Numerous proposals and ideas have been presented as the delegations representing the Colorado River Basin states have been working on the development of the new Colorado River management guidelines that will go into place in 2026 when the 2007 interim guidelines expire.  
 
In the 20 September 2023 issue of this University of Arizona (UA) Vegetable Integrated Pest Management (IPM) Newsletter, I posted an article describing an analysis and set of proposals regarding future management of the Colorado River that was presented by Wheeler et al., 2022 in Science (Silvertooth, 2023 and Wheeler et al., 2022).
 
Wheeler et al. (2022) recognized that agriculture is responsible for more than 70% of the Colorado River water use and noted that the Lower Basin has been irrigating less than one-half of the area irrigated by the upper basin, but the agricultural revenues of the Lower Basin are more than three times that of the Upper Basin (USBR, 2015).
 
The lower basin states and Mexico have been fully utilizing their water allocations from the Colorado River in contrast to the upper basin which has not been using its full 7.5 MAF/year allocation.  For example, between 2000 and 2020 the upper basin consumptive use averaged 3.7 MAF/year plus at least 0.7 MAF/year of reservoir evaporation.  The upper basin states have plans for further development and utilization of their full allocation and they want to protect their Colorado River water allocation to support these development plans.  
 
Additional upper basin development and water use from the river exposes a much higher level of uncertainty on Colorado River water management for the future and there are concerns that it could violate the non-depletion obligation in the 1922 Compact which states the upper basin will not deplete the river’s flow to less than 75 MAF during any 10-year consecutive period.  This implies an assumption on the part of the 1922 Compact negotiators that a short-term drought could be managed within a 10-year period, but we are now dealing with drought extending over 23 years.  In addition, the 1944 Treaty requires all seven states to share in the obligation to Mexico.
 
The upper basin states have been adamant that the responsibility of balancing the shortages on the river rests fully with the lower basin states and Mexico.  The upper basin states have consistently emphasized the importance of equality between basins as outlined in the Compact but that has not actually happened in 100 years.  
 
Wheeler et al. (2022) presented a good argument supporting the position that the loss of an established agricultural industry in the Lower Basin is much more harmful than reducing plans for future development in the Upper Basin.  Thus, they proposed that further development and use of more Colorado River in the Upper Basin is objectively quite questionable.
 
Wheeler et al. (2022) ran a series of hydrological models, including the USBR Colorado River Simulation System (USBR CRSS, 2021) and developed a set of 100 scenarios.  They used this model since it is being used in the basin-wide negotiation process.  More details are provided in their article (Wheeler et al., 2022) and summarized in the article I put in this newsletter last September (Silvertooth, 2023).  
 
Many other articles have been published recently regarding how the Colorado River water is used (Dunphey, 2024; Frisvold and Duval, 2024; Richter et al. 2024; Richter, 2024; James, 2024; and Schmelzer, 2024).  Agriculture accounts for about three-quarters of human use of Colorado River water (Richter, et al. 2024).  This water is used to support approximately 15% of the farmland in the United States and it supports the production of 90% of the winter vegetables consumed in the United States and Canada from November to March every year.
 
I believe some of the best analyses on this topic have been done by Dr. George Frisvold and Dari Duval from the University of Arizona (UA) Department of Agricultural and Resource Economics (AREC).  George and Dari are part of the UA Cooperative Extension Economic Impact Analysis (EIA) Team.
 
The Frisvold and Duval report provides a strong analysis of the crops and water productivity for the Upper and Lower basins of the Colorado River.  They provide important contrasts between the upper and lower basins of the Colorado River in terms of water productivity measures associated with the crop production systems.  These measures include total crop sales per unit of water, crop sales minus crop-specific inputs per unit of water, and a blue water footprint (BWF).  
 
