Justus von Liebig was a 19th century German scientist (1803-1873) who is regarded as one of founders of organic chemistry.  He is also commonly considered as the “father of agricultural chemistry and the fertilizer industry.”

Liebig developed several important analytical methods used in a broad range of applications as well as many other important contributions and developments.  Liebig was one of the great chemistry teachers of the 19th century that served as a foundation for the robust German chemical industry of the 20thand 21st centuries.

In 1840 Justus von Liebig presented a concept that is known as the “Law of the Minimum”, which was built upon a theory that had first been developed by Carl Sprengel, a German botanist (1787-1859).  The Law of the Minimum basically states that a plant’s rate and extent of growth and overall health is dependent on the amount of the scarcest of the essential nutrients that are available to the plant (Figure 1; Liebig, 1840 and van der Ploeg et al., 1999).

The Law of the Minimum has been further applied into a general model of all organisms and biological functions, including the limiting effects of other environmental factors i.e., sunlight and water in terrestrial ecosystems, as well as excesses of nutrients and other environmental factors (Bruuselma and Nigon, 2023; Davidson, 2016; and Mosaic, 2023).

An important way to consider the Law of the Minimum is that the growth of plants, or crops, is not dependent on the total amount of nutrients available, but rather by the scarcest nutrient or resource (i.e., water).  This is particularly important in relation to nutrients such as nitrogen, which is the nutrient required in largest amounts by plants, and it is the most common limiting plant nutrient.  In desert agriculture, water is commonly the first most common limiting factor in plant growth and development, closely followed by bio-available nitrogen.

The Law of the Minimum is important to understand in managing fertilizer and other agronomic inputs to a crop.  This has been demonstrated when fertilizer prices are high, particularly for nitrogen and phosphate fertilizers, and growers may be inclined to reduce or eliminate fertilizer applications.

Liebig’s Law of the Minimum is most applicable for nutrients and plant growth factors that are mobile in the soil.  This is particularly relevant for nitrogen, which is available to plants in the nitrate form (NO3--N), which is mobile in the soil.  Thus, (NO3--N) moves with soil-water. 

Accordingly, the Liebig Law of the Minimum also pertains to water in a soil-plant system.  Other growth factors or nutrients will not compensate for a deficiency in a given nutrient or plant growth factor.  Plant-available nitrate-nitrogen (NO3--N) or water are good examples, there are no substitutes.

The Liebig Law of the Minimum is an important concept in soil fertility and plant nutrition and overall agronomic crop management in an irrigated production system.

Figure 1.  Graphic illustration of the Law of the Minimum with shortest stave in
the barrel representing the most limiting nutrient in the soil-plant system.

References:
Bruulsema, T, and Nigon, L.L. Crops & Soils Magazine, November–December 2023 American Society of Agronomy.  pp.  54-59.

Davidson, D. 2016.  Nutrient Management Magazine.https://www.no-tillfarmer.com/articles/5648-no-till-notes-how-to-plan-your-summer-fertility-program?v=preview

Liebig, J. 1840.  Die organische Chemie in ihrer Anwendung auf Agri- Sprengel, C. 1831. Chemie fu¨ r Landwirthe, Forstma¨nner und Cameralisten (Chemistry for agronomists, foresters, and agricultural econo-cultur und Physiologie (Organic chemistry in its applications to agri-culture and physiology). Friedrich Vieweg und Sohn Publ. Co., mists). Volume 1. Vandenhoeck und Ruprecht Publ. Co., Go¨ ttingen, Germany. Braunschweig, Germany.

Mosaic.  2023.  How Law of the Minimum Impacts Crops' Nutrient Use. In: No-Till Farmer. https://www.notillfarmer.com/articles/12637-how-law-of-the-minimum-impacts-crops-nutrient-use

Vander Ploeg, A.R;   Böhm, W.; and M. B. Kirkham.  1999.  On the Origin of the Theory of Mineral Nutrition of Plants and the Law of the Minimum. Soil Sci. Soc. Am. J. 63:1055–1062.

