A significant decline in insect pest activity has occurred over the past 2 weeks. These changes are consistent with cooler, seasonal temperatures. We all know that weather influences produce crop growth and ultimately can create wide fluctuations in markets. Similarly, our local weather can significantly impact pest activity on desert produce crops.    For insects, their activity and abundance are closely aligned with weather. The reason for this is that temperature is the driving force behind insect development, growth and behavior. Unlike many animals, insects are poikilothermic (“cold-blooded”); that is, they are unable to regulate their body temperature. Their internal temperature varies along with that of the ambient environmental temperature. Consequently, insect pests such as whiteflies, beet armyworms, cabbage loopers, diamondback moths, and leafminers are more active and develop rapidly when temperatures average ~85° F; in contrast, they are less active and develop much slower under cool, winter conditions.   That is one of the primary reasons these insect pests can be so abundant on produce crops in Sep-Nov.  Behavioral activities such as flight, movement, reproduction, feeding and oviposition are similarly influenced by seasonal temperatures. But temperature requirements for insects vary with species (see table below).  For example, the optimal temperature for growth and development of beet armyworms and diamondback moths is the same (86 °F), but diamondback moth can complete a generation quicker and can develop over a much broader range of temperature. Thus, they can be more problematic season long if not adequately controlled.  Then you have Bagrada bug which tend to prefer warmer weather for development.  Its lower developmental threshold of 62°F is the main reason the pest is generally hard to find during the winter months.  In contrast, green peach aphids, which we annually find on winter produce crops, thrive in cooler weather (optimal temperature for growth is 55°F.  That’s the main reason we don’t find them on summer crops; it is just too hot for them.  In general, extreme hot (> 120°F) or cold temperatures (<32 °F), can be lethal or greatly restrict insect growth and behavior.  Consequently, temperature and other weather factor such as rainfall, humidity, sunlight and wind play a major role in determining insect activity and abundance on local desert crops; but they can also suppress insect abundance under extreme conditions. For a more detailed explanation on the impact of weather on insects visit Weather Influences Desert Insect Pests.

Improvements of irrigation and crop water management are always central to any discussions in the agricultural communities of the desert Southwest regarding higher crop production efficiencies.  That is particularly true in these days of water shortages.
In any crop production setting the crop (plant)-soil-water relationships are essential to producing a healthy and productive crop.  In desert agriculture, water is our first limiting agronomic (crop and soil) factor and there is no substitute for that.
Amid all the discussions about improvements in irrigation efficiency, the focus on plant-soil-water relations needs to be continually emphasized.  The objective of any irrigation system is to provide adequate irrigation water to the soil for the benefit of the crop.  Thus, it is important to understand the soil conditions and the actual crop-water needs for each irrigation event.

Every combination of a soil and a specific crop is unique, and that delicate relationship is compounded by the above ground environment the plant is growing in, the meteorological conditions.  The dynamics of crop-water demand change with each plant species and it will vary daily within a given crop in response to soil conditions, stage of growth, and meteorological conditions, i.e., temperature, humidity, wind speed, solar radiation, etc.   These meteorological factors must be appropriately considered for efficient irrigation management, irrespective of any type of irrigation system, i.e., flood, sprinkler, drip, etc.
In Arizona we are fortunate to have the Arizona Meteorological Network (AZMET) in place and fully operational with high quality data being collected from agricultural areas across the state on an hourly basis.  At present, this data is summarized daily from 25 agricultural sites and seven urban sites across the state.  https://ag.arizona.edu/azmet/

Dr. Paul Brown, Extension Specialist in Biometeorology (retired) began the development of the AZMET system in 1985 and the full operation of the system began in January 1986.  Prior to his retirement a few years ago, Dr. Brown managed and directed the AZMET system along with a robust research and Extension education program to provide numerous crop production tools that this system supports.  Together, Paul Brown and Bruce Russell developed an excellent weather system that is available to us all.   Dr. Jeremy Weiss now directs the AZMET program.

The meteorological data collected by AZMET include temperature (air and soil), humidity, solar radiation, wind (speed and direction), and precipitation.  AZMET also provides a variety of computed variables, including heat units (degree-days), chill hours, dew point, and reference crop evapotranspiration (ETo).  AZMET data are summarized in a variety of formats, including several ready-to-use summaries and comma-delimited (raw) ASCII text files that can be imported into most database and spreadsheet programs (Russell, 2011).
I have participated in numerous discussions recently regarding efforts to manage water resources in a broad sense, such as within an area or district, as well as in individual crop fields where the use of satellite-based evaporation (ET) estimates are being considered for application.  In Arizona, that should not be necessary since we have AZMET stations on the ground that are well-placed in agricultural areas with high quality data available daily.  The AZMET system provides direct measurements of daily atmospheric conditions that our crops are dealing with in each of the 25 locations.

With AZMET and the information directly available and accessible, in my view we should be using this system for our weather-based needs for crop management and not a remote satellite system.  Even if someone insists on using satellite-based systems, it will need ground truthing and AZMET data would be essential for that.
We should be using the AZMET data and related crop management tools.  This system has been developed by the University of Arizona Cooperative Extension System and it is openly available for direct access and use.

References:
Russell, B. 2011.  AZMET.  The Arizona Meteorological Network : A Brief Overview.  University of Arizona Cooperative Extension.  https://ag.arizona.edu/azmet/azmet04.htm

Fungal transmission of viruses: 
Several viruses have been shown to be transmitted by soil-inhabiting fungi and protists. Two of the common fungal species that transmit viruses in vegetable cropping system are Olpidium spp. and Polymyxa spp. There is specificity between the zoospores of the fungi and virus particles for successful transmission to occur. Not all soilborne fungi can transmit viruses.
 
