Every season is unique, and this fall was no different in terms of insect pressure on desert produce crops. 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 historical data see.  Pest Abundance on Desert Produce and Melon Crops – Fall 2024

Whitefly/CYSDV:   Whitefly populations in fall melons were lighter this fall compared to previous years, and areawide, adult movement was below average for much of the fall. Overall, adult counts in traps placed in commercial melon fields continued to be low, slightly higher than last year. CYSDV incidence in cantaloupe fields was considerably lower than last fall, highest in the Dome Valley/Wellton areas (~30%). In contrast, virus incidence in Texas Hill, Roll, and Tacna was well below 10%. Surprisingly, incidence infields in the Yuma Valley was estimated at ~5% where historically virus has been heavier. Whitefly nymph populations were significantly lower in experimental broccoli plots at the Yuma Ag Center (YAC) in 2024, and apparently light and variable throughout the desert growing area based on PCA reports.  

Beet armyworm (BAW), cabbage looper(CL), and corn earworm (CEW):  BAW pressure this fall was very heavy, but CL was almost non-existent. In our research plots, BAW were active well into early November due to unusually high temperatures during October that were ideal for development and oviposition. Worm pressure became sporadic later in Nov due to below average cool temperatures. Pheromone trap catches for BAW were above average during November, while CL were well 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, particularly in Dome Valley and Wellton.

Diamondback moth (DBM):  DBM was not a problem again for most desert growers, but control issues continue for several PCAs on transplanted cabbage and cauliflower originating from coastal California. In several transplanted fields, Verimark was providing less than 14days of residual control, and several PCAs have reported poor-marginal residual control with standard foliar insecticides. To date, there have been no reports of yield losses, but control costs for some PCAs have been significantly higher than normal. In our research plots, the larval populations peaked in early 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. Areawide pheromone trapping showed that DBM moth activity peaked well above average in mid-October in traps located near transplanted brassica fields.

Aphids: Flights of winged adults started out a little later this year with trap captures beginning in late October.  Overall, winged aphid populations have been the highest we’ve seen during Nov in the past 10 years.  We’ve had several reports from PCAs throughout the area (Bard, Yuma Valley, Wellton and Dome) of small aphid colonies showing up on lettuce and brassica crops. We’re also picking up small colonies at YAC, more than we typically see in the fall.   Most of the aphids colonizing produce cops have been green peach aphids, with several instances of the “red morph” appearing.  So far, no reports of lettuce aphid on fall lettuce, unlike last season when lettuce aphid was found as early as November.

Western Flower Thrips (WFT) / Bean thrips (BT) / INSV:  WFT pressure on non-treated lettuce plants at YAC was lighter than the past several seasons.  Larvae were most abundant in late October and have declined significantly since.  Areawide trapping showed that adult activity was below average for most of the fall. Although INSV infected plants inorganic transplants were again detected in early November in Tacna, to date virus incidence in surrounding direct-seeded lettuce remains non-detectable in these areas.  High numbers of BT showed up in Yuma Valley in mid-October following heavy winds out of the W-NW.

As part of the Southwest Ag Summit (SWAS) that took place in Yuma in late February, we conducted a breakout session on Thursday, 22 February 2024 titled “Colorado River Water Shortage: Agricultural Perspectives”.  
This session provided a brief review of the background, the current situation on the Colorado River, and very importantly it included an outlook on the current discussions among the basin states 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.  Both the upper and lower basin states have now submitted draft proposals to the Bureau of Reclamation (BoR) on 6 March 2024.
This breakout session at the Southwest Ag Summit provided up to date information and first-hand insight into the process.  The participants were each uniquely qualified to offer valuable perspectives on these issues.  
The participants included Elston Grubaugh, Wellton-Mohawk Irrigation and Drainage District, who introduced the discussion and served as program moderator.  Bart Fisher, Palo Verder Irrigation District and State of California Colorado River Water Board member, Fisher Ranch, Blythe CA, provided a California perspective with a background of extensive experience in Colorado River management over several decades.  Hank Auza, Yuma County Water User’s Association President and Yuma Ag Water Coalition representative, Barkley Co. of Arizona, Yuma AZ, provided an Arizona perspective.  
Elston has extensive experience working in irrigation districts on both the California and Arizona sides of the Colorado River.  He has a valuable perspective, and he plays an important role in the management of Colorado River water in the Yuma area.  We are fortunate to have Elston provide his direction for this program and offer his point of view.
Both Bart and Hank are directly involved in the ongoing reconsultation negotiations directed at developing the new Colorado River management guidelines that will go into place in 2026.  Both are part of their state's delegation in the current negotiations and represent the lower basin.  Bart and Hank are not only responsible for representing California and Arizona, but they are both active farmers in the Palo Verde Valley and Yuma area valleys, and they bring valuable perspectives to the discussions.
The goal of negotiations among the seven U.S. Colorado River basin states has been to submit a single document proposing guidelines to the BoR.  However, as was discussed at this program at the SWAS, the upper and lower basin state groups have been dealing with significant differences and were not able to come to a consensus agreement.  As a result, the upper and lower basin delegations each submitted separate proposals to the BoR in early March.
There is still a chance that both the upper and lower basin state groups can reach a common agreement for a unified proposal.  In the meantime, both proposals are under review by the BoR. Officials with the BoR have indicated that they will be working with the basin states in the next six months to develop a consensus draft proposal for post-2026 river management by the end of 2024.
Further details on the two proposals submitted on 6 March 2024 by the upper and lower basin groups and contrasting the two will be forthcoming in a future article.
For the excellent program that was provided at the 2024 SWAS, I want to thank Elston, Bart, and Hank for their outstanding presentations.  Each of the participants in this program brought a wealth of knowledge and experience to the discussion.  
Specifically for Bart and Hank, we are all indebted to them for their contributions and hard work while serving on the lower basin state delegations during these critical and challenging negotiations.  Their firsthand perspectives and contributions to this program are very much appreciated.

