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

On 14 June 2022, the U.S. Senate Energy and Natural Resources Committee held hearings in Washington, D.C. to review the conditions and impacts of drought in the western U.S., including the Colorado River. The timing of these hearings was important in recognition of the fact that Lake Mead is at its lowest level ever at 28% capacity and Lake Powell is at 27%. If the current level of water use is allowed to persist any longer with the low inputs going into the Colorado River system, there is a possibility of system failure. Thus, there is a very real danger that water supply and delivery as well as hydro-electric power generation capacities could be seriously jeopardized if major changes are not made on the overall management of the Colorado River system immediately.
Bureau of Reclamation (BoR) Commissioner Camille C. Touton described the need to achieve additional reductions on Colorado River allocations. The BoR is engaging in discussions with the seven basin states that depend on the Colorado River to develop a plan for the reductions, and it needs to be done in the next 60 days. As Commission Touton described, the BoR has the authority to “act unilaterally to protect the system, and we will protect the system.” (Bureau of Reclamation, 28 June 2022)
Commissioner Touton stated that the seven basin states on the Colorado River must reduce allocations by 2 to 4 million acre-feet (maf) and that the decision regarding how to do that must be done in 60 days, mid-August 2022. She was not specific on what all that this will entail but Commissioner Touton did say that the BoR is “working with the states and tribes in having this discussion.” Thus, people in the seven basin states are working hard right now to develop proposals for consideration in addressing this immediate need. The U.S. Department of Interior has the authority and could impose cuts if the states fail to reach an agreement on their own. In the case of the Colorado River, by some estimates agriculture is responsible for nearly 80% of all Colorado River water allocations. However, with the fallowing and water transfers from ag to urban systems that have taken place in some of the Colorado River Valleys, agricultural use on the Colorado River is now ~65%. Considering states like California and Arizona are 95% and 90% urban, respectively, many urban sectors consider agricultural allocations to be the most vulnerable to reductions.
In Arizona, the full allocation of Colorado River water is 2.8 maf, which has been reduced in 2022 by the Tier One cuts associated with the Drought Contingency Plan (DCP) by 512,000 acre-feet (kaf). Agriculture is responsible for approximately 70% of total water diversions in the state and the DCP reduction is primarily being taken from the agricultural districts on the Central Arizona Project (CAP) in central Arizona, mainly Pinal County due to previous agreements and lower priority rankings of water allocations.
Based on irrigation, Arizona agriculture produces the highest yields per acre and some of the highest quality crops found anywhere in the world. Arizona also supports a huge seed industry that is important regionally, nationally, and globally. Crop production systems in Arizona support animal production systems including dairy, beef, and poultry. Arizona citizens are direct beneficiaries of these production systems. Over the past 40 years, crop production systems in Arizona and the desert Southwest have continually improved and we are now more efficient and using less water per acre to produce high yields and high-quality crops.
It is important for us to fully describe and demonstrate the good stewardship we provide for soil and water natural resources that we depend upon in the production and management of cropping systems. However, the tendency of facts being facts but perceptions often becoming people’s reality, we must recognize that it can be challenging to communicate to non-agricultural audiences the basic facts about agriculture and water use and the good stewardship being employed. For example, effectively communicating an understanding that agriculture is a process of managing living organisms; animals, and crop plants, in the field under natural environmental conditions is a challenging objective. Some people tend to think that agriculture is a factory level production process, something engineered, or managed by computer algorithms. In reality of course, irrigated agriculture is a highly sophisticated system managed daily by people in the field working with the constant changes and challenges presented to a large extent from the environment as well as markets and a plethora of other external factors.
Errant perceptions of agriculture and the management of crop production systems can be dangerous at times when we are dealing with critical resource management issues, such as water shortages. Thus, it is important for those of us working in production agriculture to communicate and demonstrate how we are serving as good stewards of the natural resources with which we work. It is good for those of us working in agricultural production systems to review the basics of how we manage water in the production of crops and the good stewardship that is employed in daily operations. Farmers and agronomists have no interest or motivation to put any more inputs into the production of a crop than is necessary.
Farmers and agronomists are constantly striving for higher efficiencies agronomically, economically, and environmentally to conserve precious natural resources. As we have often heard “A measure of what we value is the level of energy or time we invest in taking care of it.” Arizona agriculture has invested a lot of time, energy, and money into the improvement of crop production efficiencies, and we continue to work on these improvements.
We have a good story to tell on the stewardship record of Arizona agriculture and our continued commitment to making improvements in production efficiencies. There are representatives working hard on behalf of Arizona and desert Southwest agriculture to present the case for supporting our agricultural systems and help develop plans for mitigation and response. However, given the chance to do so, we all need to be prepared to communicate the message agriculture’s good water stewardship to appropriate audiences. We all need to prepare for the changes that are coming.

Reference:
Bureau of Reclamation, 28 June 2022 https://www.usbr.gov/ColoradoRiverBasin/

Lettuce dieback is a soil-borne disease caused by two closely related viruses from the family Tombusviridae Tomato Bushy Stunt Virus (TBSV) and Lettuce Necrotic Stunt Virus (LNSV) that has been reclassified as Moroccan Pepper Virus (MPV). The disease has been observed throughout the main lettuce producing areas of California and Arizona. 
 
