The situation on the Colorado River has not changed appreciably since last summer when the Bureau of Reclamation (BOR) made a bold announcement on 14 June 2022 with BoR Commissioner Camille C. Touton describing the need to make substantial reductions of 2 to 4 million acre-feet (MAF). As Commission Touton described, the BOR has the authority to “act unilaterally to protect the system, and we will protect the system.” (Bureau of Reclamation, 28 June 2022). She stated that the BOR was allowing the basin states 60 days to come up with a plan. In the absence of a plan from the basin states, the BOR would be ready to take action.
Since June, the BOR has been engaging in discussions with the seven U.S. basin states that depend on the Colorado River to develop a plan for the reductions, and the anticipated decisions from the BOR have not materialized.
The basic arithmetic on the Colorado River is as follows:
16.5 MAF is currently the allocated amount of water budgeted with 7.5 MAF allocated to both the upper and lower basins, plus 1.5 MAF allocated to Mexico:
(7.5+7.5 MAF = 15 MAF U.S. + 1.5 MAF Mexico = 16.5 MAF total)
In the past two decades, the average annual flow of the Colorado River from 2000 - 2018 has been approximately 12.4 MAF, which is 16 % lower than the 1906-2017 average of 14.8 MAF/year. Thus, we can see where the 4 MAF differential is determined.
A reduction of Colorado River water allocations from 16.5 MAF to 12 MAF represents a 27% reduction. That is in line with the climate and hydrological reality we are dealing with. That would be a huge reduction for the Colorado River basin and a painful experience for many entities in the desert Southwest.
On 16 August 2022, after the 60 days provided by Commissioner Touton had expired, U.S. Department of the Interior Deputy (DOI) Secretary Tommy Beaudreau with Assistant Secretary for Water and Science Tanya Trujillo announced that the 2023 Colorado River Operational Plan would move to Tier 2a reductions associated with the Drought Contingency Plan (DCP), which was ratified by the lower basin states in 2019 (Figure 1).
Figure 1. Reductions in Colorado River allocations according to the 2007 Interim Guidelines, Minute 323, Lower Basin Drought Contingency Plan, and Binational Water Scarcity Contingency Plan. Total volumes in thousand acre-feet (KAF) units. Source: U.S Bureau of Reclamation.
The Tier 2a changes will require an additional 80 thousand acre-feet (KAF) being reduced from Arizona’s 2.8 MAF allocation of Colorado River water (Figure 1). This will result in a 592 KAF total reduction from Arizona’s allocation, which includes the 512 KAF reduction for Arizona from Tier 1, that was first imposed in January 2022 (512 + 80KAF from Arizona = 592KAF, which is a 21% reduction in Arizona’s Colorado River allocation. In addition, Tier 2a reductions include 25 KAF from Nevada, an 8% annual allotment reduction and 104 KAF, or 7% of Mexico’s annual allotment.
The Tier 1 and Tier 2a reductions have wiped out the CAP allocations to the agricultural irrigation districts in central Arizona. No water savings will be required for California in 2023 under these operating conditions. If or when Tier 2b reductions are put in place California will take a 200 KAF reduction (Figure 1).
The developments and actions from the BOR and DOI since June have been basically “business as usual” since the DCP was already in place and the water levels in Lake Mead would warrant Tier2a or even Tier 2b reductions without any further actions on the part of the BOR or DOI.
In the 60 days following the June BOR announcement, the major agricultural districts on the lower Colorado River, including Arizona and California irrigation districts on the mainstem of the river, came together to form a coalition and develop a draft plan in response. They presented a proposal to reduce nearly 1.0 MAF of irrigation water by agreeing to cut 1.0 AF/acre throughout the districts. They were also seeking financial compensation of $1,500/acre, resulting in a total cost of nearly $1.4B to help farmers in these districts make changes and investments to achieve greater efficiencies with water allocated from the Colorado River.
This effort on the part of the lower Colorado River irrigation districts to develop this proposal in 60 days was substantial and remarkable in many ways. Also, the state of Arizona has demonstrated a willingness to step up and contribute to the conservation needs of the Colorado River system by retaining more than 800 KAF behind Lake Mead in 2022. In addition to the 512 KAF reduction required of Arizona from DCP Tier 1 reductions (Figure 1), the state of Arizona voluntarily contributed more than 300 KAF to leave in the river system. That too was remarkable and quite impressive.
