Fall melon production is underway and transplanting/direct seeding of produce crops is close behind. PCAs will soon be faced with several important insect management decisions.  As crops begin to emerge, you can expect to encounter several insect species that can potentially cause serious economic losses to crop stands.  These seedling pests include flea beetles, crickets, grasshoppers, darkling beetles, earwigs, and saltmarsh caterpillars (‘woolly worms’). These insects all have chewing mouthparts, and most are capable of consuming large amounts of leaf tissue in a short period of time. Seedling crops at the cotyledon stage are most susceptible; these pests can devour entire cotyledons or outright kill small seedlings.  If left unprotected, transplants and larger seedling plants can sustain significant feeding damage on the terminal growing points or newly emerged leaves.  Not only can this feeding stunt plant growth but can result in lack of stand uniformity and ultimately, lack of uniform maturity at harvest. Host crop sources for flea beetle, crickets and "woolly worm" infestations include several summer crops (e.g., Sudan grass, cotton, and alfalfa), volunteer melons, and weeds (e.g., purslane, pigweed). 
Flea beetles are notorious for building up on weeds, particularly purslane, and alfalfa this time of the year. Fortunately, growers have been vigilant about field sanitation, and weeds are few and far between throughout the valleys. Be aware of beetle migration from recently harvested hay adjacent to your germinating crops. Crickets have also been especially abundant this summer, so keep a sharp eye for them, particularly under sprinkler pipe. Also be on the lookout of grasshoppers this fall. They can easily sneak up on you especially if we have an active monsoon.  Salt marsh caterpillars have not been seen in years but are known to disperse from alfalfa and Pima cotton (non-Bt).  Experience suggests that melon fields planted next to these crops and weedy areas are at a high risk from these seedling pests, particularly flea beetles. As cotton and Sudan grass are harvested or terminated during the next several weeks, these seedling pests typically move to the next available host crop; lettuce, cole crops and melons.  
Fortunately, there are many registered insecticide alternatives available that can be applied via sprinkler chemigation (i.e., pyrethroids) or foliar sprays (i.e., pyrethroids, methomyl, neonicotinoids) that can cost-effectively reduce their abundance and damage to susceptible produce and melon seedlings. Additionally, insecticide seed treatments are available for lettuce and broccoli that will protect stands from flea beetles and bagrada bug (i.e., Nipsit) for 14–21 days.  For more information on insect pests of leafy vegetables and melons at stand establishment please see:

1) Management of Insect Pests at Stand Establishment on Desert Produce and Melons
2) Palestriped Flea Beetles in Leafy Vegetables and Cole Crops

Crop Consumptive Use and Measurement 
While striving to continually improve efficiency in the management of our irrigation systems, it is important to understand basic crop water use patterns.  Estimating and tracking actual crop-water use can be a valuable tool in understanding crop-water demand and irrigation management.  
 
In desert crop production systems, water is the first limiting factor and irrigation is a primary driving force in the growth and development of the crop.  
 
In the process of irrigating a field to support a crop, there are two primary objectives that we must address in a desert crop production system: 1) replenish the plant-available water in the soil profile and 2) provide sufficient irrigation water to accomplish the necessary leaching of soluble salts.  In some cases, particularly with cool season plants, e.g. lettuce and cole crops, we sometimes irrigate to cool the soils for seed germination and stand establishment when seed placement is made in warm or hot soils.
 
In a soil-plant system the dynamics of water-balance involves inputs (rainfall and/or irrigation) and several routes of possible water loss (Figure 1).  The soil provides the water-holding capacity that offers water available for plant uptake through the root system.  Ideally, we want all the irrigation water that we apply to be taken up by the crop for optimum plant health and water use efficiency.

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

In managing irrigation events, we must take into consideration the amount of soil-water that has been depleted from the field by the crop since the last irrigation and we must also consider the water holding capacity of the soils in the field (Table 1).  Deep percolation is often regarded as a loss of soil-water but in desert agriculture, but a sufficient degree of deep percolation is needed to remove soluble salts from the plant rootzone, e.g. leaching requirements.

Table 1. Soil texture and water holding capacity.

Comparing actual crop-water demand and crop irrigation practices can be important in our efforts to understand crop management needs and field-level irrigation efficiencies.
 
The collective loss of water from a field due to evaporation from the soil surface and transpiration of water vapor from the plants under standard conditions is referred to as “evapotranspiration, ET”.  
 
Collectively, water used from the soil and plant system in a field is also referred to as “crop consumptive use”.  It is important to understand this process to continually improve the management and stewardship of our water resources as we irrigate to replace water loss from the soil-plant system through the ET process, Figure 1.
 