This year we have been receiving  some samples that looked like lettuce dieback disease. The samples came positive for a new virus named as Lettuce dieback associated virus and negative for tomato bushy stunt virus. In the past we  have seen  symptoms in resistant cultivars (with Tvr1 gene) which suggests that the new virus is involved in the symptomology. 
 
The virus is soilborne, and has been found to have more correlation with the dieback disease more than Tomato bushy stunt virus. Flooding or poor drainage, high salinity, plant stress, and soil saturation have been associated with high incidence of virus . 
 
If you have plants showing symptoms of Tomato bushy stunt virus, please bring the samples to Yuma Plant Health Clinic for diagnosis. 

 
https://www.extension.iastate.edu

At the UC Cooperative Extension Automated Technology Field Day in Salinas, CA a couple of weeks ago, 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 is highlighted here. I’ll discuss other technologies in future articles.
The first is an autonomous robot that uses lasers to kill weeds (Fig. 1a). The machine, developed by Carbon Robotics¹, identifies weeds from camera captured images of the bedtop using artificial intelligence techniques. The device is equipped with eight CO₂ lasers that emit laser beams roughly 0.25” in diameter in short, < 50 millisecond bursts. As such, it is best suited for controlling small weeds (< 3-4 leaf stage) in high density crops such as baby leaf spinach, spring mix, carrots, and onion. The machine worked well in the demonstration plot, annihilating small weeds, turning plant material into black charcoal (carbon!) and grey ash, and causing significant damage to and potentially killing larger weeds (Fig. 1b).
The percentage of weeds targeted and travel speed (significantly less than 1 mph) of the 80” wide (1 wide bed) machine was comparable to that shown in videos on the company’s website (https://carbonrobotics.com/). The version the company is marketing, however, is a 20’ wide (3 wide beds) tractor pulled implement, and according to sales representatives, has upgrades that increase travel speed. This combination should provide adequate machine productivity (acres/hour).
Company reps reported that the first production units are being delivered to commercial farms presently. Some will be operating in the Yuma area this fall. If interested, I would be more than happy to work with you to help conduct and design experiments for assessing the machine’s performance – % weed control by species, % of weeds targeted, hand weeding labor savings, machine work rate (acres/hour), etc. Please feel free to contact me anytime at siemens@cals.arizona.edu.
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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.

Fig. 1. Autonomous laser weeding machine developed by Carbon Robotics¹ a) demonstration at UCCE Automated Technologies Field Day and b) image of bedtop weed control post treatment.

What is the “seed bank”? It’s the reserve of viable seeds present in your soil surface or mixed with your soil at different depths. There are also other vegetative propagules that can contribute to increase your weed infestations such as tubers, solons etc.

How can we reduce our seedbank? When we fallow the fields during the summer preemergence herbicides can be applied with good results because weeds geminate after irrigations or rain.

The chart here shows that summer weeds germinate starting February-March and peak germination is in June and in some cases, they continue germinating until October.

Preemergence herbicides are often used for fallow weed control only when at least 30 -45 days or longer are available¹. We must take into consideration most preemergence herbicides last about 3 months depending on soil conditions. Others like Eptam may last only like 3-4 weeks because of volatility².
Also contact herbicides like Paraquat (Gramoxone, Firestorm), Carfentrazone (Aim, Shark), Pyraflufen (ET), Pelargonic Acid (Scythe) and others are used. These products act quick and leave little or no residual but must be applied when weeds are not too large. The systemic used most frequently is still Glyphosate. It has no residual and is broad spectrum herbicide. Another product registered for fallow use is Oxifluorfen (Goal, Galigan).

Another method used for lowering the seed bank in the summer is “Solarization”. Transparent polyethylene is effective for heating the soil. It is sufficient 4-6 weeks for satisfactory control of most weeds. Some weeds are very sensitive to solar heating of the soil. Sweet clover because of hard seeds and Nutsedge because of the tubers are hard to kill with solarization. Also, Bermuda because of the rhizomes is not easy to control.
Another method is water to germinate and kill weeds mechanically or with herbicides. Some weeds like Common purslane have succulent stems and can survive after cultivation. They could re-root from the nodes and produce seeds. Therefore, carefully monitor plants to uproot them small. Tillage has a negative effect on perennials such as nutsedge and Bermuda. By repeat irrigating and disking we really are spreading them instead of killing them.

References:

1. https://cals.arizona.edu/crop/vegetables/advisories/more/weed236.html
2. https://cals.arizona.edu/crop/vegetables/advisories/more/weed225.html

WEED DYNAMICS AS INFLUENCED BY SOIL SOLARIZATION - A REVIEW R.H. Patel, Jagruti Shroff, Soumyadeep Dutta and T.G. Meisheri, Anand Agricultural University, S A College of Agriculture, Anand - 388 110, India

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.