Now that the weather has finally returned to normal for mid-October, the worm pressure we’ve been experiencing should begin to decline.  However, with many early-planted head lettuce crops beginning to rosette and folding-in to form heads, it would be wise to keep a keen eye out for corn earworm (CEW).  This fall could be important as pheromone trap catches spiked last week in several locations (see graph below) moths continue to be active.  Although pheromone trap counts don’t always correlate to field infestations, we have associated peak CEW moth trap counts with larval CEW activity in surrounding lettuce fields in the past.  Even with the cooler temps expected this next week, moth activity should be expected in fields and that means eggs being deposited in or on developing heads.

CEW can be very damaging in early fall head lettuce crops. On older plants beginning to form heads, larvae will migrate to the succulent terminal growth. If not controlled before the plant leaves fold in, they are protected from foliar sprays. By this time in plant growth, at-planting soil applications of Coragen or Verimark may not be effective enough to protect the heads. Once head formation begins, newly hatched larvae will usually bore into the head almost at once upon hatching.  Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera larvae, rendering the heads unmarketable.  Larvae may enter the head from any point on the plants but can often be found burrowing in from the lower half of the head. 

If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, it is virtually impossible to control the larvae with insecticides. Thus, pay careful attention for newly oviposited eggs (laid singly) on lettuce plants. If you are beginning to find eggs and suspect that CEW are active in the field when plants are beginning to head or cup over, you should treat as soon as possible.  Moreover, during mid-late October and early November it is probably a good idea to prophylactically apply a pyrethroid, methomyl or acephate in combination with larvicides (e.g., Radiant, Coragen, Proclaim) when heads begin to form.  The UA nominal threshold for CEW in head lettuce from the beginning of heading to harvest is1-2 larvae / 100 plants (1-2%).  Repeated insecticide treatments may be required to maintain low population levels if heavy pressure is sustained near harvest. Lab bioassays have shown that CEW larval mortality is most rapid when exposed to Lannate at 0.5 lbs (>90% mortality in 1 hour after exposure) and pyrethroids at high rates (>90% mortality in 3 hours), followed by Radiant,5 oz (>90% mortality in 12 hours).  By 24 hours, mortality was 100% for all the treatments including Coragen and Proclaim.  For more information on CEW management see Corn Earworm Management on Desert Produce.

Numerous proposals and ideas have been presented as the delegations representing the Colorado River Basin states have been working on the development of the new Colorado River management guidelines that will go into place in 2026 when the 2007 interim guidelines expire.  
 
In the 20 September 2023 issue of this University of Arizona (UA) Vegetable Integrated Pest Management (IPM) Newsletter, I posted an article describing an analysis and set of proposals regarding future management of the Colorado River that was presented by Wheeler et al., 2022 in Science (Silvertooth, 2023 and Wheeler et al., 2022).
 
Wheeler et al. (2022) recognized that agriculture is responsible for more than 70% of the Colorado River water use and noted that the Lower Basin has been irrigating less than one-half of the area irrigated by the upper basin, but the agricultural revenues of the Lower Basin are more than three times that of the Upper Basin (USBR, 2015).
 
The lower basin states and Mexico have been fully utilizing their water allocations from the Colorado River in contrast to the upper basin which has not been using its full 7.5 MAF/year allocation.  For example, between 2000 and 2020 the upper basin consumptive use averaged 3.7 MAF/year plus at least 0.7 MAF/year of reservoir evaporation.  The upper basin states have plans for further development and utilization of their full allocation and they want to protect their Colorado River water allocation to support these development plans.  
 
Additional upper basin development and water use from the river exposes a much higher level of uncertainty on Colorado River water management for the future and there are concerns that it could violate the non-depletion obligation in the 1922 Compact which states the upper basin will not deplete the river’s flow to less than 75 MAF during any 10-year consecutive period.  This implies an assumption on the part of the 1922 Compact negotiators that a short-term drought could be managed within a 10-year period, but we are now dealing with drought extending over 23 years.  In addition, the 1944 Treaty requires all seven states to share in the obligation to Mexico.
 
The upper basin states have been adamant that the responsibility of balancing the shortages on the river rests fully with the lower basin states and Mexico.  The upper basin states have consistently emphasized the importance of equality between basins as outlined in the Compact but that has not actually happened in 100 years.  
 
Wheeler et al. (2022) presented a good argument supporting the position that the loss of an established agricultural industry in the Lower Basin is much more harmful than reducing plans for future development in the Upper Basin.  Thus, they proposed that further development and use of more Colorado River in the Upper Basin is objectively quite questionable.
 
