Effective control of western flower thrips (WFT) to prevent cosmetic scarring and contamination is important in spring lettuce crops, and now that INSV has been found infecting plants in Yuma lettuce, management becomes even more important.  For most of the growing season, WFT numbers have been below average based on sticky trap counts, field reports and population densities here at YAC. However, in the past week WFT populations have increased in most growing areas. This is not surprising as we typically observe “bioconcentration" of WFT during March and April on late lettuce as surrounding produce acreage declines. Each time a lettuce field is harvested, and disked, adult thrips 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 of WFT very difficult, particularly in March, as adults can continually re-infest fields following spray applications.  Unfortunately, bioconcentration is likely to be even more intensified with the increase in late lettuce we have this season.  So, what management approaches can you take to manage thrips and hopefully reduce the potential incidence of INSV.  The first line of defense should be sanitation. Growers should disc under producecrops immediately following harvest. The longer a harvested crop remains above ground, the more insects that can build up and move to adjacent lettuce fields, especially with the dry, windy, and warm weather we typically have in March and April.  So far INSV incidence is light, and on average less than 1% infections has been reported in fields. However, the longer the season progresses and thrips begin to move, the threat of INSV spreading increases.
Controlling WFT with insecticides is the best approach to minimizing cosmetic feeding damage and may reduce spread of INSV within fields. For adults, which can easily be found on the leaf surface, your best choices of insecticide are methomyl (Lannate) or acephate at a high label rate.  They are the most efficacious products against adult WFT, but are also effective against larvae. Radiant is not as consistently efficacious against adults, but a 7 oz or higher rate will provide the best knockdown and residual control of WFT larvae. Torac, via contact activity, is relatively effective against WFT, and is most efficacious applied by ground on smaller plants when populations are lighter.  Remember, the key to preventing cosmetic damage by WFT is to maintain larval populations at low levels.  The cryptic or thigmotactic behavior of thrips often makes them difficult to find on lettuce plants. Research has shown that if you can see a few adults and larvae on the plant, it means that there are likely 8 to 10-fold more thrips actually on the plant (hiding near the base of the plant between midribs).  This behavior also means that spray coverage is important, particularly with contact insecticides like Lannate. There are other insecticides such as Minecto Pro, Exirel, Movento and Beleaf that can provide suppression (50% control or less) against WFT larvae, but don’t expect much activity against adults. For more information on the identification, biology, ecology, and management of thrips on desert produce please visit Western Flower Thrips Management in Desert Produce – 2023.

Root systems 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, and root systems have unique characteristics among plants species.  
 
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.
 
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.
 
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.  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 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 generally long-lived.  In contrast, fibrous roots tend to be smaller, short-lived, with less branching.  As roots age, they become more important 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) and organic matter.
We do not see the plant root system on a regular basis 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. So, it is good to review and understand root structure and function as we work to manage crop plants for optimum growth and development.

Figure 1.  Basic root tip anatomy.


Figure 2.  Examples of taproot and fibrous root systems.

Bindu Poudel-Ward, Martin Porchas Sr., Martin Porchas Jr., Neeraja Singh, Johan Murcia, and Rebecca Ramirez, and Jason Furr 
Yuma Agricultural Center, University of Arizona, Yuma, AZ

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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 16, 2023 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. 

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 24 and final reading was taken on March 13, 2023. Spray treatment were applied on February 16, February 23, and March 2 of 2023,(see table).  Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

            The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Orondis Ultra provided the most effective control against the disease. No phytotoxicity was observed in any of the treatments in this trial. 

There are many innovative automated weeding technologies coming out of Europe. One of these is ARA, the high precision, smart spot sprayer being developed by Ecorobotix[1] (Yverdon-les-Bains, Switzerland). Early prototypes were solar powered, autonomous robots that used a spider-like, three-axis delta robot to precisely deliver herbicides to target weeds (Fig. 1). The company has since moved on to a much simpler solution – a fixed boom, tractor pulled implement (Fig. 2). The 19.7’ wide smart sprayer is equipped with 156 individually controlled spray nozzles spaced 1.6” resulting in a spot spray resolution of 5.6 inch² (2.4 x 2.4 inch). The claimed travel speed is 4.5 mph equating to a work rate of 10 ac/hr. The machine uses computer imaging and artificial intelligence for crop/weed differentiation to identify and target weeds. AI weeding models have been developed for a variety of crops including several vegetable crops – onion, lettuce and spinach. In addition to weed control, the smart sprayer can be used to spot apply beneficial products to only the crop plant. A company video showing the device operating in onion crops can be found by clicking here or on the image below.

As I have mentioned before, robotic and automated weeding technologies are advancing at a very rapid pace. If you know of a new technology that would be of interest and appropriate for this newsletter, please feel free to contact me.

Fig. 1. Solar powered autonomous weeding robot developed by Ecorobotix,
Switzerland. The unit is equipped with three-axis delta robot arms to precisely
deliver herbicides to target weeds (Photo credit – Ecorobotix).

Fig 2. Precision weeding machine developed by Ecorobotix, Switzerland. The unit
is equipped with individually controllable spray nozzles mounted on a 19.7’ wide
spray boom to spot spray weeds (Photo credit – Ecorobotix).



Fig. 3. Precision spray boom comprising 156 spray nozzles for spot spraying
weeds. Spot spray resolution is 2.4 x 2.4 inches. (Photo credit – Ecorobotix,
Switzerland).

[1] Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.

Image by: Jim Daily

Hare Barley, Mediterranean, or Wild Barley (Hordeum murinum) has been increasing at the Yuma AZ Valley and the Mesa. This week we have received some samples for ID from our friend PCAs.
It’s a cool season annual grass native to Europe with dense stiff awned spikes. Early in the season before the flower spikes develop, they can be a very good forage but when the spikes emerge can injure the mouths, eyes, nasal passages, ears, and skin of animals.
It is found throughout California up to 3300 feet (1000 m) and inhabits agricultural land, disturbed sites, and unmanaged natural areas³. The seedheads are unbranched, awned, stems and leaves are hairless, and the ligules are membranous. The collar region and auricles can be seen in the image below from the University of CA³.
The Hordeum murinum complex is the most widespread of all the other Hordeum species, and the origin of its distribution of was Central Europe, the Mediterranean area, North Africa, and Western Asia¹.

Collar region of (left to right) hare (wild) barley, wheat, and wild oat.
Photo by Jack Kelly Clark³.

References:

1.   Retrieved from: https://en.wikipedia.org/wiki/Hordeum_murinum
2. https://weeds.nmsu.edu/factsheet.php?weed_id=101
3. https://ipm.ucanr.edu/PMG/WEEDS/hare_barley.html

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.