We have historically ended our Areawide Pheromone and Sticky Trap monitoring for insects around the first of April as the produce season ends. Beginning last year however, we continued our Areawide Trapping Network throughout the summer and are doing so now to continue to collect trapping data from all 16 areawide trap locations year-round.  So why is this additional trapping data useful? For several reasons. First, understanding the activity of some of our key pests when produce is not available (during the summer) may give us an indication of what to expect as the fall produce season begins. This may be particularly helpful for predicting moth flights and whitefly flights in August-September coinciding with early transplanting and direct seeded crops.  Another example is keeping track of corn earworm which can unexpectedly show up near the beginning of fall harvests. Secondly, trapping for pests during the summer has shown us that 2 of our more important produce pests are not caught in traps during the summer. We presume this is due to the absence of brassica crops and weeds for diamondback moth, and high daytime temperatures lethal to aphids. The fact that trap catches resume in the fall supports our conclusion that these pests are absent in the summer, only to reenter the desert via winds and/or transplants in the fall. And finally, it gives me something to do in the summer.  So, visit the Areawide Summer Trap Network if you’re curious what our key pests are up to. We also taken on another interesting project to monitor thrips activity during the summer. This involves plant sampling using a dislodgement sampling method (beat pan) to determine the relative abundance of thrips adults and larvae on alfalfa, cotton, melons, wheat, Sudan grass, and weeds.  This is being conducted to supplement our yellow sticky trap data that only indicates thrips adult flight movement an area. With this plant sampling we should be able to determine the primary host plants thrips are colonizing in the cropping season during the long hot summer. We are also trying to determine whether these crops allow for the reproduction of thrips. So far, all the crops and weeds we have sampled have shown that thrips will reproduce and complete their life cycle on them. This is important, particularly for weeds, as we are trying to determine whether INSV can be survive the summer in the absence of lettuce. It is also important because it allows us to determine potential exposure of thrips to key insecticides like Radiant and Lannate for resistance management purposes. These crops essentially serve as untreated refugia that likely sustains insecticide susceptibility and is the reason these products are still effective against thrips.  We will be conducting this work throughout the summer, as well as through next produce season. We will be providing data in each Veg IPM update. For the most recent sampling data see our Areawide Thrips Monitoring.  As always, if you have any ideas on thrips monitoring or insect trapping, we’d be glad to listen and discuss. As my dad used to say, “to solve the problem, you must first understand the problem”. 

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.

Gearing up for the produce season, we already have been seeing plenty of fields transplanted with cole crops (cauliflower, cabbage, broccoli, etc). Below are the few common diseases to watch out for.  

Damping-Off
This disease commonly affects seeds and young transplants and is caused by the soil-borne fungi such as Pythium, Fusarium, Rhizoctonia etc. Infected seeds decay in the soil. Seedlings and young transplants will “damp-off” or rot at the soil line, before they eventually collapse and die.

The fungus, Rhizoctonia solani, causes wirestem. Stems of plants become constricted and brittle at the soil line. The plant becomes stunted and may rot at the soil line. This disease is more severe on fall cole crops when the soil is warm. We have seen lot of this problem in the fields last year. Make sure you get certified disease-free seedlings.

Prevention & Treatment: Cultural controls include planting on raised beds and providing good drainage. In greenhouse where transplants are grown, use new potting soil and new or thoroughly cleaned and disinfested containers and trays. Wash used containers with soapy water to remove all traces of old soil mix, and then briefly submerse containers in a 10% bleach solution. Allow to dry before planting in containers. Both in greenhouse and fields: avoid overwatering and wet feet in plants/seedlings.

