Now that the weather has finally returned to normal for mid-October, the worm pressure we’ve been experiencing should begin to decline.  However, with many early-planted head lettuce crops beginning to rosette and folding-in to form heads, it would be wise to keep a keen eye out for corn earworm (CEW).  This fall could be important as pheromone trap catches spiked last week in several locations (see graph below) moths continue to be active.  Although pheromone trap counts don’t always correlate to field infestations, we have associated peak CEW moth trap counts with larval CEW activity in surrounding lettuce fields in the past.  Even with the cooler temps expected this next week, moth activity should be expected in fields and that means eggs being deposited in or on developing heads.

CEW can be very damaging in early fall head lettuce crops. On older plants beginning to form heads, larvae will migrate to the succulent terminal growth. If not controlled before the plant leaves fold in, they are protected from foliar sprays. By this time in plant growth, at-planting soil applications of Coragen or Verimark may not be effective enough to protect the heads. Once head formation begins, newly hatched larvae will usually bore into the head almost at once upon hatching.  Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera larvae, rendering the heads unmarketable.  Larvae may enter the head from any point on the plants but can often be found burrowing in from the lower half of the head. 

If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, it is virtually impossible to control the larvae with insecticides. Thus, pay careful attention for newly oviposited eggs (laid singly) on lettuce plants. If you are beginning to find eggs and suspect that CEW are active in the field when plants are beginning to head or cup over, you should treat as soon as possible.  Moreover, during mid-late October and early November it is probably a good idea to prophylactically apply a pyrethroid, methomyl or acephate in combination with larvicides (e.g., Radiant, Coragen, Proclaim) when heads begin to form.  The UA nominal threshold for CEW in head lettuce from the beginning of heading to harvest is1-2 larvae / 100 plants (1-2%).  Repeated insecticide treatments may be required to maintain low population levels if heavy pressure is sustained near harvest. Lab bioassays have shown that CEW larval mortality is most rapid when exposed to Lannate at 0.5 lbs (>90% mortality in 1 hour after exposure) and pyrethroids at high rates (>90% mortality in 3 hours), followed by Radiant,5 oz (>90% mortality in 12 hours).  By 24 hours, mortality was 100% for all the treatments including Coragen and Proclaim.  For more information on CEW management see Corn Earworm Management on Desert Produce.

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.”

Yuma Agricultural Center, University of Arizona, Yuma, AZ
This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 12, 2022, on double rows 12 in. apart on beds with 42 in. 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, which contained two 25 ft rows of lettuce. Plants were thinned on October 5, 2022 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	103	78	90	0.22
October	91	64	77	0.95
November	74	46	59	0.00
December	69	42	53	0.21

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 2^nd and 12^th 2022. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The most effective soil amendments were Rhyme, Regalia and Regalia +Jet Ag. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial. 

Interested in staying up to date on the latest robotic ag technologies? FIRA USA is hosting a 3-day Robotics and Autonomous Farming Solutions in Action Forum September 19-21^st in Salinas, CA. The focus is on autonomous farming and agricultural robotic solutions. The event includes high-level keynote speakers, breakout sessions, a trade show and in-field demos of automated/robotic planting, weeding and harvesting equipment. Last year’s conference was excellent with informative presentations/panel discussions, plenty of time to network, 20 robots on display and top-level company representatives on hand to answer questions. This year’s program looks to be outstanding as well with over 25 robots and 12 robot demos scheduled already. For more information, visit https://fira-usa.com/.

We have a large amount of summer grasses emerging right now in the desert. Identification is very important. Knowing the field history is helpful to plan your preemergence herbicide applications.
There is a tendency to group summer grasses together and called them all watergrass, or barnyard grass especially because they are so difficult to identify at early growth stages. 
Some of these grasses respond differently to herbicides. For example, sprangletop is only controlled by the high rates of Select (clethodim) and clethodim generics and missed by other postemergence herbicides such as Post (sethoxydim) and Fusilade (fluazifop).
Others like Field Sandbur (Cenchrus pauciflorus) and Sandbur (Cenchrus echinatus) are tolerant to these herbicides which don’t achieve acceptable control.
From the more than 25 annual grass species found in our area during the summer I listed in 13 commonly found below that are in the Section VI of the PCA study guide.
Also, the following is a link Summer Annual Grass Identification to a publication by Barry Tickes with images and description of the 6 genera and 12 species of summer annual grasses that are common here.
 
Summer Annual Grasses

Barnyardgrass	Echinochloa crus-galli
Red sprangletop	Leptochloa filormus
Prairie Cupgrass	Eriochloa contracta
Field sandbur	Cenchrus spinifex
Yellow foxtail	Setaria glauca
Feather fingergrass	Chloris virgata
Crowfootgrass	Dactyloctenium aegyptium
Junglerice (Watergrass)	Echinochloa colona
Mexican sprangletop	Leptochloa fusca
Southwestern Cupgrass	Eriochloa acuminata
Southern sandbur	Cenchrus echinatus
Green foxtail	Setaria viridis
Sixweeks grama	Bouteloua barbata

 

 

 

Figure 1. Left southern sandbur and right field sandbur

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.