Planting of fall melons is rapidly approaching and as growers begin to prepare local fields for fall planting they should be considering the threat of cucurbit yellow stunting disorder virus (CYSDV). This whitefly transmitted crinivirus was first identified in desert melons in the fall of 2006 where widespread infection on cantaloupes, honeydews and other melons occurred. CYSDV can cause significant losses in melon fruit yield and quality, and without question, desert melon crops have been seriously affected by this virus. Melon IPM has also been impacted by CYSDV where insecticide usage on fall melons has increased significantly. Over the past ten years we have been studying the epidemiology of CYSDV and trying to understand the complex relationships between the virus, vector and our local cropping system. Our ultimate goal is to develop practical approaches for reducing CYSDV impact on fall melon production. In addition, we continue to develop new information on chemical control of the whitefly vector (Bemisia whitefly adults). Last fall, whitefly populations were light and CYSDV incidence on fall melons was at an all-time low. Thus far, whitefly numbers this spring and summer have been relatively light compared to previous years and the incidence of CYSDV was low on spring melons. How the low numbers translate into virus incidence on the fall melon crop is unknown. However, our experience suggests that growers should anticipate CYSDV to be present. Further, given the aggressive management programs that PCAs and growers are now using, it will be interesting to see how CYSDV impacts melon production this fall. Our research to date suggests that fall melons produced near cotton or near areas where spring melons were recently produced are at the highest risk of infection. When possible, growers should attempt to isolate fall plantings as far away as possible from these sources of whiteflies and CYSDV. Growers forced to plant fall melons near these crops should be vigilant in minimizing adult whitefly infestation levels with insecticides during pre-bloom growth stages. To view a summary of the status of CYSDV in Yuma County and guidelines for management visit 2016 Guidelines for Whitefly and CYSDV Management on Melons.

Cartoonist: Juan Pena 
Hey John, did you paint your truck? No Bill . . . it’s the whitefly!

The drought-related pressures on the Colorado River system that have been impacting the entire basin and region for 23 years have slackened briefly due to the wet winter in 2023 that included a good snowpack in the mountains, better rainfall throughout the basin, and improved flows into the river.  The current water level at Lake Mead on Hoover Dam is 1,068.25 ft. above sea level on 3 January 2024.  That level is 160.75 ft below full pool of 1,229.00 ft. (Figure 1).

 

In mid-December 2023 representatives from each of the seven Colorado River Basin states met in Las Vegas, NV during the annual Colorado River Water Users Association conference.  The focus of current discussions among the basin states is to negotiate a new compromise for the guidelines of use under conditions of water shortage.  These new guidelines will go into place at the end of 2026.  The immediate goal is to draft proposals by March 2024.
 
The negotiations are incentivized by having the opportunity for the post-2026 guidelines being developed by the basin states themselves as opposed to litigation or legislation.  A major concern driving this process among the basin states that basin state representatives should be able to do this better than turning the process over to people and entities that have less direct familiarity with the situation and no real “skin” in the game.  
 
The 1963 decision by the Supreme Court of the United States in of the Arizona v California case directed the federal authority on the management of the Colorado River to the Department of the Interior and the Bureau of Reclamation (BoR).  However, the basin states have the chance to negotiate their future management plans on the Colorado River.  If they fail to do so in the allotted time, the process will be managed by the federal government.  
 
The basic water budget challenge is based on the following basic statistics:
 

• The current water budget on Colorado River allocations is 16.5 million acre-feet (maf)/year.
• Average annual flow on the Colorado River from 1906-2017 was 14.8maf/year.
• The average annual flow between the years 2000 - 2018 has been approximately 12.4maf/year.
• That is 16% lower than the 20^th century average flow.
• It is estimated that 1.5 maf/year is lost due to evaporation and system loss.
• Thus, the 4 maf/year target reduction that has been identified by the BoR is basically the difference between the 16.5 maf/year allocated versus the 12.4 maf/year average flow in the first two decades of this century.

