Historically, management of western flower thrips in lettuce was targeted at preventing damage by thrips feeding on marketable leaves. Left unchecked, cosmetic scarring could result in downgrading of quality, or even rendering the crop unmarketable.  In fall lettuce, PCAs could typically allow thrips to build up on young lettuce plants and later prevent feeding damage on marketable leaves with 1-2 well timed foliar insecticide applications. However, that all changed last spring with the discovery of Impatiens Necrotic Spot Virus (INSV) in late spring crops.
To manage thrips with the intent of suppressing or prevent INSV infection it’s important to understand how western flower thrips acquire and transmit the virus.  Based on the experiences in Salinas the past 2 seasons, we’ve learned that INSV infections occur two ways.  First, Primary infection or spread occurred where INSV infected adults from an outside host source migrate into lettuce, feed, and transmit INSV to otherwise healthy plants. In theory, the more infected thrips moving into the field, the higher the incidence of primary infection. An adult thrips can only transmit the virus; it cannot acquire the virus from an infected plant.   Secondary infection or spread occurs when thrips larvae acquire INSV by feeding on an infected plant (either lettuce or nearby weeds), complete development and emerge as infected adults, capable of transmitting INSV throughout the field or nearby lettuce fields/weeds. Keep in mind, adults only transmit INSV, whereas only larvae acquire the virus from an infected plant.
This has led us to many questions about the virus and its epidemiology in desert cropping systems relative to last year.  First, why did it suddenly appear last March when it had not previously been reported in our cropping system. In 31 years as a vegetable entomologist in Yuma, I have never seen INSV or TSWV (a related tospovirus) in desert lettuce. Anecdotally, it has been presumed that INSV arrived in the desert on infected lettuce transplants or infected adults hitching a ride to Yuma on transplants or equipment originating in Salinas. Not knowing the exact sources of INSV last season, the question is: will the virus reappear again this season? Given that Salinas has battled INSV all summer and produce a fair amount of the lettuce and brassica transplants grown in Yuma, we must assume that INSV will arrive in the desert at some point. So, until we have a better understanding of INSV epidemiology on desert lettuce, it is recommended that PCA’s and growers adjust their thrips management programs this season, particularly in high-risk areas. Below are several recommendations that PCAs should consider this season. 

1. Season-long sanitation. Maintaining a clean cropping system via cultural management is the foundation of an effective thrips/INSV control program by eliminating sources of both the virus and the vector. Local research has determined that several desert weed species serve as reservoirs for both thrips and INSV.  Reduction of thrips/INSV is likely with thorough weed control, both in and around produce fields. Additionally, once lettuce harvest begins, growers should disk crop residue as quickly as possible following harvest to reduce prolonged thrips reproduction and spread. 

1. Scouting for thrips is important. Research has shown that visual sampling for thrips can underestimate the actual numbers on the plant due to their small size and  cryptic nature. If you can see a few adults and larvae on a plant, it means that there are likely several-fold more thrips on the plant that you cannot find hiding near the base of the plant between midribs.
2. Focus on minimizing Secondary spread.   Because adults can be difficult to control, prevent larvae from completing development to the adult stage and moving throughout the field. It’s hard to prevent primary infection from the outside but minimizing larvae populations should help suppress the secondary spread of INSV if it is present in the field. In other words, “Nip the thrips” populations in the bud.
3. Early and aggressive spray timing in high-risk areas.  It is advisable that PCAs preventatively treat lettuce fields early and aggressively in these areas at a high risk of INSV infection:
   • Lettuce and brassica transplants originating from Salinas should be treated before or shortly after transplanting. 
   • Direct-seeded lettuce fields grown adjacent to, or near lettuce and brassica transplanted fields originating from Salinas should be treated early and aggressively. 
   • Lettuce grown in areas where significant INSV was found last spring (i.e., Tacna, Roll, Wellton, Bard) should be watched closely and treated preventatively when thrips first appear. 
4. Using Insecticides Differently.

• Consider incorporating Lannate or Torac with chemical thinners/smart sprays.
• Consider combining Lannate or Torac with armyworm, looper and whitefly sprays early when thrips pressure is light.
• Consider tightening spray intervals (6-7 d) with heavier thrips pressure, or the first signs of INSV in the immediate area.
• Consider rotating Minecto Pro or Exirel with Radiant for armyworm, looper and whitefly control in fall lettuce, and similarly when aphids appear later, consider rotating Beleaf and Acephate  with Movento. All these products have shown to provide control or suppression of western flower thrips larvae.

5.Test symptomatic plants immediately.   The earlier you discover INSV in a field the better chance you have of reducing secondary spread within the field and, perhaps as important, to surrounding lettuce in the area.  The UA Diagnostic Plant Pathology Diagnostic Lab and Dr. Bindu Poudel-Ward can confidentially confirm the presence of INSV on symptomatic plants. So please don’t hesitate to have symptomatic plants tested for INSV infection.

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. 
 

 
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.

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.