Lettuce aphid (commonly referred to as red aphid) showed up early this year in organic lettuce and had not been reported in conventional lettuce until the past few weeks. It now appears to be spreading and showing up more regularly in lettuce fields throughout the area.  Over the past two weeks I have had several conversations with PCAs concerning lettuce aphid in both organic and conventional lettuce with reports of infested fields in Roll, Bard, Dome Valley, Wellton and Yuma Valley.  They are beginning to build up to high numbers at the Yuma Ag Center, and in fact are the predominant aphid species present in my lettuce efficacy trials. This is not real common. The last time lettuce aphids were this abundant on desert produce was the spring of 2012.  Keep in mind, daytime high temperatures in the 70-80's are ideal for lettuce aphid population growth, and the 14-day weather forecast suggests that lettuce aphid will be around for a while. 
 
A few things to consider about lettuce aphids relative to the other aphids we commonly see. Lettuce aphids prefer to colonize the terminal growth, and generally found in the heads or hearts. Sampling should be focused in the terminal growth of young plants, and in the heads and hearts of older plants. When they are present under ideal temperatures (like right now) they can reproduce prolifically, producing many more winged adults than other aphid species.  This is likely why we are beginning increased dispersal and new infestations. 
 
Finally, a few suggestions for management. If your lettuce is young and not closed in yet, consider using an aphicide with contact activity like Sequoia. Assuming sprays can reach new growth, you should see dead aphids with 3-5 days. Also, avoid using pyrethroids on smaller lettuce. This will conserve some of the natural enemies like syrphid fly and lady beetle larvae that may provide some additional control. On older lettuce you best choice is Movento at 5 oz/ac.  It is advised that you increase your rate of penetrating adjuvant to 0.375 % vol/vol or higher on larger plants. This should help move the product into the vascular tissue and improve systemic activity.   Don’t expect to initially see a lot of dead aphids. It normally requires 7-10 days of activity before significant reduction in the infestation is observed. Sooner when temperatures are in the 80’s. Look for the wingless adults (larger brown forms); their absence is a good sign that you are cycling them out.  Obviously, use of pyrethroids is more important on lettuce approaching harvest in order to prevent contamination by trash bugs.  For more information on lettuce aphid please refer to Lettuce Aphid on Spring Produce. 

Name That Pest Below:
Name the Pest that caused this damage to broccoli

On Tuesday, 15 August 2023 officials from the U.S. Bureau of Reclamation (USBR) presented their 24-Month study reports with projections and operational plans for 2024 (USBR, 15 August 2023).  We are still dealing with the drought but there is some improvement in the 2024 plans for Colorado River water allocations for Arizona.
 
The wet winter and spring experienced in the Southwest in 2023 has provided some relief on the dire situation we were facing on the Colorado River system and reservoir levels have improved.  But unfortunately, one good precipitation season does not solve all the problems and they will still need to be dealt with.
 
The current plan for lower Colorado River water management is basically a return to the Drought Contingency Plan (DCP) Tier 1 schedule (Figure 1).  

Fgure 1.  Drought Contingency Plan Tier reductions for Arizona.

Tier 1 plans take us back to an 18% reduction or 512,000 acre-feet (KAF) of Arizona’s Colorado River allocation of 2.8 million acre-feet (MAF).  Arizona was operating under Tier 1 guidelines in 2022.  
 
The irrigation districts in central Arizona that have lost access to Central Arizona Project (CAP) water will not be receiving any additional water in 2024 based on this plan.  The districts immediately adjacent to the mainstem of the Colorado River will continue to receive the same amount of water as they have been receiving the past two years.  For Arizona and the other lower basin states, these are basically the same water allocation guidelines that were in place in 2022.
 
The urban areas and American Indian tribes will not experience any additional reductions based on the USBR plans. However, some cities and tribes have volunteered to reduce their Colorado River water allocations in exchange for payments from the federal government.
 
For example, in 2023 Arizona, California, and Nevada agreed to a plan that will conserve an additional 3 MAF of Colorado River water through 2026 in exchange for $1.2 billion from the federal government.  If approved by the USBR, this plan would reduce Colorado River allocations to the Imperial Irrigation District in California, which has some of the most senior water rights on the river.
 
