There are more than 100 chemical elements known to man today.  However, only 16 have been proven to be essential for plant growth.  The essential elements for plant growth are in the upper portions of the periodic table with lower atomic numbers, indicating the lighter and more volatile elements that are in higher concentrations closer to the earth’s surface and part of the rocks that commonly serve as the parent materials for soils.
 
For a nutrient to be classified as essential, certain rigid criteria must be met.  These criteria are as follows (Havlin, et al., 2014; Troeh and Thompson, 2005; Weil and Brady, 2017; Warren et al., 2017):
 

1. The element is essential if a deficiency prevents the plant from completing its vegetative or reproductive cycle.
2. The element is essential if the deficiency in question can be prevented or corrected only by supplying the element.
3. The element is essential if it is directly involved in the nutrition of the plant and is not a result of correcting some microbiological or chemical condition in the soil or culture media.

 
The essential elements and their chemical symbols are listed in Table 1.  Three of the 16 essential elements – carbon, hydrogen and oxygen – are supplied mostly by air and water.  These elements are used in relatively large amounts by plants and are non-mineral, often referred to as organic nutrients and they are supplied to plants by carbon dioxide and water. 
 
The other 13 essential elements are mineral elements and must be supplied by the soil and/or fertilizers.  Not all are required for all plants, but all have been found to be essential to some (Tisdale & Nelson).
 
 
 
Table 1.  Essential plant nutrients, chemical symbols, and sources.

Mostly from air and water (non-mineral)	Mostly from air and water (non-mineral)	From soil and/or fertilizers (mineral)	From soil and/or fertilizers (mineral)	From soil and/or fertilizers (mineral)	From soil and/or fertilizers (mineral)
Element	Symbol	Element	Symbol	Element	Symbol
Carbon	C	Nitrogen	N	Iron	Fe
Hydrogen	H	Phosphorus	P	Manganese	Mn
Oxygen	O	Potassuim	K	Zinc	Zn
		Calcium	Ca	Copper	Cu
		Magnesium Mg	Mg	Boron	B
		Sulfur	S	Molybdenum	Mo
				Cholorine	Cl

 
 
The essential plant nutrients may be grouped into three categories.  They are as follows:
 

1. Primary nutrients - nitrogen, phosphorus and potassium
2. Secondary nutrients - calcium, magnesium and sulfur
3. Micronutrients - iron, manganese, zinc, copper, boron, molybdenum, and chlorine

 
This grouping separates the elements based on relative amounts required for plant growth and is not meant to imply any element is more essential or important than another (Troeh and Thompson, 2005; Weil and Brady, 2017; Warren et al., 2017).
 
Primary Non-Mineral Nutrients: Carbon, Hydrogen and Oxygen
Carbon is the backbone of all organic molecules in the plant and is the basic building block for growth.  After absorption of carbon dioxide (CO₂) by the leaves of the plant, carbon is transformed into carbohydrates by combining with hydrogen and oxygen through the process of photosynthesis.
 
Metabolic processes within the plant transform carbohydrates into amino acids and proteins and other essential components.
 
The essentiality of all mineral nutrients is associated with their use in structural plant components and/or physiological and biochemical reactions associated with essential processes in plant growth and development.  Plants cannot complete the life cycle if they are deficient in an essential nutrient.
 
References
Havlin, J.L., Beaton, J.D., Tisdale, S.L. and Nelson, W.L. 2014. Soil Fertility and Fertilizers; An Introduction to Nutrient Management. 6th Edition, Prentice Hall, Upper Saddle River, NJ.
Troeh, F.R. and Thompson, L.M. (2005) Soils and Soil Fertility. Sixth Edition, Blackwell, Ames, Iowa, 489.
Warren, J., H. Zhang, B. Arnall, J. Bushong, B. Raun, C. Penn, and J. Abit. Oklahoma Soil Fertility Handbook. Published Apr. 2017; Id: E-1039
Weil, R.R. and Brady, N.C. (2017) The Nature and Properties of Soils. 15th Edition, Pearson, New York.

I am seeking samples of downy mildew on lettuce from around Yuma County to support the Michelmore Lab and their ongoing efforts to help characterize the downy mildew populations of the United States. The Michelmore Lab has led the charge on a survey of Bremia variants since 1980 and has been instrumental in demystifying the gene-for-gene nature of lettuce resistance to downy mildew.

