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.

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 18, 2024 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 19  and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results.   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. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. 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.