At events and in the halls of the Yuma Agricultural Center, I’ve been hearing murmurings predicting a wet winter this year…

As the Yuma Sun reported last week, “The storms of Monday, Aug. 25 [2025], were the severest conditions of monsoon season so far this year in Yuma County, bringing record-rainfall, widespread power outages and--in the fields--disruptions in planting schedules.”

While the Climate Prediction Center of the National Weather Service maintains its prediction of below average rainfall this fall and winter as a whole, the NWS is saying this week will bring several chances of scattered storms.

These unusually wet conditions at germination can favor seedling disease development. Please be on the lookout for seedling disease in all crops as we begin the fall planting season. Most often the many fungal and oomycete pathogens that cause seedling disease strike before or soon after seedlings emerge, causing what we call damping-off. These common soilborne diseases can quickly kill germinating seeds and young plants and leave stands looking patchy or empty. Early symptoms include poor germination, water-soaked or severely discolored lesions near the soil line, and sudden seedling collapse followed by desiccation.

It is important to note that oomycete and fungal pathogens typically cannot be controlled by the same fungicidal mode of action. That is why an accurate diagnosis is critical before considering treatments with fungicides. If you suspect you have seedling diseases in your field, please submit samples to the Yuma Plant Health Clinic or schedule a field visit with me.

National Weather Service Climate Prediction Center: https://www.cpc.ncep.noaa.gov/

AI is in the news all the time being touted as the most influential human innovation in history. Why? I’m not sure exactly as generally few specifics are given, but recently came across an article that gave me some insight as to what the experts are talking about. The piece focuses on a project by Google DeepMind¹: two AI robots playing soccer (Paul, A., 2024). There’s a couple of things that struck me most about the robots. The first was how human-like their behavior and actions were. They reminded me of a couple of 5-year-olds playing soccer. The second is the manner in which they learned. Unlike traditional programming methods where every action is meticulously coded, these robots were given the objective of scoring a goal and only provided instructions on how to stand up and kick a ball. The rest they taught themselves using deep reinforced learning (AI) methods. The news program 60 Minutes also reported on the AI soccer playing robots (Fig. 1). Check out the article here and the 60 Minutes segment in the video below. I think you’ll be impressed.

Fig. 1. 60 Minutes Segment: Google DeepMind demos AI training robots to play soccer / football. (Credit: 60 Minutes). References

References
Paul, A. (2024). Watch two tiny, AI-powered robots play soccer. Miami, Fla.: Popular Science. Available athttps://www.popsci.com/technology/deepmind-robot-soccer/.
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[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.

The Southwest Agricultural Summit that recently took place in Yuma included a breakout session on Thursday, 21 February 2024 titled “New Developments in Weed Control”.
In this session Jose Antonio Cabrera representing BASF technical services for Coastal CA and Arizona provided a review of the new technologies being developed by his company in the Weed Control area. This includes new active ingredients as well as novel encapsulation technologies. The breakout session also included the lecture “Registration Support for Pest Management Tools in Specialty Crops, The IR-4 Project: Purpose and Process” by Roger B. Batts. “The IR-4 Project was established in 1963 by the U.S. Department of Agriculture to ensure that specialty crop farmers have legal access to safe and effective crop protection products. Helps growers address pest management concerns, develops data necessary for the registration of safe and effective pest management solutions with the U.S. Environmental Protection Agency¹.
Roger is the Weed Science biologist from the NC State University IR-4 headquarters. If you have questions such as: What is the IR-4 Mission? Why is IR-4 Needed? What are the programs within the IR-4 project? you will find some answers in the IR-4 Presentation Slides here.
We are currently conducting trials in Yuma in coordination with this project that could result in the addition of new labels and weed control tools for our Arizona vegetable growers.
Thank you for attending the SW Ag Summit Weed Science breakout session.
 