Lettuce fields right now are covered with downy mildew after the unusual amount of rain we got this year in the desert southwest. 
Another disease to look out for is downy mildew in onions. 
Downy mildew of onions is caused by the fungus-like Stramenopile Peronospora destructor. The pathogen produces abundant sporangia that germinate directly acting as spores. Reported hosts other than onions include shallot, leek, garlic and chives. The fungus overwinters in volunteer hosts, cull piles, and debris. Spores are wind borne. Spores of the fungus present in soil or bulbs germinate, infect roots or bulbs, and develop systemically in the plant. Spores that land on the leaf surface produce local lesions that can spread systemically to younger tissue. Infection can spread rapidly under cool (34– 82 °F), damp conditions generating new inoculum within the field. The pathogen requires cool temperatures and the presence of free moisture (rainfall, dew or overhead irrigation) to infect onion plants. Under those conditions repeated disease cycles may occur with devastating results.
 
Disease management:  Regular scouting of field is important to assess disease severity and apply preventative fungicides. Disease management includes use of disease free bulbs, transplants and seed. Crop rotation with non host (small grain, corn) for at least 3 years. Destroy volunteer plants, debris and cull pile. Better soil drainage, better circulation, preventative spray can reduce disease occurrence. Always rotate fungicide from different groups to avoid resistance build up.

Pics : https://www.omafra.gov.on.ca/IPM/english/onions/diseases/downy_mildew.html
Sources: 
https://amarillo.tamu.edu/
https://barron.extension.wisc.edu/

Our newly constructed self-propelled steam applicator is designed to inject steam into the soil and raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (140°F for > 20 minutes). After the soil cools (< ½ day), the crop is planted into the disinfested soil. We have done some preliminary testing and are very encouraged. Results show that the machine is able to reach target temperatures at reasonable travel speeds, provide uniform temperature distribution across the bed and form nicely shaped beds suitable for subsequent planting. We still have some bugs to work out and identified improvements to make before shipping the unit to Salinas, CA where we will conduct field trials with crops this summer. If you are interested in seeing the machine operate or more information about soil steaming for soilborne pest control, please feel free to contact me.
Check out a video of the machine operating by clicking here or on the image below.

Fig. 1. Initial testing of self-propelled steam applicator video.

Acknowledgements
This project is sponsored and funded in part by the Propane Education and Research Council (PERC), Arizona Specialty Crop Block Grant Program and USDA-NIFA. We greatly appreciate their support.

The Southwest Agricultural Summit that recently took place in Yuma included a breakout session on Thursday, 21 February 2024 titled “New Developments in Weed Control”.
In this session Jose Antonio Cabrera representing BASF technical services for Coastal CA and Arizona provided a review of the new technologies being developed by his company in the Weed Control area. This includes new active ingredients as well as novel encapsulation technologies. The breakout session also included the lecture “Registration Support for Pest Management Tools in Specialty Crops, The IR-4 Project: Purpose and Process” by Roger B. Batts. “The IR-4 Project was established in 1963 by the U.S. Department of Agriculture to ensure that specialty crop farmers have legal access to safe and effective crop protection products. Helps growers address pest management concerns, develops data necessary for the registration of safe and effective pest management solutions with the U.S. Environmental Protection Agency¹.
Roger is the Weed Science biologist from the NC State University IR-4 headquarters. If you have questions such as: What is the IR-4 Mission? Why is IR-4 Needed? What are the programs within the IR-4 project? you will find some answers in the IR-4 Presentation Slides here.
We are currently conducting trials in Yuma in coordination with this project that could result in the addition of new labels and weed control tools for our Arizona vegetable growers.
Thank you for attending the SW Ag Summit Weed Science breakout session.
 
 
Reference:

1. https://www.ir4project.org/

 

Get your free copy of the Weed Seedling Identification Pocket Guide at the Yuma
Agricultural Center.

 

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 7, Apr 3, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts remain  at low levels  in all areas, well below average for this time of year. 
 
Beet armyworm:          
Trap increased areawide; about average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts increased to seasonal highs; above average for this time of season.
 
Diamondback moth:       
DBM moth counts increased in most areas. About average for this time of the year.
 
Whitefly:                      
Adult movement negligible, average for late winter. 
 
Thrips:                          
Thrips adult counts increased in most areas. Below average compared with previous years.
 
Aphids:                         
Aphid movement decreased in all areas; below average for late-March.
 
Leafminers:                   
Adults remain low in most locations, average for March.