The BWF is defined as “the volume of surface and ground water consumed
(evaporated) as a result of the production of a good” (Mekonnen and Hoekstra, 2011).  Frisvold and Duval provided an excellent analysis on the agricultural use of the Colorado River water revealing a BWF of 1.2 acre-feet/$1,000.00 (U.S. dollars) in the Lower Basin and 7.6 acre-feet/$1,000.00 in the Upper Basin.  The counties with the highest consumption of water per acre have lower BWF values.  It is important to recognize the sixfold difference in the value of agricultural production per acre-foot of water used in crop production in the Lower Basin states versus the Upper Basin states.
 
Wheeler et al. (2022) found that the Lower Basin states of the Colorado River are more than three times as productive as the upper basin.  In contrast, Frisvold and Duval determined with a strong and appropriate economic analysis that the BWF in the Lower Basin is 6X greater than the upper basin.  
 
Frisvold and Duval have provided an important set of facts and analyses in their recent work.  In my view, they present a strong and fully legitimate line of consideration that is hopefully utilized in the negotiations and broader discussions in the western water arena for future management of the Colorado River.  These are important points in the storm of emotions that are emanating from many sources and those who do not recognize the value to the population that is being provided from the agricultural systems in the lower Colorado River basin.
 
References
Dunphey, K.  2024. The Colorado River is running dry.  Where is all the water going?  A new study explores water use in the Colorado River basin.  Utah News Dispatch.
https://utahnewsdispatch.com/2024/03/29/colorado-river-study-looks-at-how-water-is-used-in-utah/
Frisvold, G.B. and Duval, D.  2024. Agricultural Water Footprints and Productivity in the Colorado River Basin. Hydrology 2024, 11, 5.https://doi.org/10.3390/hydrology11010005
https://experts.arizona.edu/en/publications/agricultural-water-footprints-and-productivity-in-the-colorado-ri
 
James, I. 2024.  Hay grown for cattle consumes nearly half the water drawn from Colorado River.  Los Angeles Times, 28 March 2024. https://www.latimes.com/environment/story/2024-03-28/alfalfa-hay-beef-water-colorado-river
 
Mekonnen, M. and Hoekstra. 2011.  The green, blue and grey water footprint of crops and derived crop products. Hydrol. Earth Syst. Sci. 2011, 15, 1577–1600.
 
Richter, B.D., Lamsal, G., Marston, L. et al. 2024.  New water accounting reveals why the Colorado River no longer reaches the sea. Commun Earth Environ 5, 134 (2024). https://doi.org/10.1038/s43247-024-01291-0
Richter, B.D. 2024. Why Do We Grow So Much Alfalfa?  Sustainable Waters, 4 April 2024. https://www.sustainablewaters.org/why-do-we-grow-so-much-alfalfa/
Schmelzer, E.  2024.  Where does all the Colorado River water go? A huge amount goes to grow cattle feed, new analysis shows.  Denver Post, 7 April 2024.
 
Silvertooth, J.C.  2023.  Management Proposals for Colorado River Water.  University of Arizona Vegetable Integrated Pest Management Update.  AZ Veg IPM Update, Vol. 14, Num. 19.
 
USBR.  2015. “Moving Forward Effort: Phase 1 Report” (DOI, May 2015); https://www.usbr.gov/lc/region/programs/crbstudy/MovingForward
 
USBR, “DRAFT CRSS: Key modeling assumptions, June 2021 model” (DOI, 2021); http://bor.colorado.edu/Public_web/CRSTMWG/CRSS
 
Wheeler, K., Udall, B., Wang, J., Kuhn, E., Salehabadi, H., & Schmidt, J. 2022.  What will it take to stabilize the Colorado River? Science, 377 (6604): 373-375.

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.

