It is springtime in the desert and a new spring melon/cantaloupe crop is developing, particularly in the lower Colorado River valleys.  Cantaloupes (Cucumis melo ‘reticulatus’ L.) or “melons” are one of the important spring and fall vegetable crops of Arizona and the desert Southwest.  Technically, “true” cantaloupes (Cucumis melo ‘cantaloupensis’) are rough, warty fruit, primarily grown in Europe.  On a production scale, cantaloupes are not grown commercially in the United States.  However, in the United States “cantaloupe” has become a general name of all netted, musk-scented melons (Simonne et al., 1998 and Soto, 2012).  
 
The primary cantaloupe production in the U.S. takes place in four states (Table 1).  More than 80% of the U.S. production is in California and Arizona, which is totally irrigated acreage.
 

	2019	2020	2021
Arizona	14,000	11,100	9,300
California	27,800	21,900	23,400
Florida	2,300	1,300	1,500
Georgia	3,900	2,806	2,700
United States (total)	48,000	37,100	36,900

 
Table 1.  Harvested acreage of major cantaloupe production states, 2019-2021.  USDA-National Agricultural Statistics Service. https://www.nass.usda.gov/Statistics_by_State/California/Publications/Crop_Releases/Vegetables/vegean22.pdf
 
Cantaloupes in the U.S. are generally divided into eastern and western types.  The eastern type is characterized by round-shaped fruits, usually about five to seven pounds, sutured (sutures are the green lines that divide the rind into several sections), with variable levels of netting (netting is the network of cork-like marks that cover the rind), and large seed cavities.  The western type is characterized by oval-shaped fruits of three to four pounds, sutureless, and a coarsely netted rind (Simonne et al., 1998 and Soto, 2012).
 
According to the United States Department of Agriculture (USDA) National Agricultural Statistical Services (NASS), the harvested Arizona cantaloupe acreage from 1992 to 2021 has ranged from 9,300 to 23,300 acres with an estimated production value ranging from $38M to $82.5M.  Most of the Arizona cantaloupe production takes place in Yuma, Maricopa, and Pinal Counties.  Among the nine states with recorded cantaloupe production, Arizona commonly ranks second to California in acres and total production.  (USDA, 2021 and Murphree, 2015).
 
There are several cantaloupe varieties and melon types grown in the desert Southwest.  The Hami melon is a type of muskmelon, originally from Hami, Xinjiang, China that has been grown in this region before and has recently been more popular and planted more acres in this region the past few years.  In Mandarin Chinese “Hami gua” is a term often used in reference to cantaloupes.  These melons are commonly referred to as the “Chinese Hami melon” or the “snow melon”. The outer skin of Hami melons is generally light in color with white, pink, yellow, or green shading.  The inside flesh is commonly sweet and crisp.  
 
Being able to accurately describe and predict important stages of crop growth and development (crop phenology) and harvest dates is important for improving melon crop management (e.g. fertilization, irrigation, harvest scheduling, pest management activities, labor and machinery management, etc.). Since plants operate on “thermal time”, they have no regard for calendars or time as we commonly measure it.  So, it is best to monitor and predict plant development based on the actual thermal conditions in the plant’s environment.  Various forms of temperature measurements and units commonly referred to as heat units (HU), growing degree units (GDU), or growing degree days (GDD) have been utilized in numerous studies to predict phenological events for many crop plants (Baker and Reddy, 2001 and Soto, 2012).
 
Boswell (1929) first documented the concept of heat summations relative to vegetable crop production in 1929.  Thereafter, HU accumulation techniques have been successfully applied to numerous vegetable production systems like cantaloupe (Baker et al., 2001).  
 
The use of HU accumulations has been shown to be an efficient technique for modeling and predicting growth stages in crops (such as cantaloupes) as compared with the traditional days after planting (DAP) method, since variations among seasons and locations can be better normalized using heat units accumulated after planting (HUAP) calculations rather than DAP.  
 