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.  This information can be valuable in crop water and irrigation management.  
 
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.  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:
 
ETc = ETo * Kc
 
The appropriate Kc values are specific for each crop species and stage of growth.  We have commonly used 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.  In recent years, we now use the Kc values found in 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.
 
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 specific crop and date of planting, which are 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.
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 accumulative ETc from 9/15/22 to 9/20/22 is 1.06 inches in the North Gila Valley and 0.90 in the Yuma Valley.

Figure 2.  Example of AZMET Crop Water Use estimates on 3 October 2022 for lettuce planted on 1 September 2022 in the lower Colorado River Valley.

The next step with the development of this crop-water management tool will be to include cumulative crop water use, cumulative ETc, during the growing season for a given crop and planting date in the lower Colorado River areas.
 
Dr. Weiss and I are working with this model in the field to evaluate and test it.  This crop water use tool can serve a valuable role in our continued efforts to improve irrigation and water management efficiencies.  I encourage farmers, agronomists, and field crop managers to review this information and check that against depletion rates of soil plant-available water actually observed in the field.
 
We appreciate your review and any feedback and/or suggestions you may have.
 
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.
 
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.

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches 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. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

Interested in the latest ag technologies? There are a couple of events coming up next month that are worth reminding everyone about. The first is FIRA USA which is a 3-day event being held October 18-20^th in Fresno, CA. The focus is on autonomous farming and agricultural robotics solutions. The event includes top-level keynote speakers, breakout sessions, a trade show and in-field demos of automated/robotic harvesting, weeding and planting equipment. The emphasis is on specialty crops, many related to vegetable crop production so it looks to be an informative program. For more information, click here or on the image below.

If you are unable to attend FIRA USA, another option is the University of Arizona’s 3^rd AgTech Field Day. The event will be held Tuesday, October 25th at the University of Arizona’s Yuma Agricultural Center. The program will feature many of the technologies presented at FIRA being demoed in the field.

As mentioned in the previous issue, we’d like to showcase as many innovative ag technologies as possible at our UA Field Day. There is still room on the program, so please contact me if you are interested in demoing your equipment or know someone that is. It’s an open invitation - private companies, and university and government researchers are all welcome!

Fig. 1. FIRA-USA conference held October 17-20^th in Fresno, CA.
(Photo credits: FIRA-USA).


Fig. 2. The University of Arizona’s 3^rd AgTech Field Day will be held Oct. 25^th,
2022, at the Yuma Agricultural Center, Yuma, AZ. (Photo from UA’s 2^nd AgTech
Field Day held in 2021).

We published this booklet last July. Please let us know what you think by responding our five questions in the link provided below. The first 25 respondents WILL RECEIVE a copy of the guide. Additionally…first five to take the survey and ID the weeds in the cover of the booklet will also get a Navy Blue UA Vegetable IPM HAT.

ANSWER 5 QUESTIONS HERE

There are abundant resources for weed identification of mature plants. These include very complete guides such as “Weeds of California and Other Western States” by Joseph DiTomaso published by University of California. “An Illustrated Guide to Arizona Weeds” by Kittie F. Parker with excellent drawings by Lucretia Breazeale Hamilton. There are also several phone apps for weed identification. However, the cotyledons of weeds frequently have a different shape than the true leaves, which makes identification of seedlings difficult for some species. The purpose of this pocket booklet is to provide a quick reference with good images that can be carried in your truck to help you identify the most common broadleaved weeds in Southwestern and Central Arizona.

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. 12, No. 23, Nov 17, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts continued to decline over the past 2 weeks across all locations and about average for this time of the season. 
 
Beet armyworm:         
Trap counts decreased in most locations, but well below average for late-October. Most activity in Yuma, dome and Gila Valleys.
 
Cabbage looper:          
Cabbage looper trap counts declined in most areas but increased in the Bard and Yuma Valley. Activity below average for early November.
 
Diamondback moth:     
Adults peaked in Gila and Yuma Valleys and above average in all locations for this time of year. Traps located adjacent to cauliflower and broccoli transplants had the highest trap captures 
 
Whitefly:                     
Adults remains active in Dome Valley, Wellton, and Roll consistent with melon crops completing harvest, but below average movement for this time of season. 
 
Thrips:                          
Thrips adult movement increased in most locations last week,  particularly in Dome Valley, Wellton, and Tacna. Activity about average for early November.
 
Aphids:                        
Aphid movement increased sharply in Bard, N. Yuma Valley and N. Gila Valleys over the past 2 weeks. Activity average for this time of year.
 
Leafminers:                  
Adult activity increased sharply in the Gila Valley, Roll and Wellton; about average for this time of season.