With the produce season rapidly winding down, it’s time to begin thinking about insect management in melons. Spring melon crops are rapidly growing, and so are insect pest populations. Cabbage loopers and leafminers are becoming evident in some areas, and PCAs should start ramping up their monitoring and sampling. More importantly, whitely populations are quietly becoming abundant on the spring melons of all sizes. Adults can easily be found on recently planted melons located at the Yuma Ag Center, and reports from local PCAs suggest that adult populations are beginning to show up on older plantings. As temperatures increase and crops/weeds mature, avoidance of excessive feeding from whitefly nymphs should be the primary concern on all melon types. Although CYSDV does occur in later spring melons, it is rarely yield limiting. But honeydew and sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability is whiteflies are not adequately controlled.  Our research has shown that to prevent fruit yield and quality losses on spring melons, a foliar insecticide treatment should be applied on threshold; that is, when average adult numbers exceed 2 per leaf when averaged across an entire melon field. At this level of adult abundance, immature populations are beginning to colonize. Timing sprays based on the adult threshold has been shown to significantly reduce the chance of yield / quality losses during spring harvests.  This threshold applies for the use of recommended IGRs (Courier, Knack, Cormoran, and Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion), neonicotinoid-like compounds (Sivanto prime and Transform), diamides, (Exirel and Minecto Pro) and the new feeding disruptors (PQZ and Sefina).  For more information on whitefly management and available insecticides, go to these documents on Insect Management on Spring Melons: Whiteflies and Whitefly Control Chart-Spring Melons -2023. Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine bee safety of a product before making an application in a melon field.  If applications are necessary during bloom, only apply a product that is considered bee safe (e.g., PQZ, Sefina, Sivanto, Assail). We also recommend that insecticides only be applied when honeybees are not actively working in the field (e.g. 10:00 pm – 3: 00 am). 

After more than 22 years of severe drought, watersheds across western North America are experiencing critical water levels that threaten agricultural and domestic supplies.  The Colorado River shortage is emblematic of these shortages.
 
These external factors are significantly impacting crop production systems at the field level in the desert Southwest.  Irrigation districts in central Arizona, particularly Pinal County, have lost access to Colorado River water allocations via the Central Arizona Project because of Tier 1 and Tier 2a reductions from the Drought Contingency Plan.  Reductions have also been imposed on Nevada and Mexico allocations.  Water levels in Lakes Powell and Mead are at less than 25% capacity and continue to decline due to insufficient action to arrest this worsening situation.
 
Since diversions to agriculture represent approximately 80% of the Colorado River water use, the basic arithmetic on the balancing of the river’s water budget will depend significantly on how agricultural diversions are ultimately managed in the process.  Further reductions of Colorado River water diversions to agricultural districts seems rather inevitable but many uncertainties remain with discussions and negotiations ongoing.
 
Water is the first and most limiting agronomic factor in crop production.  To deal with these challenging conditions from the water shortages at the field level agronomically, the crop and soil factors, there are some fundamentals that we can refer to for assistance.  
 
Dr. Jeremy Weiss, program manager for the University of Arizona AZMET system, has recently developed a valuable tool that provides 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.  Accumulations of ETc values over the previous week and a range of dates are shown based on a date of planting, which is selected by the user.  In this model, 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.
 
To access this crop-water estimate tool please refer to the following link:
 
https://viz.datascience.arizona.edu/azmet/azmet-crop-water-use-estimates/
 
For example, using lettuce (either iceberg or romaine) with a 1 November planting date through 11 December, we can see from this model the reference evaporation, listed as “water use” (ETo) and the cumulative crop evapotranspiration (ETc, or total crop-water use) of lettuce since the selected planting date.  
 
Since planting on 1 November through 11 December, a total crop water use, or the ETc, has been 3.57 inches in the Yuma Valley.  Last week, from 5-11 December, ETc has been 0.56 inches in the Yuma Valley.
 
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 = 9.8 X 0.2 = 1.96 ~ 2 inches
 
Thus, total crop water demand in this case = 10 + 2 = 12 inches total
 
Contrasting this estimate of total crop-water use with the amount of irrigation water that was applied to the field can provide an estimate of the agronomic efficiency for a given field of lettuce.  We can do the same thing using this tool for other primary leafy green vegetable crops.
 
We are working in times of decreasing water availability and increasing scrutiny in agriculture.  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. 

