The produce harvest season is well underway and fall acres are slowly beginning to finish up. Although pest pressure is decreasing with cooler temperatures, the forecast of El Nino (warm,  wet weather) conditions could be ideal for insect growth and survival this winter and spring.  So, it’s very possible you could observe above average insect numbers come January, particularly if growers are lax in their post-harvest farming practices right now. Insect dispersal from alternate crops and weed hosts can often be significantly reduced with timely cultural practices following harvest.  The longer a harvested crop remains above ground, more insects can build up and move to adjacent plant hosts-especially in dry and warm weather.  Thus, sanitation and clean culture are important cultural practices that can be employed by growers on a field by field, and area-wide basis to reduce pest populations during the winter and spring.  And sanitation will be very important this year for preventing the spread Impatiens Necrotic Spot Virus (INSV) infecting lettuce crops. We reported last time that INSV has moved into the desert again on coastal transplants and those fields are now being harvested. With this comes the potential for INSV to spread to adjacent direct-seeded fields within a 1-mile radius of the transplants. Remember, INSV is transmitted by western flower thrips (WFT) adults but acquired only by 1^st and 2^nd instar larvae feeding on infected lettuce and weed hosts.  It is a complex pathosystem that makes WFT management more important than ever. It will be important to minimize immature development and adult dispersal as much as possible. And we can’t rely solely on insecticides to accomplish this.  So, the fewer WFT moving around in the cropping systems, the less chance for spread of INSV. As a first line of defense, growers should disc under lettuce crop residues immediately after harvest of fall and winter crops.  Neglected post-harvested lettuce crops can serve as a significant reservoir for INSV, and for infected WFT also.  Clean culture is also important for preventing potential INSV infections.   Weeds are notorious for harboring important plant viruses and their insect vectors. We’ve experienced this for years in the desert with aphid-borne potyviruses and whitefly criniviruses. Research has shown that several common weed species we find growing in the desert serve as hosts to both WFT and INVS. More importantly, little mallow and nettleleaf goosefoot can be found throughout the desert during the winter and WFT reproduce prolifically on these weed hosts.  So, maintaining a clean culture via thorough weed control in and around crops can help prevent WFT buildup and dispersal, and potentially the spread of INSV in spring crops. Keep those ditch banks clean. For more information on Thrips and INSV management, visit this link:  Thrips and INSV Management in Desert Lettuce

Yogi Berra once retorted “You can observe a lot by just watching”

Springtime in the desert serves host to a new spring melon/cantaloupe crop.  That is particularly true in the lower Colorado River valleys.  Cantaloupes (Cucumis melo ‘reticulatus’ L.) or “melons” are one of the important spring and fall vegetable crops of Arizona and the desert Southwest.  
 
Technically, “true” cantaloupes (Cucumis melo ‘cantaloupensis’) are rough, warty fruit, primarily grown in Europe.  On a production scale, cantaloupes are not grown commercially in the United States.  However, in the United States “cantaloupe” has become a general name of all netted, musk-scented melons (Simonne et al., 1998 and Soto, 2012).  
 
Being able to accurately describe and predict important stages of crop growth and development (crop phenology) and harvest dates is important for improving melon crop management (e.g. fertilization, irrigation, harvest scheduling, pest management activities, labor, and machinery management, etc.). Since plants operate on “thermal time”, they have no regard for calendars or time as we commonly measure it.  So, it is best to monitor and predict plant development based on the actual thermal conditions in the plant’s environment.  
 
Various forms of temperature measurements and units commonly referred to as heat units (HU), growing degree units (GDU), or growing degree days (GDD) have been utilized in numerous studies to predict phenological events for many crop plants (Baskerville and Emin, 1969; Brown, 1989; Baker and Reddy, 2001; and Soto, 2012).  A graphical depiction of HU computation using the single sine curve procedure is presented in Figure 1 (Brown, 1989).
 
