It’s never too early to start planning for next produce season. And this includes maintaining a clean culture with effective weed control.  I think most PCAs and growers recognize that weed management is important in leafy vegetable and melon production for all the obvious reasons.  However, weed management is also essential for another important, but often overlooked, reason.  Weeds can serve as host plants for many important insect pests, and when not controlled in the field they can be an impediment to insect control. Weeds can serve a beneficial role by harboring insect natural enemies and pollinators, but the consequences resulting from weeds harboring insect pests often outweigh benefits they potentially provide.   Although flowering weeds can provide a reservoir for natural enemies, and a source of nectar and pollen for a pollinators, these same weedy refuges can serve as host sources for many key insect pests that cause economic damage to vegetable crops.  Weeds found on field margins and ditch banks can provide insect pests with suitable resources needed for rapid population growth which subsequently can lead to insect infestations occurring in adjacent vegetable crops.   In addition, many weed species can provide insects with host plants that serve as a bridge between cropping seasons when vegetables crops are not in production (May-August).  Volunteer melons and cotton are also considered weeds (“a plant out of place”). If not removed in a timely manner, these weedy volunteer plants can sustain large numbers of insect pests that can disperse onto newly planted fields.  Weeds can also serve as alternate host plants for three important groups of viruses that affect vegetable and melons; tospoviruses, potyviruses and criniviruses.  For example, one of the primary insect vectors of the tospovirus, Impatirens Necrotic Spot Virus (INSV), is the western flower thrips.  Not surprising, common desert weed species such as lambsquarters, nettleleaf goosefoot, cheeseweed and purselane can all harbor large thrips densities and serve as reproductive hosts for thrips. More importantly, these weeds are known reservoirs of INSV, and weeds collected in Yuma over the past year have tested positive for INSV.   Finally, weeds can serve as impediments to insecticide applications.  Dense weed foliage in vegetable and melon fields can negatively influence foliar spray applications by intercepting spray droplets before reaching the target crop, which can result in less insecticide deposition and unacceptable crop damage.  Soil applied insecticides (e.g., imidacloprid, Coragen, Verimark) can also be impacted by unmanaged weed growth. Weeds growing unchecked during stand establishment can compete with the seedling plants for water and fertilizer, but they can also compete with crop plants for soil insecticides. Excessive weed densities can significantly intercept insecticides in the soil profile and reduce the amount available for uptake by the target crop.   For more information on this topic, please visit Weed Interference with Insect Management in Desert Crops.

Green peach aphid infesting cheeseweed leaf adjacent to lettuce field

There have been ongoing negotiations for several years directed at developing the new Colorado River management guidelines that will go into place in 2026 when the 2007 interim guidelines expire.  
 
The goal of negotiations among the seven U.S. Colorado River basin states has been to submit a single document proposing guidelines to the Bureau of Reclamation (BoR) within the U.S. Department of the Interior.  However, the upper and lower basin state groups have been dealing with significant differences and were not able to come to a consensus agreement.  As a result, the upper and lower basin delegations each submitted separate proposals to the BoR in early March.
 
Both proposals are under review by the BoR officials who have indicated that they will be working with the basin states in the next six months to develop a consensus draft proposal for post-2026 river management by the end of 2024.
 
To help review the differences between the two proposals, I have summarized the basic parameters in Tables 1 through 4 (Davis, 2024a and Hager, 2024a).
 
To help review the differences between the two proposals, I have summarized the basic parameters in Tables 1 through 4 (Davis, 2024a and Hager, 2024a).
 
 
Lower Basin Proposal Summary
Table 1.  Outline of lower basin proposal for Colorado River water management based on reservoir levels of Lakes Powell and Mead.

Reservoir Levels (%)	Lower Basin Reductions (MAF/Year)*	Upper Basin Reductions (MAF/Year)
70	0	0
59-69	0-1.5**	0
39-58	1.5	0
≤ 38	X	X

Note: 
*MAF = million acre-feet
**Up to 1.5 MAF/year reductions for the entire lower basin depending on the reservoir levels between 59-69%.  Divisions of water reductions among the lower basin states is not specified.
X = 1.5-3.9 MAF/year total reductions for the total Colorado River system.  The specific amounts of water reductions in each of the upper and lower basins with reservoir levels at 38% or less are not specified in the current lower basin proposal.
 
Table 2.  Annual reductions in Colorado River water allocations for the lower basin states when the reservoir water levels are between 39-58% in both reservoirs, based on the lower basin proposal.

