It seems within the last week whitefly adults have become easier to find on spring melons. As temperatures continue to increase, damage to spring melons from whitefly feeding should be a concern. Sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce fruit quality and marketability. Although whitefly numbers have been low up to now, PCAs should not be complacent in their monitoring and sampling. With the warmer weather we are now experiencing, numbers are likely to increase rapidly in the next few weeks. Our research has shown that to prevent melon yield and quality losses, a foliar insecticide treatment should be applied when a threshold of 2 adult whiteflies per leaf is exceed. This threshold applies for the IGRs, neonicotinoids and synergized pyrethroids. (Please go to the following documents for more information on whitefly management, thresholds and insecticide efficacy). Note: CYSDV virus symptoms have already been observed on a few cantaloupe plants in a field in the Yuma Valley. Lab results are not back yet, but if you spot suspicious CYSDV symptoms on melon leaves this spring please let us know.

In the last issue of this UA Vegetable IPM Newsletter, I presented a melon (Cucumis melo ‘reticulatus’ L.) crop phenology model (Figure1; Silvertooth, 2025). This model can be useful in predicting and tracking crop development and identifying important stages of crop growth and development (crop phenology).

Use of a crop phenology model can be applied to basic crop management (e.g. fertilization, irrigation, harvest scheduling, pest management activities, labor, and machinery management, etc.). For use of the crop phenology model, good local weather data with heat unit information is needed. In Arizona we have an excellent weather system with the Arizona Meteorological Network, AZMET.

Since cantaloupes are a warm season crop, we use the86/55 ºF heat unit (HU) thresholds for phenological tracking. Key stages of growth or “guideposts” indicated in Figure 1represent the average or “target” values that are subject to a slight degree of natural variation, which is normal.

This melon crop phenology model was developed under fully irrigated and well-managed conditions. That is important since non-irrigated fields are more likely to experience water stress, which significantly disrupts crop development patterns.

Referring to the data from AZMET for several locations in the Yuma area, the HU accumulations (86/55 ºF thresholds) from 1 January 2025 to a set of four possible 2025 planting dates are listed in Table 1. The HU accumulations from 1 January2025 to 15 April 2025 for these sites are listed in Table 2.

The HU accumulations after planting (HUAP) for these four possible planting dates for three Yuma area locations to 15 April 2025 are shown in Table 3. The HUAP values in Table 3 are simply the difference between the values in Tables 1 and 2. An example for the Yuma Valley, 15 January 2025planting date is: HU - 73.1 HU = 645.6 ~ 646 HUAP.

The information in Table 3 can help serve as a reference to check for melon crop development in the field against this phenological model in Figure 2. Several cantaloupe/melon types are being in this region including western shipper type melons, Tuscan melons, and Hami melons. In the past, each of these melon types have tracked closely with this phenological model.

For melon crops in the lower Colorado River Valley at this time, we can expect to find fields planted and watered up in mid-January to have crown set melons beginning to develop netting, which may not be as apparent on the Hami melons. These fields could have crown fruit ready for harvesting in about three weeks, based on normal HU accumulation patterns for this time of year. For fields planted and wet dates near the first of March, these fields should be vigorously flowering.

 

Reference:
Silvertooth, J.C. 2025. Tracking Cantaloupe (Melon) Crop Growth and Development. University of        

Arizona Vegetable IPM Newsletter, Volume 16, No.7, 2 April 2025.


Table 1. Heat unit accumulations (86/55 ºF thresholds) after 1 January 2025 on four possible 2025 planting dates utilizing Arizona Meteorological Network (AZMET) data for each representative site.

Yuma Valley: https://azmet.arizona.edu/application-areas/heat-units/station-level-summaries/az02

Yuma North Gila: https://azmet.arizona.edu/application-areas/heat-units/station-level-summaries/az14

Roll: https://azmet.arizona.edu/application-areas/heat-units/station-level-summaries/az24

Table 2. Heat unit accumulations (86/55 ºF thresholds) after 1 January 2025 to 14 April
2025 utilizing Arizona Meteorological Network (AZMET) data for each representative site.


