The leafy vegetable harvest season is well underway and fall produce acres are slowly beginning to disappear.  Although pest pressure is decreasing with cooler temperatures, the forecast of La Nina (warm, dry weather) conditions could be ideal for insect growth and survival this winter and spring.  So, it’s very possible you could observe above average insect numbers come January, particularly if growers are lax in their post-harvest farming practices right now. Insect dispersal from alternate crops and weed hosts can often be significantly reduced with timely cultural practices following harvest.  The longer a harvested crop remains above ground, more insects can build up and move to adjacent plant hosts-especially in dry and warm weather.  Thus, sanitation and clean culture are important cultural practices that can be employed by growers on a field by field, and area-wide basis to reduce pest populations during the winter and spring.  And sanitation will be very important this year for preventing the spread Impatiens Necrotic Spot Virus(INSV) infecting lettuce crops. We reported last time that INSV has moved into the desert again on coastal transplants and those fields are now being harvested. We’re also seeing INSV spread to adjacent direct-seeded fields within a 1-mile radius of the transplants. Remember, INSV is transmitted by western flower thrips (WFT) adults but acquired only by 1^st and 2^nd instar larvae feeding on infected lettuce and weed hosts.  It is a complex pathosystem that makes WFT management more important than ever. It will be important to minimize immature development and adult dispersal as much as possible. And we can’t rely solely on insecticides to accomplish this.  So, the fewer WFT moving around in the cropping systems, the less chance for spread of INSV. As a first line of defense, growers should disc under lettuce crop residues immediately after harvest of fall and winter crops.  Neglected post-harvested lettuce crops can serve as a significant reservoir for INSV, and for infected WFT also.  Clean culture is also important for preventing potential INSV infections.   Weeds are notorious for harboring important plant viruses and their insect vectors. We’ve experienced this for years in the desert with aphid-borne potyviruses and whitefly criniviruses. Research has shown that several common weed species we find growing in the desert serve as hosts to both WFT and INVS. More importantly, little mallow and nettleleaf goosefoot can be found throughout the desert during the winter and are key hosts of INSV.  WFT also reproduce prolifically on these weed hosts.  So, maintaining a clean culture via thorough weed control in and around crops can help prevent WFT buildup and dispersal, and potentially the spread of INSV in spring crops. Keep those ditch banks clean. For more information on Thrips and INSV management, visit this link:  Thrips and INSV Management in Desert Lettuce
 
Yogi Berra once retorted “You can observe a lot by just watching”
What he really meant to say was…….. When in doubt, Scout

Root systems provide the foundation for plant development.  At the time of seeding and plant establishment, it is important to monitor and evaluate the newly developing root systems; subsequent plant growth depends on them.  
 
Roots are responsible for all water and nutrient uptake by the plant, and they provide the physical anchoring and support of the plant structure.  Each plant and crop species has its own “personality” and growth habits, including root systems.  Accordingly, root systems have unique characteristics among plants species.  
 
Young plant roots, particularly at the time of germination and stand establishment, are generally the most sensitive plant part to soil and water salinity.  In fact, seedling plant sensitivity to salinity can often be measured by approximately ½ of the tabulated salinity tolerance guidelines.  
 
In general plant root systems constitute 30-50% of the total plant dry matter.  When post-harvest plant residues are incorporated into the soil, the root systems provide a significant contribution to that plant material and final carbon (C) contributions to the soil, which is an important factor contributing to soil health.
 
The first thing a seed develops in the germination process is a primary root that grows downward into the soil.  We often refer to this as the “stinger” root that extends from a germinating seed.  New cells are formed at the tip of the primary root as it extends downward into the soil forming a “thimble-shaped” cluster of cells called a root cap (Figure 1).  
 
The root cap serves as a type of shield that helps the root penetrate the soil matrix and protect the developing root tissue.  As the root grows downward into the soil the root cap cells are sloughed off creating a slimy surface that helps lubricate the root as it extends deeper into the soil.
 
The growing point (apical meristem) for the developing root is just behind the root cap and this is the zone of new cell formation that facilitates root growth and replaces the cells that are sloughed off as the root grows through the soil.  The new cells elongate and serve to extend the roots into the soil (Figure 1).
 
The most active parts of the plant root system for mineral nutrient and water uptake are in the tiny root hairs that are formed in zone behind the apical meristem.  Root hairs are only formed in the relatively new and freshly developed root tissue.  The root hairs are extremely small, tender, and physiologically active.  Healthy fresh young roots and root hairs should be clean and white.
 
Root hairs are often referred to as “feeder roots” due to their high-level of activity in securing water and nutrients from the soil for the growing plant.  In the process of transplanting, it is important to protect the feeder roots as much as possible and promote their health to ensure rapid adaptation to the new soil environment.
 
Young plants have the capacity to develop basic aboveground tissue to perform sufficient photosynthesis for establishment and growth due to the plant’s ability to take up mineral nutrients and water from the soil from the root system.  Sometimes it can appear that plants are not growing rapidly while the young crop is investing energy and resources into root system development, which is the foundation for the subsequent plant growth and development.
 
The depth of the roots will vary according to the soil physical conditions and effective soil depth, soil fertility and salinity management, plant-available water, and of course the natural rooting characteristics of the plant.
 
In general, there are two basic types of plant root systems.  Broadleaf plants (dicotyledonous) and coniferous plants (gymnosperms) commonly have a taproot system the extends downward through the soil developing root branches from the primary root stem (Figure 2).
 
