After Bemisia whiteflies invaded the desert in 1991, production of fall melons became very difficult, and acreage declined in many desert growing areas. With the Section 18 registration of Admire 2F in 1993, growers could effectively control whiteflies again and soon began to profitably produce fall melons in Yuma, and central Arizona. Then in 2007, a new challenge emerged for melon growers when Cucurbit Yellows Stunting Disorder Virus (CYSDV) became established throughout the desert Southwest. It’s taken some time, but economic production of fall melons is back on track in Arizona. In the past several growing seasons, whitefly populations during the fall have been lighter than normal, and CYSDV incidence on fall melons had been held below 20% incidence except for the 2021 season when CYSDV incidence increased dramatically even though whitefly abundance was relatively light (see graph below). This occurred due to abandoned watermelons (~200 acres) in the Tacna area that were left untreated all summer. The watermelon acreage was found 1-5 mile southeast (upwind) of several cantaloupe and honeydew fields and had an abundance of whiteflies and heavily infected with CYSDV.  Although the abandoned watermelons had not been irrigated during the summer, heavy monsoon activity in July and August (>3” rain), sustained foliage in the fields and allowed both whitefly adults and CYSDV to build up to unusually high levels. We estimated that the incidence of CYSDV in all the cantaloupe/honeydew fields in the Tacna and Roll areas was greater than 80% at harvest. Melon yields were significantly impacted, and several fields were not harvested.  These results stress the importance of cultural management of whiteflies exemplified by results of the fall 2022 and 2023 season (as well as the 2015-2020 growing seasons) in the Tacna/Roll growing area. To download the most recent information for whitefly and CYSDV management in fall melons go to 2024 Guidelines for Whitefly / CYSDV Management on Fall Melons.  
 
The epidemiology of CYSDV is a complex relationship between the virus, the adult whitefly vector, and our local melon cropping system.  It has been our goal over the past 17 years to understand this pathosystem and develop practical approaches for reducing CYSDV impact on fall melon production. We continue to develop new information on cultural and chemical control tactics for adult whiteflies (see 2024 Guidelines).  Our knowledge to date suggests that fall melons produced near cotton, alfalfa or near areas where spring melons were recently produced are at the highest risk of infection. When practical, growers should isolate fall melon plantings as far away as possible from these sources of whiteflies and CYSDV. Growers forced to plant fall melons near these crops should be vigilant in minimizing adult whitefly infestation levels with insecticides during pre-bloom growth stages. This can be achieved with at-planting and side-dress applications of soil insecticide (Venom, Scorpion, Sivanto) and well-timed applications of foliar sprays including PQZ and Sefina, feeding disruptors with a high degree of bee safety. Based on local research, both products will provide excellent adult knockdown and CYSDV suppression when used in a fall management program.  Transform, Assail, Minecto Pro and Exirel are also labeled for use on melons and provide rotational alternatives for adult knockdown.  Bottom line: cost-effective chemical tools are available, but minimizing whitefly abundance in the surrounding crop landscape (e.g., cotton, volunteer melons) is critical for them to be most effective.

In arid and semi-arid regions, water is our first limiting factor in a crop production system, followed closely by bio-available nitrogen (N).  Thus, our management of water and N are critically important to produce a healthy crop with good yields and quality.
 
Water and nutrient demands coincide with the fruiting cycle and efficient management of irrigation water and plant nutrients is enhanced by tracking crop development in the field.  The use of heat units (HUs) with 86/55 ^oF upper and lower thresholds can be applied to warm season crops in the desert Southwest in relation to the thermal environmental impacts on the development of all crop systems (Brown, 1989), including chiles, (Figures 1 and 2).
 
Crop Phenology Relationship to Water and Nitrogen Demand
 
Phenological guidelines have been developed for many crops, including New Mexico type chiles (Soto-Ortiz and Silvertooth, 2007 and Silvertooth, et al, 2010; Figure 1).  This phenological guideline can be used to identify or predict important stages of crop development that impact physiological requirements.  For example, a phenological guideline can help identify stages of growth in relation to crop water use (consumptive use) and nutrient uptake patterns (Figure 3).
 
This information allows growers to improve the timing of water and N inputs to improve production efficiency.  For some crops or production situations HU based phenological guidelines can be used to project critical dates such as harvest or crop termination.  Many other applications related to crop management (e.g., pest management) can be derived from a better understanding of crop growth and development patterns.