The Gila River Indian Community (GRIC), which has a Colorado River allocation of 653 KAF, committed in April 2023 to relinquish temporarily 125 KAF in exchange for $400 per AF from the federal government.  The federal government is also funding GRIC infrastructure projects to increase wastewater reuse in irrigation.
 
Thus, some of the Colorado River water that is technically allocated to Arizona under Tier 1 guidelines will stay in Lake Mead due to previously agreed upon conservation measures.
 
Regarding other lower basin states and the current USBR plan, Nevada will have slightly more Colorado River water in 2024 than in 2023.  Mexico will deal with a 5% reduction in Colorado River water from their base and once again California will not be suffering any required cuts in their Colorado River water allocation.
 
Overall, this is good news.  We have some temporary relief on the Colorado River system and no additional reductions will be required in 2024.  This puts the seven Colorado River basin states and Mexico in a better position to negotiate the guidelines and agreements required for 2026 since all the existing agreements expire in two years.
 
Reference
 
USBR, 15 August 2023. 24-Month Study reports.   

• 24-Month Study Projections (Overview)
• August 2023 Most Probable  
• August 2023 Probable Minimum 
• August 2023 Probable Maximum   

August 2023 Lake Powell and Lake Mead: End of Month Elevation Charts

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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. between bed centers.  All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned Jan 4, 2024  at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	MaxTemp(°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Downy mildew (caused by Bremia lactucae) rating was done on variety Eblin, Bobcat, and 180 (partially funded by AILRC grant). Disease was first seen on 1-30-24. Please see attached excel file for chemicals application date. Disease rating was done on February 29^, 2024. Disease severity was determined  by rating 10 plants within each of the five replicate plots per treatment using the following rating system: 0 = no downy mildew present; 0.5 = one to a few very small downy mildew colonies on bottom leaves; 1 = downy mildew present on bottom leaves of plant; 2 = downy mildew present on bottom leaves and lower wrapper leaves; 3 = downy mildew present on bottom leaves and all wrapper leaves; 4 = downy mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = downy mildew present on entire plant.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most of the treatments exhibited activity against the disease to some extent. Latitude, Amara, Eject, Previcure flex exhibited good control in the variety Eblin (highly susceptible variety). Whereas Cevya, Stargus, Latitude, Amara, Revus, Thrive 4 M, Actigard, Instigo+Carbose+intereact showed activity against the pathogen in variety Bobcat. Please see excel file for the full list of chemicals and their efficacy. The lettuce variety 180 was resistant to the disease and no downy mildew was observed on the particular variety. No phytotoxicity was observed in this field.

Mark C. Siemens, Department of Biosystems Engineering
Vol. 14, Issue 16, Published 8/9/2023
Pre-Season Vegetable IPM Workshop
Mark C. Siemens
Vol. 14, Issue 17, Published 8/23/2023

The Pre-Season Vegetable IPM Workshop will be taking place TOMORROW, Wednesday, August 23^rd at the Yuma Agricultural Center. Come learn about the latest IPM products, practices and trial results from university and industry experts. Registration begins at 7:30 am and the program starts at 8:00 am. Agenda below. Looking forward to seeing everyone there!

 

In the absence of Dacthal (DCPA) growers are looking for different herbicide options for Broccoli and Onions.
The following is data from a broccoli trial done in 2010 by Tickes/Pena, which compares Prowl, Goal Tender, Prefar, Treflan, Devrinol and Dacthal at different application timings. Plots were visually evaluated for weed control of  Goosefoot (Chenopodium murale), Malva (Malva parviflora), and Yellow Sweet Clover (Melilotus oficinalis). The label recommendations for Devrinol are “Use the lower rate on light soil (coarse textured-sandy), and the higher rate on heavy soil (fine textured-clay)”. The rate goes from 1-2 lbs on the DF-XT 50% formulation.
We hope this information is useful in our decision making for broccoli herbicide programs. 

 

Area wide Insect Trapping Network   VegIPM Update, Vol. 11, No. 21, October 14, 2020

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

Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley. 

Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.

Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.   

Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.

Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard.  Numbers beginning to slowly trend upward

Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year.  Still early, anticipate they will begin to show up in heavier numbers in mid-late October.

Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.