Keeping up to date with the latest developments in automated weeding machines is challenging. It’s a very fast-moving space with significant private and public investment. At the 2024 Southwest Ag Summit “Ag Tech: Innovations in Weed Control Technologies” breakout session, university experts and cutting-edge innovators will provide updates on laser weeding, high precision smart spot sprayers, robotic/automated weeders and band steam (agenda below).The session will be held TOMMOROW Thursday, February 22^nd from 1:30-3:30 pm at Arizona Western College in Yuma, AZ.
As I mentioned in the last newsletter, there will also be a Field Demo where several of these technologies and other state-of-the-art automated weeders will be demonstrated operating in the field. The Field Demo is scheduled for TODAY, Wednesday, February 21^st. Breakfast will be served at 7:00 am and demonstrations begin at 8:00 am. The event will also be held at AWC.
We will also have our 3^rd generation prototype steam soil disinfestation machine on display at the event (Fig. 3). It is a self-propelled machine designed for commercial field scale operations. The device injects steam into the soil prior to planting to raise soil temperatures to levels sufficient to kill soilborne pathogens and weed seed (typically 140 °F > 20 minutes). We have had very good results with our previous prototypes and would like to demonstrate soil steaming to interested growers next season with the new machine. In addition to obtaining grower feedback on the viability of soil steaming, a second objective is to validate our small plot research results at the field scale level. If you are interested in the technique and would like a demo on your farm, please let me know. I would be happy to collaborate with you.
For more information about the Southwest Ag Summit, visit https://yumafreshveg.com/southwest-ag-summit/.

Fig. 1. Agenda for the “Ag Tech: Innovations in Weed Control Technologies”
educational session at the 2024 Southwest Ag Summit. The session will be held
Thursday, February 22nd at Arizona Western College, Yuma, AZ.


Fig. 2. 2024 Southwest Ag Summit Field Demo agenda. The event will
be held at Arizona Western College in Yuma, AZ.


Fig. 3. Self-propelled machine designed for injecting steam into the
soil prior to planting to raise soil temperatures to sufficient levels to
control soilborne pathogens and weed seed. Unit will be on display at
the 2024 Southwest Ag Summit, Yuma, AZ. (Photo credit: Peter de
Groot).

This is lettuce..what do you think?:

send your comments here: marcop@ag.arizona.edu

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EPA’s Herbicide Strategy & Proposed Mitigations on Agricultural Herbicide Use 

We Need Your Input! 

The Environmental Protection Agency (EPA) is seeking public comment on its Draft Herbicide Strategy Framework to protect threatened and endangered species. The Strategy outlines proposed mitigations on agricultural herbicide use that could have significant impacts on production of field crops and specialty crops in the lower 48 states.

The Arizona Pest Management Center will submit comments to EPA to communicate the challenges and potential impacts of the proposed Strategy on our agricultural industries, but we need your help.  

We need input from growers, applicators, pest control advisors, registrants and others on the feasibility of EPA’s proposed mitigations for Arizona production systems. If you are concerned about EPA’s proposed changes and willing to share your knowledge of what works in Southwest agriculture, your input could help make a difference. 

Please consider responding to our online survey by clicking the link below. The survey takes around 12 minutes and is completely anonymous. The data you provide will only be used in aggregate to communicate local farming practices and concerns related to herbicide mitigations to the EPA. Taking this survey is also a good way to learn more about EPA’s specific proposed changes. Please respond by October 19.

Survey Link: https://uarizona.co1.qualtrics.com/jfe/form/SV_1QUBcXiIVgjFDHE

Thank you!

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

Corn earworm: CEW moth counts down in all traps over the last month; about average for December.

Beet armyworm: Moth trap counts decreased in all areas in the last 2 weeks but appear to remain active in some areas, and average for this time of the year.

Cabbage looper: Moths increased in the past 2 weeks, and average for this time of the season.

Diamondback moth: Adults increased in several locations last, particularly in the Yuma Valley most traps.  Below average for December.

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

Thrips: Thrips adult movement continues to decline, overall activity below average for December.

Aphids: Winged aphids still actively moving but declined movement in the last 2 weeks. About average for December.

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