Irrigation efficiency has been receiving a lot of attention in recent months, particularly with the Colorado River system water shortages that we have been experiencing.  There are several ways to define irrigation efficiency.  The primary definitions for irrigation efficiency include water conveyance and delivery systems, agronomic, economic, and environmental efficiencies.
 
Water Conveyance and Delivery System Efficiency
 In the desert Southwest we have the benefit of good engineering and infrastructure with the highly developed systems of dams, primary and secondary canals, pumps, laterals, and ditches that move water from rivers and groundwater supplies to areas of need, which are often managed by irrigation districts.  
 
Our ability to move water from the original source to the field is a critical aspect of managing water resources and there is an “efficiency” consideration associated with that.  This level of efficiency is largely a function of system engineering design, maintenance, and management.  
 
Economic Efficiency
 Economic efficiency is often considered to be the primary factor defining the financial sustainability of a farming operation.  Water is a crop input and the costs associated with irrigating a crop include the costs of the water and delivery (pumps, equipment, maintenance, labor, etc.).  Water is consistently the most expensive and critical input provided to a crop in Arizona and the desert Southwest.  Economic efficiency essentially considers the “return on the investment” and profitability of irrigating a crop.
 
Environmental Efficiency
 Considerations of irrigation efficiency from an environmental perspective is very broad and encompassing and it can include a combination of factors previously discussed (water conveyance systems, agronomic, and economic considerations).  Environmental efficiency of an irrigation system is the product of the overall stewardship of water as a natural resource with multiple considerations for beneficial use.
 
Agronomic Irrigation Efficiency
 Agronomic (crop and soil) considerations are centered on our ability to provide irrigation water for the sustainable production of a crop in the field.  The three primary demands for crop water management include: 1) providing water for seed germination and stand establishment, 2) providing irrigation water to match crop-consumptive water use, and 3) sufficient irrigation water to leach soluble salts from the root zone so that the soils can support crop production in a sustainable manner (Figure 1).  
 
Agronomic efficiency at the field level focuses on the crop water demand (CWD) through crop consumptive use, often referred to as the crop evapotranspiration (ETc), which is the combination of evaporation and transpiration from the crop.  Total crop water demand should also include the leaching requirement (LR), which is dependent upon the crop and salinity of the irrigation water.  



Agronomic efficiency can be estimated by considering the difference between total crop water demand, CWD and the volume of irrigation water applied (IWA).

The Leaching Requirement (LR) can be estimated by use of the following calculation:

Where: 
 
EC_w = salinity of the irrigation water, electrical conductivity (dS/m)
EC_e = critical plant salinity tolerance, electrical conductivity (dS/m)
 
This is a good method of for the LR calculation that has been utilized extensively and successfully in Arizona and the desert Southwest for many years.  We can easily determine the salinity of our irrigation waters (EC_w) and we can find the critical plant salinity tolerance level from open access tabulations of salinity tolerance for many crops (Ayers and Westcot, 1989).  Additional direct references are from Dr. E.V. Maas’ lab at the University of California (Maas, 1984: Maas, 1986; Maas and Grattan, 1999; Maas and Grieve, 1994; and Maas and Hoffman, 1997).  
 
Estimating Field Level Irrigation Efficiencies
 The focal point of any irrigation system, from the regional, district, farm, and field levels is to provide water to produce a crop.  The crop is the centerpiece of the entire operation.  Therefore, it is entirely appropriate to consider irrigation efficiency at the field level in agronomic terms, by use of Equation 2.  
 
We need three factors to estimate agronomic field level irrigation efficiency for a crop: 1) crop evapotranspiration (ETc), 2) the crop and field leaching requirement (LR), and 3) a measure of the irrigation water applied (IWA) to the field in question.
 