 
Reference:

1. https://www.ir4project.org/

Get your free copy of the Weed Seedling Identification Pocket Guide at the Yuma
Agricultural Center.

Integrated pest management (IPM) involves the utilization of a combination of several tactics for the effective management of pests. This concept was developed by entomologists and is currently adopted by pest managers to target many kinds of pests, including insects, weeds, and pathogens. Most IMP tactics fit well in both conventional and organic crop production. It is not uncommon that most pest management techniques that are approved for organic crop production are not very effective as a stand-alone tactic. Therefore, it is essential to use a combination of pest management techniques that will complement each other to control the pests adequately. This is like a many little hammers approach, where each of the management tactics is a little hammer hammering on the pests. When planning your IPM programs targeting pests in organic crop production, it is important to consider planting resistant/tolerant varieties, scouting regularly, implementing economic thresholds (when possible), practicing cultural control, physical/mechanical control, and biological control, and applying biopesticides when necessary. 

• Resistant varieties: Resistant varieties are crucial for effective IPM in organic crop production. When available, the use of resistant varieties should be the first line of defense against pests. Resistant varieties help save on production costs and mitigate environmental impacts associated with insecticides and their applications. 

• Cultural control: Cultural control includes cropping systems (trap cropping and push-pull), planting date (early planting or late planting), crop rotation, and growing of crop varieties with early maturity traits. Implementing trap cropping and/or push-pull systems can cause the diversion of insect pests. Early or late planting, crop rotation, and variety with early maturity traits can favor the avoidance of damaging insect pest pressures. 

• Scouting: Proper and timely scouting helps determine the levels of pest infestations, allowing the pest manager to trigger control action in a timely fashion. Scouting also helps to prevent unnecessary insecticide applications. 

• Economic thresholds: The economic threshold determines the pest or injury level at which control action should be taken. The economic threshold works side by side with scouting. This helps to determine when a management action should be triggered, allowing a reduction of unnecessary insecticide utilization, which will consequently help in delaying or mitigating resistance. 

• Physical/mechanical control: This method includes establishing physical barriers, plowing, and sanitation (elimination of volunteer crops and other potential hosts). Plowing can help to bury soil insect pests deep into the ground, directly kill them, and expose soil insects to adverse weather conditions, birds, and other predators, which will adversely impact these pest populations. 

• Biological control: This method involves using insect pests’ natural enemies, including predators such as spiders, lady beetles, syrphid fly larvae, big-eyed bugs, pirate bugs, lacewing larvae, and parasitoids such as parasitic wasps and flies. 

• Biopesticides: Biopesticides are based on botanical extracts, entomopathogenic fungi, entomopathogenic bacteria, or entomopathogenic viruses that have adverse effects on insect pests. Entrust, Bt, Pyganic, AZA-Neem, M-Pede, Celite, and Venerate are commonly used insecticides for insect pest control in organic crops grown in Arizona. 

The implementation of IPM permits to manage pests economically while preserving the environment and reducing negative impacts on human health. In other words, IPM aims at managing pests in an economically viable, socially acceptable, and environmentally safe manner. It is important to note that all the IPM tactics are not always viable in all situations (IPM is not a one-size-fits-all). Therefore, the management techniques choice for an IPM program should be done on a case-by-case basis. 

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

Corn earworm: CEW moth counts down in most over the last month, but increased activity in Wellton and Tacna in the past week; above average for this time of season.

Beet armyworm: Moth trap counts increased in most areas, above average for this time of the year.

Cabbage looper: Moths remain in all traps in the past 2 weeks, and average for this time of the season.

Diamondback moth: Adults decreased to all locations but still remain active in Wellton and the N. Yuma Valley. Overall, below average for January.

Whitefly: Adult movement remains low in all areas, consistent with previous years.

Thrips: Thrips adults movement decreased in past 2 weeks, overall activity below average for January.

Aphids: Winged aphids are still actively moving, but lower in most areas. About average for January.  

Leafminers: Adult activity down in most locations, below average for this time of season.