Hope you are all enjoying the summer so far and keeping busy. Although, we’re about 2 months away from the Fall produce season, it’s never too early to begin thinking of IPM strategies you will be using to battle key insects next season. This includes keeping track of their typical activity during June, July, and August. Below is a short discussion detailing individual pests. 
 
Aphids:    The major aphid species that are important in produce crops each spring include green peach aphid, foxglove aphid and lettuce aphid.  These species are considered cool season pests and are biologically most active during the winter and spring when temperature average around (55-65 F). We do not find them on summer crops as the high temperatures prohibit their activity. They essentially become extinct each summer only to reappear in the fall to infest crops in Oct-Dec migrating into the desert via N-NW winds that occur after the monsoons.
 
Diamondback Moth (DBM):  Another key pest that disappears each summer but for a different reason than for aphids. The host range of DBM is limited to only brassica crop and plants. Although brassica weeds are common during the winter, they occur during the summer due to high temperatures and dry conditions. Thus, like aphids, DBM populations from the previous spring season become “extinct” during the summer when brassica crops and weeds are absent. They reappear each fall migrating in on high winds associated with tropical storms from Mexico, or arrive into the region on infested brassica transplants from California.
 
Whiteflies:       A resident pest that occurs year-round in the desert. As a warm season pest, whiteflies are most abundant on fall produce crops, and seldom a problem during the winter and spring. Peak abundance occurs during the summer months on cotton, and again in September and October on fall brassica, leafy vegetables and fall melons.  Thus, it is important to control whiteflies in cotton prior to defoliation to prevent large migrations onto fall produce crops. In addition, whiteflies can be found on several weeds such as purslane, goosefoot, ground cherry, and sunflowers. Sanitation in and around fields being prepped for fall plantings is important. Preventatively, growers should consider applying soil, system insecticides such as imidacloprid or Verimark to Fall produce crops.

Beet Armyworm (BAW):  A warm-season pest that occurs year-round in the desert. They tend to reach peak abundance twice a year. Generally, the most important peak is in September and October when weather is ideal for their development, flight activity and oviposition. A second peak occurs in late spring. Activity is generally light during the summer, occurring primarily in alfalfa crops. Although BAW is known to migrate in from the south via monsoon and tropical storms, resident populations annually occur in alfalfa during the summer. Thus, to minimize BAW in fall produce crops, thorough management of BAW can potentially minimize their movement onto Fall produce crops.  Weeds are also a source of BAW (purslane, goosefoot, sunflower and Russian thistle) so sanitation in and around fields is important.
 
Western Flower Thrips (WFT):  Also a resident pest that can be found in the desert year round. WFT is most abundant on lettuce in the late spring, but peaks in abundance on alfalfa, melons and cotton is May and June. During the late summer numbers drop dramatically where thrips can be found on melons and alfalfa and weeds like goosefoot and purslane. WFT slowly move into lettuce again in early fall and are least abundant during the winter.  Sanitation of weeds during the summer can help reduce thrips abundance moving into the fall crops and weeds.
 
For more information see:   Keeping Track of Major Produce Pests During the Summer

The management of salt and sodium (Na) concentrations in agricultural soils is a constant challenge in desert crop production systems.  The failure to manage salinity and sodicity has contributed to the demise of many agricultural systems and civilizations over the course of human history, particularly in arid and semi-arid regions (Adams and Hughes, 1990 and Gelburd, 1985).  For example, the Hohokam civilization flourished in the Salt, Gila, and Verde River Valleys of what is now Arizona during the millennium current era (CE) 450-1450 CE but their civilization collapsed and dispersed.  Based upon all available evidence, archeologists believe that drought and salinization of their agricultural soils contributed significantly to the collapse of this civilization (Fish and Fish, 2002; Short, 2019).
 
In the 29 June 2022 edition of the University of Arizona Vegetable Integrated Pest Management Newsletter, Volume 13, No. 12, I posted an article “Reclamation of Saline and Sodic Soils”, describing saline and sodic soils and reclamation requirements.  In all cases associated with saline and/or sodic soils, additional irrigation water to accomplish sufficient leaching of soluble salts is required above and beyond meeting crop consumptive use needs.
 