For more than 36 years we have had the benefit of excellent weather data collection in Arizona from the Arizona Meteorological Network (AZMET), which was first developed and directed by Dr. Paul Brown and now Dr. Jeremy Weiss.  For warm season crops, such as cantaloupes, we have been working with HUs that have both upper and lower temperature thresholds (86/55 ^oF), as first described by Baskerville and Emin (1969) and shown in Figure 1 (Brown, 1989).  Crop phenology models have been successfully developed using HUs with 86/55 ^oF thresholds for other common warm season crops in the desert Southwest, such as cotton (Silvertooth, 2001) and New Mexico type chiles (Silvertooth et al., 2010).
 
Baker et al., (2001) developed a muskmelon phenology model that could be run with easily obtainable weather station data and used by growers to quantify phenological development and aid in projecting harvest dates.  The average model accuracy in predicting harvest dates ranged between 1 to 3 days for the data set used to construct the model.  Also, after the evaluation of the performance of two GDD models to predict commercial harvest dates in 30 commercial melon fields in California, Hartz (2001) found that the two models were useful in predicting the date of harvest initiation.  The standard deviation for the prediction of harvest date from emergence date represented between 2-3 days of normal growing-degree-day accumulation.
 
Beginning in 2000, we began working to develop and test a phenology model for desert cantaloupe production for Arizona conditions.  Following data collection over 10 years with spring cantaloupe fields, primarily in the Yuma area, we were able to develop and test the basic cantaloupe phenology model shown in Figure 2 (Silvertooth, 2003; Soto et al., 2006; and Soto, 2012).  This melon crop phenology model was developed under fully irrigated conditions.  Guideposts indicated in Figure 2 represent general average or “target” values and a slight degree of variation is normal, similar to some of the earlier models previously mentioned.  It is important to note that water or nitrogen stress are two factors that will significantly alter physiological development.  
 
We are currently working to evaluate and update this melon crop model.  I encourage those who are working with spring cantaloupe production this season to test and evaluate this crop phenology model in the field under various planting dates, varieties, and conditions.  We appreciate your feedback.
 
 
References:
 
Baker, J.T., and V.R. Reddy. 2001. Temperature effects on phenological development and yield of muskmelon. Annals of Botany. 87:605-613.
 
Baskerville, G.L., and P. Emin.  1969. Rapid estimation of heat accumulation from maximum and minimum temperatures. Ecology 50:514-517.
 
Boswell, V. R. 1929. Factors influencing yield and quality of peas. Maryland Agric. Exp. Sta. Bull. 306.  
 
Brown, P. W.  1989.  Heat units. Ariz. Coop. Ext. Bull. 8915. Univ. of Arizona, Tucson, AZ.
 
Hartz, T.K. 2001. Development and testing of a growing degree day model to predict melon harvest time. California Melon Research Board. 2001. Annual Report.   
 
Murphree, J. 2015. Fun Statistics about Arizona Agriculture’s Melons and Sweet Corn. Arizona Farm Bureau https://www.azfb.org/Article/FunStatistics-about-Arizona-Agricultures-Melons-and-Sweet-Corn
 
Silvertooth, J.C.  2001.  Following cotton development over the fruiting cycle.  University of Arizona Cooperative Extension Bulletin No. AZ 1206.
 
Silvertooth, J.C. 2003. Nutrient uptake in irrigated cantaloupes. Annual meeting, ASA-CSSA-SSSA, Denver, CO.
 
Silvertooth, J.C., P.W. Brown, and S. Walker. 2010. Crop Growth and Development for Irrigated Chile (Capsicum annuum). University of Arizona Cooperative Extension Bulletin No. AZ 1529
 
Simonne, A., E. Simonne, R. Boozer, and J. Pitts. 1998. A matter of taste: Consumer preferences studies identify favorite small melon varieties. Highlights of Agricultural Research. 45(2):7-9.
 
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.
 
