The Colorado River watershed and water distribution system (Figure 1) is one of the largest in the U.S. The main channel of the Colorado River extends over 1,450 miles, covers 244,000 square miles in the drainage basin, and has the greatest elevation fall of any watershed in North America. The Colorado River supports more than 40M people, nearly 6M acres of cropland, 30 native American tribes, and provides large amounts of electrical power generation for the southwestern U.S.
Figure 1. The Colorado River watershed. Source: USGS.
The average annual flow in the Colorado River between 1906-2017 was 14.8 million acre-feet (MAF), Figure 2. The allocated water for diversion on the Colorado River has been 16.5 MAF (15 MAF in the U.S. + 1.5 MAF to Mexico). Thus, there has been a structural deficit of at least 2.0 MAF for many years. Between 2000 and 2018, the average annual flow has been ~ 12.4 MAF, which has further compounded the problem creating an overall deficit of ~ 4.0 MAF.
Figure 2. Colorado River Annual Flow, 1905-2010 with an overall average and
10-year average. Source: Bureau of Reclamation.
The foundation to the governance of the Colorado River is commonly referenced to the “Law of the River”, which is based on the Colorado River Compact of 1922 (CRC of 1922) and a collection of laws, contracts, agreements, definitions, and precedents from previous legal cases. Thus, the Law of the River is not one distinct entity but rather an amalgam of various components. A key foundational component is the CRC of 1922 which was formally negotiated among the basin states to define how much water from the Colorado River can be used by each state on an annual basis. Other agreements contribute to the aggregate Law of the River, including a 1944 Treaty, that agreed to send Colorado River water allocations to Mexico.
The CRC of 1922 was developed following a period of relatively high annual flows. Based on the records associated with the transactions leading to the signing of the CRC of 1922, the hydrologists and other scientists were providing data and interpretations to the commission that significantly influenced the CRC of 1922.
The CRC of 1922 established the operational base of Colorado River water allocation providing 15 MAF allocated among the seven basin states. Even though annual flow in the river has been less than that in most years, river managers have been able to make it work for 100 years. However, due to the annual average flow of the past 20 years being ~ 12.4 MAF, the allocation of Colorado River water based on the original CRC of 1922 has not been sustainable (Figure 2).
The Colorado River Basin is managed in a complex and multi-level legal structure that involves many stakeholders. The Colorado River watershed is divided into the Upper and Lower Basins. The Upper Basin includes the states of Wyoming, Colorado, Utah and New Mexico. The Lower Basin includes Arizona, California and Nevada. A binational treaty governs the releases to Mexico from both the Upper Basin and Lower Basin (1944 Water Treaty and Minute 319).
Due to the impacts of the recent drought, the basin states negotiated interim guidelines to deal with Colorado River water shortages and determined the reductions for each state depending on the elevation of water in Lake Mead in 2007. The reductions associated with a shortage of Colorado River water were further augmented in 2019 by the Drought Contingency Plan (DCP) among the basin states, with specific guidelines for both the upper and lower-basin states.
Within the overall structure of the Law of the River, the basin states and the Boulder Canyon Project Act water contractors must work collectively to address their water supply issues. In the Lower Basin, water supplies are administered by a federal water master, designated as the Secretary of the Interior working through the Bureau of Reclamation. In the Upper Basin, the Upper Colorado River Commission administers compliance with the 1922 Colorado River Compact. In addition, every basin also has its own unique set of laws governing the water rights that apply within those states.
The 2007 Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for both Lake Powell and Lake Mead are set to expire in 2026. The seven Colorado River Basin states and stakeholders must work together to develop the new criteria that will replace those guidelines. At present, there is a gridlock in those negotiations between the Upper and Lower Basin states and it must be resolved in 2025 to replace those guidelines expiring in 2026.
References
Jay-Russell, M.T. (2013). What is the risk from wild animalsin food-borne pathogen contamination of plants?. CABI Reviews 4(8),1-16.https://doi: 10.1079/PAVSNNR20138040
Fig. 1. Bird fecal matter on romaine lettuce.
Fig. 2. Gull flying over romaine lettuce being harvested.
Fig. 3. Gulls flying over irrigation canal near lettuce field
being harvested.
Fig. 4. Bird fecal matter on lettuce harvesting equipment.
Today, the EPA posted in the Federal Register an Emergency Order suspending the Registrations of All Pesticide Products Containing Dimethyl Tetrachloroterephthalate (DCPA). We will include the link to the official document at the end of the article.
The notice says in the II. Emergency Order paragraph the following:
“Effective immediately, no person in any state may distribute, sell, offer for sale, hold for sale, ship, deliver for shipment, or receive and (having so received) deliver or offer to deliver to any person any pesticide product containing DCPA. Additionally, in accordance with FIFRA section 6(a)(1), EPA has elected not to permit the continued use of existing stocks, consistent with its policies applicable to cancellations where the Agency has identified significant risk concerns. See 56 FR 29362, 29367, June 26, 1991 (FRL-3845-4)”.
Also, the same paragraph in the document states clearly: “Accordingly, this Emergency Order expressly prohibits any person from using any pesticide product containing DCPA for any purpose. However, EPA will allow continued distribution of existing stocks of DCPA for the express purpose of returning any DCPA product to the registrant of such products”.