Black Rot
Black rot is another common disease we observed in the fields last growing season. Black rot is caused by a bacterium, Xanthomonas campestris pathovar campestris, and can affect all vegetables in the crucifer family. Above-ground parts of the plant are primarily affected, and symptoms may vary depending on the type of plant, age of the plant and the environmental conditions. In general, yellow, V-shaped lesions appear along the tips of the leaves with the point of the V directed toward a vein. When lesions enlarge, wilted tissue expands toward the base of the leaves. Veins turn black or brown. Infection may spread into the stems. Cutting into the stems often reveals a black-brown discoloration with a yellowish slime present. Symptoms on cauliflower may appear as numerous black or brown specks, black veins and discolored curds.

Prevention & Treatment: With no effective curative measures available, preventative measures are very important. The bacteria survive the winter on plant debris and on weeds, such as wild mustard and Shepherd’s purse. It also can survive in and on seeds from infected plants. It can remain alive on plant residue buried in the soil for up to two years. The disease is easily spread by splashing water, wind, insects and garden tools. High temperatures and humidity favor development of the disease.

Use certified disease-free seed and transplants. If source of the seeds is unknown, or infested seed lots must be used, treat seed with hot water to eradicate pathogenic bacteria. Cabbage, broccoli, and Brussels sprouts can be treated at 122 °F for 25 minutes, while seeds of cauliflower, kale, turnip, and rutabaga are treated for 15 minutes. However, this treatment may reduce the viability of seed.

Choose varieties tolerant to black rot.  Do not plant cole crops where black rot has occurred in the past two to three years. Select well-drained sites with good air circulation.

Downy Mildew
This disease is caused by the fungus Peronospora parasitica and can attack both seedlings and mature vegetable plants. Infected plants develop a gray mold on the lower leaf surface. The upper leaf surface of infected plants first turns yellow and then may turn brown or necrotic. Leaves wither and die. Symptoms differ from powdery mildew in that the downy mildew fungus grows only on the lower surface of the leaf. Development of the disease is favored by moist conditions.

Downy mildew symptoms on a collard leaf. Justin Ballew, ©2020, Clemson Extension

Prevention & Treatment: Use varieties with resistant varieties. Rotate with crops other than cole crops or greens. Remove plant debris immediately after harvest. Use wide plant spacing to promote drying of leaves. For chemical control, make sure to rotate the fungicides to avoid development of resistance.

Alternaria Leaf Spot
Alternaria leaf sport is a common problem and sometimes may not be of economic importance.  However, if the plants are already weak or physically damaged providing the site of infection, the disease can cause economic losses.

Article source: https://hgic.clemson.edu/

2024-2025 growing season field trials

With the start of 2024-2025 growing season, we are gearing up for field trials on vegetables. Listed below are our research trials for this growing season addressing the need of the agriculture community. For more information and/or collaboration contact: bpoudel@arizona.edu

Integrated management of downy mildew in lettuce:

Three different most commonly grown iceberg lettuce cultivar will be evaluated against downy mildew using different chemical treatments. Partially funded by Arizona Iceberg Lettuce Research Council.

Sclerotinia drop of Lettuce

In this game of all or nothing, we will continue to do field trials on sclerotinia drop of lettuce. We will be doing trials on both species S. sclerotirum and S. minor.

Powdery mildew of lettuce

We will continue with field trials on powdery mildew of lettuce.

Downy mildew of Spinach

Downy mildew of spinach field trials won’t start until January of next year. But we are requesting industry reps to contact us ahead of time.

For more information: bpoudel@arizona.edu,928-920-1110

 

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. 14, No. 1, Jan 11, 2023
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts are down areawide average for this time of year. 
 
Beet armyworm:         
Trap counts increased in most ll locations; about average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts increased in most traps and about  average for this time of season.
 
Diamondback moth:      
DBM moths continue to increase in all areas. About average for this time of the year.
 
Whitefly:                       
Adult movement light and is typical for this time of year. 
 
Thrips:                          
Thrips adult counts beginning to slowly increase in the past 2 weeks. Currently, below average compared with previous years.
 
Aphids:                        
Aphid movement increased significantly in North Yuma and Gila Valleys consistent with winds and storms. About average for early January.
 
Leafminers:                   
Adult activity up in many locations, and above average for January.