Hope you are all enjoying the summer so far and keeping busy. Although, we’re about 2 months away from the Fall produce season, it’s never too early to begin thinking of IPM strategies you will be using to battle key insects next season. This includes keeping track of their typical activity during June, July, and August. Below is a short discussion detailing individual pests. 
 
Aphids:    The major aphid species that are important in produce crops each spring include green peach aphid, foxglove aphid and lettuce aphid.  These species are considered cool season pests and are biologically most active during the winter and spring when temperature average around (55-65 F). We do not find them on summer crops as the high temperatures prohibit their activity. They essentially become extinct each summer only to reappear in the fall to infest crops in Oct-Dec migrating into the desert via N-NW winds that occur after the monsoons.
 
Diamondback Moth (DBM):  Another key pest that disappears each summer but for a different reason than for aphids. The host range of DBM is limited to only brassica crop and plants. Although brassica weeds are common during the winter, they occur during the summer due to high temperatures and dry conditions. Thus, like aphids, DBM populations from the previous spring season become “extinct” during the summer when brassica crops and weeds are absent. They reappear each fall migrating in on high winds associated with tropical storms from Mexico, or arrive into the region on infested brassica transplants from California.
 
Whiteflies:       A resident pest that occurs year-round in the desert. As a warm season pest, whiteflies are most abundant on fall produce crops, and seldom a problem during the winter and spring. Peak abundance occurs during the summer months on cotton, and again in September and October on fall brassica, leafy vegetables and fall melons.  Thus, it is important to control whiteflies in cotton prior to defoliation to prevent large migrations onto fall produce crops. In addition, whiteflies can be found on several weeds such as purslane, goosefoot, ground cherry, and sunflowers. Sanitation in and around fields being prepped for fall plantings is important. Preventatively, growers should consider applying soil, system insecticides such as imidacloprid or Verimark to Fall produce crops.

Beet Armyworm (BAW):  A warm-season pest that occurs year-round in the desert. They tend to reach peak abundance twice a year. Generally, the most important peak is in September and October when weather is ideal for their development, flight activity and oviposition. A second peak occurs in late spring. Activity is generally light during the summer, occurring primarily in alfalfa crops. Although BAW is known to migrate in from the south via monsoon and tropical storms, resident populations annually occur in alfalfa during the summer. Thus, to minimize BAW in fall produce crops, thorough management of BAW can potentially minimize their movement onto Fall produce crops.  Weeds are also a source of BAW (purslane, goosefoot, sunflower and Russian thistle) so sanitation in and around fields is important.
 
Western Flower Thrips (WFT):  Also a resident pest that can be found in the desert year round. WFT is most abundant on lettuce in the late spring, but peaks in abundance on alfalfa, melons and cotton is May and June. During the late summer numbers drop dramatically where thrips can be found on melons and alfalfa and weeds like goosefoot and purslane. WFT slowly move into lettuce again in early fall and are least abundant during the winter.  Sanitation of weeds during the summer can help reduce thrips abundance moving into the fall crops and weeds.
 
For more information see:   Keeping Track of Major Produce Pests During the Summer

In desert agriculture we have an abundance of motivation to manage water efficiently.  Water is the first limiting factor in crop production systems in the desert Southwest.  Agriculture is responsible for the use of approximately 70% of all the freshwater use in Arizona and some estimates indicate about 80% of the Colorado River water diversions.  
 
Crop production systems in the desert Southwest are experiencing increasing pressure to document and improve irrigation efficiency.  Following more than two decades of drought in the western U.S., many watersheds are experiencing critical water shortages.  A great deal of scrutiny is being applied to crop production systems in this region.
 
There are several ways to define irrigation efficiency.  The primary definitions for irrigation efficiency include agronomic, economic, and environmental orientations.
 
In my view, the agronomic efficiency of irrigation is fundamental and at the core of why we irrigate, which is for the benefit of the crop being grown.  The crop plants are the centerpiece of the production process and the soil-plant system itself represents the primary objective of irrigation management.
 
Agronomic Irrigation Efficiency
 
Agronomic (crop and soil) considerations are centered on our ability to provide irrigation water for the sustainable production of a crop in the field.  The three primary demands for crop water management include: 1) providing water for seed germination and stand establishment, 2) providing irrigation water to match crop-consumptive water use and avoid crop water stress, and 3) provide sufficient irrigation water to leach soluble salts from the root zone so that the soils can support crop production in a sustainable manner (Figure 1).  
 
Agronomic efficiency at the field level focuses on the crop water demand (CWD) through crop consumptive use (crop evapotranspiration, ETc, which is the combination of evaporation and transpiration from the crop) and leaching requirements (LR) which are dependent upon the crop and salinity of the irrigation water.  
 
Agronomic efficiency can be estimated by considering the difference between ETc + LR = CWD and the volume of irrigation water applied (IWA).