Lower Basin State	Reduction (acre-feet)
Arizona	760,000
California	440,000
Nevada	50,000
Mexico*	250,000

*Contingent upon Mexico’s agreement with the reductions.
Based on the lower basin proposal, reservoir levels at 38% of capacity and lower would result in reductions from 1.5 to 3.9 MAF/year, depending on the levels of water depletion in Lakes Powell and Mead.  The exact splits in water reductions between the upper and lower basins in this range of reservoir depletion is not specified in the lower basin plan, at least based on the materials used for this review.  Accordingly, the share of water reductions that Arizona and California would take are not specified either. 
For reservoir levels of less than or equal to 38%, the cuts would gradually tighten until the reservoirs fall below 23% of capacity.  At that point, all Colorado River basin states would have to take maximum collective reductions of 3.9 million acre-feet a year.
Upper Basin Proposal Summary
Table 3.  Outline of reductions in water releases from Lake Mead based on the upper basin proposal.

% of Capacity	Release Reductions (MAF/year)*
90	0
70-90	0-1.5
20-70	1.5
≤ 20	1.5-3.9

*MAF = million acre-feet
Specifically for Lake Mead, the Upper basin states proposal includes points:
— If Mead is at least 90% full, the Lower Basin states would take no cuts in their supplies.
— If Mead is between 70% and 90% full, the Lower Basin states would lose up to 1.5 million acre-feet per year.
— If Mead is 20% to 70% full, Lower Basin states would lose 1.5 million acre feet a year.
— If Mead is 20% full or lower, Lower Basin states would have to take cuts of up to 2.4 million acre-feet on top of the 1.5 million they’re already taking.
For Lake Powell, the Upper Basin states proposed a series of shrinking water releases depending on the lake’s elevation:
— If Powell is 81% to 100% full, the lake will release anywhere from 8.1 to 9 million acre-feet of water annually to send to Lake Mead for use by Lower Basin states.
— If Powell stands anywhere from 20% of 81% full, the lake will release somewhere between 6 million and 8.1 million acre-feet a year to Mead.
— If Powell is less than 20% full, it will send to Mead 6 million acre-feet a year.
Table 4.  Outline of water releases from Lake Powell based on the upper basin proposal.

% of Capacity	Lake Powell Water Release (MAF/year)*
81-100	8.1-9
20-80	6.0-8.1
< 20	6.0

*MAF = million acre-feet
It is important to note that the upper basin proposal puts the entire reduction of Colorado River water use on the lower basin states.  Essentially, the upper basin states see the need for Colorado River water reductions as lower basin responsibility entirely.
 
To help keep the conversation interesting, the Gila River Indian Community (GRIC) Governor Stephen Roe Lewis announced on 13 March 2024 at the University of Arizona Water Resource Research Center Annual Conference in Tucson, Arizona (WRRC, 2024) that their community is opposed to the lower basin proposal and with a letter to the BoR, GRIC is seeking to reinforce their existing rights to water and gain a stronger place and voice in the negotiations regarding future access to Colorado River water via the Central Arizona Project (CAP).  Sixteen other tribes in the Colorado River basin signed the 11 March letter from GRIC to the BoR.  Eight of those tribes are from Arizona (Davis, 2024b and Hager, 2024b).
 
The GRIC and some other tribes are pushing for the BoR to find other supplies of water to replace any water that is cut from CAP deliveries or provide financial compensation, particularly to cover existing and/or potential tribal water rights for Colorado River water.
 
There are many interesting ramifications that are possible from these recent developments.  The BoR has two proposals to review from the upper and lower basins and now the added dimension of the GRIC opposition.  These recent requests from GRIC and some other tribes will need to be taken into consideration along with the proposal elements from both the upper and lower basins.
 
References
Davis, Tony.  2024a.  States are far apart on new Colorado River water-saving plans sent to U.S. agency.  Arizona     Daily Star, 13 March 2024.

Davis, Tony.  2024b.  Tribes to feds: Don't take our Colorado River water unless you replace it.  Arizona Daily Star, 24 March 2024.

Hager, Alex.  2024a.  Colorado River States Have Two Different Plans for Managing Water. Here’s Why They Disagree.  KUNC, 13 March 2024.

Hager, Alex.  2024b.  Gila River Indian Community rejects states’ plan for Colorado, works with feds.  Arizona Capitol Times, 17 March 2024.

