This is turning out to be one unusual aphid season. Initially, with the heavy rainfall we received so far (2.54” in Yuma Valley), I expected green peach aphids to blow through the roof.  To date however, in our lettuce trails at YAC, green peach aphids are 5X lower than this time last season. But they are about normal on our broccoli plots.   The good news is, as temperatures remain in the high 70’s in the next two weeks, we should see green peach aphid population decline in lettuce. But keep an eye out for them on late broccoli/cabbage/cauliflower and brassica seed crops. They tend to stick around longer on the Cole crops.
 
However, Lettuce aphids, Nasonovia ribisnigri, (aka., red aphid) have begun to show up in lettuce throughout the desert growing region.  I’ve had several calls from PCAs reporting light colonies beginning to build, and we’ve been picking them up on our lettuce at the Ag Center for two weeks. I would consider this normal, compared to the 2022 season where lettuce aphid was present all winter/spring. Of course, we had a much milder winter that season. These recent findings are typical for the desert, where we generally associate lettuce aphid with the warmer growing conditions in late-February and March.  Experience has taught us that daytime high temperatures in the 70-80s are ideal for lettuce aphid population growth compared to green peach aphid, which prefers highs in the 50-60’s. Our local weather forecast suggests that high temperatures will be in the high 70s to low 80’s with moderate nighttime lows in the 50-60’s for the next two weeks. These conditions are conducive for lettuce and foxglove aphid population growth, so be prepared to battle them.
 
A few things to remember about lettuce aphids relative to the other aphids we commonly see. First, the immature nymphs are small and have a red appearance, whereas the apterous (wing-less) adults are typically a large brown colored aphid with dark bands running across the abdomen (see images below).  Second, among the crops we grow locally, lettuce aphids are only found on the lettuce types (Lactuca spp.). Lettuce aphids prefer to colonize the terminal growth, and can often be found in heads or hearts, whereas green peach aphids are often found on the frame leaves in high numbers before moving into the heads. Sampling should be focused on the terminal growth of young plants, and in the heads and hearts of older plants. Third, they can reproduce prolifically, producing many more alates (winged) adults than other species, which can quickly lead to widespread abundance in a field and dispersal throughout a growing area.  Finally, as the old proverb goes "he who hesitates is lost". If lettuce aphid nymphs or adults are found on your lettuce, it is recommended that you respond quickly with an insecticide treatment.  The product of choice is Movento at 5 oz/ac. Because of its systemic activity, Movento will reach aphids in the protected terminal growth.  Be sure to include a penetrating adjuvant for best results at a rate of at least 0.25% v/v.  It normally requires about 7 days of activity before significant reduction in the infestation is observed but can take longer (14+ days) in cool, cloudy weather. Sequoia, Sivanto, Beleaf, PQZ and Versys are good rotational products if spray coverage to terminal growth can be reached on smaller open plants. For more information on lettuce aphid please refer to 1) Lettuce Aphid on Spring Produce-2024 and 2) Aphid Management on Desert Produce-2024.   If you’re finding lettuce aphid on organic lettuce, good luck; we’ve not had much success in controlling them with organically-approved biopesticides (azadirachtin, pyrethrins, soaps, oils, entomopathogens, etc.).

 

Rapidly changing conditions are a common feature in the agricultural arena.  Things are in a constant state of flux in terms of climate, economics, methods of operation, etc.  However, in the past few years, principally during the pandemic and post-pandemic times, changing conditions in agriculture for the desert Southwest have been extremely rapid and substantial.
 
Supply chain issues have been disruptive to many sectors of the economy and that has certainly affected agricultural operations.  Things that have commonly been standard or easy things to manage in the past such as the simple need of replacing equipment or parts have become complicated and expensive.  
 
We have become aware of fragile supply chains and the exposure of single points of failure that can have huge domino effects in many facets of our society, including agricultural industries.  For example, during the pandemic it cost nearly $40,000 to move a shipping container from Asia to the U.S. and now things are starting to catch up and it has been reported that containers can now be shipped from Asia to the U.S. for less than $3,000.00.  
 
Fertilizer prices for many materials have more than doubled in recent years, primarily due to basic supply and demand pressures.  Fertilizer supplies have been subject basic economic pressures and further exacerbated by the war in Ukraine and the associated changes in natural gas supplies.  
 
Fertilizer Supply and Cost
In a recent report from DTN market analysis (Formerly: Telvent DTN, Data Transmission Network) for the second week of November, retail U.S. fertilizer prices were not substantially different than in October but did have some slight variations with five fertilizers showing marginally lower prices than in October and three other key fertilizers tracking slightly higher.  It is important to note that DTN designates a “significant” difference in prices with a move of 5% or more.
 
The five fertilizers that were marginally lower in price included monoammonium phosphate (MAP), potash, urea, 10-34-0, and anhydrous ammonia.  Di-ammonium phosphate (DAP), urea ammonium nitrate (UAN)-28, and UAN-32 were slightly higher in price in mid-November, Table 1.  Costs per pound of nitrogen (N) is shown for primary N sources in Table 2.

MAP	Potash	Urea	10-34-0	Anhydrous	DAP	UAN-28	UAN-32
$978	$848	$812	$753	$1,415	$930	$584	$681

Table 1.  Mid-November retail prices in U.S. markets for several fertilizers.  Source: DTN
 

Anhydrous Ammonia	UAN-28	UAN-32
$0.88	$1.04	$1.06

Table 2.  Comparative prices per pound of N.  Source: DTN
 
Crop commodity prices have been higher recently, sometimes to the extreme.  However, the increasing costs of crop production have generally overrun the increasing returns on a strong market.  In a recent report on western crop production conditions, estimates of cost of production increases in the past year are 135% higher than in 2020 while the return values to farmers have been about 127% higher.  Thus, a nearly 10% negative differential exists which exerts a strong impact on the crop production systems of the desert Southwest.
 