Wheeler et al. (2022) ran a series of hydrological models, including the USBR Colorado River Simulation System (USBR CRSS, 2021) and developed a set of 100 scenarios.  They used this model since it is being used in the basin-wide negotiation process.  More details are provided in their article (Wheeler et al., 2022) and summarized in the article I put in this newsletter last September (Silvertooth, 2023).  
 
Many other articles have been published recently regarding how the Colorado River water is used (Dunphey, 2024; Frisvold and Duval, 2024; Richter et al. 2024; Richter, 2024; James, 2024; and Schmelzer, 2024).  Agriculture accounts for about three-quarters of human use of Colorado River water (Richter, et al. 2024).  This water is used to support approximately 15% of the farmland in the United States and it supports the production of 90% of the winter vegetables consumed in the United States and Canada from November to March every year.
 
I believe some of the best analyses on this topic have been done by Dr. George Frisvold and Dari Duval from the University of Arizona (UA) Department of Agricultural and Resource Economics (AREC).  George and Dari are part of the UA Cooperative Extension Economic Impact Analysis (EIA) Team.
 
The Frisvold and Duval report provides a strong analysis of the crops and water productivity for the Upper and Lower basins of the Colorado River.  They provide important contrasts between the upper and lower basins of the Colorado River in terms of water productivity measures associated with the crop production systems.  These measures include total crop sales per unit of water, crop sales minus crop-specific inputs per unit of water, and a blue water footprint (BWF).  
 
The BWF is defined as “the volume of surface and ground water consumed
(evaporated) as a result of the production of a good” (Mekonnen and Hoekstra, 2011).  Frisvold and Duval provided an excellent analysis on the agricultural use of the Colorado River water revealing a BWF of 1.2 acre-feet/$1,000.00 (U.S. dollars) in the Lower Basin and 7.6 acre-feet/$1,000.00 in the Upper Basin.  The counties with the highest consumption of water per acre have lower BWF values.  It is important to recognize the sixfold difference in the value of agricultural production per acre-foot of water used in crop production in the Lower Basin states versus the Upper Basin states.
 
Wheeler et al. (2022) found that the Lower Basin states of the Colorado River are more than three times as productive as the upper basin.  In contrast, Frisvold and Duval determined with a strong and appropriate economic analysis that the BWF in the Lower Basin is 6X greater than the upper basin.  
 
Frisvold and Duval have provided an important set of facts and analyses in their recent work.  In my view, they present a strong and fully legitimate line of consideration that is hopefully utilized in the negotiations and broader discussions in the western water arena for future management of the Colorado River.  These are important points in the storm of emotions that are emanating from many sources and those who do not recognize the value to the population that is being provided from the agricultural systems in the lower Colorado River basin.
 
References
Dunphey, K.  2024. The Colorado River is running dry.  Where is all the water going?  A new study explores water use in the Colorado River basin.  Utah News Dispatch.
https://utahnewsdispatch.com/2024/03/29/colorado-river-study-looks-at-how-water-is-used-in-utah/
Frisvold, G.B. and Duval, D.  2024. Agricultural Water Footprints and Productivity in the Colorado River Basin. Hydrology 2024, 11, 5.https://doi.org/10.3390/hydrology11010005
https://experts.arizona.edu/en/publications/agricultural-water-footprints-and-productivity-in-the-colorado-ri
 
James, I. 2024.  Hay grown for cattle consumes nearly half the water drawn from Colorado River.  Los Angeles Times, 28 March 2024. https://www.latimes.com/environment/story/2024-03-28/alfalfa-hay-beef-water-colorado-river
 
Mekonnen, M. and Hoekstra. 2011.  The green, blue and grey water footprint of crops and derived crop products. Hydrol. Earth Syst. Sci. 2011, 15, 1577–1600.
 
Richter, B.D., Lamsal, G., Marston, L. et al. 2024.  New water accounting reveals why the Colorado River no longer reaches the sea. Commun Earth Environ 5, 134 (2024). https://doi.org/10.1038/s43247-024-01291-0
Richter, B.D. 2024. Why Do We Grow So Much Alfalfa?  Sustainable Waters, 4 April 2024. https://www.sustainablewaters.org/why-do-we-grow-so-much-alfalfa/
Schmelzer, E.  2024.  Where does all the Colorado River water go? A huge amount goes to grow cattle feed, new analysis shows.  Denver Post, 7 April 2024.
 
Silvertooth, J.C.  2023.  Management Proposals for Colorado River Water.  University of Arizona Vegetable Integrated Pest Management Update.  AZ Veg IPM Update, Vol. 14, Num. 19.
 