Since 2000, we have been working on the development and annual testing of a phenology model for desert cantaloupe production for Arizona conditions.  The basic cantaloupe phenology model is shown in Figure 2 (Silvertooth, 2003; Soto et al., 2006; and Soto, 2012).  This melon crop phenology model was developed under fully irrigated conditions.  
 
Guideposts indicated in Figure 2 represent general average or “target” values and a slight degree of variation is normal.  It is important to note that water or nitrogen stress are two factors that will significantly alter physiological development of a crop.  
 
Referencing the data from the Arizona Meteorological Network (AZMET) and several locations in the Yuma area, the HU accumulations (86/55 ºF thresholds) from a range of possible 2024 melon planting dates to 28 April are listed in Table 1.  These HU accumulations can be referenced against the melon phenology model in Figure 2 and crop conditions in the field.
 
I encourage those who are working with spring cantaloupe production this season to test and evaluate this crop phenology model in the field under various planting dates, varieties, and conditions.  The information in Table 1 can help serve as a reference to check melon crop development in the field against this phenological model.  We appreciate your feedback.
 
References:
 
Baker, J.T., and V.R. Reddy. 2001. Temperature effects on phenological development and yield of muskmelon. Annals of Botany. 87:605-613.
 
Baskerville, G.L., and P. Emin.  1969. Rapid estimation of heat accumulation from maximum and minimum temperatures. Ecology 50:514-517.
 
Brown, P. W.  1989.  Heat units. Ariz. Coop. Ext. Bull. 8915. Univ. of Arizona, Tucson, AZ.
 
Silvertooth, J.C. 2003. Nutrient uptake in irrigated cantaloupes. Annual meeting, ASA-CSSA-SSSA, Denver, CO.
 
Simonne, A., E. Simonne, R. Boozer, and J. Pitts. 1998. A matter of taste: Consumer preferences studies identify favorite small melon varieties. Highlights of Agricultural Research. 45(2):7-9.
 
Soto, R. O. 2012. Crop phenology and dry matter accumulation and portioning for irrigated spring cantaloupes in the desert Southwest.  Ph.D. Dissertation, Department of Soil, Water and Environmental Science, University of Arizona.
 
Soto-Ortiz, R., J.C. Silvertooth, and A. Galadima.  2006.  Nutrient uptake patterns in irrigated melons (Cucumis melo L.).  Annual Meetings, ASA-CSSA-SSSA, Indianapolis, IN.
 

Location	15 January	1 February	15 February	1 March
Yuma Valley	994	893	832	680
Yuma N. Gila	972	856	797	650
Yuma South	961	862	802	655

Table 1.  Heat unit accumulations (86/55 ºF thresholds) from four possible 2024 planting dates utilizing Arizona Meteorological Network (AZMET) data for each representative site.
 
Yuma Valley:https://ag.arizona.edu/azmet/02.htm
Yuma South: https://ag.arizona.edu/azmet/36.htm
Yuma North Gila: https://ag.arizona.edu/azmet/14.htm

Figure 1. Graphical depiction of heat unit computation using the single sine
curve procedure. A sine curve is fit through the daily maximum and minimum
temperatures to recreate the daily temperature cycle. The upper and lower
temperature thresholds for growth and development are then superimposed
on the figure. Mathematical integration is then used to measure the area
bounded by the sine cure and the two temperature thresholds (grey area).
(Brown, 1989)


Figure 2. Heat Units Accumulated After Planting (HUAP, 86/55 ^oF)

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

 
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on January30 2023, February 9, 2023 and February 22, 2023.Disease was first seen on February 13,2022. Disease rating was done on March 15, 2022.   Disease severity was determined  by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 0.5 = one to a few very small powdery mildew colonies on bottom leaves; 1 = powdery mildew present on bottom leaves of plant; 2 = powdery mildew present on bottom leaves and lower wrapper leaves; 3 = powdery mildew present on bottom leaves and all wrapper leaves; 4 = powdery mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = powdery mildew present on entire plant. These ratings were transformed to percentage of leaves infected values before being statistically analyzed. Yield loss due to rejected lettuce heads would likely begin to occur on plants with a powdery mildew rating above 2.0 (percentage of leaves infected value of 40).         
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. All treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides were Rhyme, Merivon and Quintec.