 
Some notable progress is being made for conservation of Colorado River water with agreements among lower basin states and tribes that will conserve more than 1.5maf/year through 2026.  For example, California water agencies have recently agreed to conserve up to 643,000 acre-feet/year through 2025.  The Quechan Indian Tribe has reached an agreement with federal water managers to save up to 39,000 acre-feet/year through 2025.  Arizona has agreed to conserve up to 348.00 acre-feet/year through 2026.  All these temporary agreements are being supported with federal funding.
 
With agriculture responsible for 70% of the diversions on the Colorado River, these negotiations are extremely important for the future of agriculture in this region and our capacity to support high population densities that are now common and rapidly growing.
 
These types of negotiations are certainly challenging in dealing with a limited water supply and a lot of demand.  There are many competing interests involved.  Yet, we are confident that the representatives we have will be able to work this out and come to a set of functional agreements.

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 18, 2024 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. 
 

Month	Max	Min	Average	Rainfall
January	68	42	54	1.14 in
February	73	47	59	0.50 in
March	77	50	63	0.31 in

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19  and final reading was taken on February 26, 2024. 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-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. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.

Time flies. February is right around the corner and that means it is farm equipment/ag trade show season. Upcoming regional events include the World Ag Expo, Tulare, CA, February 13-15, the Southwest Ag Summit, Yuma, AZ, February 20-22, and AgroBaja, Mexicali, Mexico, March 7-10.  If you are interested in the latest ag tech and farm machinery, all are outstanding events and well worth attending. For more information, click on the links below.

Fig. 1. Upcoming farm equipment/ag trade show events: World Ag Expo, Tulare,
CA, February 13-15, 2024 theSouthwest Ag Summit, Yuma, AZ, February 20-
22,2024 and AgroBaja, Mexicali, Mexico, March 7-10, 2024.

Before making decisions for weed control it’s imperative to have a proper identification of the plant species. There are two names for plants:
The common name, which is a name that people come up with in a certain region to describe a particular weed and it varies by region and therefore can be confusing. Then we have an exact scientific name for each species that is based in the binomial nomenclature system started by Carl Linnaeus in 1753. This binomial (or two term) system includes the genus and the species, which is used worldwide¹.
 
Some very close species from the same family can be controlled by the same product but occasionally their herbicidal susceptibility varies. Such is the case of Chenopodium murale (goosefoot) and Chenopodium album (lambsquarter) two very close and similar species. A product like Pursuit (Imazethapyr) has good activity on goosefoot but can’t control lambsquarters. With accurate identification in a mixed population, you would be able to determine what strategy to use or select the herbicide that would control both species. 
 
There are about 75 weeds most common in Arizona and are included in the PCA² study guide, but many other species could be introduced to the State and complicate our crop production systems. Two great tools for weed identification are the books “An Illustrated Guide to Arizona Weeds” that lists 172 species, and “Weeds of California and Other Western States” which has at least one photograph of 735 weeds.
Another weed identification tool is the book “Weeds of the West”.
Additionally, there are many phone applications that can be used as identification tools such as “id weeds”, “PlantNet”, “PictureThis”, “iNaturalist”, “Seek”, “PlantSnap” and “LeafSnap”. When we have problems with weed ID we contact the UA herbarium.
Thank you for sending samples for Weed ID to the IPM Team it is always a learning experience.

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

Corn earworm: CEW moth counts down in most traps over the last week; about average for early October.

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

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

Diamondback moth: Adult activity spiked 2 weeks ago, particularly in the Yuma and Dome Valleys, but down over the past week. Average for this time of season.

Whitefly: Adult movement increasing Tacna consistent with melon harvests; overall about average for early October.

Thrips: Thrips adult movement peaked 2 weeks ago but down ovr the past week, overall activity above average.

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

Leafminers: Adult activity increased significantly last week in several locations, above average for this time of season.