May 18, 2022Weeds and Insect Management in Desert ProduceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
The fact that we live in a harsh desert environment is being impressed upon us rather vigorously after more than two decades of severe drought. Climatologists have marked the current drought as a megadrought and the worst experienced in the desert Southwest in more than 1,200 years. We are living in unprecedented times in terms of water shortages on the Colorado River watershed and system (Figure 1) along with increasing demand for water from this river over the past several decades which is depleting the two giant reservoirs, Lakes Mead and Powell. These conditions have resulted in the 2021 declaration by the U.S. Department of the Interior (DoI) and Bureau of Reclamation (BoR) for reductions in allocations from the Colorado River with Tier 1 restrictions associated with the Drought Contingency Plan (DCP, Table 1).
Figure 1. The Colorado River watershed that includes seven western U.S. states and 2
Mexican states, supports >40M people, >5.5M acres of farmland, and 22 Native American
tribes. Source: USGS.
Table 1. Drought Contingency Plan reductions in Arizona’s allocation from the Colorado River.
FAS = feet above sea level; KAF = thousand acre-feet; MAF = million acre-feet
According to the DCP, Tier 1 requires a 512,000 acre-foot (AF) reduction in Arizona’s 2.8MAF annual allocation. This reduction is primarily being taken from the agricultural irrigation districts associated with the Central Arizona Project (CAP), heavily impacting agricultural areas in Pinal County. It is important to note that urban/metropolitan and tribal water allocations are not reduced in Tier 1 conditions (Figures 1 and 2). In response to the drought and the declining water supply in the Colorado River system, additional mitigation actions are being taken beyond the DCP reductions to further support the level of water in these storage reservoirs which have been steadily declining since 2000.
Figure 2. General outline of reductions in water allocations by general source associated
with the Drought Contingency Plan.
The situation on the Colorado River system and the responses have been changing rapidly. On 3 May 2022 we learned that the BoR is holding back 480KAF from Lake Powell from the originally planned 7.48MAF release in fiscal year 2022. Also, the BoR is also releasing an additional 500KAF from the Flaming Gorge reservoir on the Wyoming – Utah border. Both steps are being taken to protect the hydroelectric power generation capacity of the Glen Canyon Dam (Lake Powell). If the lake falls to 3,490 ft. above sea level (FAS) at Glen Canyon Dam there would not be enough water to operate the generators in Glen Canyon Dam that provides power to the western electrical grid and serves as a primary source of electrical power to Wyoming, Utah, Colorado, New Mexico, Arizona, Nevada, and Nebraska. This is due to the placement of the penstocks that were built into the dam that provide water to the electrical generation turbines. If the water level were to drop below the 3,490 FAS level it could cause cavitation and severe damage to the electrical turbines and the dam structure. The nearly 1MAF of extra water being held in Lake Powell behind the Glen Canyon Dam is intended to protect the electrical power generation and integrity of the dam.
So, this translates to nearly 480KAF less water moving through the Grand Canyon and into Lake Mead in FY22 and it puts the lower basin (the region below Lake Powell, Figure 1) one step closer to Tier 2 reductions.
The BoR periodically runs a series of model projections regarding the water levels at the dams for both Lakes Mead and Powell. Results from these models recently projected future water levels at the dams for the end of calendar year (CY) 2022 and 2023. For Lake Mead the end of CY 2022 projections include a most probable level of 1,049.37 FAS and the lowest probable level at 1,047.10 FAS. These results project the need for a Tier 2a level declaration by the end of CY 2022.
For the end of 2023, Lake Mead projections include a most probable level 1,035.63 FAS, which would trigger Tier 2b reductions in Colorado River water allocations to Arizona and a most probable minimum level of 1,020.63 FAS, which would necessitate Tier 3 reductions.
Due to the recent changes in river management plans that have been announced by the BoR associated with Lake Powell, these model projections for the end of CY 2022 and 2023 are probably high and probably project an overly optimistic condition. But we can see that the probability of moving into the Tier 2a, 2b, and Tier 3 reductions are very likely to occur by the end of 2023, if not sooner.
The warnings of John Wesley Powell, the famous one-armed Civil War Veteran who first directed an expedition down the Colorado River and the Grand Canyon in 1869, are certainly very prescient in the face of the circumstances we are dealing with today. In an address to the Montana Congressional Convention in 1889 he offered the following statement: “All the great values of this territory have ultimately to be measured to you in acre feet”. That is incredibly prophetic and certainly true in the reality of conditions that we are dealing with on the Colorado River today.
Essentially what we have today on the Colorado River is a supply and demand problem. Very simply, our demand and extractions from the Colorado River have been greater than the supply and what the river can provide. As a result, the great reservoirs on the river system, the savings accounts so to speak, have been depleted. We must come to grips with that reality and decide how the allocations of Colorado River water must be adjusted to bring them into an appropriate balance with the water we do have in the river.