WRRC.  2024. University of Arizona Water Resource Research Center Annual Conference in Tucson, Arizona.  Presentation recordings: https://wrrc.arizona.edu/news-events/2024-conference/wrrc-2024-conference-agenda

As we hear towards harvesting season for melons, we might  be seeing some bacterial fruit blotch inf the fruits. Though I hope we do not see them, I wanted you to be prepared for your own diagnosis in case you do. Bacterial fruit blotch (BFB) of melon  is caused by the bacterium Acidovorax avenae subsp. Citrulli. The bacteria produces large olive green to brown water-soaked lesions on fruit, making them unmarketable. 

Symptoms of BFB on seedlings begin with water-soaked areas on the lower surface of the cotyledons and inconspicuous lesions on leaves. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die.

Greenhouse conditions are usually favorable for dispersal and establishment of pathogen. Thus, good greenhouse practices and sanitation is extremely important. Clean transplant trays must be used (disinfect trays if they will be reused) and new soil. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening. The bacterium can spread on mist and aerosols. Relative humidity should be kept low through proper watering and good air circulation in the greenhouse. Separate different seedlots, to reduce lot-to-lot spread. Monitor these isolated seedlings daily and destroy trays where symptoms develop. The remaining trays should be sprayed with a labeled bactericide and the applications continued until the plants are transplanted to the field. 

The pathogen can be seedborne, so growers should only use seed that has been tested for the presence of the pathogen by a reputable testing facility. Management of BFB includes a combination of preventing the introduction of the pathogen, sanitation to eliminate any inoculum present, and the use of bactericides if the disease appears. There are no commercially available watermelon cultivars that are resistant to bacterial fruit blotch, but there is some variation in susceptibility among cultivars.

The Yuma Fresh Vegetable Association recently published a video highlighting the importance of crops raised in Yuma during the “offseason”. The video is well done, covering most crops including durum wheat, melons, hay, sorghum sudangrass, cotton, medjool dates and citrus. Even if you’re well versed in Yuma agriculture, I think you’ll find the piece interesting and informative.

Check it out by clicking here or on the image below.

Fig. 1. Yuma Fresh Vegetable Association’s “Yuma : Always in Season video. (Photo Credit: Yuma Fresh Vegetable Association)

We promised to publish your comments on the last article on Napropamide. Your honest opinion is welcomed, and we understand that sometimes your views and experiences will differ from ours.

You have reported that uniformity of broccoli harvesting was affected by the application of Napropamide. Having too many harvesting events can obviously increase the cost of your operations. 

Thank you for communicating this to us. According to some authors in crops such as wheat yield can be improved by minimizing plant-to-plant variability in seedling emergence¹. We value your perspective as we are all working for the benefit of the industry. 

The evaluations conducted at the UA Yuma Agricultural Center were not taken to harvest and therefore no crop maturity data was collected this season. Hopefully will do this in future trials. 
 
Other comments: 
“Thanks for the Devrinol trial work. I had almost forgot about this material. We used to use it on Cantaloupe and Tomatoes up here years ago. I recall one experience where a new grower used it under plastic and suffered high plant stunting and death. In most cases in open furrow production, it worked great”. –PCA/Grower
 
“I reduced the rate to 1pt and worked good”. --PCA

Note on Dacthal
We wanted to share some information on the revision of the registration of DCPA. 
On April 1, 2024 the EPA published new information on Dacthal here:  EPA publication on DCPA released yesterday. It was a warning that has been posted in various web sites.

Previously on March 27, 2024 response (EPA-HQ-OPP-2011-0373-0112) to the registrant the EPA says the following: “Given our inability to identify and agree on a mitigation strategy that addresses EPA’s concerns, the agency is currently exploring the regulatory options available to it under FIFRA Section 6. Due to the serious potential risks posed by DCPA use, EPA will be pursuing these regulatory options as soon as practicable.” Therefore, we are awaiting final decision.
Some members the industry are expecting this herbicide to be available this season.  The Vegetable IPM Team encourages you to  check the latest information following the link :https://www.regulations.gov/docket/EPA-HQ-OPP-2011-0374/document?postedDateFrom=2024-04-01&postedDateTo=2024-04-03

Thank you very much for your comments they are very useful and beneficial for the industry.
 
 
 
 References

1. https://cdnsciencepub.com/doi/10.4141/cjps95-098

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