Table 3. Heat unit accumulations (86/55 ºF thresholds) after planting (HUAP) from four
possible 2025 planting dates and three sites in the Yuma area on 15 April 2025 utilizing
Arizona Meteorological Network (AZMET) data for each representative site. Each value
is rounded to the next whole number. Note: the values in Table 3 are determined by
taking the difference between the HUs foreach representative site and four planting
dates in Tables 1 and 2.


Figure 1. Melon (cantaloupe) phenological development model expressed in Heat Units
Accumulated After Planting (HUAP, 86/55°F).

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 28, 2023 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 17, 2024  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 Temp (°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 15,2024, February 23, 2024, March 4, 2024, and March 12, 2024and .Disease was first seen on February  26,2024. Disease rating was done on March 15, 2024.   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. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides were Rhyme, Merivon, Quintec, Cevya, Luna Sensation, Luna Experience, and Elisys. 

For those interested in in-row weed control, checkout the quality video below (Fig. 1) on how finger weeders (Fig. 2) are being used on a 3,600 acre organic cotton farm in Texas. The grower states that finger weeders help him achieve 95-97% weed control and are a highly cost-effective tool for lowering hand weeding costs. 

Fig. 1. Carl Pepper discusses how finger weeders are used to control in-row weeds on
his 3,600 acre organic cotton farm. Click here or on image to view. (Photo credit: Tilmor
LLC, Dalton, OH)


Fig. 2. Finger weeders, an in-row weeding tool, operating in seedling cotton. Finger
weeder pairs are centered on the seed row and overlapped slightly to loosen soil in the
row and uproot small weeds.

Thank You

In 2010 we started publishing the Arizona Vegetable IPM Updates to a small number of friends. It was embraced by the community because of contributions from Mike Matheron, John Palumbo and Barry Tickes in the Plant Pathology, Entomology and Weed Science areas. Mike, John and Barry are the original IPM dudes. 

I was honored to be part of the team editing and sending the Newsletter for almost
16 years. 


This is my last update, and I would like to thank the UA team and the agricultural community for the opportunity to work with you. 

Biological control is an important IPM tool globally. This pest suppression technique is especially important for managing pests in organic crop production. There are various biological control techniques, including conservation biological control, classical biological control, and augmentative biological control. Conservation biological control is the practice of providing habitat to support abundant populations of naturally occurring arthropods that attack crop pests. However, classical biological control and augmentative biological control involve the release of arthropod predators and parasitoids, usually non-native, into the field or greenhouses. This article focuses on conservation biological control.

The contribution of native beneficial insects to pest control has been estimated to be approximately $4.5 billion annually in the United States alone. However, the benefits of beneficial insects areoften overlooked. Research conducted across the country has shown evidence that conserving natural habitats leads to an increase in beneficial arthropod populations and a reduction in pest problems on farms. Beneficial arthropod predators and parasitoids often rely on natural or semi-natural areas adjacent to the field for their persistence. Between growing seasons, these natural and semi-natural areas provide alternative food sources, overwintering, and nesting habitats for natural enemies, thereby promoting their populations. To complete their life cycle, natural enemies require more than just prey or hosts; they also need refuge sites and alternative food sources.

Neighboring natural and semi-natural habitats serve as sources of natural enemies during the growing seasons to suppress crop pests. The establishment of wildflower margins around crop fields increases the abundance of beneficial insects that search for pollen and nectar. For example, many adult parasitoids sustain themselves with pollen and nectar from nearby flowering plants while searching for hosts. Most natural enemies do not disperse far from their overwintering sites; access to permanent habitat near or within the field gives them a jump-start on early pest populations.

Farms with diverse and dense populations of natural enemies are likely to exhibit the following characteristics:

- Have small fields surrounded by natural vegetation.
- Composed of diversified cropping systems and plant populations in or around fields include perennials and flowering plants.
- Crops are managed organically or with minimal agrichemicals.
- Soils are high in organic matter and biological activity and, during the off-season, covered with mulch or vegetation.

Figure 1. Syrphid fly feeding from sweet alyssum flowers.


Figure 2. Mix flowers planted on strips between rows of celery to provide food and
shelter for natural enemies.