The leaching requirement (LR) can be estimated by use of the following calculation:

Where: 
 
EC_w = salinity of the irrigation water, electrical conductivity (dS/m)
EC_e = critical plant salinity tolerance, electrical conductivity (dS/m)
 
This is a good method of LR calculation that has been utilized extensively and successfully in Arizona and the desert Southwest for many years.  This method considers the quality of the irrigation water being used and the salinity tolerance of the crop.  
 
We can easily determine the salinity of our irrigation waters (EC_w) and we can find the critical plant salinity tolerance level from readily available tabulations of salinity tolerance for many crops (Ayers and Westcot, 1989).  Additional direct references are from Dr. E.V. Maas’ lab at the University of California (Maas, 1984: Maas, 1986; Maas and Grattan, 1999; Maas and Grieve, 1994; and Maas and Hoffman, 1997).  
 
To deal with crop water management at the field level agronomically, the crop and soil factors, there are some good tools that we can easily access for assistance. 
 
Dr. Jeremy Weiss, program manager for the University of Arizona AZMET system, developed some valuable tools last year that provide actual crop evapotranspiration (ETc) estimates from several AZMET sites in the lower Colorado River Valley and for several key vegetable crops, including lettuce (iceberg and romaine), broccoli, cauliflower, cabbage, and spinach.  
 
He has made some nice modifications to this tool and I think you will find the enhancements very useful and beneficial.
 
This tool provides accumulations of ETc values for this current season utilizing the crop planting date selected by the user and any range of time up to the present.  The Kc values presented in FAO-56 are used for appropriate stages with each crop.  The reference evapotranspiration (ETo) measurements are taken directly from each AZMET site listed.  Thus, by this method ETc estimates are made by use of equation 3.  These provide good crop-water use estimates for our crops in this region.


To access this crop-water estimate tool please refer to the following link:
 
https://viz.datascience.arizona.edu/azmet/azmet-crop-water-use-estimates/
 
If we enter information for a lettuce crop planted on 1 September 2023 through 10 November for the Yuma South site, we get the following information from this tool:
 
“Estimated total water use at the AZMet Yuma South station for lettuce since the planting date of September 1, 2023 and through the end date of November 10, 2023 is 11.47 inches. Total precipitation over this period is 0.40 inches.”
 
Similar estimates are provided by this model for several AZMET weather stations in the Yuma production area: Roll, Yuma North Gila, Yuma South, and the Yuma Valley.  The Yuma Valley station is at the University of Arizona Yuma Agricultural Center and the Yuma South site is near Somerton, Arizona.  A map of AZMET sites can be found in the following link:
 
https://ag.arizona.edu/azmet/mapsites.htm
 
When we include the leaching requirement for the crop, an overall estimate of field level irrigation efficiency can be made.  We can estimate the leaching requirement as follows assuming an electrical conductivity for Colorado River water of 1.1 dS/m and the lettuce crop salinity tolerance of 1.3 dS/m.
 
 Leaching Requirement (LR) = ECw/((5 X ECe)-ECw)
 
LR = 1.1 dS/m / (5 X 1.3) – 1.1 = 1.1/5.4 = 0.20 = 20% leaching requirement
 
LR = 11.5 X 0.2 = 2.3 ~ 2.3 inches
 
If 12 inches of irrigation water was required in this field for total crop consumptive use, then the total crop water demand in this case is consumptive use plus the leaching requirement: 
 
Total crop water demand (in this example) = 12.0 + 2.3 = 13.8 or ~ 14 inches total
 
Considering the total crop-water demand from this AZMET crop-water use tool plus the leaching requirement, we can compare that with the amount of irrigation water that was actually applied to the field.  This can provide an estimate of the agronomic efficiency for a given field of lettuce, or any of the for other leafy green vegetable crops that we commonly grow in this area and select from tool’s menu.  
 
It serves us well to measure and understand the relationship between crop demand (consumptive use plus leaching requirements) versus the irrigation water that is applied to a given field.  
 
References
 Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9), D05109.
 
Ayers, R.S. and D.W. Westcot. 1989 (reprinted 1994). Water quality for agriculture.  FAO Irrigation and Drainage Paper 29 Rev. 1. ISBN 92-5-102263-1. Food and Agriculture Organization of the United Nations Rome, 1985 © FAO.
https://www.fao.org/3/t0234e/t0234e00.htm
 
Erie, L.J., O.A French, D.A. Bucks, and K. Harris. 1981. Consumptive Use of Water by Major Crops in the Southwestern United States.  United States Department of Agriculture, Conservation Research Report No. 29.
 
Khokhar, T. 2017.  World Bank. 
https://blogs.worldbank.org/opendata/chart-globally-70-freshwater-used-agriculture
 
Maas, E.V. 1984. Crop tolerance to salinity.  California Agriculture, October 1984. https://calag.ucanr.edu/archive/?type=pdf&article=ca.v038n10p20
 
Maas, E.V. 1986. Salt tolerance of plants. Appl. Agric. Res., 1, 12-36.
 
