It seems at the end of every fall, I make the same comment “insect pressure this season was the most unusual and unexpected I’ve experienced in a long while”. That’s probably because I have a short memory. But, a quick look at both recent and historic data on pest abundance recorded from our University of Arizona research plots and areawide sampling/trapping suggests that insect pressure this fall was historically low for some pests, while unusually heavy for other pests compared with previous years. (see Pest Abundance on Desert Produce and Melon Cops in 2017) 

Whitefly/CYSDV: Areawide, whiteflies in fall melons were at the lowest levels we’ve measured over the past 11 years. Accordingly, CYSDV incidence at harvest in cantaloupe fields was the lowest we’ve seen since the virus first showed up in 2007. The virus incidence in over 32 melon planting was very low in most fields, but a few hot spots were observed in Roll and Wellton in fields adjacent to cotton and alfalfa. For the most part, whiteflies were similarly light in produce crops with an occasional flare-up in some isolated areas. 

Beet armyworm, cabbage looper and corn earworm: Pretty average worm year in Yuma. Population abundance on untreated lettuce at the YAC this fall was lower than last year, but higher than 2015. Activity appeared to slow down dramatically in early November, even with the warm nighttime lows we experienced. Anticipated more activity in to December. Corn earworm was very light. 

Bagrada bug: The pest was almost non-existent this year. For a third year, they were so light in my research plots that we were not able to conduct any efficacy trials. Bagrada abundance in the past two falls has been the lowest we’ve observed since the invasive stink bug first showed up in 2010. Similar trends have occurred in California, and we’re not sure why? 

Thrips: The western flower thrips pressure this fall was heavy, but the pest was not as abundant as last fall. Our fall trials showed that they averaged over 40 / plant in the non-treated checks, which translates into significant damage to lettuce if not controlled. Similarly, bean thrips showed again in October, but were only about half as abundant as they were in 2016. Nonetheless these numbers cause significant scarring to seedling plants. 

Flea beetles: Beetle activity at YAC was considerably lower than last what we experienced last fall. In fact, we had difficulty getting any decent flea beetle studies conducted. However, had reports of sustained flea beetle movement onto lettuce (with significant feeding damage) from alfalfa and other sources earlier in the fall. 

Diamondback moth (DBM): Well DBM was obviously not a problem for local desert growers in 2017. Did not receive a single report of difficulty in controlling populations. Verimark Tray drenches performed well, as did conventional chemistries (including Coragen, pyrethroids and Lannate). Research showed that transplants were very clean this year, whereas migratory populations of DBM accounted for most of the in-field populations. This was consistent with areawide Pheromone trapping that showed DBM trap captures began following storms that occurred in early September. At YAC, the DBM larval population on direct-seed broccoli was 2-3 times higher than we’ve previously recorded; a result of migration. Larval number still remain moderate (6 larvae/ 10 plants) in early December. Remember: DBM is usually a spring pest in the desert, so keep your eyes open for larvae and damage on those late cole crops and seed crops. 

In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall.

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/

This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation 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, which contained two 25 ft rows of lettuce. Plants were thinned on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.

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. 15, No. 17, Aug 21, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts decreased areawide; about average to previous years.
 
Beet armyworm:         
BAW moth counts are up in south Yuma valley and Dome valley; about average for August

Cabbage looper:           
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:      
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                      
Adult movement continues to decrease, average for this time of the year.
 
Thrips:                          
Thrips adult activity continues to decline, average for August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity declining and average for August.