USDA Stats: 2021 State of Agriculture Overview.
https://www.nass.usda.gov/Quick_Stats/Ag_Overview/stateOverview.php?state=ARIZONA

Figure 1. Graphical depiction of heat unit computation using the single sine
curve procedure. A sine curve is fit through the daily maximum and minimum
temperatures to recreate the daily temperature cycle. The upper and lower
temperature thresholds for growth and development are then superimposed
on the figure. Mathematical integration is then used to measure the area
bounded by the sine cure and the two temperature thresholds (grey area). (Brown, 1989)

Figure 2. Heat Units Accumulated After Planting (HUAP, 86/55 ^oF)

We have learned a lot about viruses in the past few newsletter articles and one of the striking features of most plant viruses is that they always need a host. And the relationship between a virus and its host plant is very specific. So where do the viruses go when we do not have lettuce or melon in the field? And how do they come back at the right time to infect the crops?  (clue insect vector). The answer is weeds. A lot of the most economically important viruses are economically important viruses not just because of the losses they cause, but also because of the losses they cause in variety of plants. Viruses have small genome size that allows them to evolve faster. Viruses over time have evolved to adapt and increase their host range.
Below are some common viruses in agriculture and the number of plants they infect/overwinter. Keep in mind that there are many plants that can act as a reservoir for virus but have not been reported yet, so this is not an exclusive list. 
 
Alfalfa mosaic virus (AMV): Alfalfa, lettuce,indive, sunflower, datura, amaranth, different species of pigweed, milkweed, annual fleabane, ixeye daisy, hairy galinsoga, smallflower galinsoga, different species of mustards, common lambsquarters, hedge bindweed, field bindweed, cucurbits, different species of clover and vetch, beans, broad beans, lima beans, lupine, pea soybean, ground Ivy, healall, okra, purslane, pimpernel, black nightshade, pepper, tomato, petunia, eggplant, potato, garden pansy etc. 
 
Cucumber mosaic virus (CMV): pigweed, horseweed, oxeye daisy, coffee weed, Canada thistle, bull thistle, hairy galinsoga, Jerusalem artichoke,  prickly lettuce, wild chamomile, hawkweed, groundsel, Canada goldenrod, sowthistle, endive, sunflower, lettuce, mustard, radish, chickweed, lambs quarters, morning glory, cucurbits, common teasel, alfalfa, beans, lima beans, mung beans, geranium, ground Ivy, okra, purslane, jimsonweed, ground cherry, horsenettle, black nightshade, pepper, tomato, petunia, eggplant, potato, burning nettle, garden pansy. 
 
Lettuce mosaic virus (LMV): lettuce, bristly oxtongue, spinach. 
 
Bidens mottle potyvirus: lettuce, endive, horseweed, hairy beggarticks, virginia pepperweed, Mexican pricklepoppy. 
 
Celery mosaic virus (CeMV): Celery, giant hogweed
 
Papaya ringspot virus (PRSV): Bur cucumber, creeping cucumber, balsom pear, cucumber, cantaloupe, watermelon, summer squash, pumpkin, gourd, winter squash, butternut squash, 
 
Tomato spotted wilt virus (TSWV): Tomato, potato, pigweed, hairy beggarticks, oxeye daisy, coffeeweed, prickly lettuce, annual sowthistle, ebdive, sunflower, lettuce, shepherd’s pruse, chickweed, hedge bindweed, cantaloupe, muskmelon, bean, broad bean, mung bean, cutleaf evening primerose, broadleaf plaintain, purslane, jimsonweed, bittersweet nightshade, black night shade, pepper, tomato, petunia, eggplant, potato. 
 
Tobacco mosaic virus(TMV):  White campion, jimsonweed, pepper, tomato, tobacco. 
 
Turnip mosaic virus(TurMV):  pigweed, wild carrot, bachelo’s button, Canada thistle, hairy galinsoga, smallflower galinsoga, common catsear, pineapple weed, dandelion, endive, sunflower, lettuce, mustard, brassicae crops, corn cockle, chickweed, common lambsquarter, spinach, cucumber, alsike clover, lupine, redstem filaree, ground Ivy, okra, velvetleaf, common pokeweed, purselane, jimsonweed, black nightshade, tomato, petunia..
 