The combination of two separate processes whereby water is lost on the one hand from the soil surface by evaporation and on the other hand from the crop by transpiration, is referred to as evapotranspiration (ET). Evaporation is the process whereby liquid water is converted to water vapor (vaporization) and removed from the evaporating surface (vapor removal). Water evaporates from a variety of surfaces, such as lakes, rivers, pavements, soils, and wet vegetation. Energy is required to change the state of the molecules of water from liquid to vapor. Direct solar radiation and, to a lesser extent, the ambient temperature of the air provide this energy (Fig:1). 

Figure 1: Key factors driving ET in agriculture include solar radiation, temperature, wind,
humidity, and plant and soil water loss.

Transpiration consists of the vaporization of liquid water contained in plant tissues and the vapor removal to the atmosphere. Crops predominantly lose their water through stomata. These are small openings on the plant leaf through which gases and water vapor pass. The water, together with some nutrients, is taken up by the roots and transported through the plant (Fig: 2).

Figure 2: A diagram illustrates the process of transpiration in plants, where water is
absorbed by roots, moves through the stem, and evaporates from the leaf surfaces.

Why evapotranspiration (ET)?
ET is the largest component of the hydrological cycle and is one of the most critical variables in irrigation management, crop production, and the sustainability of agriculture. It has a direct impact on water resources availability and use, water quality, and the earth’s energy balance. Daily evapotranspiration (ET) rates are needed for irrigation scheduling. The evapotranspiration rate is normally expressed in millimeters (mm) or inches (in) per unit of time (e.g., an hour, day, week, month, or even an entire growing period or year).

Reducing evapotranspiration (ET) can lead to significant water savings by minimizing unnecessary water loss through soil evaporation and plant transpiration. By applying irrigation more efficiently only when and where it's needed, plants can maintain optimal moisture levels, reducing stress and promoting better growth. This can enhance nutrient uptake, improve plant health, and ultimately lead to higher yields. Moreover, conserving water through reduced ET is especially critical in arid regions, where freshwater resources are limited, and efficient water use is essential for sustainable agricultural production.

Below are strategies to reduce ET

• Irrigation Management: Implement precision irrigation by applying water only when needed based on real-time soil moisture data (Fig: 3). Use weather stations and sensors to optimize irrigation scheduling, and adopt drip or micro-irrigation systems to deliver water directly to the root zone, reducing evaporation and overall ET losses.
• Agronomic Strategies: Improve soil management through reduced tillage where applicable. While no-till is not typically suited for bedding systems used in leafy greens, other soil-conserving practices can still help retain moisture. Select crop varieties or hybrids that are more drought- and heat-tolerant, including short-season types to limit ET exposure. Adjust planting dates to avoid peak evaporative and heat stress periods, and adopt eco-fallow crop rotations (e.g., two crops over three years) to enhance soil water conservation and reduce overall ET.

Figure 3: Figure 3. Soil moisture sensor installation at the Valley Research Center,
Yuma, AZ.

Results of pheromone and sticky trap catches can be viewed here.
Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 24, Dec 1, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts remained low over the past 2 weeks across all locations and about average for this time of the season. 
 
Beet armyworm:          
Trap counts decreased in most locations, and well below average for late-November. Most activity in Yuma Valley.
 
Cabbage looper:          
Cabbage looper trap counts remained low in most areas but increased in the Yuma Valley. Activity below average for late November.
 
Diamondback moth:     
Adults peaked in Bard, Gila and Yuma Valleys and slightly above average for this time of year. Traps located adjacent to cauliflower seed crops had the highest trap captures 
 
Whitefly:                      
Adults remains active in Dome Valley and Roll consistent with melon crops completing harvest, but below average movement for this time of season. 
 
Thrips:                          
Thrips adult movement decreased in most locations last week, and most active in Dome Valley, Wellton, and Tacna. Activity about average for mid-November.
 
Aphids:                         
Aphid movement peaked so far this season with highest activity in Dome Valley, Bard, N. Yuma Valley and N. Gila Valleys over the past 2 weeks. Activity average for this time of year.
 
Leafminers:                  
Adult activity increased sharply in the Dome, Yuma, and Gila Valleys, about average for this time of season.