Grass plants and their relatives (monocotyledonous plants) produce fibrous root systems that branch extensively and radiate out into the soil from the plant base (Figure 2).
 
In general, taproots tend to be deeper with extensive branching from the primary root, develop woody tissue on older roots, and are generally long-lived.  In contrast, fibrous roots tend to be smaller, short-lived, with less branching.  
 
As roots age, they become more fully developed in conducting nutrients and water to the growing points of the plant, both above and belowground.  In all cases, the young and freshly developed root hairs (feeder roots) are the primary zone of water and mineral nutrient uptake.
 
As root systems age, the older roots will die, and new root tissue is formed.  As dead roots are sloughed off, the discarded tissue is attacked by naturally occurring, beneficial soil organisms (bacteria, fungi, protozoa, and worms) the release mineral nutrients and produce soil organic matter.  Turnover of root tissue is an extremely important aspect of plant contributions to soil carbon (C), organic matter, and general soil health.
 
We do not see the plant root systems and we cannot watch root hair development.  But it is good to be conscious of root system development since all mineral nutrient, water uptake, and structural support is provided through the roots.  
 
It is necessary to sacrifice a few plants occasionally and evaluate root system health and development.  Accordingly, it is good to review and understand normal root structure and function as we work to manage crop plants for optimum growth, development, and yield.

Figure 1.  Basic root tip anatomy.


Figure 2.  Examples of taproot and fibrous root systems.

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 staying up to date on the latest robotic ag technologies? FIRA USA and a number of other entities are organizing a 3-day forum focused on autonomous farming and agricultural robotics solutions. The event will be held October 22-24 in Woodland/Sacramento, CA. The program includes top-level keynote speakers, breakout sessions, a trade show and field demos. Over 35 robots will be demoed and/or on display including 8 machines designed for weeding vegetable crops. Some of the latest technologies for in-row weeding will be featured including lasers (2 companies) and high precision spot spraying (3 companies). If you are interested in ag tech, FIRA 2024 promises to be a quality event and one well worth attending. For more information, visit https://fira-usa.com/.

Fig. 1. Robotic technologies on display and being demoed in the field at
FIRA USA 2024. The event will be held October 22-24 in Woodland/Sacramento,
CA. (Photo credits: FIRA USA).

We are receiving some summer grass samples for identification. As you know the seedlings look very similar. 
PCAs have mentioned, and we can corroborate that some species respond differently to herbicides. As an example, we have seen that Sprangletop (Leptochloa filiformis) is not controlled with selective postemergent herbicides like Fusilade or Poast.  We have seen only good results with a high rate of clethodim (Select), and the generics off the same active ingredient. Sandbur is also tolerant to these herbicides.
These two weeds frequently come back from crowns surviving the winter which makes spring preemergence herbicides applied ineffective.
The following are common species of summer annual grass here:
 

echinochloa	water grass and barnyard grass
leptochloa	red sprangletop and mexican sprangletop
eriochloa	southwestern cupgrass and prairie cupgrass
cenchrus	field sandbur and red sandbur
setaria	green foxtail and yellow foxtail and
chloris	feather finger grass and truncate finger grass

 
 Check out the Summer Annual Grass ID publication which contains pictures and descriptive characteristics of each of these species.

I am delighted to embark on my first produce season here in Yuma, AZ. I am looking forward to becoming acquainted with the growing region this fall as we begin identifying tools that can enhance our pest management strategies, specifically focusing on organic solutions for managing insect pests in the Desert Southwest. It is also important for me to gain a deeper understanding of the challenges and issues you are facing in the field. We are eager to evaluate both current and new biopesticides in our upcoming trials and look forward to engaging with potential collaborators. 

Here is a list of our fall 2024 trials: 

1- Evaluation of selected bioinsecticides against Lepidopteran pests in Brassicas 

2- Evaluation of selected bioinsecticides against whiteflies in Brassicas 

3- Alternative bioinsecticides for thrips management in lettuce 

4- Assessing the effectiveness of beneficial insects (T. brassicae, T. pretiosum, and green lacewings) release for diamondback moth control in Brassicas 

I hope everyone’s season gets off to a fantastic start. Please contact me or Macey if you have specific pest issues, biopesticides, or other organic IPM practices you would like us to evaluate. Your expertise is truly invaluable to us! 

Contact Information: 

• Wilfrid Calvin
Assistant Professor & Extension Specialist
Cell: (979) 709-9762
Office: (928) 782-5861
e-mail: wilfridcalvin@arizona.edu 
 

• Macey Keith
Assistant in Extension
Cell: (928) 580-5785
e-mail: maceyw@catmail.arizona.edu 

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 17, Aug 25, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts increased in the past two weeks particularly in Wellton and Roll.  
 
Beet armyworm:         
Trap counts remain low in most locations and are trending similar to last summer.
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this fall, and summer compared to last season.
 
Whitefly:                      
Adult movement increased significantly in July and early August but has slowed considerably in the past 2 weeks. 
 
Thrips:                          
Thrips adult movement has declined significantly over the past 4 weeks and numbers are comparable to this time last year.
 
Aphids:                        
Aphid movement has been absent since early June typical with high summer temperatures, and the monsoon flow.  
 
Leafminers:                  
Adult activity trending downward to low numbers over the past month.
 
Diamondback moth:     
DBM trap counts have been zeroed out in all trap locations since late June consistent with trends observed over the past 4 years.