You can find and download the document posted in the journal today following this link:
https://live-azs-vegetableipmupdates.pantheonsite.io/sites/default/files/2024-08/240807_EPA_DCPA_ORDER_2024-17431.pdf
References:
Included below is a list of organic insecticides that you can consider for your organic IPM programs. Although there are few alternative organic insecticide options, it is important to rotate when possible. Like conventional insecticides, continuous exposure to the same biopesticides may pose some risk of further reducing their efficacy and leading to the development of resistance.
A good organic insecticide rotation practice is to alternate selective organic insecticides with broad-spectrum organic insecticides. The use of selective organic insecticides favors the increase of beneficial arthropod populations which may help to keep the pest population in check and delay repeated application of insecticides. When the population of lepidopteran pests is low, spraying Bt-based insecticides first and pyrethrin or Spinosad-based products thereafter is a good strategy. Proper insecticide rotation is important because it can help reduce insecticide application frequency, resulting in reduced crop production costs.
Tank-mixing can help improve the efficacy of some organic insecticides against some target pests. Tank-mixing a Bt insecticide with pyrethrin, such as Xentari + Pyganic or Dipel + Pyganic, can be an effective combination for controlling lepidopteran larvae. Additionally, combining Pyganic and a neem-based insecticide like Aza-Direct can be a favorable combination for small lepidopteran larvae. Tank-mixing Entrust (spinosad) and M-Pede can help suppress flea beetles and bagrada bugs.
Organic lettuce is a high-demand crop for organic nitrogen sources. Lettuce requires a substantial amount of nitrogen to support its growth, particularly during the heading stage when most nitrogen uptake occurs. This demand is driven by its rapid growth rate and the production of large leaf biomass. The organic iceberg lettuce production system is gaining importance both locally and nationally due to the growing demand for healthy, hygienic, and safe food, along with the need for long-term sustainability (McGrady et al, 1991; Koide & Bache, 2021).
In arid regions like Yuma, AZ, where annual precipitation is often less than 3 inches, long periods of drought and frequent heat waves create challenging conditions for soil health. Limited rainfall restricts natural moisture replenishment, leading to soil dehydration and reduced microbial activity. Prolonged drought intensifies soil compaction and salinity buildup, while extreme heat accelerates organic matter decomposition, further depleting essential nutrients. These factors collectively hinder soil fertility, making it more difficult to sustain productive organic lettuce farming without strategic soil health management practices.
Therefore, many questions arise about whether combining fertilizers with biostimulants may improve soil health, particularly soil water retention while also enhancing crop growth, development, and yield. Several studies indicate that the combination of biostimulants with organic fertilizers has a positive effect on soil structure and mitigates stress and crop yield (Rodgers et al., 2020 Li et al., 2021; Zhang et al., 2021). They enhance soil physical properties and boost crop productivity in multiple ways. The potential of biostimulant to align with sustainability policies offers promising prospects for the future of agriculture. Given the environmental challenges associated with current fertilization practices, there is a pressing need to prioritize research that optimizes plant-microbe interactions to establish more sustainable agricultural systems. Biostimulants can positively influence a plant’s response to stress and adverse environmental conditions, promoting growth by enhancing germination, root development, and the plant's ability to access water and minerals.
Thus, investigating the magnitude of the potential impacts of coupled organic fertilizer and biostimulant on soil properties (i.e., soil water retention), lettuce crop growth development and yield for local or regional conditions can result in more effective, relevant, and practical information that can aid users in making management decisions. To address the identified knowledge gaps, preliminary field experiments were conducted during the Fall 2024 growing season at the Valley Research Center, University of Arizona Yuma Agricultural Center. These experiments aimed to establish foundational data to support this proposal.
The field (Figure 1) was planted on October 29th, 2024, and the pre-sprinkler irrigation strategy was utilized to ensure germination which was noticed on November 06, 2024. On December 5, when the lettuce was about 1 inch tall, the first application of 2 quarts/acre biostimulant (FBS Organics® Zicron®) was applied via the subsurface irrigation system. A second application of 1 gallon/acre was applied on January 9, 2025.
To quantify changes in soil water retention, three types of high-tech sensors (Figure 2) were installed after crop emergence to continuously monitor soil moisture levels, along with other key parameters. Additionally, plant height (Figure 3) measurements have been taken to assess the impact of biostimulants combined with organic fertilizers on crop growth and development. Finally, yield differences will be evaluated after harvest to determine the overall effectiveness of these treatments (Figure 4). Stay tuned for the results and conclusions after harvesting.
Figure 1. Satellite image view of the organic research field in the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
Figure 2. Nitrate-N sensor and soil moisture sensor from AquaSpy and soil
moisture and salinity sensors from Sentek were installed between two healthy
plants in the organic lettuce production field at the Valley Research Center at the
University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
Figure 3. Plant height measurements in the field at the Valley Research Center at
the University of Arizona, Yuma Agricultural Center, Yuma, Arizona
Figure 4. Lettuce few weeks before harvesting in the field at the Valley Research
Center at the University of Arizona, Yuma Agricultural Center, Yuma, Arizona.