Olipdium brassicae  is an obligate parasite, meaning the fungus always needs a host plant to survive (brassicae, cucumber, carrot, lettuce). The fungius that act as vector of s viruses survive the time in between crops by producing resting spores.  A virus that we  often see in the desert, Lettuce big vein virus, is transmitted fungus  Olpidium brassicae . Lettuce big vein virus is acquired by the zoospore (motile spores)  as well as resting spores of the fungus. 
  
The other soilborne virus  we see in the desert it Tomato bushy stunt virus is soilborne but has no known vectors. Thought it was predicted to be transmitted by a fungus Olpidium brassicae, new research findings have rules out the particular fungal vector. But there is a possibility that the virus has some soilborne vector. 
 
Common viruses with fungal vector: 
Cucumber necrosis virus: Olpidium bornovanus
Beet necrotic yellow vein virus: Polymyxa betae
Beet soilborne mosaic virus: Polymyxa betae
Beet soilborne virus:Polymyxa betae
Beet virus Q: Polymyxa betae

Nematode transmission of viruses
Two genera of viruses; Nepoviruses (Nematode transmitted polyhedral viruses) and Tobraviuses (Tobacco rattle virus) are transmitted by nematodes.  Xiphinema (Dagger nematodes), Longidorus (needle nematodes), Trichodorus and Paratrichodorus (stubby root nematode) vector transmit different species of viruses. 
 
Virus transmission by nematodes happens in 7 different but interrelated steps. 

1. Ingestion: The process where the nematode ingests the virus particle along with the plant material/sap. 
2. Acquisiton: The unique receptor in the nematode identifies the virus, so he virus particles stay intact within the nematode. 
3. Adsorption: The phenomena of the virus being intact instead of disintegrated in the nematode digestive system. 
4. Retention: Once adsorption, the virus particle can be retained in nematodes anywhere from months to even years. 
5. Release: The virus particles are released onto new plants when nematodes commences feeding on new plant. 
6. Transfer: The virus particles get transferred to new plant. 
7. Establishment: The virus particles establish themselves in the new host plant. 

 
It is a sophisticated and thankfully a very specific relationship. Not all nematodes transmit virus, neither do nematodes vector all plant viruses. Nematodes and nematode transmitted viruses are of a bigger problem in perennial agriculture system such as citrus orchards and grapevines. 
Viruses transmitted by nematodes: 
tobacco rattle virus: beans, beets, peppers, potatoes, and spinach and 100 others
tomato ringspot virus-tomato, cucumbers, 
peach rosette mosaic virus: peach, blueberries 
cherry rasp leaf virus: cherry, apple
grapevine fanleaf virus: grapes and grape hybrids

Seed transmission:  About 1/7 th of the known plant viruses are transmitted through seeds. Different viruses have different host ranges (the plants that they can infect). Tobacco mosaic virus, Cucumber mosaic virus are some viruses with a very wide host range and they may not be seed transmissible in all plants they infect. Seed transmission plays a huge role in virus epidemiology. Not only they can be a primary source of infection, leading to an epidemic in the field upon conducible environment, seed transmission is an effective way for long distance travel of the virus, thus introducing the virus to new places. You have heard of USDA regulations/restrictions on different crops, from certain foreign countries to avoid introduction of infected seeds/plant materials. 
 
Seed transmission can occur simply by contamination of seeds, as in tomato seeds by Tobacco mosaic virus. This can be readily inactivated by seed treatments. 
The second type of seed transmission occurs when the virus is present in the embryo tissue that can happen prior to fertilization or takes place at pollination. Pea seed-borne mosaic virus is a well studied plant virus in this category. 
 
 
Pollen Transmisison:  Some viruses are transmitted from plant to plant via pollen. As in seed transmission, pollen transmission has two mechanisms, gametic infection of embryo and direct infection of mother plant. 
 
Vegetative propagation: An important horticultural practice, and unfortunately a very effective method for perpetuating and spreading viruses. In clonally propagated plants, an infected mother plant which could be asymptomatic could be used to make hundreds and thousands of daughter plants, which will all have the virus. Any vegetative parts  such as bulbs, corms, runners, and cutting will be infected. 
 
Grafting: Essentially a form of vegetative propagation, once the organic union has been established and plants (Scion and Stock) function as a single plant. In experimental front, grafting is used as a virus transmission methods, when all other methods fail.

At the 2024 Southwest Ag Summit Field Demo a couple of weeks ago, many of the latest technologies were demonstrated in the field. Most were related to pest control. Several of the technologies demonstrated or on display at the event are brand new to the Yuma, AZ area. The new technologies presented included an implement designed for cultivating high density crops (Fig. 1a), a field scale drone sprayer (10.6 gal) (Fig. 1b), a high precision spot sprayer (Fig. 1c) and a self-propelled machine that disinfests soil prior to planting using steam. Updated versions of laser weeders, camera-guided cultivators and smart, automated in-row weeding machines (mechanical) were also demonstrated. Over the next several years, it will be interesting to watch the technologies in this space evolve further and become integrated into our cropping systems.

Fig. 1. New pest control technologies demonstrated/on display at the 2024
Southwest Ag Summit Field Demo included a) Oliver¹ high density cultivator b)
DJI Agrospray T40 drone sprayer c) Ecorobotix ARA high precision spot sprayer
and d) UC Davis/University of Arizona self-propelled steam applicator for
disinfesting soil prior to planting.

[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.

 

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

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

Corn earworm: CEW moth counts increased in most traps; about average for early October.

Beet armyworm: Trap counts increased in most areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts still most locations, below average for this time of the season.

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; about average for early October.

Leaf miners: Adult activity light in all areas, about average for this time of season