No other basin states have offered anything of substance other than suggestions that some other entity take the cuts in water allocations. Thus, the collective efforts among basin states that Commissioner Touton was calling for in June have not materialized.
California has recently offered to leave 400 KAF in Lake Mead with the caveat that the state receives financial support for Salton Sea remediation. However, to the best of my knowledge, California has not described what they would do for Salton Sea remediation.
The Gila River Indian Community (GRIC) has recently offered to 250 KAF of water under their control for the Colorado River system, with 125 KAF from their direct Colorado River allocation plus another 125 KAF of water they have stored in underground aquifers that they are willing to sell as part of deal offered.
On 28 October 2022, the DOI announced that the BOR will analyze the existing guidelines for operating the Hoover and Glen Canyon Dams for Lakes Mead and Powell, respectively. This most recent announcement has generated a great deal of speculation with some observers suggesting that the DOI/BOR are ready to act soon. Others are thinking that perhaps this will translate to another year of review and analysis on the part of the DOI and BOR.
So, there are still a lot of questions and uncertainty coming from the federal entities with the Colorado River situation.
Meanwhile, Mother Nature and the basic hydrology of the Colorado River basin is not changing or waiting for the feds or some great basin-wide coalition to come up with a plan. We are still using water at a rate that is much greater than is being provided from precipitation in the watershed.
What we have at stake is the Colorado River system as a water source that supports 40 M people in the Southwest, approximately 6.0 M acres of cropland, and 30 native American tribes among seven U.S. states and two states in Mexico. If water levels fall too low in Lakes Powell and Mead, not only is there a lack of hydropower that can be generated but also large volumes of water cannot be moved to areas that need it, including agricultural districts.
This is a serious condition for desert agriculture in this region since more than 70% of the Colorado River's water is used for irrigation. This water is used to irrigate 15% of the nation's farmland and produce 90% of the winter leafy green vegetables. We have a lot at stake locally, regionally, and nationally.
Additional references:
Allhands, Joanna. Arizona Republic, 2 November 2022: https://www.azcentral.com/story/opinion/op-ed/joannaallhands/2022/11/02/federal-action-save-lake-mead-powell-colorado-river-too-late/8242368001/
Bureau of Reclamation, 28 June 2022 https://www.usbr.gov/ColoradoRiverBasin/
Charles, Dan. National Public Radio, 4 October 2022.
https://laist.com/news/climate-environment/meet-the-california-farmers-awash-in-colorado-river-water-even-in-a-drought
Sanchez, Camryn. Arizona Capitol Times, 3 November 2022: https://azcapitoltimes.com/news/2022/11/03/arizona-lawmakers-push-california-to-cut-water-usage/
It’s unfortunately a very great season to be a plant pathologist…
We have confirmed the first sample of Fusarium wilt on lettuce submitted to the Yuma Plant Health Clinic from Yuma County. The stunted seedlings looked like any other typical case of damping-off at the seedling stage. When plated on culture media, subsequently confirmed Fusarium colonies grew abundantly from the declining plant tissues. If you’re not already on guard and scouting, this is a warning that Fusarium is active in Yuma County.
Adding on to this early alert, we’ve received a surge of submissions of young brassicas to the clinic. Several severely wilted and declining plants from around Yuma County have cultured positive for Pythium, likely as an opportunistic invader coming in on the back of all the early-season rain that brought stress to seeds and young transplants. Growers may want to consider oomycides, but only if the seedling disease is first confirmed to be Pythium. Remember, many seedling diseases caused by true fungi are indistinguishable from those caused by Pythium.
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
Cooperative Extension – Yuma County
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109
At the UC Cooperative Extension Automated Technology Field Day in Salinas, CA a couple of weeks ago, several automated technologies were showcased operating in the field for the first time to a general audience. One of the “new” machines designed specifically for in-row weeding in vegetable crops is highlighted here. I’ll discuss other technologies in future articles.