USBR.  2015. “Moving Forward Effort: Phase 1 Report” (DOI, May 2015); https://www.usbr.gov/lc/region/programs/crbstudy/MovingForward
 
USBR, “DRAFT CRSS: Key modeling assumptions, June 2021 model” (DOI, 2021); http://bor.colorado.edu/Public_web/CRSTMWG/CRSS
 
Wheeler, K., Udall, B., Wang, J., Kuhn, E., Salehabadi, H., & Schmidt, J. 2022.  What will it take to stabilize the Colorado River? Science, 377 (6604): 373-375.

The soft-rot bacterium, Erwinia carotovora subsp. carotovora  (syn.= Pectobacterium carotovorum subsp. carotovorum), enters through growth cracks or wounds caused by cold temperatures, insects, other disease organisms, or by mechanical means. Under warm, humid conditions, uninjured tissue may become infected through natural openings.  Prolonged moisture from rain or irrigation and mild temperatures encourage disease development. Insects, tools, rain, clothing, or affected plant tissue can spread the bacteria. The bacteria survive in soil and plant debris.
Symptoms appear as small, water-soaked areas and enlarge rapidly.  Tissue becomes soft and mushy, and within a few days the affected plant part may collapse. An offensive odor usually is present.
Management: 
Cultural: 

• Set out plants in rows to allow good air drainage.
• Cultivate carefully to minimize injuring plants.
• Control frequency and source of irrigation water.Avoid frequent irrigation during head development. Time irrigation to allow the head to dry rapidly. Avoid stagnant water sources.
• Clean and spray storage walls and floors with copper sulfate solution (1 lb/5 gal water). Bactericides such as Clorox, Lysol, and quaternary ammonium products also are effective.
• In storage, use a buffering material such as straw or paper to prevent injury to the heads.
• Keep storage house humidity between 90% and 95% and the temperature between 32°F and 39°F.

Chemical control
·    Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. 

• Cease at 3 to 6 quarts in 100 gal water. For greenhouse plants only. Preharvest interval is 0 days. 4-hr reentry. 

 

Interested in staying up to date on the latest robotic ag technologies? The International Forum for Agricultural Robotics, FIRA, hosts two annual conferences focusing on robotics and autonomous farming solutions, one in Europe and one in the USA. They recently uploaded recordings of sessions from the 2024 World FIRA, held in Toulouse, France to YouTube. The site also contains playlists of themed breakout sessions from previous European and USA events (over 400 videos total). Highlights include panel discussions with growers and company executives, robot demos, and inno’pitches from startup companies. Most of the content, particularly from the USA events, is high quality and worth viewing. 
Check it out by clicking here or on the image below.

We are currently doing a trial for Hairy Feeabane control (Conyza bonariensis) with several combinations and wanted to share some preliminary results. Application was done last March 22 when the weeds were approximately 0.5-3” diameter and burn down activity was evaluated 5 days after treated (5DAT). We are sharing the first evaluation with you since the weed is abundant at this time in the Yuma Mesa. This is the initial evaluation, so mortality and final control will be rated later.
In recent conversations with PCAs we talked about Rely (glufosinate) activity and they have seen good performance of the product especially when weeds are small and according to some researchers this product’s works better with high relative humidity¹ (Tickes 2010).
This preliminary data shows that Rely and Sharpen both wit AMS (Ammonium Sulfate) and MSO (Methilated Seed Oil) appeared effective at the 5DAT evaluation. There are other PPO herbicides that we are testing like UA850 that looks promising in some combinations such as the combination with Roundup+AMS+MSO. More details will be shared at a later date when additional data is collected.

References: 

1. The influence of temperature and relative humidity on the efficacy of glufosinate-ammoniumD. M. ANDERSON,C. J. SWANTON,J. C. HALL,B. G. MERSEY First published: April 1993

Results of pheromone and sticky trap catches can be viewed here.
 
Beet armyworm:               
CEW moth increased the Tacna/Roll area last week, but areawide below average for mid-September.
 
Beet armyworm:         
Trap counts about the same in all locations, below average for mid-September.
 
Cabbage looper:         
Cabbage looper numbers remained low consistent with mid-September.
 
Diamondback moth:   
DBM moths beginning to appear in traps in Tacna/Dome Valley.
 
Whitefly:                     
Adult movement increased in the past week, consistent with cotton defoliation and harvest. Above average for mid-September. 
 
Thrips:                           
Thrips adults increased in most locations, and trending above average to previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer and September. 
 
Leafminers:                   
Adult activity tending downward in most locations, below average for mid- September.