The American consumer is seeing this as well.  In the American Farm Bureau Federation’s 37th annual cost survey from volunteer shoppers for Thanksgiving dinner has shown that prices are up 20% this year.  This increase is in addition to the 14% increase experienced in 2021.
 
Nutrient Management
Developing a conservative approach to nutrient management is often considered a risky venture in crop production systems, particularly with a short season crop like a leafy green vegetable that has a premium on quality as well as yield.  However, under high fertilizer price conditions and/or tight supply, there is a greater incentive to develop and employ a more conservative approach to nutrient management.
 
To maximize nutrient management efficiency, the 4R concept of plant nutrient management and application can be helpful.  The 4R concept consists of applying:
 
 1.   Right fertilizer source at the
 2.   Right rate, at the
 3.   Right time and in the
 4.   Right place
 
Along with the 4R nutrient management approach, assessing plant-available forms of the nutrients present in the soil by evaluating soil tests with appropriate indices is a good step in the develop of a more efficient nutrient management program.  Then splitting nutrient applications, particularly mobile nutrients such as N in line with crop uptake and utilization are good steps towards higher fertilizer use efficiency by the crop.  Thus, timing, methods, and rates of nutrient applications are critical (e.g, 4R management).
 
In agriculture we know quite well that we have no control over markets and the costs of crop production inputs.  However, we can control these inputs in the field, and we do have some tools at our disposal that can be helpful in the process.

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%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches 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. 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. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

Over the last couple of years, we identified and developed two high speed, precision spot sprayers to apply herbicides to weeds with minimal off-target spray while traveling at speeds that are viable for commercial vegetable farming operations (2 mph). The first is a spray assembly designed for controlling in-row weeds that are close to crop plants (1-cm spot spray resolution). The second is a high precision (sub-centimeter spot spray resolution) sprayer designed for spot spraying cotyledon stage weeds in spinach and leaf lettuce crops. We tested the device in the laboratory and found that weed control efficacy was greater than 95% (3 species), percentage of off-target spray was less than 3% and no crop injury was observed. The work was presented at the 2021 California Weed Science Society Annual Meeting. Click here or on the image below ) to view the presentation and see video of the devices in action. 

We are now working towards developing a high precision, automated/robotic weeding machine for vegetable crops. This fall, Evan McGinnis, Biosystems Engineering Ph.D. candidate, initiated work to develop AI-based imaging software for detecting and targeting weeds. Once developed, the software will be integrated with the precision spot sprayer and tested in the field. Stay tuned for updates!

Acknowledgements

This work is supported by the Arizona Specialty Crop Block Grant Program and the USDA NIFA Specialty Crops Research Initiative USDA-NIFA-SCRI-004530. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Fig. 1. Images from “Centimeter Scale Resolution Sprayer for Precision In-Row Weed Control” presentation given at the 2021 California Weed Science Society Annual Meeting. Click here or on image to view the presentation.

The IPM team frequently receives questions from our friend PCAs in Yuma regarding possible injury with herbicide combinations. A recent inquiry was about the addition of Prowl (pendimethalin) to Prefar herbicide preplant.
We found in our archives an evaluation that was done in 2002 by Barry Tickes from Arizona Cooperative Extension that addressing this question. The evaluation was located on 8^th Street and the Levee in Yuma CO and included the following treatments: Dacthal at 10 and 12lb, Prefar at 6qt alone and with the addition of 0.5pt Prowl. All treatments were applied in 20 gallon/A spray volume as a 50% band on 42-inch beds. The plot size for this experiment was 600 ft. x 8 beds. Immediate incorporation was done with sprinkler irrigation. The results reported are in the following table:

Herbicide	Rate	Phyto (%Stunting)	Control: Nettleleaf Goosefoot	Control: Groundcherry
1. Dacthal	10lb	0	95	90
2. Dacthal	12lb	0	95	95
3. Prefar	6qt	0	30	0
4. Prefar+Prowl	6qt+0.5pt	20	50	0
5. Untreated	--	0	0	0

As can be seen the addition of 0.5pt of pendimethalin to 6qt of bensulide produced 20% stunting in this case. 

Results of pheromone and sticky trap catches can be viewed here.
Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 22, Nov 3, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts declined considerably over the past 2 weeks across all locations and about average for this time of the season. 
 
Beet armyworm:         
Trap counts decreased in most locations, but well below average for late-October. Most activity in Yuma and Gila Valleys.
 
Cabbage looper:          
Cabbage looper trap counts declined in most areas but increased in the N. Yuma Valley. Activity below normal compared to previous years. 
 
Whitefly:                       
Adults remains active in Dome Valley, Wellton, and Gila Valley, but below average movement for this time of season. 
 
Thrips:                         
Thrips adult movement increased in most locations in the last 2 weeks, particularly in Dome, Wellton, and Tacna. Activity remains below average for late-October.
 
Aphids:                         
Aphid movement increased again sharply in Bard and Yuma and Gila Valleys consistent with N and E winds over the past 2 weeks. Capture about average for this time of year.
 
Leafminers:                 
Adult activity increased sharply in the Gila Valley and Wellton but remains below average for this time of season.
 
Diamondback moth:    
Adults remains active in Dome Valley, Wellton, and Gila Valley, but below average movement for this time of season. Traps located adjacent to cauliflower and broccoli transplants had significantly higher counts, particularly in Dome Valley and Gila Valley.