Arizona, California, and Nevada.  The DCP augments the 2007 shortage-sharing agreements put in place by the states who are dependent on the Colorado River. 
 
On 16 August 2021, the Bureau of Reclamation declared that Lake Mead will be in a Tier One shortage level beginning 2022.  The elevation of the lake is and will continue to be below 1,075 feet above sea level.  As a result, Arizona will now be subject to significant cuts in water deliveries from the Colorado River based on Tier 1 reductions in water allocations, that are part of the DCP, and this will go into effect in January 2022 (Figure 1).  This will result in Arizona reducing Colorado River water use by 512,000 acre-feet (AF), or 18% of Arizona’s total allocation of 2.8 AF.  Tier 1 reductions primarily impact the CAP water allocations, which will be reduced by 30%.  Under Tier 1 reductions, agricultural CAP water allocations will be reduced by 65%, primarily affecting Pinal County agriculture.  Statewide municipal & industrial and tribal allocations will not be reduced under Tier 1 guidelines.  Yuma area water allocations will not be reduced under Tier 1.
 
We continue to monitor Lake Mead conditions and if lake levels drop to 1,050 and 1,045 ft., we will enter Tier 2 (a and b, respectively) conditions which will increase total reductions of Colorado River water to Arizona to 590,000 and then 640,000 AF, or 21 and then approximately 23% of Arizona’s total allocation.  The ADWR provides a good source of information and the prospects on these changing conditions.
 
Good management and stewardship of our water resources in the field is always important and we are particularly alert to that now.
 
For additional information please refer to the ADWR, CAP, BOR, and the University of Arizona Water Resource Research Center websites:
https://new.azwater.gov/
https://www.ibwc.gov/Files/CF_CR_LBDCP_073019.pdf
https://library.cap-az.com/documents/departments/planning/colorado-river-programs/CAP-FactSheet-DCP.pdf
https://www.cap-az.com/
https://wrrc.arizona.edu/

Figure 1. Colorado River water reductions in 2022 for CAP users after DCP
mitigation.  Reference: Arizona Department of Water Resources (ADWR) and the
Central Arizona Project (CAP).

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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. between bed centers.  All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned Jan 17, 2024  at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max Temp (°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 15,2024, February 23, 2024, March 4, 2024, and March 12, 2024and .Disease was first seen on February  26,2024. Disease rating was done on March 15, 2024.   Disease severity was determined  by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 0.5 = one to a few very small powdery mildew colonies on bottom leaves; 1 = powdery mildew present on bottom leaves of plant; 2 = powdery mildew present on bottom leaves and lower wrapper leaves; 3 = powdery mildew present on bottom leaves and all wrapper leaves; 4 = powdery mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = powdery mildew present on entire plant. These ratings were transformed to percentage of leaves infected values before being statistically analyzed. Yield loss due to rejected lettuce heads would likely begin to occur on plants with a powdery mildew rating above 2.0 (percentage of leaves infected value of 40).         
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides were Rhyme, Merivon, Quintec, Cevya, Luna Sensation, Luna Experience, and Elisys. 

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.

It is common to keep produce fields clean only to find a carpet of purslane when preparing ground for the next season. Some of this is from the seed bank that hadn’t yet germinated or been blow or carried into the field but a significant amount comes in the water. We recently worked with Brad Chavez from Greenline Equipment and Jim Nunes from Nunes Farms to test an irrigation water filter system designed GLE to filter the smallest weed seed. We have tried various techniques for filtering weed seed over the years and were surprised by how well this system worked. We injected alyssum seed into a sprinkler system on a 17 acre field in the Gila Valley. The field was divided into 2 acre plots and half of them were irrigated with filtered water and half were unfiltered. Alyssum seed supplied by Select Seed is 0.5 mm to 0.75 mm in diameter or the same size as purslane seed. We recovered 86% of the filtered seed that was injected through the system in the filters and were unable to find any alyssum plants in the filtered plots compared to 136 seeds/ sq. ft in the unfiltered plots. This system won’t clean up a field in one season but can eliminate a significant source of weed seed and significantly reduce weed problems when used over a period of years.
Please click on the following link for more information on the Weed Seed Filtration Systems.

This technology was developed by Greenline  Equipment and has a PATENT
PENDING  for G-PAWDS™️ PORTABLE AUTOMATED WATER DELIVERY SYSTEM.

Area wide Insect Trapping Network   VegIPM Update, Vol. 13, No. 13, Jun 29, 2022
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased in the past 2 weeks, but still higher than the previous 2 summers.
 
Beet armyworm:        
Trap counts remain active in some locations (Yuma Dome Valley and Tacna) but lower than last summer
 
Cabbage looper:         
Cabbage looper numbers remain low consistent with the lack of activity this fall compared to last season.
 
Diamondback moth:      
DBM counts very low and average for this time of the year.
 
Whitefly:                      
Adult movement continuing to increase, particularly in Gila and Yuma Valleys consistent with melon harvests.
 
Thrips:                           
Thrips adult decreasing in most locations, and trending comparable to this previous years.
 
Aphids:                        
Aphid movement is absent consistent with what we typically observe in the summer. 
 
Leafminers:                   
Adult activity has highest in Yuma Valley, and above average for late-June.