Maas, E.V. and S.R. Grattan.  1999. Crop yields as affected by salinity, Agricultural Drainage, Agronomy Monograph No. 38.
 
Maas, E. V., and Grattan, S. R. (1999).  Crop yields as affected by salinity, agricultural
drainage, Agronomy Monograph No. 38, R. W. 
 
Maas, E. V., and Grieve, C. M. 1994. “Salt tolerance of plants at different growth stages,” in Proc., Int. Conf. Current Developments in Salinity and Drought Tolerance of Plants. January 7–11, 1990, Tando Jam, Pakistan, 181–197.
 
Maas, E. V., and Hoffman, G. J. (1977).  “Crop salt tolerance: Current assessment.”

Bindu Poudel-Ward, Martin Porchas Sr., Martin Porchas Jr., Neeraja Singh, Johan Murcia, and Rebecca Ramirez,and Jason Furr 
Yuma Agricultural Center, University of Arizona, Yuma, AZ
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 15, 2022 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 5, 2023  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	Max	Min	Avg	Rain
November (2022)	74°F	47°F	60°F	0.00
December (2022)	69°F	42°F	54°F	0.11
January	67°F	42°F	55°F	0.16
February	70°F	41°F	55°F	0.37
March	75°F	46°F	62°F	0.28

 
 
Downy mildew (caused by Bremia lactucae) rating was done on variety Magosa. Disease was first seen on 1-9-22. Foliar applications were made on January 13^th, January 24^th, and February 1^st 2022. Disease rating was done on February 3^, 2023. Fungicide application was done on : Feb-08, 2023, Feb 20, 2023 and March 2, 2023. 
Disease rating was done  March 15, 2023. 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. The most effective fungicides, that held the percentage of leaves that were infected to 20% or less, included Cevya, Reason, Torac EC and Stargus +Torac.

Due a lack of effective post-emergence herbicides, most vegetable crops are hand weeded following cultivation to remove in-row weeds. This operation is costly and finding labor to perform the task has become increasingly difficult. Precision micro-sprayers for delivering herbicides have been developed, but lack sufficient speed, accuracy and off-target spray control to be commercially viable. To address this, a high speed, centimeter scale resolution sprayer that can spot apply herbicides to weeds with minimal off-target spray while traveling speeds that are viable for commercial farming operations was developed. The objective of this research was to evaluate the performance of the device in terms of spray delivery accuracy, off-target spray quantity, weed control efficacy and crop safety. The spray assembly comprised 12 custom-built spray modules spaced 1 cm apart. The device was tested with lettuce in the laboratory at a travel speed on 2.0 mph while targeting three weed species at three stages of growth. Results showed that targeting accuracy of spray delivered was ± 2 mm and that the percentage of off-target spray was less than 3%. Weed control efficacy exceeded 95% and there was no observable crop injury. Improvements to the original design were identified and the enhanced sprayer was found to provide sub-centimeter precision. Practical applications of the technologies developed include precision spot spraying of weeds in lettuce, carrot, onion, spring mix and other vegetable crops. A remaining technical challenge for the realization of an automated precision weeding machine is the development of a camera imaging system capable of reliable crop/weed differentiation. Field testing of the precision spot sprayers is also needed.
Click the following link to watch presentation on Centimeter Scale Resolution Spot Sprayer.
https://www.youtube.com/watch?v=XBNGsIu27K0

The Yuma IPM Team has received requests for herbicide efficacy data generated locally for Onion and Broccoli. 
We are currently doing some evaluations for direct seeded broccoli. Some of the treatments suggested by PCAs and growers are Devrinol DF XT at the rate of 1.0 and 2.0 lb, also Devrinol 2-XT at the rate of 1.0 and 2.0 qt. Additional preemergence herbicides included in the trials are Prefar 6 qt, Trifluralin 1.5 pt. Other treatments included are Goal Tender and Prowl with a directed application at 3-5 leaves. In a separate broccoli test we are looking at different incorporation timings of Devrinol due to some stunting issues reported. Our trial includes 12, 24, 36 hour sprinkler irrigation incorporation times for the liquid and dry formulations. Phytotoxicity will be evaluated and reported to you in this newsletter and University of Arizona Workshops.
 
For onions we established trials including treatments suggested such as Ethotron SC at 32 fl oz to a fine soil. Also included Prefar, Dual Magnum and Treflan preemergence. We will compare with Outlook plus Prowl and Goal Tender at 3 leaf stage.
Additionally, Corteva Agriscience is also focused in providing some options for weed control in both broccoli and onions. Some of their products been evaluated at the Agricultural Center are Rinskor (Hulk) and Enversa at post and preemergence. 
We thank you for your treatment suggestions, which are incredibly helpful for designing the experiments we are conducting. We are looking forward to sharing the results with you.

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.

Leaf miners: Adult activity light in all areas, about average for this time of season