As spring melon planting gets underway and I’ve seen a few cantaloupe fields under plastic, and Yuma beds are being prepared. One field I observed last week being listed had excessive produce crop residue in and on top of the beds.   I immediately thought of the threat of seed corn maggots on early planted melons with the cooler soil temperatures we see this time of the year. Seed corn maggot (SCM) is a pest that should be avoided whenever possible since control after the fact is near impossible.  SCM are always a concern in melon crops planted during late January and February, and are most prevalent under cool, wet conditions.    SCM can cause significant stand reductions in melons and other large seeded crops (e.g., cotton, corn, beans) due to the maggots feeding on germinating seed, roots and stems of young seedlings and transplants.  If larvae populations are high in the soil, replanting parts or all of an infested field is often necessary.  Not only is this an inconvenience to the grower, but replanting is expensive and can disrupt harvest schedules.  Unfortunately, once maggots have been found infesting the soil during stand establishment, there is usually nothing you can do.  Thus, avoidance of the problem is the most effective way of preventing stand reductions.  First, weather plays a major role in determining the damage potential for SCM. Melon stands are more susceptible to SCM during wet, cool spring weather in which seed germination is slowed or delayed.  These conditions (low soil temperatures, rainfall, and/or excessive irrigation) give SCMs a chance to develop in the soil and attack the seeds before they can emerge. SCM larvae will begin developing at soil temperatures as low as 50 °F. The minimum temperature for melon germination is 60 °F.  Current soil temperatures at planting depth have been around 60 °F for the past 2 weeks, giving SCM the advantage. However, I’ve also observed SCMs take down direct seeded cantaloupe and transplanted watermelon stands established under warm, dry conditions when flies were abundant.  Secondly, our cropping system plays a key role.  Melon crops following produce are the most often attacked because SCM adults are attracted to freshly tilled soils with high levels of decomposing organic matter and will readily lay eggs in the soil (particularly moist soil). This includes heavy plant residue remaining after harvest of the previous lettuce or brassica crop, as well as applications of composted manure prior to planting.  Growers would be encouraged to delay planting melons into fields under these conditions.  However, if growers decide to plant in these conditions, then it would be wise to use a preventative insecticide applied in-furrow at planting to minimize the impact from SCM and give seedlings a fighting chance.   A few alternatives are available that have shown activity against SCM and may be practical for their management in spring melons. For more information, visit Seed Corn Maggot in Spring Melons, 2022.

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

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.

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. 14, No. 21, Oct 18, 2023           
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth increased in Tacna/Roll/Dome last week, and areawide about average for mid-October.
 
Beet armyworm:          
Trap counts highest in Tacna, Wellton and Dome, but below average for October.
 
Cabbage looper:         
Cabbage looper numbers increased in Tacna/Roll/Wellton but still below average.
 
Diamondback moth:    
DBM moths are beginning to appear in traps in Yuma Valley, trending below average for early October.
 
Whitefly:                      
Adult movement increased in the past 2 weeks and above average for mid-October.
 
Thrips:                         
Thrips adult activity down over the past week, and trending below average in October.
 
Aphids:                        
Winged adults continue to be captured for the season, consistent with heavy winds from W-NW. Can expect aphid flights to increase in the coming weeks.
 
Leafminers:                  
Adult activity increased significantly in Tacna associated with maturing melons. Trending above average for mid-October.