Aphids continue to be abundant in area lettuce and it is turning out to be the heaviest green peach aphid (GPA) pressure I’ve seen in several years. In untreated lettuce plots at YAC, GPA populations have steadily been increasing since early February. For example, aphid numbers increased from an average of 8 GPA/plant to greater than 48 GPA /plant in untreated lettuce over the past 2 weeks.  In my experience, this is largely due to weather conditions. Temperatures summarized from the UA AZMET station at YAC shows that average temperatures from Jan 1 to Feb 20 have been about 55 °F (4 degrees cooler than last winter). This winter relative humidity has been almost 10% higher and we’ve had 3X more rainfall than last year. These are ideal conditions for GPA population growth in the desert – cold and wet. These conditions can also make control more difficult. I’ve had numerous discussions with PCAs concerning the slow activity of the insecticides used for desert aphid control.   I’ve observed for years that translaminar and systemic insecticides work slower under cold desert growing conditions.  Cold weather will limit movement in the plant, particularly xylem/phloem mobile products like Movento, because plant growth and transpiration are limited under cold, cloudy weather.  But as weather gets warmer, the activity of systemic insecticides improves dramatically.  With translaminar insecticides (aphids have to ingest the toxin)  the challenge is getting spray coverage on the older frame leaves where GPA feed and colonize. This can be a real challenge on larger plants. 
The good news is that most products I’ve evaluated so far this season are performing as expected, but may be taking longer to achieve the level of control that you would like to see. Below are the results of an on-going aphid efficacy trial I’m conducting at YAC on iceberg lettuce planted 9 Dec. The first spray was applied on 3 Feb by ground at 23.6 gpa @ 50psi. An adjuvant, Dyne-Amic was applied with each spray treatment. Lettuce plants were at the 7-8 leaf stage at the time of application. To evaluate efficacy, all live aphids were counted on 5 whole plants  per replicate at 7 and 14 days after application (DAA).  At 7 DAA (Feb 10), results were inconsistent, but most treatments provided significant reductions in GPA compared to the untreated control (65-85% control). However, at 14 DAA (Feb 17), Beleaf and PQZ provided the most consistent reductions of GPA (95% control), whereas Versys, Sequoia and Sivanto provided similar reductions in GPA abundance at ~90% control.   Not surprisingly, Movento and Senstar were less consistent under the colder weather.  So be patient with aphid control under cold weather conditions. Remember the key with the translaminar products for GPA control is getting the material to the older leaves where they are colonizing. Once the weather warms up a bit, the systemic products will be much more effective.  For more information on insecticides alternatives see Aphid Management in Desert Produce Crops - 2023

Arizona consistently produces the highest yields and quality of crops found anywhere.  This is due to the skill and expertise of Arizona farmers and the management of the valuable natural resources that we depend on, which includes the soil, water, and climate we have in this region.  Soil serves as the foundation of the agricultural systems that we all depend on.  In agriculture, we recognize that healthy soil translates to healthy crops and farms (Brady and Weil, 2008 and Parikh and James, 2012).

There are three primary aspects of soil systems that are important in healthy soil function that include physical, chemical, and biological factors (Figure 1).  These three aspects are of soil systems operate in an integrated manner, but we can consider them individually, beginning with the soil physical properties.

Figure 1.  Soil health factors and physical properties.

Soil Texture 
Soil texture determines the coarseness or fineness of a soil (Figure 2).  Soil texture is defined by the relative proportions of sand, silt, and clay particles (Figures 3 and 4).  The soil particles are defined by diameter size with sand (0.05–2.0 millimeters (mm)), silt (0.002–0.05 mm), and clay (less than 0.002 millimeters or the 2-micron (µ) fraction (10^-6 m)).  

Soil texture is a product of the geologic process of basic parent materials weathering, both physically and chemically, over long periods of time in each location making soil texture a prominent characteristic of any field or location.  Soil texture cannot be changed in a practical manner, but we can utilize appropriate management practices suited for soils of varying textures. 

Particles that are larger than 2 mm, such as rock fragments (pebbles, cobbles, stones, and boulders), are not considered in defining the soil textural class because they are relatively inert or non-reactive. 

Soil particles provide the basic building blocks of the soil system and structure.  The pore spaces between the particles and soil aggregates are extremely important since that is where most physical, chemical, and biological processes take place.

Figure 2.  Soil textural triangle.  


Figure 3.  Relative size of soil particles.


Figure 4.  Proportional relationship of soil particles.

Aggregation
Soil particles provide the basic building blocks of the soil physical structure, but the way soil particles are assembled in clumps or aggregates.  Aggregation is basically the arrangement of primary soil particles (sand, silt, clay) which are bound by soil organic matter and through other forms of particle interactions and associations.  Aggregate stability is a good indicator of soil health. 
As a result of the aggregation of soil particles, the sizes of soil pores can vary tremendously.  The proportion of large, medium, small, and very small pore spaces in soils govern the important processes of water and air movement.  In addition, soil pores provide the spaces where soil organisms and plant roots live, grow, and function.   
Clay and finer textured soils (generally, soil textures in the upper ½ of the textural triangle) have smaller soil particles and aggregate structure that contribute to small pore spaces (often less than 0.002 mm or 2 µ).  In contrast, sandy soils are dominated by pores that are larger (macropores).  As a result, finer textured soils with high silt and clay content will have much higher surface areas within in given soil volume (Figure 5) and are more reactive physically and chemically.