Figure 1.  Typical relationship between the rate of plant growth and development
and temperature.  Growth and development ceases when temperatures decline
below the lower temperature threshold (A) or increase above the upper
temperature threshold (C).  Growth and development increases rapidly when
temperatures fall between the lower and upper temperature thresholds (B).


Figure 2.  Basic phenological guideline for irrigated New Mexico-type chiles.

References
Brown, P. W.  1989.  Heat units.  Bull. 8915, Univ. of Arizona Cooperative Extension, College of Ag., Tucson, AZ.
Silvertooth, J.C., P.W. Brown, and S. Walker.  2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum).  University of Arizona Cooperative Extension Bulletin No. AZ 1529
Soto-Ortiz, R. and J.C. Silvertooth.  2007. A Crop Phenology Model for Irrigated New Mexico Chile (Capsicum annuum L.) The 2007 Vegetable Report. Jan 08:104-122. 

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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 16, 2023 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 24 and final reading was taken on March 13, 2023. Spray treatment were applied on February 16, February 23, and March 2 of 2023,(see table).  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. Orondis Ultra provided the most effective control against the disease. No phytotoxicity was observed in any of the treatments in this trial. 

At the UC Cooperative Extension 2024 Automated Technology Field Day in Salinas, CA a couple of weeks ago, 12 of the latest automated and robotic technologies were demonstrated in the field. Most were designed for weed control or thinning vegetable crops. Several of the technologies shown are relatively “new” for the 2024 season. These included laser weeders that also are capable of thinning lettuce (Fig. 1 & 2), a smart cultivator/side-dresser that cultivates between individual crop plants and simultaneously applies fertilizer at a variable rate depending on plant size (Fig. 3), a spot sprayer that utilizes superheated vegetable oil to kill weeds (Fig. 4), and a self-propelled machine that disinfests soil prior to planting using steam. Although the test runs were short, I was impressed with the possibilities for these machines. Company representatives said they will be in Arizona this upcoming season and are interested in meeting with growers. Company contact information can be found at their respective websites, or feel free to contact me if you would like additional information.

Fig. 1. Carbon Robotics’¹ (Seattle, WA) LaserWeeder^TM. The unit utilizes a vision
system to detect crop plants and weeds. A laser is used to kill unwanted plants.
The machine can be used for weeding or thinning lettuce crops (bottom).


Fig. 2. L&A¹ (Chico, WA) autonomous laser weeding/thinning robot. The unit is
equipped with a vision system to detect crop plants and weeds, and a laser to kill
unwanted plants. The machine can be used for crop thinning or weeding (weeded
carrot crop, bottom).


Fig. 3. Stout Industrial Technology’s¹ (Salinas, CA) smart cultivator/side
dresser. The unit is equipped with a vision system for detecting crop plants, and
blades that move in and out of the crop row to remove in-row weeds. Liquid
fertilizer (shown colored with blue dye) is applied at a variable rate depending on
plant size.


Fig. 4. Tensorfield Agriculture¹ (Union City, CA) precision spot spray weeding
machine. The unit has an 80” wide spray boom equipped with 232 individually
controllable spray nozzles to spot spray weeds with superheated vegetable oil
(bottom left, bottom right). A vision system is used to detect weeds and spot
spray resolution is ¼”.


Fig. 5. UA/UC Davis self-propelled band-steam applicator. Device injects steam
into the soil to kill weed seed and soilborne pathogens prior to planting.

[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.

Question to IPM team:
I applied Raptor and Pursuit to an alfalfa field. Can you provide some information on the carryover and phytotoxicity to onions?
IPM Team:      We haven’t done plant back evaluations with these products. The soil persistence that is mentioned in the AZ PCA study guide is 2-4 months for the Raptor and 3-12 months for Pursuit. The label specifies longer replanting intervals for various crops and suggests that “before planting any crop not listed elsewhere in Rotational Crop Restrictions, a successful field bioassay must be completed. The field bioassay consists of a test strip of the intended rotational crop planted across the previously treated field and grown to maturity”.
An interesting journal article “Injury to Vegetable Crops from Herbicides Applied in Previous Years”, mentions In 1995, residual imazethapyr delayed tomato maturity but did not reduce tomato yield. Other vegetable crops were not injured by herbicide residues. Then in 1997 “imazethapyr carryover injured cabbage, onion, and tomato plants and reduced tomato yield most injury occurred at 2X and 4X rates¹.
The “Carrington Research Center in NDSU did an herbicide carryover study included here which presents the “response of onions to herbicides applied to soybean the previous year²” including Raptor and Pursuit.  Also, in this study (table below) onion injury was significant in the 2X and 4X rates.