For sufficient leaching of soluble salts, the movement of soil-water down through the soil profile that carries the soluble salts below the crop root zone is required.  Not all soils are created equal and not all soils will equally accommodate deep percolation and leaching.  Therefore, one needs to evaluate soil conditions regarding the internal drainage capacity to manage fields for salinity balance and sodic soil amendment. 
 
The foundation for good overall plant health is a healthy soil that supports high quality crops and good yields.  Soils are considered “healthy” that have good soil tilth, aggregation, and structure, which is enhanced by organic matter and that leads to better soil aeration and water movement.  Soil 'tilth' is a function of the aggregation of individual soil particles (e.g. sand, silt, and clay particles) that are bound together to form a soil aggregate. Soil structure is often described as the 'crumbliness' of the soil which is basically describing the degree of soil aggregation.  Good soil structure enhances water retention, drainage, fertility, and aeration in the soil.  Soils with high sodium concentrations will have dispersed soil particles, the opposite of aggregation, which causes soil crusting and problems with water infiltration and soil aeration.  Thus, the improvement of basic soil health is important in dealing with issues such as compaction, lack of aeration, and poor drainage, each of which can contribute to problems associated with poor root growth, overall crop development, yield, and crop quality.  
 
For leaching and percolation to take place, soils must be first brought to a level of full saturation.  Additional water applied to the soil at saturation can then provide sufficient physical forces to accomplish percolation and leaching.  Plant roots do not generally do well under saturated soil conditions and will suffer in an anaerobic environment.  Thus, drainage is critical to maintain plant-available water levels in the soil and provide good aeration in the root zone.
 
The most common limitations to internal soil drainage include fine textured soils (high clay content), compaction, caliche layers (consolidated calcium carbonate, CaCO₃), a high-water table, or stratified soils with course textured layers (horizons) beneath finer textured layers.  In the alluvial soils commonly associated with crop production areas of Arizona and the desert Southwest it is not uncommon to find any of these soil conditions.  
 
The alluvial soils in Arizona can vary tremendously in both the horizontal and vertical dimensions.  There are basically two ways to find out what exists in a field in terms of basic soil profile conditions.  The first would be to augur down into the soil in a field and evaluate soil texture and horizon organization vertically by depth.  By doing this in several locations in a field one can better determine both soil variability by depth and the field’s variability in a horizontal dimension.  Secondly, one can review soil maps from the USDA – Natural Resource Conservation Service (NRCS).  In my experience working in agricultural fields across Arizona over the past 35 years, the NRCS maps do a very good job of delineating soil series across the landscape.  The soil series descriptions are good references for general descriptions of soil horizon organization.  This can vary to some extent, particularly in cases where a large amount of extensive land leveling has been done.  Otherwise, the NRCS maps are a good reference.  Nevertheless, the best method is to physically sample a soil and evaluate field variability across the field and by depth.
 
In general, soils with a clay content, greater than about 40% clay (Figure 1), should be carefully evaluated regarding natural limitations to internal soil drainage.  In soils of these textures, drainage is possible, but it can be very slow.  There are many fields, particularly in the Colorado River Valleys, that can have very slow internal slow drainage due to deep, fine textured soils.  In some cases, subsoil drains for gravity or passive movement of water have been installed. Also, in some cases pumping systems with drainage wells have been installed in soils of these types to help facilitate internal drainage.  These types of soils are also commonly sensitive to compaction issues, commonly from tillage operations.
 
High water tables can also exist due to basic geological and hydrological conditions such as proximity to a river or water stream.  These situations also commonly need the development of either gravity drains or the development of a drainage well system to pump the high-water table out of the area.  The soil profile example in Figure 2A provides an example of a soil that should have good internal drainage but with the existence of a high-water table that could severely limit the depth and capacity to fully leach and drain a soil profile of this nature.  This is an example of a case in need of either a passive or active drainage system.
 
