Some major events and developments have taken place in the past week in the Colorado river water shortage arena. As a result, we are entering into a series of substantial and complicated legal aspects associated with the Colorado River situation. Thus, a brief review of the current situation and some basic legal points of consideration can perhaps clarify some of the present challenges.
In November 2022 the Bureau of Reclamation (BoR) published a Notice of Intent (NOI) to analyze and prepare for the Supplemental Environmental Impact Statement (SEIS) regarding the “Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead” to deal with the continuing drought conditions. Since the NOI was published, representatives from the Colorado River Basin States have been meeting and working together to develop a joint Framework and Agreement Alternative and they set a target date of 1 February 2023 to submit a proposal to the BoR.
Unfortunately, the seven U.S. basin states have not been able to reach a consensus. However, six basin states, including Arizona, submitted a proposal to the BoR (1). California was not part of the six-basin state agreement and so they submitted an independent proposal for the BoR’s consideration, modeling, and analysis (2).
Now after the 1 February deadline has passed and an agreement could not be reached among all seven U.S. basin states, two sharply contrasting proposals exist.
The proposal submitted by Arizona, Colorado, New Mexico, Nevada, Utah, and Wyoming addresses a large part of the reductions of Colorado River water allocations that the BoR has targeted (2-4 million acre-feet/year, MAF/yr) by accounting for system losses that include evaporation and other losses between Lake Mead and the Imperial Dam (approximately 1.5 MAF/yr). The calculations provided in this proposal result in large reductions for California due to its large share of the river water. This proposal also addresses reductions in Colorado River allocations more rapidly than the California proposal.
The six-state plan describes collective reductions of 250,000 acre-feet (KAF) when the Lake Mead reservoir level drops to an elevation of 1,030 feet and below. The 250 KAF total would consist of 93 KAF from Arizona, 10 KAF from Nevada, and 147 KAF from California.
An additional collective reduction of 200 KAF would come from these lower basin states if Lake Mead’s elevation plunged to 1,020 feet and below.
For perspective, Lake Mead is currently at an elevation of 1,046.97 feet.
In contrast, the California proposal is heavily based on the “Law of the River” and the high-priority senior water rights of the Golden State
The current California position is consistent with earlier proposals that they have provided with an emphasis on “present perfected rights, PPRs”, their interpretation of the Law of the River, and their offer to conserve an additional 400 KAF/year through 2026. The California proposal also includes voluntary cuts of 560 KAF from Arizona and 40 KAF from Nevada. As I interpret the California proposal, I find the “voluntary” reductions from Arizona and Nevada as an interesting feature.
The California proposal also includes considerations of Lake Powell water levels and additional reductions if the elevations of that reservoir were to drop further.
What we have now is California operating alone with an argument based heavily on their interpretation of the Law of the River in contrast to the united front and a different approach to the problem presented by the six other U.S. basin states.
To understand the complexities of the current situation, some basic understanding of what the “Law of River” is, and the possible implications is important. In general, the “Law of the River” is a collection of laws, agreements, court decisions, and contracts. The Law of the River is a complex amalgam based on a series of federal laws specific to the Colorado River in combination with a series of United States Supreme Court decrees that serve to enjoin the Secretary of the Interior and the States of the Lower Division (Arizona, California, and Nevada) to a precise allocation of the water passing downriver from Hoover Dam (3, Glennon and Pearce, 2007).
Within the lower basin states there are three means by which water is allocated. First, is the allocation of water to the holder of a “present-perfected right, PPR”, consistent with a United States Supreme Court decree. The second method of water allocation is to the holder of a contract issued by the BoR under Section 5 of the Boulder Canyon Project Act of 1928. The third method of Colorado River water allocation is to the holder of a subcontract from a Section 5 contract holder (3, Glennon and Pearce, 2007).
The “present perfected rights PPRs” is an important aspect of the Law of the River. The PPRs are those rights to use Colorado River water that were acquired or “perfected” by prior appropriation under state law before the Boulder Canyon Project Act of 1928 was passed.
For further delineation of water rights on the Colorado River, the BoR has established a priority ranking of water rights to administer diversions from the river on a “first-intime-first-in-right” basis.
Priority 1 consists of present perfected rights established by the decree.
Priority 2 is for federal enclaves and reserved water rights established or effective before September 30, 1968.
Priority 3 is for Section 5 contracts issued before 30 September 1968.
Priority 4 is a complex priority, consisting of (a) Section 5 contracts issued after 30 September 1968 (in a total amount not to exceed 164,652 acre-feet of annual diversions) and (b) Contract No. 14-06-W-245 issued to the Central Arizona Water Conservation District.
Priority 5 is for water within Arizona’s 2.8 MAF allocation under the decree, but not currently being used by a right holder.
Priority 6 is for Arizona’s share of any surplus allocation released by the Secretary of the Interior pursuant to the power vested in the Secretary by Article II(B)(2) of the decree. (3, Glennon and Pearce, 2007)
Most of the present perfected rights and Section 5 contracts issued before 1968 were for agricultural purposes along the mainstem of the Colorado River. Many of the Priority 4 contracts were issued to irrigation districts that were specifically formed to divert water for agricultural use. Accordingly, agricultural diversions represent 70-80% of total diversions on the Colorado River basin.
A map and general delineation of the Yuma-area irrigation districts and priority categories is shown in Figure 1.
Figure 1. Map and delineation of the Yuma-area irrigation districts with priority
categories. Source: Yuma-area irrigation district coalition.
