With the produce season essentially finished, 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 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 -2024. 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).

In Arizona agriculture, we have the benefit of generally working with good soils that exist in alluvial valleys or the terraces immediately adjacent to the alluvial valleys, e.g. the mesa areas.  Arizona soils are geologically young and fertile but often have high levels of salinity and often sodicity.  When reclaimed and properly managed with adequate leaching, we can reduce the salinity to manageable levels to support crop production systems.  In the case of sodic conditions, appropriate amendments are needed then followed by adequate leaching.
 
In the process of applying an irrigation in the field, it is important to recognize that not all soils are created equal.  Soil types vary across the landscape and they also vary by depth for any site or location.  This is particularly true for alluvial soils which originate from water deposition over time, such as from the Gila and/or Colorado River systems.  The soils of the lower Colorado River valleys are great examples of alluvial soils and the high degree of variability we commonly experience in the field.  With some crops, particularly more deeply rooted crops, we can sometimes nearly map the soil types across a field based on crop growth patterns.  Accordingly, this type of soil variability creates some challenges for in-field management, including irrigation management.
 
Many of the rotation crops common to the lower Colorado River Valleys, such as cotton, wheat, and sudan; are excellent examples of crops that can express growth patterns as a function of soil texture, which is clearly demonstrated in response to water stress.  The courser textured parts of the field will stress earlier and consistently have reduced plant vigor.  Anyone driving a tractor for medium to heavy tillage operations in the field will literally feel soil textural changes and anyone harvesting those fields will see it as well.  The GPS field mapping systems can detect and record these areas of soil type differences through yield monitors as well in response to crop growth and vigor.
 
Soil textures vary in terms of water holding capacities and it is important to understand the dominant soil textures in the field, not only on the surface but also through the depths of the soil profile and the effective rooting depth of the crop, Tables 1 & 2 and Figure 1.  To manage a complete field or set of fields, it is necessary to determine a functional “average” of soil texture and water holding capacity.
 
In the process of irrigation, we are attempting to replenish the soil-water extracted by the crop through evapotranspiration (ET_c).  In previous articles, the determination or estimation of crop ET_c has been discussed.
 
Therefore, with irrigation management it is important to know the fields we are working with in terms of the dominant soil textures present, the degree of variability that exists, and the general water-holding capacity of the soils.  Matching irrigation timing and volumes for each event to replenish the plant-available water for each field is important in our efforts to avoid water stress and achieve and maintain irrigation efficiency agronomically, which is providing the amount of water necessary to replenish the soil-water to field capacity with some degree of additional water needed for the leaching of soluble salts. 
 
With the high degree of variability that is common among soils in the lower Colorado River Valleys, it is both important and challenging to know the soil characteristics common in each field, the water holding capacity of the dominant soils, and the level of soil-water depletion that is being replenished with each irrigation event.

Table 1. Soil texture and water holding capacity.


Table 2. Depths to which the roots of mature crops will deplete the available water supply when grown in a deep permeable, well-drained soil under average conditions. Source: Chapter 11, "Sprinkler Irrigation," Section 15, Natural Resources Conservation Service National Engineering Handbook


Figure 1. Soil volume, soil texture, and water holding capacity relationships.
Engineering Handbook.

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.

Vol. 13, Issue 1, Published 1/12/2022
Last fall, we established two trials investigating the used of band-steam to control Fusarium wilt of lettuce. We utilized the prototype band-steam applicator (Fig 1) described in previous UA Veg IPM articles (Vol. 11 (15) to inject steam into the soil prior to planting. The concept behind band-steam is to disinfest narrow bands of soil using high temperature steam. In the trials, the steam applicator was configured to treat a 4” wide by 4” deep band of soil centered on the seedline.
Experiment results were mixed. At the field site where Fusarium inoculum loads were high, band-steam provided no benefit with virtually all lettuce plants succumbing to the disease (Fig 2a). However, at the trial site where Fusarium inoculum levels were moderate, disease incidence was reduced by more than 40%, and plants appeared to be healthier and more vigorous (Fig. 2b). We’ll be harvesting these plots soon so stay tuned to learn whether these differences translate into significant yield increases. 
If you are interested in trying band-steam on your farm, please let me know. We are in the process of constructing a second-generation band-steam applicator that has a higher capacity steam generator and simpler design than our first prototype and are seeking collaborators.

Acknowledgements
This work is partially funded by the Arizona Specialty Crop Block Grant Program
A special thank you is extended to Larry Ott and Gila Valley Farms for allowing us to conduct this research on their farm.

Fig. 1. Band-steam applicator principally comprising a 35 BHP steam generator mounted on a bed-shaper applicator sled.


Fig. 2. Lettuce seedlings at field sites with (a) very high and (b) moderate levels of Fusarium wilt of lettuce inoculum. Band-steam (left) and untreated (right) plots are shown.

Bi-Weekly Weed Survey of Yuma County starts today
A Bi-Weekly survey of weeds of agricultural areas in Yuma County began two weeks ago and is reported in today’s edition of the IPM Updates. Survey results will continue to be reported in Vegetable IPM Updates every two weeks. This survey was initiated and will be conducted by Marco Pena.
 
The purpose of the survey is to provide information to help you make weed management decisions and will include weed species, location and infestation level. Twenty four points have been marked for sampling. They are distributed from San Luis to Texas Hill. A three to five acre radius will be surveyed around each point. Results will be reported on an aerial photograph of the county. A separate map will be provided for each species found. We know that we can’t find every weed out there across the county and will make an interactive map so that you can include infestations that we have missed. Just send us an image of the weed species and the GPS location from your phone and we will add it to the map.
 
We hope that this will be ongoing project that will alert you to what weeds we have found and create an historical perspective for changes over time. We will be adding more species as the project continues and we appreciate your input on how this program can be modified and improved so please let us know what you think.

The scale used on this survey for the infestation level on each weed is color coded as follows:

Color Code	Infestation Level	Plants / acre
White	ND: Not Detected	0
Blue	P: Present	1-3 pl/ac
Yellow	L: Low	4-50 pl/ac
Orange	M: Medium	51-200 pl/a
Red	H: High	Above 200 pl/ac

The following image contain the location of our 24 sampling points. To access all the Yuma county weed maps with other species including some that weeds found to host the INSV virus please visit Spatial Distribution of weeds in Yuma County.

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth light in the past 2 weeks, below average for the beginning of the produce season.
 
Beet armyworm:          
Trap counts increasing in all locations, about average for early September.
 
Cabbage looper:           
Cabbage looper numbers remained low consistent with early September.
 
Diamondback moth:      
DBM moths not active in any trap since June; expected this time of the year.
 
Whitefly:                       
Adult movement increased in the past week, above average for early September. 
 
Thrips:                           
Thrips adults light in most locations, and trending above average to previous years.
 
Aphids:                         
Aphid movement is absent and consistent with what we typically see during the summer and September. 
 
Leafminers:                   
Adult activity tending downward in most locations, below average for early September.