To determine crop evapotranspiration (ETc) we need a good reference evapotranspiration (ETo) measurement for the field site in question.  Reference evapotranspiration (ETo) values multiplied by an appropriate crop coefficient (Kc) can provide very good estimates on actual crop evapotranspiration (ETc) rates as shown in the following equation:


Reference Evapotranspiration (ETo)
 
The Arizona Meteorological Network (AZMET) is a system that provides both historical and real-time weather information that can be used to track reference evapotranspiration (ETo) measured at a standardized and properly calibrated weather station site.  Reference evapotranspiration values can be obtained daily from AZMET for the nearly 30 sites in Arizona, including several sites in the Yuma area and the lower Colorado River Valleys.  
 
Very importantly, the AZMET data is of a very high quality and the integrity of the system has been very well managed for over 36 years, first under the direction of Dr. Paul Brown and now with Dr. Jeremy Weiss.  This information is valuable in crop water and irrigation management.  
 
Crop Coefficients (Kc)
 The appropriate crop coefficient (Kc) values are specific for each crop species and stage of growth.  We commonly use crop coefficient (Kc) values that are provided in the publication “Consumptive Use by Major Crops in the Desert Southwest” by Dr. Leonard Erie and his colleagues, USDA-ARS Conservation Research Report No. 29.  Crop coefficients from the publication FAO 56 “Crop Evapotranspiration-Guidelines for Computing Crop Water Requirements-FAO Irrigation and Drainage Paper 56” (Allen et al., 1998) are also sometimes used.  Reference information for Kc values can be obtained in these publications for common crops grown in this region.
 
Example: Irrigation Efficiency Calculation
 If we consider an example lettuce crop irrigated with water that has ECw = 1.1 dS/m and the total seasonal crop consumptive use (ETc) = 30 inches
 
Using Equations 1-3, an overall estimate of field level irrigation efficiency can be made.  From Equation 2 we can estimate the leaching requirement (LR).

ECw = 1.1 dS/m and ECe (lettuce) = 1.3 dS/m
 
LR = 1.1 dS/m / (5 X 1.3) – 1.1 = 1.1/5.4 = 0.20 = 20% leaching requirement
 
LR = 30 X 0.2 = 6.1 ~ 6 inches
 
Thus, CWD = 30 + 6 = 36 inches total
 
For this example, we can assume: 40 inches of irrigation water was applied (IWA).
 
Therefore:  Agronomic efficiency (from Equation 1) = 36/40 = 0.9 = 90% efficiency
 
Note:  If the LR were not included in the total CWD, efficiency would be: 30/40 = 75%
That is an important difference and distinction to understand and demonstrate.
 
Irrigation efficiency has always been a major concern in the agriculture of the desert Southwest, and it always will be.  The increased levels of attention being given to irrigation efficiency is good and it is important to recognize there are many factors associated with improvements in irrigation efficiency.

Figure 1. Soil-water balance and plant relationships in a crop production system.

References
 
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9), D05109.
 
Ayers, R.S. and D.W. Westcot. 1989 (reprinted 1994). Water quality for agriculture.  FAO Irrigation and Drainage Paper 29 Rev. 1. ISBN 92-5-102263-1. Food and Agriculture Organization of the United Nations Rome, 1985 © FAO.
https://www.fao.org/3/t0234e/t0234e00.htm
 
Erie, L.J., O.A French, D.A. Bucks, and K. Harris. 1981. Consumptive Use of Water by Major Crops in the Southwestern United States.  United States Department of Agriculture, Conservation Research Report No. 29.
 
Maas, E.V. 1984. Crop tolerance to salinity.  California Agriculture, October 1984. https://calag.ucanr.edu/archive/?type=pdf&article=ca.v038n10p20
 
Maas, E.V. 1986. Salt tolerance of plants. Appl. Agric. Res., 1, 12-36.
 
Maas, E.V. and S.R. Grattan. 1999. Crop yields as affected by salinity, Agricultural Drainage, Agronomy Monograph No. 38.
 
Maas, E. V., and Grattan, S. R. (1999). Crop yields as affected by salinity, agricultural
drainage, Agronomy Monograph No. 38, R. W. 
 