Watermelon mosaic virus (WMV) :   mustard, common lambquarters, spinach, cucumber, watermelon, cantaloupe, squash, buttercup, red clover, common vetch, alfalfa, beans, lupine, pea, henbit, common mallow, okra, common pokeweed, jimsonweed, nightshade, 
 
Zucchini yellow mosaic virus (ZYMV) : cucumber, cantaloupe, watermelon, squash, zucchini, pumpkin, gourds. 
 
 
Source: Cornell.edu

Over the last month, we’ve been developing a prototype wide bed steam applicator for injecting steam at shallow depths to kill weed seed prior to planting. The device principally comprises a 65 BHP steam generator mounted on a trailer and an elongated bed shaper (Fig. 1). The apparatus applies steam via shank injection and from ports on top of the bed shaper. The goal is to raise soil temperature to >140 °F for > 20 minutes, levels known to kill weed seed (Baker & Roistacher, 1957). Development is still in progress but results of preliminary tests are encouraging as soil surface temperatures were relatively uniform and exceeded 160 °F (Fig. 2). Experiments with baby leaf spinach crops will be conducted in the next couple of weeks. Stay tuned for trial results and reports on weed control efficacy and labor savings. 
References
Baker, K. F., and C. N. Roistacher. 1957. The U.C. system for producing healthy container grown plants. Calif. Agric. Exper. Sta. Ext. Serv. Manual 23.
Acknowledgements
This work funded in part by the Arizona Specialty Crop Block Grant Program. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the USDA or the Arizona Department of Agriculture.

Fig. 1. Wide bed steam applicator principally comprising a 65 BHP steam
generator mounted on a trailer and a bed shaper applicator sled.


Fig. 2. Video of wide bed steam applicator. Soil surface temperature is presented
using an infrared thermometer gun.

We have seen abundant Shepherdspurse recently in Yuma, AZ. Most of us are familiar with this winter annual broadleaf weed but we are adding a brief description:
Scientific name: Capsella bursa – pastoris
Season: Winter Annual 
Habitat: Present in all crops and ditch banks, home gardens. 
Cotyledons: Oval with a short petiole. 
Leaves: First true leaves with hairs and spoon shape. Can have different shapes and form a rosette soon after emergence.
Young plants: Are mostly basal rosettes.
Mature plants: grow up to 20” with flower stems with sparse small leaves.
Flowers and Fruit: Flowers are pale pink and fruits are heart shaped or triangular seed pods.
 
Shepherdspurse is from the mustard or crucifer family, which includes many crops grown here such as broccoli, cauliflower, kale, kohlrabi, mustard greens and others.
In our production practices we commonly select some weed species that survive our methods of control. This weed has been around for a long time and has become increasingly widespread in recent years. The similarities with brassica crops add to the difficulty to control the weed as well as plant characteristics and growth habits.
In vegetables, Kerb can control shepardspurse when the product placed in the seed germination area close to the surface. If the product leaches the efficacy decreases. Dacthal, Prefar, Prowl, and Balan are less effective on this weed¹.
Shepherspurse has proliferated in alfalfa recently and we are conducting some trials for its control. The results will be shared with PCAs and posted in our website when we finish collecting the data.

Fig 1. Images of an untreated plot compared to Raptor + Pursuit + Butyrac 200 +
NIS in alfalfa 4DAT.

Reference:
1.https://ag.arizona.edu/crops/vegetables/advisories/more/weed31.html
2.https://ipm.ucanr.edu/PMG/WEEDS/shepherdspurse.html#:~:text=Mature%20plant&text=Leaves%20vary%20in%20shape%20and,reduced%20in%20size%2C%20and%20stalkless.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 7, Apr 3, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts remain  at low levels  in all areas, well below average for this time of year. 
 
Beet armyworm:          
Trap increased areawide; about average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts increased to seasonal highs; above average for this time of season.
 
Diamondback moth:       
DBM moth counts increased in most areas. About average for this time of the year.
 
Whitefly:                      
Adult movement negligible, average for late winter. 
 
Thrips:                          
Thrips adult counts increased in most areas. Below average compared with previous years.
 
Aphids:                         
Aphid movement decreased in all areas; below average for late-March.
 
Leafminers:                   
Adults remain low in most locations, average for March.