Their group invites growers across the United States to submit downy mildew infected plant samples, which are then used to culture the Bremia on live host plants. The team then inoculates a panel of lettuce varieties carrying known resistance genes to determine the race of each isolate they receive. Identifying which races occur in which specific fields is essential to guiding the breeding of new resistant cultivars and maximizing the effectiveness of host-based genetic disease management. The data obtained from these tests are also used to designate new Bremia races through the International Bremia Evaluation Board.

Your contribution will help breed better lettuce for Yuma. This means less breakdown of resistance in the field, and better yields for Yuma growers. To facilitate these submissions the Yuma Plant Health Clinic will be setting up a separate drop-off point and submission sheet for downy mildew sample submissions in the same hallway we use for standard plant diagnostic submissions. The drop-off point will be clearly labelled and consist of a chest-style refrigerator and printed copies of the submission form. It is vital to keep these samples cool so they remain viable for future inoculations, so please place your samples inside of the refrigerator before you leave.

Shipping will be handled by the clinic. All we ask is that you fill out the submission form as completely as you can. An example of the questions that are asked in that form so you can prepare ahead of time can be found HERE . 

As part of their efforts to promote agtech, Western Growers is developing a freely available image library of key specialty crops. The idea is to create a database of labeled/annotated images that startups and researchers can use as training sets to develop AI software for automated/robotic machines. Sets of images of mature iceberg, romaine, broccoli, cauliflower and strawberry crops have been completed and are available at https://github.com/AxisAg/GHAIDatasets/tree/main/datasets. These images are useful for creating AI models for automated harvesting machines.

Last season, in collaboration with Axis Ag, Inc., we worked to expand the database to include images of crops at all growth stages. This will allow users to develop AI tools for crop thinning, weeding and crop health monitoring. Francisco Calixtro, a UofA Yuma student majoring in Ag Systems Management, spent the winter collecting images of various vegetable crops throughout their growth cycle using an Amiga¹ (farm-ng, Watsonville, CA) robot equipped with a camera. These images will be sorted, labeled and uploaded to the image library. We’ll announce when these data sets become available. 

Special thank you to Jason Mellow, Axis Ag, Inc. and to the many growers who allowed us to capture images of their fields.

Fig. 1. Francisco Calixtro, UofA Yuma student, operates an Amiga¹ (farm-ng,
Watsonville, CA) robot equipped with a camera to capture images of various
vegetable crops at different growth stages. Images will be labeled and
uploaded to a freely available image library to facilitate development of AI
software for automated/robotic machines. (Photo credits: Jason Mellow and
Francisco Calixtro)

[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.

In our last newsletter we talked about the importance of proper weed identification before making decisions on control measures. We mentioned some of the literature that the Vegetable IPM Team uses at the Yuma Agricultural Center.
An increasing number of PCAs and growers are using several phone applications for weed ID.
In this update I would like to share some data that was collected from a group of students of the 2024 PLS 300 Applied Weed Science class.
Professor Barry Tickes asked his students to download two phone applications and test the accuracy of the weed species ID. The recommended applications used were PlantNet and PictureThis Plant Identifier, which according to some  Pest Control Advisors are reasonably accurate.
We provided a display of 9 weeds to the students to take images and upload to the phone apps for ID and here are the results obtained:
 
Weed                                         PictureThis                  PlantNet
 
Annual bluegrass                            6                                        0
 
Creeping woodsorrel                      8                                        6
 
Nettleleaf goosefoot                       4                                        3
 
Prickly lettuce                                 8                                        0
 
Spiny sowthistle                              6                                        1
 
Spinach                                            8                                        6
 
Malva                                              6                                         1 
 
Silversheath knotweed                    5                                         0  
 
Littleseed canarygrass                     0                                         0        
 
       PictureThis Plant Identifier performed better than PlantNet in this evaluation. Interestingly in 2022 the weed science class evaluated PlantNet with results showing that 84.6 % of the time the application was correct. If you have another application that you recommend, please send it in your comments and we will share it with others in this newsletter.   

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

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 3, Feb 7, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts increased in the Rol and Dome Vallley areas, above average for this time of year. 
 
Beet armyworm:         
Trap counts low; lower than average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts increased in most traps and about average for this time of season.
 
Diamondback moth:       
DBM moths counts increased in most areas. About average for this time of the year.
 
Whitefly:                       
Adult movement negligible, typical for mid-winter. 
 
Thrips:                          
Thrips adult counts remain low, likely in response to rainfall in late December. Currently, numbers are below average compared with previous years.
 
Aphids:                        
Aphid movement increased significantly in the past two weeks, particularly in North Yuma and Gila Valleys. Highest numbers we’ve seen in 11 years.
 
Leafminers:                   
Adults remain low in most locations, average for January.