Every season is unique, and this fall was no different in terms of insect pressure on desert produce crops. A quick look at both recent and historic data on pest abundance recorded from our University of Arizona research plots and areawide trapping and sampling suggests that insect pressure was unusual for several pests. For a look at the data see graphs below.  Pest Abundance on Desert Produce and Melon Crops – Fall 2023
 
Whitefly/CYSDV:   Whitefly populations in fall melons were lighter this fall compared to previous years, and areawide, adult movement was above average. However, adult counts in traps placed in commercial melon fields were the lowest we’ve seen in 17 years.  CYSDV incidence in cantaloupe fields was slightly higher than experienced last fall and was unusually high in the Dome/Wellton areas. In contrast, virus incidence in Texas Hill in 2023 was below 5% and was estimated at ~25% in fields produced in the Yuma Valley where historically virus has been heavier. Whitefly nymph populations were significantly higher in experimental broccoli and cauliflower plots at the Yuma Ag Center (YAC) in 2023, but apparently light throughout the desert growing area based on few reports from PCAs.

Beet armyworm (BAW), cabbage looper (CL), and corn earworm (CEW):  BAW and CL pressure in the early fall was moderate, although still below levels seen in 2020. BAW and CL larval pressure was consistently present through much of November due to ideal temperature for development and oviposition. Worm pressure has been sporadic since then, likely due to cooler temperatures in the past 2-3 weeks. Pheromone trap catches for both BAW and CL were below average. CEW trap catches peaked in early-October and failed to be much of an issue at harvest in most locations. However, we did receive reports from PCAs battling CEW in lettuce throughout the area.

Diamondback moth (DBM):   DBM was not a problem again for local desert growers in the fall of 2023. PCAs began reporting the presence of larvae in late October but pressure never built up much after that. Areawide pheromone trapping showed that DBM moth activity began later this fall and on average, much lower than we typically find. However, trap counts began to increase rapidly during November.  At YAC, the larval populations peaked during November and the most abundant we’ve seen since 2017. Field efficacy trials in broccoli and cabbage showed that the populations were very susceptible to all industry standard insecticides. 

Aphids     Flights of winged adults started out much later this year with significant trap captures beginning in November. Overall, winged aphid populations have been the lightest we’ve seen during Oct in many years. However, trap counts have increased significantly since mid-November in the Yuma and Gila Valleys consistent with the recent winds out of the N-NW.  We did receive reports of green peach aphid nymphs colonizing lettuce and brassica crops in October, but no reports for the past several weeks.  We’ve had a few reports recently of lettuce aphids showing up in the Wellton area in conventional lettuce fields downwind of organic romaine transplants. 

Western Flower Thrips (WFT) / INSV:  WFT pressure on non-treated lettuce plants at YAC was higher than the past several seasons.  Areawide trapping showed that adult activity was average during their peak activity in October, but movement has declined significantly thereafter. Traps placed on edges of lettuce fields showed that WFT activity was higher than last fall. Adult movement peaked in all crops around mid-October, coinciding with melon and alfalfa harvests. In fall lettuce, adult and larvae densities on plants were higher than in fall 2022, especially during November. Although INSV infected plants in organic transplants were again detected in October in Tacna, Roll, and Yuma Valley, to date virus incidence in surrounding direct-seeded lettuce remains non-detectable in these areas.

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

1. Six basin states SEIS proposal letter. 31 January 2023
   https://www.snwa.com/assets/pdf/seis-letter.pdf

1. California SEIS proposal letter.  31 January 2023 https://files.constantcontact.com/5aeb98ab501/5c9d8509-b45b-43fd-b230-5aaec293eca5.pdf

1. Glennon, R. and M.J. Pearce.  2007.  Transferring Mainstem Colorado River Water Rights: The Arizona Experience.  Arizona Law Review.  49:235-256.

Bindu Poudel-Ward, Martin Porchas Sr., Martin Porchas Jr., Neeraja Singh, Johan Murcia, and Rebecca Ramirez, and Jason Furr 
Yuma Agricultural Center, University of Arizona, Yuma, AZ

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 ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 16, 2023 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 CO₂backpack 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 Feb 24 and final reading was taken on March 13, 2023. Spray treatment were applied on February 16, February 23, and March 2 of 2023,(see table).  Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

            The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Orondis Ultra provided the most effective control against the disease. No phytotoxicity was observed in any of the treatments in this trial. 

Over the last couple of years, we have been investigating the use of band-steam to control weeds and soilborne pathogens. The technique has been discussed in previous mechanization UA Veg IPM articles (link). Briefly, the concept behind band-steam is to disinfest narrow bands of soil centered on the seedline using high temperature steam prior to planting. After the soil cools (<1 day), the crop is planted into the disinfested band (Fig. 1). Weed emergence and disease inoculum is reduced in the seedline. Weeds outside the seedline can be easily removed through cultivation.

Trials results have been impressive, particularly for in-row weed control (Fig. 2). We’ll be demonstrating our 2^ndgeneration prototype band-steam applicator and sharing study results at the 2023 Southwest Ag Summit Field Demo, February 22^nd (Fig. 3) We’ll also discuss and like to get your input on a new project – development and evaluation of a commercial scale band-steam applicator. The goal of the project is to build a self-propelled steam applicator and evaluate the viability of band steaming at the commercial field scale level. We’re in the preliminary design process now; a concept sketch is shown in Fig. 4. We’d love to get your input/feedback at this stage of the process. Please feel free to reach out to me anytime.

Fig. 1. Treatment sequence: 1) steam is injected into soil where seedline will be
located, then 2) later the crop is planted in the steamed seedline. 


Fig. 2. Weed control in lettuce seedlines of beds treated with band-steam (right)
and untreated (left).


Fig. 3. 2^nd generation band steam applicator to be demoed at the 2023 Southwest
Ag Summit Field Demo held February 22^rd, 2023 in Yuma, AZ
(https://yumafreshveg.com/southwest-ag-summit/).


Fig. 4. Concept drawing of a proposed commercial style steam applicator. The
unit has a propane fueled engine and steam generator. The steam injection occurs
at the back of the machine. Water is carried in tanks below the engine, and rubber
tracks are proposed to disperse the weight and avoid soil compaction.

We have recently received winter grass samples for identification and one of the most common has been Annual Bluegrass (Poa annua). Native to Europe it is distributed worldwide we find it invading homeowner landscapes, golf courses, and agricultural fields. It reproduces only by seeds¹ and can have several generations per year. The leaf blades are about 3 in long and plants are about 4 to12 inches tall. The flowering part is about 1to 4 inches long There are several species of the genus Poa but we included in this article the most typical characteristics of the Poa annuaspecies³.
Please check the highlighted features of this grass in the illustrations below:

1. The leaf blades end in a boat shaped tip.
2. The ligule is membranous.
3. Flower head outline looks like a triangle
4. Auricles are absent
5. Collar narrow and smooth

When leaves are looked through light two transparent lines on both sides of the midrib can be seen ²

Figure1. Key characteristics of annual bluegrass. (Images: M. Peña and Jim
Converse Proturf Guide to the Identification of grasses).


Figure 2. Proturf Guide to The Identification of Grasses, Jim Converse

References:

1. Parker, K. F. (1972). An Illustrated Guide to Arizona Weeds. University of Arizona Press.
2. Read more at: https://www.turffiles.ncsu.edu/weeds-in-turf/annual-bluegrass/
3. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7464.html

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

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

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.