There are many good examples of drainage systems that have been developed in this region.  In the Yuma area the irrigation districts managed by the Yuma County Water Users Association and Wellton-Mohawk Irrigation and Drainage District have developed systems of drainage wells that actively pump water out of the high-water table situations into the drainage canals for movement out of the valleys.  In the past 30 years these districts have expanded the use of drainage wells and the internal drainage of many fields have been dramatically improved.  The Imperial Valley of California is a good example of a large, irrigated area with tile drains that have been installed in many fields that are designed to facilitate movement of water out of the fields into the drainage canals by the force of gravity, or passively.
 
Soils with caliche layers can be encountered in many parts Arizona with crop production.  In many cases the presence of a caliche layer in a soil profile will define the lower limit of the effective crop root zone.  Fields of that type should be managed with an understanding of that limit in soil and rooting depth.  Perching of water above a caliche layer can be a problem not only to drainage but to root development and the possibility of developing anoxic conditions in a saturated zone.  Thus, irrigation management needs to be balanced with soil depth and drainage capacity in fields of this type, (Figure 2B).
 
The organization of soil horizons by depth can also affect the internal soil drainage capacity.  When a distinct boundary between a finer textured soil horizon (e.g. clay, silty clay loam, clay loam, etc.) occurs with an underlying course soil horizon (e.g. fine or coarse sand) this boundary zone will serve as a “check valve” on the soil water percolation process.  Thus, water can perch above the boundary until a sufficient hydraulic head is developed and water percolation will proceed.  This can serve to slow the percolation process substantially, usually for a short period of time, but it can be enough to make leaching through that soil profile and root zone more difficult.  Perching of water above a soil textural boundary layer can also create a zone of saturated soil and anoxic conditions.  As a result, it is important to recognize the presence of these conditions when they exist in the field (Figure 2C and 2D).
 
All four examples of the soil profiles shown in Figure 2 exist in Arizona agricultural fields and with appropriate management, they can each be productive fields.  Thus, it is important to evaluate soil conditions in the field and manage appropriately to maintain soil-plant water relations for the crop, good soil aeration, and manage the leaching of soluble salts for crop sustainability. 
 
 
References:
 
Adams, WM, and F.M.R. Hughes.  1990. Irrigation development in desert environments. In: Goudi AS (ed) Techniques for desert reclamation. Wiley, New York, pp 135–160.
 
Fish, S.K. and P.R. Fish.  2002.  The Hohokam Millennium. School for Advanced Research Press, Santa Fe, NM. p.1-11.
 
Gelburd, D.E. 1985.  Managing salinity lessons from the past. J. Soil Water Conserv. 40(4):329–331.
 
Shahid, S.A., Zaman, M., Heng, L. 2018.  Soil Salinity: Historical Perspectives and a World Overview of the Problem. In: Guideline for Salinity Assessment, Mitigation and Adaptation Using Nuclear and Related Techniques . Springer, Cham. https://doi.org/10.1007/978-3-319-96190-3_2
 
Short, H.L. 2019.  Agricultural Soils and the Failure of a Prehistoric Population. J. Environ. Quality.48: 1652-1663.
 
Silvertooth, J.C. 2022.  Reclamation of Saline and Sodic Soils.  University of Arizona Vegetable Integrated Pest Management Newsletter, 29 June 2022, Volume 13, No. 12.
 
 

Country	Millions of Hectares	% of Irrigated Lands
India	20.0	36.0
China	7.0	15.0
United States	5.2	27.0
Pakistan	3.2	20.0
Soviet Union	2.5	12.0
Total	37.9	24.0
Global	60.2	24.0

Table 1. Soil salinity caused by irrigation in major irrigating countries and globally. From: Shahid, et al. 2018. Soil Salinity: Historical Perspectives and a World Overview of the Problem.

Figure 1. Soil textural triangle.


Figure 2.  Examples of soil profiles and horizon organization by depth.

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.