The first is an autonomous robot that uses lasers to kill weeds (Fig. 1a). The machine, developed by Carbon Robotics1, identifies weeds from camera captured images of the bedtop using artificial intelligence techniques. The device is equipped with eight CO2 lasers that emit laser beams roughly 0.25” in diameter in short, < 50 millisecond bursts. As such, it is best suited for controlling small weeds (< 3-4 leaf stage) in high density crops such as baby leaf spinach, spring mix, carrots, and onion. The machine worked well in the demonstration plot, annihilating small weeds, turning plant material into black charcoal (carbon!) and grey ash, and causing significant damage to and potentially killing larger weeds (Fig. 1b).
The percentage of weeds targeted and travel speed (significantly less than 1 mph) of the 80” wide (1 wide bed) machine was comparable to that shown in videos on the company’s website (https://carbonrobotics.com/). The version the company is marketing, however, is a 20’ wide (3 wide beds) tractor pulled implement, and according to sales representatives, has upgrades that increase travel speed. This combination should provide adequate machine productivity (acres/hour).
Company reps reported that the first production units are being delivered to commercial farms presently. Some will be operating in the Yuma area this fall. If interested, I would be more than happy to work with you to help conduct and design experiments for assessing the machine’s performance – % weed control by species, % of weeds targeted, hand weeding labor savings, machine work rate (acres/hour), etc. Please feel free to contact me anytime at siemens@cals.arizona.edu.
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[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.
Fig. 1. Autonomous laser weeding machine developed by Carbon Robotics1 a) demonstration at UCCE Automated Technologies Field Day and b) image of bedtop weed control post treatment.
As
we are all aware the most commonly used herbicides in lettuce production are
Kerb (Pronamide), Balan (Benefin), and Prefar (Bensulide). Our weed complex for
lettuce grown in the low desert includes summer annual weeds grasses and
broadleaves early in the season as well as winter annuals, which are a problem
during the cooler months. Most of these are controlled with preemergent
herbicides although escapes are common and must be controlled postemergence.
Occasionally when herbicides and cultural practices are not sufficient
expensive hand weeding is required for commercially acceptable weed control. To
illustrate numbers from our 2016 Crop losses report showed that 91% of the
lettuce surveyed required some hand hoeing even when 82% of the acres was
treated with Pronamide. Also Bensulide and Benefin were applied at lower
percent.
Therefore, evaluation of new effective herbicides is always welcomed. We
conducted a couple of projects at the Yuma Agricultural Center to look at weed
management in transplanted lettuce to determine Pre and Post-Transplant weed
control as well as crop safety of other active ingredients such as
S-metholachlor (Dual Magnum), Pendimethalin (Prowl), DCPA (Dacthal) and compare
them with Pronamide (Kerb) and other products.
Transplanting lettuce and the use of planting tape has opened the possibility
of using herbicides that injure direct seeded lettuce but may be safer to
plants with a developed root system. Additionally, they could show more
efficacy in controlling some weeds present in our area.
We are still collecting results from these trials and will publish them
soon in this Newsletter as well as in the upcoming Lettuce Crop Losses Workshop.
Prowl Applied Pre-transplant
This time of year, John would often highlight Lepidopteran pests in the field and remind us of the importance of rotating insecticide modes of action. With worm pressure present in local crops, it’s a good time to revisit resistance management practices and ensure we’re protecting the effectiveness of these tools for seasons to come. For detailed guidelines, see Insecticide Resistance Management for Beet Armyworm, Cabbage Looper, and Diamondback Moth in Desert Produce Crops .
VegIPM Update Vol. 16, Num. 20
Oct. 1, 2025
Results of pheromone and sticky trap catches below!!
Corn earworm: CEW moth counts declined across all traps from last collection; average for this time of year.
Beet armyworm: BAW moth increased over the last two weeks; below average for this early produce season.
Cabbage looper: Cabbage looper counts increased in the last two collections; below average for mid-late September.
Diamondback moth: a few DBM moths were caught in the traps; consistent with previous years.
Whitefly: Adult movement decreased in most locations over the last two weeks, about average for this time of year.
Thrips: Thrips adult activity increased over the last two collections, typical for late September.
Aphids: Aphid movement absent so far; anticipate activity to pick up when winds begin blowing from N-NW.
Leafminers: Adult activity increased over the last two weeks, about average for this time of year.
