Foxglove Aphids: In the past two weeks, foxglove aphid (FGA), has increased dramatically in our untreated control lettuce plots here at the Yuma Ag Center. We’ve also had reports from PCAs of difficulty in controlling FGA, which is more abundant than I’ve seen in the past 5-6 years. In my opinion, this is the reason more spray applications are necessary for FGA control this season. Green peach aphids are also still prevalent in high numbers in our cole crops, but are rapidly declining in lettuce. Because aphid species are inherently different in their susceptibility to insecticides, the proper choice of product is important for achieving adequate control. In my lettuce trials, Sequoia, Sivanto, and Beleaf have provided the most consistent knockdown and residual control of FGA. For more information on FGA and insecticide alternatives for the various aphid species please view our Aphid Control Chart-2017 and Foxglove Aphid on Desert Lettuce Crops.

Thrips: In contrast, western flower thrips have been very light this spring, largely due to heavier than average rainfall and cooler weather for the past few weeks. However, as drier conditions prevail, PCAs should expect thrips numbers to steadily increase with the warmer weather. This is particularly important on late-lettuce where “bioconcentration" of thrips occurs each year as lettuce acreage declines. Each time a lettuce field is harvested and disked, adult thrips populations disperse from these areas into the next available lettuce field. As the number of lettuce acres becomes reduced near the end of the season, this creates a bottleneck effect that concentrates high numbers of thrips adults on the remaining fields under production. This can often make chemical control very difficult, particularly in March, as thrips adults may continually re-infest fields following spray applications. See the Thrips Control Chart 2017 for more information. 

Diamondback Moth (DBM): Reports of DBM infestations are still coming in from PCAs as the season begins to end, and at the Yuma Ag Center, DBM can be found on broccoli and cabbage in extremely high numbers. In fact, we were unable to establish 2 acres of broccoli plots due to the extreme damage caused by larvae on seedling plants. The entire 2 acres was essentially destroyed. Trap catches show that DBM are still actively moving (see DBM Trap Network). Thus, any late season brassica crops grown in the Yuma Valley are susceptible to high DBM numbers, particularly with the warmer weather to come. We have also found DBM infesting brassica seed crops, with the larvae feeding on the developing seedpods. Products that are providing efficacy in the field include: Radiant, Proclaim, Exirel, Entrust, Avaunt, Dibrom and XenTari. Avoid applying Coragen, Voliam Xpress, Belt and Vetica due to DBM resistance to these products. 

In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall. 

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. 11, No. 22, October 28, 2020

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

Corn earworm: Moth activity is about average for mid-October, particularly in Dome Valley and south Yuma Valley. 

Beet armyworm: Moths remain active throughout the desert, especially active in Tacna and Dome Valley.

Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae are yet to show up in many fields.   

Whitefly: Adult movement has been about average for this time of year. Activity highest in Tacna near fall melons.

Thrips: To date, thrips activity has been seasonably low at all trap locations; activity increased significantly in Roll. 

Aphids: Aphids beginning to show in most traps along the Colorado River (Bard, Gila, Yuma) which is normal for this time of year.  Recent high winds may begin to disperse them throughout the area.

Leafminers: Adult activity below normal for September, but high numbers caught in Wellton in areas where melon harvest has commenced.