As mentioned in a previous article, last month at the UC Cooperative Extension Automated Technology Field Day in Salinas, CA, several automated technologies were showcased operating in the field for the first time to a general audience. One of the “new” machines designed specifically for in-row weeding in vegetable crops was discussed previously, a second is highlighted here.
Vision Robotics¹ (https://www.visionrobotics.com/) demoed an innovative mechanical in-row weeding machine (Fig. 1). As with most other automated weeding machines currently on the market, in-row weeds are controlled with knife blades that cycle in and out of the crop row. Each knife blade however is controlled independently by an electric motor rather than in coupled pairs. Another feature is that the imaging system calculates a prescribed path for the blades to follow based on a contour of the crop plant and a user defined offset distance from the contour (Fig. 2) Because electric motors are used, blade position can be continuously and precisely controlled, thus facilitating close cultivation.
In the demo, the prototype seemed to work pretty well, but the run was short, and it was difficult to fully evaluate its performance. The video they shared of their imaging system with path planning and blade movement operating in real time impressed and showed good promise (Fig. 2). The innovation was recently patented, and the company is planning commercial units for interested customers.
Developments such as these are worth investigating as our and other researchers’ studies have shown that automated in-row weeding machines control about 50-66% of the in-row weeds, and the majority of uncontrolled weeds were observed to be close to the crop plant (Lati et al., 2016; Mosqueda et al., 2021).

References
Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.
Mosqueda, E., Smith, R. & Fennimore, S. 2021. 2020 Evaluations of automated weeders in lettuce production. ANR Blogs. Davis, Calif.: University of California Davis. Available at: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=45566.

Acknowledgements
A special thank you to Tony Koselka, Vision Robotics Inc., for uploading the videos referenced in this article.
____________________
[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.

Fig. 1. Prototype in-row weeding machine developed by Vision Robotics¹ demonstration at UCCE Automated Technologies Field Day. Clear here  or on the image to view the machine in action.


Fig. 2. Plant contour and cultivating blade path planning of prototype in-row weeding machine developed by Vision Robotics¹. A contour of the crop plant is traced (left) and a prescribed path a user defined distance from this contour (right) is determined for the blade tips to follow. Clear here  or on the image to view the system in action.

What is the difference between resistance to herbicide and tolerance? Sometimes we use the terms inconsistently or interchangeably. For example, some manufacturers of transgenic varieties refer to them as herbicide-tolerant entities and other authors refer to them as resistant-varieties.
The WSSA (1998) helped us define this concept:
Tolerance is the “inherent ability of a species to reproduce and survive after herbicide treatment”. This means no selection or genetic manipulation occurred to create it, the plant is “naturally tolerant”. Some weeds are pulled around to some herbicides due to morphological, physiological, and genetic plant characteristics.
Resistance is the “ability of a plant to survive and reproduce following an exposure to an herbicide dose that is normally lethal to the wild type” of that species¹. Resistant weeds appear due to genetic selection by herbicide over a period of time. This usually take several lifecycles.

We are evaluating some fields at the Yuma Mesa in Yuma, AZ for possible Pigweed (Amaranthus palmeri) resistance to glyphosate. In one case after the application of glyphosate we can see dead plants as well as perfectly healthy plants next to each other, which indicates the presence of resistant individuals. In other case plants do not show symptoms of herbicide activity except when applying an extremely high rate (8x) of glyphosate.
It is very important to examine the field history. For instance, if the field is coming from citrus and only glyphosate was used frequently it is possible you inherited the problem of weed resistance. Will continue with our evaluations and keep you informed of our findings.

Figure 1. Susceptible and Non-Susceptible Pigweed (Amaranthus palmeri) after
glyphosate application.


Figure 2. Pigweed (Amaranthus palmeri) population not showing symptoms
after glyphosate application.

Reference:

1. Vijay K. Nandula, Glyphosate Resistance in Crops and Weds, pages 35-38. https://www.google.com/books/edition/Glyphosate_Resistance_in_Crops_and_Weeds/aRGw5VDUdfYC?hl=en&gbpv=1&dq=define+herbicide+resistance&pg=PA35&printsec=frontcover

Area wide Insect Trapping Network   VegIPM Update, Vol. 13, No. 18, Sep 7, 2022
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased in the past 2 weeks, below average for the beginning of the produce season.
 
Beet armyworm:        
Trap counts dropped in all locations, well below average for early September.
 
Cabbage looper:          
Cabbage looper numbers remained low consistent with early September.
 
Diamondback moth:      
DBM moths not active in any trap since June; average for this time of the year.
 
Whitefly:                       
Adult movement increased in the past week, about average for early September. 
 
Thrips:                          
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity tending downward in most locations, below average for early September.