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.

Despite the commercialization of numerous automated weeding machines, most fields are still hand weeded. A reason for this is that automated weeding machines cannot remove weeds close to the crop plant or are not highly efficient yet at doing so. 

A technique that I’ve been curious about for some time now to minimize the number of weeds close to crop plants is the use of early (seedling stage of growth) close cultivation. Early close cultivation can be accomplished using a camera guided cultivator equipped with specially designed cultivating tools. Examples of the technology and technique were demoed at our 2016 and 2022 AgTech Field Days by K.U.L.T.-Kress, LLC¹, the manufacturer of the equipment. The systems basically comprised a camera vision system for tracking the crop row, a toolbar attached to a parallel linkage that facilitated side-to-side movement and small cultivator assemblies for each of the seedlines (Fig. 1). In the demos conducted in lettuce, cultivating tools were positioned such that the uncultivated band was only about 2” wide (Fig. 2). If the crop were thinned by hand hoe or chemically, only a small area (roughly  2” x 2”) around the keeper plant would remain that had not been cultivated or treated with an herbicide material (Fig. 3). Assuming that existing weeds were controlled, and no new weeds emerge, the number of weeds close to the crop plant would be minimal. I realize soil disturbance near the crop plant is not desired but cultivating 1” away from seedling lettuce should be comparable to, and not cause any more crop injury than thinning seedlings spaced 2” apart with a hand hoe. I’m curious what your thoughts are on this. I’d love to hear your feedback.

[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.

Fig. 1. K.U.L.T.-Kress camera guided cultivator (a) equipped with cultivating tools
designed for close cultivation (b). (Photo credits: Mazin Saber, University of
Arizona)


Fig. 2. Close cultivation of seedling lettuce with a camera guided
cultivator. Close up view (a) and far view (b). (Photo credits: Mazin Saber,
University of Arizona)


Fig. 3. Close cultivation of seedling lettuce with camera guided
cultivator leaves a roughly 2” wide uncultivated band around the
seedline (a). Thinning by hand hoe or chemically would kill plants in the
seedline (red shaded area) and leave a small area (roughly 2” x 2”)
(indicated by white box) around the keeper plant that had not been
cultivated or treated with an herbicidal material (b). Assuming no new
weeds emerge, the number of weeds near the crop plant that are
difficult and time consuming to remove is minimal.


Fig. 4. Video of camera guided cultivator equipped with cultivating tools
designed for close cultivation operating in six-line seedling romaine
lettuce. Click here or on the image to see the video. (Video credit: Mazin
Saber, University of Arizona)

 

The subject of Prefar (bensulide) residue in the soil and waiting period before spinach was was brought to the IPM team in the past. Inadvertently some sections of fields with bensulide residue could be scheduled for planting spinach too soon. The rotational crop instructions on the label say: “All other crops should not be planted for 120 days and the soil must be tilled to a minimum of 4 inches prior to replanting”. The Section VI of the PCA Sudy Guide recommends 4 months recropping interval for Alfalfa, wheat and Cotton. 
The site Gowan.com explains specifically: “Do not use Prefar 4-E on spinach or Swiss Chard as severe phytotoxicity will occur”¹.
We also heard different opinions, some minimizing the persistence on this herbicide in fine textured soils. So, we tried it in our clay soil at the Yuma Ag Center with a 40% Clay, 38% Sand, and 22% Silt.
After a bensulide lettuce evaluation was completed, we reworked the beds and planted spinach. This was done 45 days after treated.
Here’s how the stand was affected:

Figure1. Effect of bensulide herbicide residue in spinach stand. Broadcast “DI” means delayed incorporated and “II” Immediately incorporated with sprinkler irrigation. 
 
Additionally, leaves, roots and plant lengths were evaluated showing vigor reduction in treated plots.


Figure 2. Bensulide effects to spinach stand 45 planted 45DAT.

1. https://www.gowanco.com/products/prefar-4-e

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased considerably y in the past 2 weeks and about average for late summer
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Wellton) particularly near alfalfa
 
Cabbage looper:         
Cabbage looper numbers remain low consistent previous years.
 
Diamondback moth:      
DBM moths were not caught in any trap since June; average for this time of the year.
 
Whitefly:                      
Adult movement decreased in past 2 weeks consistent with previous years
 
Thrips:                         
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity has highest in Wellton and Dome Valley, and slightly above average for early August