The overall situation with the Colorado River offers some good news and some bad news for all of us depending on this water to live, work, and survive in this desert. The average annual flow of the Colorado River between 2000 and 2018 has been approximately 12.4MAF, which is 16 % lower than the 1906-2017 average of 14.8MAF/year. So, the good news is with the recognition that we have ~ 12MAF average annual flow in the Colorado River under these megadrought conditions. The bad news is that the Colorado River system is budgeted for 16.5MAF of allocated water between the U.S. and Mexico. Thus, there is a functional difference of >4MAF and the fact is that we must reconcile that difference and fast action is needed, much faster than our water governance systems normally operate.
Arizona agricultural is responsible for ~ 70% of the water diversions on the Colorado River and agriculture is taking the reductions now with Tier 1 and will carry much of the responsibility for the Tier 2 reductions. How agriculture fares in this process of Colorado River management in response to the water shortages is critical for the future of Arizona agriculture and the overall complexion of life in the desert Southwest.
I believe agriculture will prevail, but a lot of hard work, difficult decisions, and changes are ahead of us in the near future. Agriculture has some strong and effective groups working in this decision-making arena for water governance on the Colorado River and we need to be sure that practical agricultural considerations are being made in the process with both short and long-term implications.
This season we have already found few lettuce infected with bacterial soft rot. Though it rarely takes down the whole field, the symptom are not so pleasant. Bacterial soft rot in lettuce can occur in the field as well as post harvest.
It is caused by several types of bacteria, but primarily subspecies and pathovars of Erwinia caro-tovora and E. chrysanthemi. Other bacterial species that cause soft rot include Pseudomonas cichorii, P. marginalis, and P. viridiflava. They have a wide host range host range and includes genera from nearly all plant families
In lettuce fields, the symptoms are observed close to the harvest time. The tissue, mostly around inside the head of head lettuce softens and becomes mushy or watery. Slimy masses of bacteria and cellular debris frequently ooze out from cracks in the tissues. Decaying tissue, which may be opaque, white, cream-colored, gray, brown, or black frequently gives off a characteristically putrid odor. The odor is caused by secondary invading bacteria
that are growing in the decomposing tissues.
The bacteria overwinter in infected fleshy tissues in storage, in the field, garden or greenhouse, in the soil (especially in the rhizosphere around the roots of many plants), and on contaminated tools, equipment, containers, and in certain insects. The bacteria enter primarily through wounds made during planting, cultivating, harvesting, grading, and packing and through freezing injuries, insect and hail wounds, growth cracks, and sunscald. They may
also follow other disease-producing organisms. Uninjured tissues may become infected when the humidity approaches 100 percent or when free moisture is present. Rains, poorly drained or waterlogged soils, and warm temperatures favor infection in the field, as does high humidity in storage or transit.
The bacteria multiply rapidly by dividing in half every 20 to 60 minutes under ideal conditions at
temperatures between 65° and 95° (18° and 35°C). Minimum temperatures for development is between 35° and 46°F (2° and 6°C); and maximum between 95° and 105°F (35° and 41°C.
The bacteria are spread by direct contact, hands, tools and farm machinery, insects, running or splashing water, contaminated, water in washing vats, clothing, and decayed bits of tissue.
Promptly and carefully destroy infected plants. Maintain well aerated field, avoid close planting and overhead irrigation.
To minimize post harvest losses, avoid mechanical injusry after harvest, packing and shipping. Do not pack produce when wet. Store and ship produce at temperatures near 4°C (39°F).
Interested in the latest automated weeding technologies? University of California Cooperative Extension will be hosting the 2022 Automated Technology Field Day where fifteen of the newest commercial thinning and weed control technologies will be demonstrated in the field. Featured technologies, some showcased for the first time to a general audience, include laser weeders, “smart” precision spot sprayers, autonomous in-row weeding machines, “smart” in-row cultivators, and the UC Davis steam weeder. Company representatives will be on-hand to discuss their equipment. The event will be held from 9:00 am – 12:00 noon, Wednesday, June 8th in Salinas, CA. For additional information, see the event flyer below.
Hairy fleabane is a summer annual weed from the Asteraceae family and occasional biennial in our area found in cultivated areas and citrus orchards, alfalfa fields, roadsides and ditch banks, landscapes and around buildings. The seedlings are oval to egg shaped and very similar in size (~0.4-0.8mm) to horseweed (Conyza canadiensis), which makes it very hard to distinguish one from the other in the field.
Hairy fleabane grows about 4 feet, branches from the bottom and leaves are pubescent also stems are covered with stiff hairs. The growth habits of horseweed (marestail) are different in that they grow up to 10 feet tall and branches from the upper half of the plant.
You can find Fleabane flowering right now in the Yuma area especially the Yuma Mesa. The IPM Team has received calls from our friends PCAs and growers stating that the Fleabane survives the application of Glyphosate, which has been reported for both conyzas. So, we got some trials in progress looking for options to control Fleabane as well as other weeds that have shown tolerance to Roundup such as White sweet clover or malva in different crops.
The results from the evaluations will be shared in this newsletter.
1. UC/IPM Retrieved from http://ipm.ucanr.edu/PMG/WEEDS/hairy_fleabane.html