Maas, E. V., and Grieve, C. M. 1994. “Salt tolerance of plants at different growth stages,” in Proc., Int. Conf. Current Developments in Salinity and Drought Tolerance of Plants. January 7–11, 1990, Tando Jam, Pakistan, 181–197.
 
Maas, E. V., and Hoffman, G. J. (1977). “Crop salt tolerance: Current assessment.”

Hi, I’m Chris, and I’m thrilled to be stepping into the role of extension associate for plant pathology through The University of Arizona Cooperative Extension in Yuma County. I recently earned my Ph.D. in plant pathology from Purdue University in Indiana where my research focused on soybean seedling disease caused by Fusarium and Pythium. There, I discovered and characterized some of the first genetic resources available for improving innate host resistance and genetic control to two major pathogens causing this disease in soybean across the Midwest.

I was originally born and raised in Phoenix, so coming back to Arizona and getting the chance to apply my education while helping the community I was shaped by is a dream come true. I have a passion for plant disease research, especially when it comes to exploring how plant-pathogen interactions and genetics can be used to develop practical, empirically based disease control strategies. Let’s face it, fungicide resistance continues to emerge, yesterday’s resistant varieties grow more vulnerable every season, and the battle against plant pathogens in our fields is ongoing. But I firmly believe that when the enemy evolves, so can we.

To that end I am proud to be establishing my research program in Yuma where I will remain dedicated to improving the agricultural community’s disease management options and tackling crop health challenges. I am based out of the Yuma Agricultural Center and will continue to run the plant health diagnostic clinic located there. 

Please drop off or send disease samples for diagnosis to:
Yuma Plant Health Clinic
6425 W 8th Street
Yuma, AZ 85364

If you are shipping samples, please remember to include the USDA APHIS permit for moving plant samples.

You can contact me at:
Email: cdetranaltes@arizona.edu
Cell: 602-689-7328
Office: 928-782-5879

Thank you all very much. I look forward to meeting you all soon.

For those of you interested in the latest thoughts on ag technology, you might want to check out the keynote address given by John Deere¹ at CES 2023 earlier this week. The presentation can be found on YouTube at: https://youtu.be/1kjZMHZl538. As you might expect, there is a fair amount of company self-promotion, but it is interesting to hear their view on the current state and future of agricultural technologies. A couple of key takeaways for me were that telematics and computer vision systems will play key roles in the future and that increased precision will continue to be a focus.

 

[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.

Prefar 4-E (bensulide) is one of the old standard selective preemergent herbicides that have been used on lettuce for more than 50 years. It was developed by Stauffer and first registered for lettuce in 1968, acquired by Zeneca (ICI) in 1992 and its now a Gowan product since 1996. It is one of the few organophosphates (OP) that are used as an herbicide.
 
Bensulide controls weeds by interfering with the normal germination and seedling development. It inhibits cell division at the growing points of the roots and does not translocate or move upward into the rest of the plant. 
It is an emulsifiable concentrate that is applied at 4 to 6 qt. per acre and its only effective if the roots contact the herbicide soon after they have started to grow. It performs well on annual grasses, Purslane, Pigweed, and has activity on nettleleaf goosefoot and common lambsquarters.
 
Label recommendation is to spray to a well-prepared soil a uniform spray pattern in a 10-50 gallons per acre.
It is recommended to apply the higher labeled rates to heavier fine textured soils.
Prefar works much better when incorporated with sprinklers and requires high volumes of water. It also works best in coarse textured soils.
It must be incorporated into the top inch or two of soil only where the roots would be exposed to the herbicide right after they have begun to grow.
 
It was reported in this Newsletter that a 2017 USDA survey showed that Prefar is used in 11% of the lettuce in AZ and CA. For the same period in Yuma CO approximately 58% of the lettuce was treated with bensulide. 
 
The Vegetable IPM Team at the Yuma Agricultural Center will be conducting trials this produce season on the application timings and methods for this important herbicide. Will keep you updated so, stay tuned!.

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.