Figure 5.  Soil particle size and surface area relationships.

We can see and feel soil aggregates when we pick up a handful of soil and see the clumps or pieces of soil, which are the soil aggregates.  Soil aggregates consist of soil particles of varying sizes that are held together by both the attraction of soil particles and the binding capacity of organic matter between soil particles.  There are several general types of common soil aggregates (Figure 6).

Figure 6.  Examples of soil aggregates.

Soil Structure 
Aggregates provide a very important function of soil structure.  Aggregates also serve to hold and supply organic matter in soil; however, they also have structural functions.  Soil aggregate structures provide large and small pores with large soil pores allowing faster water infiltration into the soil.   Smaller soil pores provide the capacity of soil to hold more plant-available water.  A healthy soil will have a good soil structure, often recognized in the field as good soil “tilth”.
Poor soil structure, due to a breakdown of soil aggregation and the dispersion of individual soil particles can be a problem for water infiltration into a soil.  We can often see this in the field with soil crusting surface compaction (Figure 7a and 7b), which can also be symptom of high sodium (Na) concentrations in the soil. 
Consequently, soil structure is critical to our efforts to manage soil salinity since we need good water infiltration and percolation to accomplish adequate soil leaching to remove soluble salts from the crop root zone (Figure 8).

Figure 7a.  Importance of good soil structure.


Figure 7b.  Example of unfavorable soil structure, such as a dispersed or
compacted soil structure.


Figure 8.  Good soil structure and the relationship to leaching
capacity in a soil.

Soil health is affected by several factors including the physical, chemical, and biological properties of the soil system (Figure 1).  Of the physical soil properties, aggregation and structure are two of the most important factors affecting soil health.   Soil texture, aggregation, and structure are all inter-related and provide a strong influence on the environment that plants deal with in the field.  These soil characteristics impact root development as well as water and air movement in soil.  Managing soils to enhance these physical properties of aggregation and structure can be a real benefit for soil health and crop production systems.  
 
References:
Brady, N.C. and R.R. Weil. 2008. The Nature and Properties of Soils, 14th ed. Prentice Hall: Upper Saddle River, NJ.  Parikh, S. J. and B.R. James. 2012. Soil: The Foundation of Agriculture.  Nature Education Knowledge 3(10):2
https://www.nature.com/scitable/knowledge/library/soil-the-foundation-of-agriculture-84224268/#

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%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches between bed centers. All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

Interested in staying up to date on the latest robotic ag technologies? FIRA USA and a number of other entities are organizing a 3-day forum focused on autonomous farming and agricultural robotics solutions. The event will be held September 18-21 in Salinas, CA. The program includes top-level keynote speakers, breakout sessions, a trade show and field demos. Over 35 robots will be demoed and/or on display including 12 machines designed for weeding vegetable crops. Some of the latest technologies for in-row weeding will be featured including lasers (3 companies), high voltage electricity and high precision spot spraying (3 companies). If you are interested in ag tech, FIRA 2023 promises to be a quality event and one well worth attending. For more information, visit https://fira-usa.com/.

Fig. 1. Robotic technologies on display and being demoed in
the field at FIRA USA 2023. Event will be held September 19-21^st in
Salinas, CA. (Photo credits: FIRA USA).

Postemergence herbicides used for grass control in vegetables include Poast (sethoxydim), Select (clethodim) and Fusilade (fluazifop) and the generics of these active ingredients. When some grasses have escape or have survived the application of Pefar, Kerb and Balan these selective grass herbicides can come to the rescue and have shown to be a great tool for weed management. 

The above-mentioned herbicides are all Acetyl CoA carboxylase or ACCase inhibitors. These products work slowly and even slower at lower temperatures and shorter days. Treated grasses should stop growing immediately and will slowly turn yellow, red and gradually die as the crop grows. The process takes about 15-21days. Select (clethodim) works the faster than Poast (sethoxydim), and it  isrecommended to add a crop oil concentrate for better activity with the exception of Select Max which can be used either with crop oil concentrate or non-ionic surfactant.
  
References:

1. Retrieved from www on 23.09.06:  https://content.ces.ncsu.edu/herbicide-injury-accase-inhibitors#:~:text=Herbicide%20injury%20from%20lipid%20biosynthesis,as%20clethodim%2C%20sethoxydim%20and%20others.
2. https://live-azs-vegetableipmupdates.pantheonsite.io/sites/default/files/2023-09/230712%20MOA-Lipid_B_I.pdf

Area wide Insect Trapping Network  VegIPM Update, Vol. 14, No.5, Mar 8, 2023
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts remain low at all trap locations and average for this time of year. 
 
Beet armyworm:         
Trap counts increased over the past 2 weeks; average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts decreased slightly in most traps and below average for this time of season.
 
Diamondback moth:   
DBM moths remained low in most areas. Well below average for this time of the year.
 
Whitefly:                      
Adult movement was negligible and typical for this time of year. 
 
Thrips:                           
Thrips adult counts increased slightly in some areas the past 2 weeks. Currently, well below average compared with previous years.
 
Aphids:                      
Aphid movement decreased in most locations, and average activity for late-February.
 
Leafminers:                  
Adult activity down in most locations, and below average for late-February.