Spring melon crops are rapidly growing, and insect pest populations are not far behind. Cabbage loopers and leafminers are starting to show up, and PCAs should start ramping up their insect monitoring. Whitely populations, albeit light for this time of the year, are slowly beginning to show on 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 occurs 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 if 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 leaves have greater than 2 adult whiteflies per leaf, when averaged across an entire melon field. At this level of adult abundance, immature populations are just beginning to colonize. Timing sprays based on this adult threshold has been shown to significantly reduce 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 IPM and Whitefly Management and Whitefly Control Options-Spring 2022. 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). 

All plants have distinct habits of growth and development as a function of time (phenology).  Plant growth is a direct response to environmental conditions, particularly temperature and in some cases daylength.  As a result, tracking plant growth and development as a function if temperature conditions is a much more reliable method than the calendar.  
 
In a recent edition of this newsletter on 4 April 2023, I presented a cantaloupe phenological (crop growth and development) model based on heat units accumulated after planting (HUAP, 86/55 F^o thresholds) as shown in Figure 1.
 
Phenological models can serve as good tools for improving crop management (e.g., fertilization, irrigation, harvest scheduling, pest management activities, and labor, etc.) by identifying and predicting important stages of crop growth and development and harvest dates.  
 
Included in our work with the development of this phenological model, we have also conducted nutrient uptake and water use studies to develop a better understanding of nutrient and water demand for desert cantaloupe production (Silvertooth, 2003; Soto et al., 2006; and Soto, 2012).
 
Figure 2 presents the nitrogen (N) uptake and portioning patterns for desert cantaloupes (melons), (Silvertooth, 2003 and Soto et al. 2006).  The total N uptake for cantaloupes was found to be approximately 140 lbs. N/acre.  The maximum N flux (N uptake/day) period extends from early fruit development (crown stage) to the netting stage.
 
Water use by desert cantaloupe production was also measured in these studies and patterns of water use followed the crop coefficient (K_c) patterns provided by the Arizona Meteorological Network (AZMET) and conformed to the K_c values from FAO 56 (Allen et al., 1998 and Grattan et al., 1998). 
 
Considering N uptake and water demand patterns in relation to cantaloupe crop phenology, we can insert the overlaps as shown in Figure 1, with the red and blue lines for N and water management, respectively.  Maximum N demand occurs from approximately 500 to 1,000 HUAP, which coincides with primary fruit development.  
 
The N application window is recommended in advance of the optimum N uptake period to provide for N mineralization and the plant-available forms of N for plant uptake and utilization.
The N application window for optimum N uptake is from approximately 300 to 800 HUAP, which is from early flowering (crown blooms) to the netting stage of the crown fruit.  
 
Early and split applications during the N application window of cantaloupe crop development can help achieve optimum utilization and higher efficiencies of fertilizer N inputs.  
 
The period of maximum water demand extends from early fruiting stages of development through the maturation of the crown fruit, 300 to 1300 HUAP.
 
Considering the current water shortages and high prices of fertilizers, we have sufficient motivation to manage our crop production systems with the highest efficiency possible.  Understanding crop water and nutrient demand for each crop we are working with and using that knowledge to manage our crops most effectively, is to our benefit agronomically, economically, and environmentally.
 
Nitrogen is the plant nutrient required in largest amounts by crops and it is important for us to manage N inputs for a crop in a careful and deliberate manner.  Water and N interactions are a critical aspect of crop growth, development, and management in any system, but particularly in an irrigated crop production system.  
 
I encourage those who are working with spring cantaloupe production this season to test and evaluate this crop phenology model, particularly in relation to nutrient and water management under field conditions with various planting dates, varieties, and soil types.  We appreciate your feedback.
 
Note:   Up to date weather data, including HU accumulations since 1 January can be found for all of the Arizona Meteorological Network (AZMET) locations at the following website: https://ag.arizona.edu/azmet/
 
References:
 Grattan, S.R., W. Bowers, A. Dong, R.L. Snyder, J.J. Carroll, and W. George. 1998. New crop coefficients estimate water use of vegetables, row crops. California Agriculture 52(1):16-21. https://doi.org/10.3733/ca.v052n01p16
 
Allen, R.G., L.S. Pereira, D. Raes, and M. Smith.  1998. Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56. Food and Agriculture Organization of the United Nations. Rome (FAO). https://www.fao.org/3/x0490e/x0490e0b.htm
 
Silvertooth, J.C. 2003. Nutrient uptake in irrigated cantaloupes. Annual meeting, ASA-CSSA-SSSA, Denver, CO.
 
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, Indianpolis, IN.

Figure 1. Heat Units Accumulated After Planting (HUAP,86/55 °F)



Figure 2.  Cantaloupe (melon) N uptake and partitioning patterns.  (Soto, Silvertooth,
and Galadima 2006).  Note: kg/ha * 0.89 = lbs/acre

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum,  is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult. 
In 2022, we had  a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development. It is always a good idea to look out for any potential diseases that might occur this year! 
 
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields. 
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil. 
 
 Initial infection of seedlings usually occurs from chlamydospores (resting structure)  that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen. 
 
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management.

The Yuma Fresh Vegetable Association recently published a video about vegetable crop production in Yuma, AZ. The video is comprehensive, covering everything from Yuma’s ag beginnings, to details on current cultivation practices, to the uniqueness and importance of the region to our national food security. The story is a good one and very well told. Even if you’re well versed in Yuma agriculture, I think you’ll find the piece interesting and informative.
Check it out by clicking here or on the image below.

Fig. 1. Yuma Fresh Vegetable Association’s “Yuma – The Winter Salad Bowl” video. (Photo Credit: Yuma Fresh Vegetable Association)

With every irrigation we continue having new generations of weeds germinating. Herbicides with a good soil residual are very useful for extending good control for a longer period. The ideal scenario would be that the herbicide is present only when we need it and dissipate when we rotate to a sensitive crop. This can become a challenge when we have products that have a long soil residual. Sometimes herbicides have a low use rates and long residuals. As an example, we have some of the sulfonylureas and imidazolinones that are highly effective but have to be carefully used for some scenarios. Some of the factors affecting the persistence of herbicides are the soil characteristics, herbicidal characteristics, and environmental conditions¹.

The University of Nevada, Reno explained that problems can occur when soil where sterilant products has been applied is moved or blows from the application site to other part of a field². Interestingly recently the IPM Team received a report of a field of radishes with injury in a pattern that was consistent with the passes of the disk. It appears that accidentally a high rate of DCPA and metholachlor was applied previously. Even after land prep and irrigations the crop presented phytotoxicity symptoms. Also, a celery field located South of a treated, dusty non-agricultural area presented injury consistent with the wind blow. The damage was more severe closer to the treated area (North) and gradually disappeared as walking South into the celery field. Similarly, it has been reported that compost can be contaminated with herbicides such as clopyralid when treated plants are added to the compost mix causing symptoms to lettuce.
 
 

Reference:
1. Retrieved from: https://ag.arizona.edu/crops/vegetables/advisories/more/weed31.html
2. University of Nevada Reno:   https://extension.unr.edu/publication.aspx?PubID=3322

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