When going into the field to evaluate a crop, there are typically three fundamental points we need to take into consideration that include: 1) stage of growth, 2) general crop vigor and yield potential, and 3) anticipate the next stage of development and what we need to do in terms of field crop management. These considerations are commonly focused on aboveground crop evaluations. The root system is also an important part of the crop condition to evaluate but we commonly do not evaluate roots because of the difficulty in doing so.
Root systems and early development were described in a basic manner in a recent article on 4 September (UA Vegetable IPM Newsletter Volume 15, No. 18).
The effective root zone depth is the depth of soil used by the bulk of the plant root system to explore a soil volume and obtain plant-available moisture and plant nutrients. Effective root depth is not the same as the maximum root zone depth. As a rule of thumb, we commonly consider that about 70% of the moisture and nutrient uptake by plant roots takes place in the top 24 inches of the root zone; about 20% from the third quarter; and about 10% from the soil in the deepest quarter of the root zone (Figure 1).
The small and very fine root hairs are the most physiologically active portion of a developing root system. It is important that plants continue to develop and generate fresh young roots and an abundance of fine root hairs to maintain water and nutrient uptake.
Figure 1. General pattern for plant-water and nutrient uptake from the soil profile.
Root development patterns are dependent on the nature of the soil profile in the field. Soil profiles with compaction layers, as well as rock, clay, or caliche layers can limit and alter root development and the full exploration of the soil volume that the plants are capable of (Figure 2). So, it is good to know what the soil profile looks like in the field and understand how that will impact plant root development.
Figure 2. Generalized soil profile with major horizons.
Leafy green vegetable crops need to develop a marketable plant in a relatively short amount of time and a strong root system is essential. Transplants are commonly being used in vegetable crop production systems and the transition of transplants to field conditions is a major step in the production process. The transition is primarily experienced by the plant below ground.
Transplanted crops will have altered root systems due to the constraints within the rooting cone. Further root development beyond the original cone rooting mass is important for crop success. Thus, it is important to monitor the root system transition and the relationship to overall plant development.
Checking root systems is a plant destructive process since we need to literally excavate the roots from the soil and it does take time and effort. Accordingly, it is also important to be careful of where and how we sample plants and evaluate the root systems in a field.
Crop species can vary significantly in their patterns of root development, and it is important to know what is “normal” when evaluating crops in the field. An excellent reference for vegetable crop root system development is a 1927 publication by Dr. John E. Weaver and William E. Bruner from the University of Nebraska (Root Development of Vegetable Crops). This publication can be found at the following link:
https://soilandhealth.org/wp-content/uploads/01aglibrary/010137veg.roots/010137toc.html
A few basic examples from the Weaver and Bruner publication are provided in the following figures (Figures 3-10).
Figure 3. Cauliflower, 3 weeks after transplanting
Figure 4. Cabbage roots, 55 days after transplanting.
Figure 5. Cabbage roots, 75 days after transplanting.
Figure 6. Pepper roots, 24 days.
Figure 7. Pepper roots, 45 days (6 weeks).
Figure 8. Pepper roots, mature.
Figure 9. Lettuce roots, 3 weeks. The roots on the right were grown in compact
soil, the roots on the left were grown in loose/open soil.
Figure 10. Lettuce roots, 60 days.
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 ‘Meerkat’ was seeded, then sprinkler-irrigated to germinate seed Jan 13, 2025 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 CO2 backpack 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 Mar 5 and final reading was taken on March 6 and March 7, 2025. 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-ft2areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2area of bed was approximately 144. The percentage were then changed to 1-10scale, with 1 being 10% infection and 10 being 100% infection.
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 most effective control against the disease include Orondis ultra, Zampro, Stargus, Cevya, Eject .Please see table for other treatments with significant disease suppression/control. No phytotoxicity was observed in any of the treatments in this trial.
I thought I’d change pace this week and take the opportunity to ask you, the readers of this newsletter, if there are any ag automation/mechanization topics you would be interested in hearing more about. I am happy to do some research and share the findings in future articles. Drop me a line at siemens@cals.arizona.edu or feel free to call me at 928.782.5869. I’d love to know your interests.
Fig. 1. Futuristic farming.
(Image credits: AgTech Media Group, Dover, DE)
We are currently doing a trial for Hairy Feeabane control (Conyza bonariensis) with several combinations and wanted to share some preliminary results. Application was done last March 22 when the weeds were approximately 0.5-3” diameter and burn down activity was evaluated 5 days after treated (5DAT). We are sharing the first evaluation with you since the weed is abundant at this time in the Yuma Mesa. This is the initial evaluation, so mortality and final control will be rated later.
In recent conversations with PCAs we talked about Rely (glufosinate) activity and they have seen good performance of the product especially when weeds are small and according to some researchers this product’s works better with high relative humidity1 (Tickes 2010).
This preliminary data shows that Rely and Sharpen both wit AMS (Ammonium Sulfate) and MSO (Methilated Seed Oil) appeared effective at the 5DAT evaluation. There are other PPO herbicides that we are testing like UA850 that looks promising in some combinations such as the combination with Roundup+AMS+MSO. More details will be shared at a later date when additional data is collected.
References:
Biological control is one of the key tools for pest management in organic crop production. By maintaining permanent habitats and food sources for the pests’ natural enemies (good bugs) in the vicinity of your farms, you can ensure the continuous availability of the natural enemies. When the growing season starts, the good bugs will be readily available to attack the pests before they become established in the crops.
Researchers have found that planting a diversity of flowering plants (e.g., sweet alyssum, nasturtium, milkweeds, common cryptantha, hillside vervain, wild petunia, etc.) on a small portion of your farms or the farms’ border can provide adequate food and shelter allowing to maintain abundant and diverse natural enemy species, including syrphid flies, tachinid flies, lacewings, parasitic wasp, etc. that will attack aphids, thrips, lepidopterans, and more.
As you plan for the next season, please consider planting flowering plants on your farms’ borders or on dedicated patches to conserve natural enemies and enhance your biological control.
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: CEW moth counts down in all traps over the last month; about average for December.
Beet armyworm: Moth trap counts decreased in all areas in the last 2 weeks but appear to remain active in some areas, and average for this time of the year.
Cabbage looper: Moths increased in the past 2 weeks, and average for this time of the season.
Diamondback moth: Adults increased in several locations last, particularly in the Yuma Valley most traps. Below average for December.
Whitefly: Adult movement remains low in all areas, consistent with previous years
Thrips: Thrips adult movement continues to decline, overall activity below average for December.
Aphids: Winged aphids still actively moving but declined movement in the last 2 weeks. About average for December.
Leafminers: Adult activity down in most locations, below average for this time of season.
