Aphid populations remain heavy throughout the Yuma growing area. Green peach aphid appears to be declining a bit on lettuce and spinach but is rapidly increasing on our cabbage and broccoli. Also beginning to get reports of green peach and foxglove aphids building colonizing hearts of older celery.  But without a doubt, Lettuce aphid (LA) is the primary aphid giving growers and PCAs heartburn. As I’ve noted previously, this is the worst I’ve ever seen LA since it first showed up in the desert in 1999. LA have been colonizing plants since early December and are currently exceeding 400 aphids/head in my heaviest infested untreated iceberg lettuce plots at YAC. However, that may pale in comparison to an organic romaine field I walked in to yesterday.   And right on schedule here come the syrphid flies and lady beetles, the most efficient predators of LA. So far though these aphid-eating machines are not keeping up with the LA populations. Once the weather gets consistently in the 80’s, populations should begin to crash. But until that happens you need to be aggressive in your control.  In my conventional lettuce efficacy trials, Movento (5 oz/ac) and Senstar have been working great on LA this season. The table below shows the results of a trial conducted on iceberg lettuce beginning in late January. Other non-systemic aphicides are significantly reducing LA numbers, but not at the same levels as Movento/Senstar.  So, for late season lettuce, Movento/Senstar should be your primary product for LA and should work even better under warmer temperatures. And don’t forget, these products require a penetrating adjuvant to maximize their performance. The products I’ve had the best success with have been MSO/organosilicon blends.  So, I recommend going the highest rate of adjuvant you feel comfortable with. For late season green peach aphid management, all the standard aphid products I’ve tested this spring (Sequoia, Sivanto, Beleaf, PQZ, Versys) have provided effective control in brassica crops and lettuce.

In 2023 Arizona and the lower basin states were operating under Tier 2 reductions, consistent with the Drought Contingency Plans (DCP) for Colorado River conservation in response to the drought conditions (Figure 1).  Tier 2 conditions imposed a 592,000 acre-feet (kaf) reduction in Arizona’s 2.8 million acre-feet (maf) total allocation from the Colorado River.  These reductions have primarily impacted the irrigation districts in central Arizona.
 
For 2024, the Bureaus of Reclamation (BoR) has announced in August 2023 that the river operations will follow Tier 1 DCP reductions (Figure 1).  That is due to an increase in the water levels in Lake Mead in the past year with an excellent snowpack last winter and above average runoff in 2023.  That increase in water level at Hoover Dam in Lake Mead is primarily a function of an excellent snowpack and higher rainfall in the Colorado River basin in 2023.  Significant conservation efforts have been employed as well.

Figure 1.  2024 Tier 1 Shortage for the Colorado River operations.  Source:
Arizona Department of Water Resources.

With agriculture responsible for 70% of the diversions on the Colorado River, tracking the snowpack is an important exercise for forecasting and managing the precious water resources in this region and this watershed for sure.
 
The pressures on the Colorado River system because of the drought that has been impacting the entire basin and region for 23 years have slackened briefly due to the wet winter in 2023 with a good snowpack in the mountains, good rainfall throughout the basin, good flows into the river, and conservation.  
 
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 2).

Figure 2.  Lake Mead water height (feet above sea level at Hoover Dam) history
and critical Tier conditions.  Source: U.S. Bureau of Reclamation.

The current snowpack in the Colorado River Basin is at 74% of average and below levels of this time last year.  However, hydrological records indicate that most of the snowpack in this basin accumulates between February and April.  
 
So, it is worth watching the snowpack accumulation and it is always good to pray for more snow in mountains to the north for those of us working and living in this desert with a heavy dependence on this water.  However, while monitoring the snowpack gives us a capacity to project, none of that really counts until there is water in the river and in the reservoirs, like money in the bank.

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.

In the preceding issue of UA Veg IPM Updates, the article below was published with an incorrect link to the video mentioned. For those interested in the video, which contains trial results and insightful videos of the technologies in action, the article has been updated with the correct link and is being reposted.


A couple years ago, we conducted evaluations of various “new” technologies for cultivating weeds in cotton as compared to conventional methods. The new technologies included 1) a camera-guided side-shift hitch and 2) finger weeders, an in-row weeding tool (Fig. 1). Camera-guidance of the maneuverable hitch allows cultivating tools to be positioned close to the seed row. In the study, the uncultivated band was 3.5" for the camera-guided system, and 6” for the conventional cultivator.  The aim of evaluating these technologies was to determine their efficacy in controlling herbicide resistant weeds. Trials conducted over 3 years showed that use of camera-guidance improved weed control by more than 30% and finger weeders removed about 45% of the in-row weeds. Overall weed control using the two technologies together was roughly > 90% for broadleaf weeds and about 85% for all weeds species.
Studies conducted by Texas A&M over two years showed similar results (Dotray et. al, 2021).

It is logical to think that similar type results would be realized in vegetable crops such as broccoli and cauliflower, plants that also have fairly long plant stems at the seedling stage of growth. A better than 40% reduction of in-row weeds would significantly lower hand weeding requirements. If you are interested in trying these technologies in vegetable or other crops on your farm, please contact me. We still have the equipment and I’d be happy to work with you.

A presentation given on the trial results and videos of the equipment used operating can be found by clicking here or on image below.

References
Dotray, P.A., Keeling, J.W., & Russell, K.R. 2021. Precision cultivation with finger weeder systems. Project No. 20-190 Final Report. Cary, N.C: Cotton Inc.

Acknowledgements
Project partially funded and supported by Arizona Cotton Growers Association, Cotton Inc., KULT-Kress, LLC and Keithly-Williams Fabrication. We thank them for their support.

Fig. 1. Technologies for precision cultivation and in-row weeding
used in efficacy trials included a a) a camera-guided side-shift hitch
attached to a cultivator and b) in-row weeding tools (finger weeders).

Fig. 2. Click on image above to watch presentation on precision cultivation and in-row weeding technologies.

There are many different types of pests that affect crops grown in Arizona. The three types of pests most often cited as the source of most problems are insects, diseases and weeds. These are the same types of pests that are cited as causing the major agricultural pest problems across the U.S. and worldwide. Graphs 1-3 illustrate, however, that the relative importance of these types of pest problems differ in Arizona from the rest of the U.S. and worldwide. In terms of pesticide use, worldwide herbicides accounted for 36% of total usage, insecticides 25%, and fungicides 10% and other 29% (nematicides, rodenticides, fumigants, bird, fish and aquatic pests). In the U.S., herbicides accounted for 44%, insecticides 10%, fungicides 6%, and other 40% of pesticide use. In Arizona, however, insecticides accounted for 58%, herbicides 17% and fungicides 12%. This is only an indirect measure of the relative importance of these three areas of pest management and may be heavily influenced by the amount of pesticides used. For instance, it is common to spray for insects five or more times per season while it is uncommon to spray for weeds more than twice. None the less, these graphs illustrate that weeds are the predominant pest problem in agricultural areas across the U.S. and worldwide.

We wanted to share the information above obtained from the PCA Study Guide Section VI prepared by our "amigo" Barry Tickes who is teaching the Applied Weed Science Class at the University of Arizona this semester.

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.