Even though temperatures and humidity has dropped, worm pressure remains steady in most growing areas.   Here at the Ag Center, armyworm pressure is about average for early October, but still troublesome on new stands. Cabbage looper eggs and young larvae are now becoming abundant on all our crops, and PCAs are reporting an increase in looper pressure. Pheromone trap counts for armyworm and loopers remain below average in most areas. However, Diamondback moth larvae are unusually abundant on broccoli and transplants at the Ag Center.  I’ve had several PCA reports of diamondback pressure in transplanted and direct seeded brassica crops in the Wellton and Tacna areas. Trap catches have begun to increase also. So far, all insecticide products we’ve tested are providing good DBM control and no complaints from the field.  In one of my trials, the Verimark transplant tray drench treatment on cauliflower (Sep 5 wet date) was still active against DBM at 28 days following transplanting (see graph below).
 
Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on these pests (see the Sept 20 update).   Perhaps equally important, many of the products have unique modes of action (MOA) that can be alternated throughout the growing season. This is important because the most fundamental way to reduce the risk of insecticide resistance is to eliminate exposure of multiple generations of Leps to the same MOA.   By using a different MOA on each subsequent spray application, you can minimize the risk of resistance by Lep larvae to these insecticide compounds. In contrast, repeatedly applying insecticide products with the same MOA for Lep control in the same area will significantly increase the risk of resistance.  This is particularly important with the Diamide group of insecticides (IRAC group 28). These products can be applied as both foliar sprays and soil systemic treatments, and currently 7 Diamide products are for use labeled in leafy vegetables - all with the same MOA (Coragen, Durivo, Besiege, Minecto Pro, Verimark, Exirel and Harvanta).  To avoid confusion among the Diamides, the IRAC group number (28) is placed on each label, adjacent to the product name.  Furthermore, applying a Diamide product (i.e., Coragen/Verimark) to the soil at planting or as a tray drench, and then subsequently applying Diamide foliar sprays (i.e., Harvanta/Besiege) on the same field is not a good idea as it can expose multiple generations of Leps to the same MOA.  For example, under ideal weather conditions, one could potentially expose 5-6 generations of BAW or DBM to the same MOA given the residual efficacy of the diamides.  That’s not a good way to use these products if you want them to remain effective.   Since the Diamides, as well as the other key products currently available (e.g., Radiant, Proclaim, Intrepid, Avaunt, Bts), are critical to effective management of Leps in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds. The most effective way to delay the onset of resistance by Leps in leafy vegetables is to consider the recommendations provided in the guidelines entitled Insecticide Resistance Management for Beet Armyworm, Cabbage Looper and Diamondback Moth in Desert Produce Crops.

There is a lot of discussion these days regarding the need for crop production systems in Arizona to improve upon the efficiencies of our irrigation systems.  The focus on irrigation efficiencies has been accentuated with the current water shortages being experienced in many parts of the state and region, particularly with the Colorado River system.
 
Despite the focus on irrigation efficiency and the abundance of discussions and advice for the crop production community on how to go about the business of irrigating and producing a crop, very little, if any, comment is being made to define what is meant by “irrigation efficiency”.
 
There are several ways to define irrigation efficiency.  The primary definitions for irrigation efficiency include orientations with 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 incredible engineering with the highly developed systems of dams, primary canals, pumps, laterals, and secondary canals that move water from rivers and groundwater supplies to areas of need, which are commonly 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 in terms of how water is conveyed from the source to the field.  This level of efficiency is largely a function of system engineering and design and the system management.  
 
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 (ETc, which is the combination of evaporation and transpiration from the crop) and leaching requirements (LR, which are dependent upon the crop and salinity of the irrigation water).  
 
Agronomic efficiency can be estimated by considering the difference between ETc + LR = CWD and the volume of irrigation water applied (IWA).
 
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 a 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 easily available 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).  
 
Economic Efficiency
Economic efficiency is often considered to be primary factor defining the financial sustainability of a farming operation.  Water is a crop input and the costs associated with irrigating a crop includes the cost of the water directly and costs of delivery (pumps, equipment, maintenance, labor, etc.).  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 efficiencies previously discussed (water conveyance systems, agronomic, and economic considerations).  Environmental efficiency is a collective line of consideration regarding overall stewardship of water as a natural resource and beneficial use.
 
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.  Thus, I believe it is most appropriate to consider irrigation efficiency at the field level in agronomic terms, by use of Equation 1.  
 
We need three factors to estimate 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 to the field in question (IWA).
 
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:
 
The appropriate 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 and now most commonly from the publication FAO 56 “Crop Evapotranspiration-Guidelines for Computing Crop Water Requirements-FAO Irrigation and Drainage Paper 56” (Allen et al., 1998).  Reference information for Kc values can be obtained in these publications for common crops grown in this region.
 