Another “Evaluation of Pre and Post Emergence Herbicides on Yield Contributing and Quality Characters in Onion” found that “Imazethapyr @ 100 g a.i / ha as post emergence application (20 DAT) coupled with preemergence herbicides produced the lower (yield) values than weedy check as Imazethapyr found to be toxic to the Onion^3”.
The field study “Efficacy of imidazolinone herbicides applied to imidazolinone resistant maize and their carryover effect on rotational crops” showed sensitivity of rotational crops, from high to low, was the following: Beta vulgaris>Capsicum annum>Lycopersicum esculentum>Cucumis melo>Hordeum vulgare>Medicago sativa>Lolium multiflorum>Avena sativa>Pisum sativum>Allium cepa (onion)>Zea mays.
The label’s recommendation of doing a bioassay is very useful. Many factors can affect herbicide carryover and every case is different. Low soil moisture might not permit appropriate soil conditions for an efficient microbiological and chemical degradation of imidazolinone herbicides³. Other elements to consider are the soil texture, pH, soil temperature, microbial activity, photodegradation, previous crop, water applied after application of the herbicide, soil tillage intensity. The combinations of these elements could contribute to dissipation of these products. Also, having this information would help us determine the best IPM strategy.
 



References:

1. Greenland RG. Injury to vegetable crops from herbicides applied in previous years. Weed Technology. 2003;17(1):73-78. doi:10.1614/0890-037X(2003)017[0073:ITVCFH]2.0.CO;2
2. Herbicide Carryover Study, 1997 Richard Greenland
3. Evaluation of Pre and Post Emergence Herbicides on Yield Contributing and Quality Characters in Onion cv. N-53 M. Venkateswara Reddy* , K. Umajyothi, P. Syam Sundar Reddy and K. Sasikala
4. Efficacy of imidazolinone herbicides applied to imidazolinoneresistant maize and their carryover effect on rotational crops C. Alister1 , M. Kogan

Resistant varieties are crucial for effective insect pest management, more specifically in organic crop production. When growing crops organically, resistant varieties should be the first line of defense against insect pests. Compared to nonresistant varieties, insect-resistant crop varieties are less vulnerable to insect attacks or yield well despite insect attacks. 

Resistance in crops can be expressed through different mechanisms, including antibiosis, antixenosis, and tolerance. For the antibiosis mechanism, the resistant crops act on the life history traits of the pest, such as affecting fecundity, growth, development, and survival. Thus, this reduces the pest population. On the other hand, antixenosis is characterized by the ability of the crop to affect the behavior of the pest by deterring it after initial tasting or probing, which is non-preference. For the tolerance mechanism, however, the crops can sustain a high density of pests and still maintain their yield potential. In most cases, the overall resistance of a variety is a combination of all these three mechanisms. 

There is also a type of resistance called phenological resistance, field resistance, or pseudo-resistance, which is when the crop appears to be resistant because it is at a less susceptible stage when a pest attack occurs. This may happen either because of the rate of development of the crop or due to management practices implemented, causing the crop to escape the pest pressure. Thus, the implementation of proper agronomic practices plays a significant role in improving the ability of crops to resist pest attacks. 

In certain scenarios, additional insect control measures such as the use of bioinsecticides (in organic production) and natural enemies may be necessary in conjunction with an insect-resistant variety for comprehensive pest control. However, even in cases where additional control measures are required, the cultivation of a resistant variety can significantly delay and reduce the amount of insecticide applications needed. This underscores the economic, ecological, and environmental benefits of using insect-resistant crop varieties. 

Previous studies conducted at Yuma Agricultural Center demonstrated that resistant lettuce varieties can provide suitable control of aphids affecting lettuce in the region. Therefore, it is very important to consider cultivating insect-resistant lettuce varieties for suitable management of aphids in organic lettuce production since biological insecticide options are currently limited. My lab is planning to evaluate several lettuce varieties to determine lettuce varieties that carry resistance against aphids in an attempt to generate applicable information on varieties that could fit well within the production practices and environmental conditions of Arizona’s vegetable-growing regions. 

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.