In a recent edition of this newsletter on 20 April 2022, 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.
 
The benefits of working with and using a model like this include being able to describe and predict important stages of crop growth and development (crop phenology) and harvest dates.  This can also be a good tool for improving crop management (e.g., fertilization, irrigation, harvest scheduling, pest management activities, labor and machinery management, etc.). 
 
Included in our work with the development of this phenological model, we have also conducted nutrient uptake studies 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.  This data describes total N uptake for cantaloupes at ~ 140 lbs. N/acre.  From this data, maximum N flux (N uptake/day) period extends from early fruit development 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.  Accordingly, the N application window for optimum N uptake is from approximately 300 to 800 HUAP, which is from early flowering to the netting stage of the crown fruit.  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.
 
Considering the N application window described in Figure 1 and a maximum seasonal uptake and demand of ~ 140 lbs. N/acre, early and split applications during this period of cantaloupe crop development can help achieve optimum utilization 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 conditions we are experiencing these days in desert crop production with water shortages and extremely high prices of fertilizers, we have an abundance of 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 most non-leguminous crops and it is important for us to manage that nutrient 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.  Thus, the focus offered in this article on water and N management for desert cantaloupe production.
 
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.

Figure 1. Heat Units Accumulated After Planting (HUAP, 86/55 ^oF)



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

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.

It’s unfortunately a very great season to be a plant pathologist…

We have confirmed the first sample of Fusarium wilt on lettuce submitted to the Yuma Plant Health Clinic from Yuma County. The stunted seedlings looked like any other typical case of damping-off at the seedling stage. When plated on culture media, subsequently confirmed Fusarium colonies grew abundantly from the declining plant tissues. If you’re not already on guard and scouting, this is a warning that Fusarium is active in Yuma County.

Adding on to this early alert, we’ve received a surge of submissions of young brassicas to the clinic. Several severely wilted and declining plants from around Yuma County have cultured positive for Pythium, likely as an opportunistic invader coming in on the back of all the early-season rain that brought stress to seeds and young transplants. Growers may want to consider oomycides, but only if the seedling disease is first confirmed to be Pythium. Remember, many seedling diseases caused by true fungi are indistinguishable from those caused by Pythium.

If you have any concerns regarding the health of your plants/crops please consider submitting samples to the Yuma Plant Health Clinic for diagnostic service or booking a field visit with me:

 

Chris Detranaltes
Cooperative Extension – Yuma County
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
6425 W 8th St Yuma, Arizona 85364 – Room 109

Watch this video

Two closely related but different species of several summer annual grasses are common in the low deserts. In general, these are all easy to distinguish from each other in the field and they respond similarly to herbicides. Some of these and their distinguishing characteristics are:

Watergrass (Echinochloa colonum) and Barnyardgrass (Echinochloa crusgalli)
These are very similar but watergrass has purple bands or chevrons on the leaves and barnyardgrass often has awns or bristles at the end of the spikelets. Both respond the same to herbicides.

Red Sprangletop (Leptochloa filiformis) and Mexican Sprangletop (Leptochloa uninervia)
Red sprangletop is, in general, a lighter green color and has a finer seed head than does Mexican sprangletop which is darker green or gray and has a visibly coarser seedhead. Both form clumps or crowns that often survive through the winter months. Both are fairly tolerant to Poast (sethoxydim) and Fusilade (fluaziflop) but are controlled with high rates of Select (clethodim).

Field Sandbur (Cenchrus pauciflorus) and Southern Sandbur (Cenchrus echinatus)
Both of these equally miserable weeds are only found in sandy soils and fairly easy to distinguish. Field sandbur has thinner, gray colored leaves and yellowish burs that are longer than broad. Southern sandbur has darker and broader leaves and fatter red colored burs. Southern sandbur has a more compact seed head with distinctly more burs than does southern sandbur. Both of these are fairly tolerant to Poast (sethoxydim), Select (clethodim) and Fusilade (fluaziflop).

Southwestern Cupgrass (Eriochloa gracilis) and Prairie Cupgrass (Eriochloa contracta)
These similar grasses are fairly easy to distinguish in the field. Southwestern Cupgrass is one of the wider leafed grasses in the deserts. Prairie Cupgrass leaves are not as wide and are hairy. Southwestern is more branched than prairie and the ligule is shorter and less prominent. The branches are longer and fewer on prairie than on southwestern Cupgrass. Both respond the same to most herbicides.

Green Foxtail (Setaria viridis) and Yellow Foxtail (Setaria glauca)
Both green and yellow foxtail typically form clumps, produce lots of seed and stand more upright than many other summer annual grasses. They are not difficult to distinguish in the field. Green has a darker greenish or brown seedhead compared to the yellow. The leaves of yellow are generally longer and have more bristles (5-20) per spikelet than green, which typically has 3 or less darker colored bristles. Both respond the same to most herbicides. This link will connect you with a powerpoint presentation that will help in the identification of summer annual grasses in the deserts.

This time of year, John would often highlight Lepidopteran pests in the field and remind us of the importance of rotating insecticide modes of action. With worm pressure present in local crops, it’s a good time to revisit resistance management practices and ensure we’re protecting the effectiveness of these tools for seasons to come. For detailed guidelines, see Insecticide Resistance Management for Beet Armyworm, Cabbage Looper, and Diamondback Moth in Desert Produce Crops .

VegIPM Update Vol. 16, Num. 20

Oct. 1, 2025

Results of pheromone and sticky trap catches below!!

Corn earworm:  CEW moth counts declined across all traps from last collection; average for this time of year.

Beet armyworm: BAW moth increased over the last two weeks; below average for this early produce season.

Cabbage looper: Cabbage looper counts increased in the last two collections; below average for mid-late September.

Diamondback moth: a few DBM moths were caught in the traps; consistent with previous years.

Whitefly:  Adult movement decreased in most locations over the last two weeks, about average for this time of year.

Thrips: Thrips adult activity increased over the last two collections, typical for late September.

Aphids: Aphid movement absent so far; anticipate activity to pick up when winds begin blowing from N-NW.

Leafminers: Adult activity increased over the last two weeks, about average for this time of year.