Example
If we consider an example lettuce crop irrigated with water that has ECw = 1.1 dS/m and the crop water demand (CWD) = 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.
 
 
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
 
Assume: 40 inches of irrigation water was applied.
 
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.
 
The Arizona Meteorological Network (AZMET) system 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 the Yuma area and the lower Colorado River Valley.  Very importantly, the AZMET is very high quality and the integrity of the system has been constantly managed for over 35 years, first under the direction of Dr. Paul Brown and now with Dr. Jeremy Weiss.  This information can be valuable in crop water and irrigation management.  
 
Dr. Jeremy Weiss, program manager for the University of Arizona AZMET system, has recently developed a valuable tool that provides actual crop evapotranspiration (ETc) estimates from several AZMET sites in the lower Colorado River Valley and for several key vegetable crops. Accumulations of ETc values over the previous week are shown based on a date of planting, which is selected by the user.  In this model, the Kc values presented in FAO-56 are used for appropriate stages with each crop.  The ETo measurements are taken directly from each AZMET site listed.
 
Dr. Weiss has included the next step with the development of this crop-water management tool that can provide the cumulative crop water use, cumulative ETc, during the growing season for a given crop and planting date for common leafy green vegetable crops in the lower Colorado River areas.
  
To access this crop-water estimate tool please refer to the following link:
 
https://viz.datascience.arizona.edu/azmet/azmet-crop-water-use-estimates/
 
For example, using lettuce (either iceberg or romaine) and 1 September planting date, we can see from this model that cumulative ETc from 10/5/22 to 10/11/22 is 1.11 inches in the North Gila Valley and 0.94 inches in the Yuma Valley (Figure 2).  Cumulative ETc since the planting date is 7.19 and 6.28 inches for these two stations, respectively.
 
Dr. Weiss and I are working with this model in the field to evaluate and test it.  I encourage farmers, agronomists, and field crop managers to review this information and check that against depletion rates of soil plant-available water in the field.

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


Figure 2.  Example of AZMET Crop Water Use estimates for lettuce planted on 1 September 2022 in the lower Colorado River Valley.
 
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.”

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum,  is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult. 
 
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields. 
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil. 
 
 Initial infection of seedlings usually occurs from chlamydospores (resting structure)  that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen. 
 
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management. 

In previous articles, I have discussed using band-steam to control plant diseases and weeds. Band-steam is where, prior to planting, steam is injected in narrow bands (4” wide x 2” deep), centered on the seedline to raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (>140 °F for >20 minutes). After the soil cools (<1 day), the crop is planted into the strips of disinfested soil.

This summer, project Co-PI, Steve Fennimore, Extension Specialist – Weed Science, UC Davis has been evaluating the efficacy of using band-steam to control weeds and cavity spot (Pythium spp.) in carrot. The trials are still in progress, but so far, the technique has been found to be very promising for weed control (Fig. 1).

Using steam to control weeds in high density crops such as carrot, baby leaf spinach and spring mix may be a particularly good fit for the method. Handing weeding in these crops is labor intensive and costs are high, typically exceeding $300/acre (Fig. 2). Costs are even greater in organic crops. A benefit of steam application is that it is organically compliant.

This fall, we will be developing a steam applicator designed for use on wide beds. We’ll be trialing the device in baby leaf spinach and spring mix. If you are interested in this application, we’ll be demonstrating weed control in baby leaf spinach using steam heat at the UA 3^rd AgTech Field Day. The event will be held Tuesday, October 25^th at the Yuma Ag Center.

Acknowledgements
This work is supported by the Arizona Specialty Crop Block Grant Program and the Crop Production and Pest Management grant no. 2021-70006-35761 /project accession no. 1027435 from USDA-NIFA. We 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 U.S. Department of Agriculture.

Fig. 1. Weed control with band steaming in carrot. Steam was applied in a 4-inch band centered on the two seedlines (between the dashed white lines) prior to planting. The weeds outside of the treated band can be easily removed through cultivation. (Photo credits: Steve Fennimore, UC Davis).


Fig. 2. Hand weeding in crops seeded at high densities is labor intensive.

We published this booklet last July. Please let us know what you think by responding our five questions in the link provided below, email marcop@ag.arizona.edu and let us know if you like to receive a free of the booklet!

ANSWER 5 QUESTIONS HERE

The method for identification presented is not by using a dichotomous key or answering complicated questions about the species. The idea is to leaf through the booklet and find images that match plants you see in the field. If there are unusual characteristics, we note them in our comments for each weed. Here is a link to the guide in PDF format: HERE

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.