The famous lawman, Wyatt Earp was once quoted as saying “fast is fine, but accuracy is everything”. Of course, he was referring to his Buntline Special .45 caliber revolver with a 12 inch barrel that was presumably difficult to quickly draw from a holster. The same could be said about aphid management in desert produce crops. There are certainly “fast acting” insecticides available to control aphids, but “accuracy” in aphid identification is extremely important for cost-effective management. With the windy weather we’ve been experiencing lately, it’s no surprise that we’re seeing an increase in winged (alate) aphids showing up on desert produce crops. A quick glance at the recent Areawide Insect Trapping Network data shows that winged aphid counts found on sticky traps have increased dramatically in some locations in the Yuma and Gila Valleys. Not all of the aphids found on the traps could be identified but several were common species such as green peach and cabbage aphids. This is where the accuracy part comes in; just because you’re quick to find a few winged aphids on produce crops does not mean the these species are important to leafy vegetable and cole crops. As we discussed in a previous update most of the important aphid species you find on local produce crops do not over-summer here, but rather migrate into our cropping system during the late fall. Once the aphids reach our desert valleys, they typically move from crop to crop until they find a suitable host to feed and colonize on. It is not uncommon to find winged aphids on lettuce or broccoli that do not colonize on the crop. An example of these would be cabbage aphid alates which colonize on cole crops but not lettuce, spinach or celery. Other examples would include aphids that colonize small grains (i.e., corn leaf aphid) or alfalfa (i.e., pea aphid). Because these aphid species will not colonize produce crops, it is important to be able to distinguish them from the aphids that do colonize and require management to prevent problems at harvest (i.e., green peach aphid, foxglove aphid, lettuce aphid, cabbage aphid). Proper aphid ID can also influence your choice of insecticide, but more on that in the next update. Also, we have had reports of small colonies of cowpea aphids showing up on frame leaves in lettuce. Not to worry, experience has shown us that although small cowpea aphid colonies may be found on lettuce, the populations rarely increase in lettuce crops. So, proper aphid identification can save a PCA time and money, and prevent unnecessary insecticide applications. If you find an unusual aphid in your produce, don’t hesitate to drop it by the Ag Center and we’ll get it identified for you. But if you want to be fast and accurate you might use the attached publication Aphid Identification in Desert Produce Crops that may assist you in identifying winged and wingless (apterous) aphids important in leafy vegetables and cole crops.

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 JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation 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 on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any 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.

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. 1, Jan 12, 2022
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts remain low across all locations; average for this time of the season. 
 
Beet armyworm:         
Trap counts decreased in all locations, and well below average for mid- winter. 
 
Cabbage looper:           
Cabbage looper trap counts remained low in most locationssand below average for early January.
 
Diamondback moth:   
Adult activity steadily increasing during December. Above average for this time of year. Activity highest in Bard, Gila and Dome Valleys associated with nearby brassica seed crops. 
 
Whitefly:                      
Adult movement remained low in all locations consistent with previous seasons.
 
Thrips:                         
Thrips adult movement decreased in most locations last week, but increased sharply in Roll. Activity about average for mid-winter.
 
Aphids:                         
Aphid movement low in all locations. Trap captures average for this time of season. 

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