New automated/robotic ag technologies are coming out all the time. Ever wonder how they function in the “real world” and whether they are cost effective? Western Growers recently released a case study report on the economic impact of Carbon Robotics LaserWeeder on overall weeding costs. The study tracked expenses, productivity, and labor savings of the machine operating over one year on several thousand acres at two commercial farms, Braga Fresh and Triangle Farms. It is a well done, detailed study enriched by insightful comments and practical recommendations made by the farm managers responsible for machine operations. It’s an easy read and well worth the time for those interested in the economic and overall feasibility of laser weeding. Check it out hereby clicking the image below. I don’t want to be a spoiler, but I was surprised to learn that despite the initial high cost of the laser weeder ($1.2 million), overall weeding costs at both farms were reduced by about 40% (>$250/acre) in high-density organic crops such as spring mix and spinach.
Stay tuned. Western Growers plans to release five more automation technology case study reports within the next year. Upcoming reports include grower case studies experiences with automated weeding machines from Stout Industrial Technology, Inc. and Ecorobotix; and with autonomous ag platforms from Burro, GUSS Automation, and Bluewhite.

Fig. 1. Western Growers case study report on the economic impact of Carbon
Robotics laser weeding machine on weeding costs at two commercial leafy
green vegetable farms. Click here or on the figure to view. (Photo credit: The
Western Growers Center for Innovation & Technology)

What can I use to control an infestation of broadleaves in a wheat field that is close to harvesting?  ... our friends PCAs and growers asked.
It is well known that weeds slow harvesting operations and increase combine repair costs; product may have excessive grain moisture and/or weed seeds in wheat³. Some have reported color changes and the taste of weeds in the product.

One commonly used product has been Roundup, and the label recommendations are the following: “This product provides weed control when applied prior to harvest of feed barley and wheat. For feed barley, apply after the hard-dough stage and when the grain contains 20 percent moisture or less. For wheat, apply after the hard-dough stage of grain at 30 percent or less grain moisture” ³.
There are concerns of the presence of glyphosate in shipments from US and Canada which they attribute to “the practice of pre-harvest spraying”. Therefore, some growers are looking for alternatives to this herbicide².
Sharpen (saflufenacil) is a quick acting burndown product for broadleaf weed control in field crops and it has been labeled and approved in the US for this purpose. 
Consulting with a BASF representative we learned that Sharpen is labeled in Arizona (not CA) for this use. The recommended rate is 1-2 fl oz., adding Ammonium Sulfate adjuvant and Methylated Seed Oil. Also, apply at the hard dough stage with no more than 30% moisture, with 10 GPA by ground or 5 GPA by air. 
Knezevic (2009) stated “MSO was the adjuvant that provided the greatest enhancement of saflufenacil across all species tested. COC was the second-best adjuvant and provided control similar to MSO on many weed species. NIS provided the least enhancement of saflufenacil⁴. 
 
An Agronomy Update from Kansas State University recommended to “Consult grain buyer to see if they will accept Sharpen treated wheat because of export restrictions”⁵.

References:

1. http://canola.okstate.edu/cropproduction/herbicides/labels/Roundup%20PowerMax%20Label.pdf

2. https://sustainablepulse.com/2019/08/29/unique-hair-testing-project-reveals-high-levels-of-glyphosate-and-ampa-in-members-of-the-japanese-parliament/

3. https://www.farmprogress.com/weeds/controlling-broadleaf-weeds-in-winter-wheat-is-essential

4. Knezevic, S. Z., Datta, A., Scott, J., & Charvat, L. D. (2009). Adjuvants influenced saflufenacil efficacy on fall-emerging weeds. Weed Technology, 23(3), 340-345.

5. https://cropwatch.unl.edu/2019/ksu-pre-harvest-weed-control-wheat-sharpen-update

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