For the past several decades there has been increasing demand for Colorado River water for municipal and industrial (M&I) purposes, aka urban development. This has been accentuated by the rapidly growing populations of Arizona and other basin states and now compounded by the mega-drought that we have been experiencing for the 23 years.
The present situation on the Colorado River is both extremely complex and urgent. We are dealing with a real test of our system of governance, natural resource management, and our ability to deal with these challenges effectively.
While the basin states seem to be at an impasse, something and someone must give and there will be significant difficulties encountered as a result. This is a rapidly changing situation, and it will have a significant impact on agriculture in the lower Colorado River basin.
For the past several decades there has been increasing demand for Colorado River water for municipal and industrial (M&I) purposes, aka urban development. This has been accentuated by the rapidly growing populations of Arizona and other basin states and now compounded by the mega-drought that we have been experiencing for the 23 years.
The present situation on the Colorado River is both extremely complex and urgent. We are dealing with a real test of our system of governance, natural resource management, and our ability to deal with these challenges effectively.
While the basin states seem to be at an impasse, something and someone must give and there will be significant difficulties encountered as a result. This is a rapidly changing situation, and it will have a significant impact on agriculture in the lower Colorado River basin.
References
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.
Over the last couple of years, we identified and developed two high speed, precision spot sprayers to apply herbicides to weeds with minimal off-target spray while traveling at speeds that are viable for commercial vegetable farming operations (2 mph). The first is a spray assembly designed for controlling in-row weeds that are close to crop plants (1-cm spot spray resolution). The second is a high precision (sub-centimeter spot spray resolution) sprayer designed for spot spraying cotyledon stage weeds in spinach and leaf lettuce crops. We tested the device in the laboratory and found that weed control efficacy was greater than 95% (3 species), percentage of off-target spray was less than 3% and no crop injury was observed. The work was presented at the 2021 California Weed Science Society Annual Meeting. Click here or on the image below ) to view the presentation and see video of the devices in action.
We are now working towards developing a high precision, automated/robotic weeding machine for vegetable crops. This fall, Evan McGinnis, Biosystems Engineering Ph.D. candidate, initiated work to develop AI-based imaging software for detecting and targeting weeds. Once developed, the software will be integrated with the precision spot sprayer and tested in the field. Stay tuned for updates!
Acknowledgements
This work is supported by the Arizona Specialty Crop Block Grant Program and the USDA NIFA Specialty Crops Research Initiative USDA-NIFA-SCRI-004530. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
Fig. 1. Images from “Centimeter Scale Resolution Sprayer for Precision In-Row Weed Control” presentation given at the 2021 California Weed Science Society Annual Meeting. Click here or on image to view the presentation.
Prefar (bensulide) is an organophosphate herbicide that has been used for more than 50 years in Arizona for lettuce production. In fact, it is one of the standard herbicides used for this purpose.
The University of Arizona Vegetable IPM Team conducted a Yuma County and Imperial Valley Survey evaluating a portion of the acres checked by Pest Control Advisors. The 2017 data indicated that in 58% of the lettuce acreage reported was treated with Prefar. Similarly, in the 2018 survey 52% received a Prefar application.
This product performs well when incorporated with sprinkler irrigation at stand establishment. It also works best in course textured soil’s such as the ones found in Coachella Valley, California. One of the weeds controlled by Prefar is pigweed (Amaranthus palmeri), which was found to be resistant to glyphosate herbicide in Arizona by Dr. William B. McCloskey in 2012. Other weeds are purslane (Portulaca oleracea), goosefoot (Chenopodium murale), Lambquarter (Chenopodium album), and some species of grasses.
The list of crops in which bensulide is used demonstrates the importance of this weed control tool for the agricultural industry.
According to the 1080 Pesticide Use Reporting Database provided by the Arizona Pest Management Center the list of crops includes: Arugula, Bok choy, Broccoli, Brussel Sprouts, Cabbage, Cantaloupe, Cauliflower, Celery, Cilantro, Corn, Cress, Endive, Fennel, Mustard, Kale, Lettuce, Onion, Parsley, Squash, Swiss chard, and others.
Please read the following contribution from Dr. Al Fournier on the EPA Notice- Petition to Revoke Organophosphate Tolerances: (including Bensulide).
Al Fournier, IPM Program Manager, Arizona Pest Management Center
10 August 2022
The EPA has extended its deadline for public comment on a Petition to Revoke Tolerances and Cancel Registrations for Certain Organophosphate Uses until September 25, 2022.
The petitioners, including United Farm Workers, Earthjustice, and several other groups, request that the Agency revoke all tolerances and cancel all associated registrations for food uses of 15 listed OPs, and further requests that the Agency complete its registration review process for these chemicals no later than October 1, 2022. The pesticides are currently at various stages of review, and the proposed deadline does not align with EPA’s published schedule to complete scientific reviews.
Among 15 Organophosphates named in the petition are 10 with reported uses in Arizona (bolded below). Those with known uses in lettuce and other produce include Bensulide (Prefar) and Acephate (Orthene).
Acephate, Bensulide, Chlorethoxyfos, Chlorpyrifos-methyl, Diazinon, Dichlorvos, Dicrotophos, Dimethoate, Ethoprop, Malathion, Naled, Phorate, Phosmet, Terbufos, Tribufos
Read the full EPA Notice here: https://www.regulations.gov/document/EPA-HQ-OPP-2022-0490-0001
To submit comments to the docket, use the following link: https://www.regulations.gov/commenton/EPA-HQ-OPP-2022-0490-0001
To contribute to Arizona Pest Management Center comments, contact Al Fournier
