It appears that the weather has finally broken, although it is forecasted to be in the 80’s later this week. Nonetheless, it should soon begin to feel like “winter” in the desert. With cooler temperatures, you can expect a steady decline in insect abundance until temperatures begin to warm up again in February. Of course last winter, we had no winter. I don’t expect that again but it is always interesting to look back over this past fall in anticipation of what we might experience this spring. A quick look at both recent and historic data on pest abundance recorded from our research plots here at YAC and from our Area Wide Trap Network suggests that insect pressure this fall was heavier for some pests and lighter for others. First, whitefly adult numbers on fall melons and produce were quite a bit lower than we’ve seen the past two seasons. Unlike like last fall however, untreated melon plots on the Ag Center did not succumb to whitefly damage and we were actually able to harvest melons. Sticky trap captures of whiteflies near cantaloupe fields from Wellton to Texas Hill, were lower than last fall as well. Similarly, CYSDV incidence at harvest in cantaloupe fields in these areas was very high this fall. For some strange reason, CYSDV incidence was markedly lower in fields in the Wellton area, an area once thought to be ground central for the virus. In all cases, high traps catches were found in melon fields in close proximity to cotton fields, and virus incidence was highest in fields near where spring melons had been grown. On the other hand, beet armyworm, cabbage looper and corn earworm population abundance on untreated lettuce at the Yuma Ag Center this fall was the highest we’ve recorded in 10 years. Populations began infesting plots in early September, and remained steady throughout October and November. Egg deposition and larval development has only recently declined significantly. Our pheromone trap catches (Area Wide Trap Network) also show that moths were much more active in October and November relative to last year. The warmer temperatures, particularly nighttime temps, are largely responsible for this. In fact based on our AZMET station here at YAC, the average ambient temperatures during October and November were highest we’ve experienced in the past ten years. Finally, Bagrada bug infestations were abundant in untreated broccoli plots at YAC for the 5th consecutive year, but at lower numbers than what we have seen in the past years. As expected, populations appeared in early September, increased at a low rate through September and peaking in early October. Overall, the peak numbers observed were not as high as last year, but were higher than in 2011. However, even with these lower numbers, infestation levels in our untreated broccoli plots this year remained at damaging levels throughout most of October. In contrast, similar to last fall, western flower thrips population numbers have been relatively low. We’ve not yet begun to pick up winged green peach aphids on sticky traps or colonies in untreated lettuce plots. How these aphid and thrips numbers will translate into potential population pressure in the spring is unknown, but you should anticipate their abundance as usual. If we have a wet winter (El Nino) experience suggests that aphids may be quite abundant, where in contrast thrips don’t do well in wet growing conditions. Nonetheless, graphics showing recent trends in Whitefly, CYSDV, Lep Larvae and Bagrada abundance and a weather summary can be found at Pest Abundance on Desert Produce and Melon Cops in 2014.

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%). 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.

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.

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.