Now that the days are getting longer and the temperatures a bit warmer, aphids are likely to be more common.  Experience has also shown us that aphid population growth begins to increase significantly once the weather warms in January.  Our local weather forecast suggests that temperatures will be in the upper 60’s with moderate nighttime lows in the mid-40’s for the next two weeks. Assuming the weather service is correct, these conditions may be ideal for aphid population growth.   Similarly, with the rainfall we experienced in December, I would keep an eye for aphid pressure to start picking up on your lettuce, celery, spinach and cole crops.  Previous research has shown us that aphids tend to be more abundant during mild, wet winters. 
So far, aphid appear to be ahead of schedule. Aphid flights peaked in mid-December which is a little later than what is expected (see graph below).  There have been several reports of aphids showing up in both conventional and organic produce in the past 2 weeks, and at the Yuma Ag center, we have found enough green peach aphids colonizing small lettuce to initiate efficacy trials.  Consequently, PCAs should be extra vigilant in scouting for aphid colonies.  Be on the lookout for foxglove aphid too; they tend to be more biologically active under warmer temperatures (see Aphid ID Guide).   If a field has been treated with imidacloprid at planting, then chances are you are in pretty good shape on young produce. However, imidacloprid doesn’t last all season.  Regardless of whether you find green peach or foxglove aphid, the key to effective aphid management with foliar insecticides is to initiate sprays at the time apterous (wingless) aphids begin to colonize.  The action threshold is the presence of aphid colonies on 5-10% of plants sampled.  Of course, this requires diligent scouting and sampling.   On older lettuce, make sure you thoroughly examine developing heads/hearts. Fortunately, PCAs have many alternatives for aphid control (see Aphid Management on Desert Produce_2020).  So, keep your eyes open for new aphid colonies and treat early to keep ahead of the populations.   For more information on aphid management see:  Keys to Aphid Management in Leafy Vegetables.

The drought-related pressures on the Colorado River system that have been impacting the entire basin and region for 23 years have slackened briefly due to the wet winter in 2023 that included a good snowpack in the mountains, better rainfall throughout the basin, and improved flows into the river.  The current water level at Lake Mead on Hoover Dam is 1,068.25 ft. above sea level on 3 January 2024.  That level is 160.75 ft below full pool of 1,229.00 ft. (Figure 1).

 

In mid-December 2023 representatives from each of the seven Colorado River Basin states met in Las Vegas, NV during the annual Colorado River Water Users Association conference.  The focus of current discussions among the basin states is to negotiate a new compromise for the guidelines of use under conditions of water shortage.  These new guidelines will go into place at the end of 2026.  The immediate goal is to draft proposals by March 2024.
 
The negotiations are incentivized by having the opportunity for the post-2026 guidelines being developed by the basin states themselves as opposed to litigation or legislation.  A major concern driving this process among the basin states that basin state representatives should be able to do this better than turning the process over to people and entities that have less direct familiarity with the situation and no real “skin” in the game.  
 
The 1963 decision by the Supreme Court of the United States in of the Arizona v California case directed the federal authority on the management of the Colorado River to the Department of the Interior and the Bureau of Reclamation (BoR).  However, the basin states have the chance to negotiate their future management plans on the Colorado River.  If they fail to do so in the allotted time, the process will be managed by the federal government.  
 
The basic water budget challenge is based on the following basic statistics:
 

• The current water budget on Colorado River allocations is 16.5 million acre-feet (maf)/year.
• Average annual flow on the Colorado River from 1906-2017 was 14.8maf/year.
• The average annual flow between the years 2000 - 2018 has been approximately 12.4maf/year.
• That is 16% lower than the 20^th century average flow.
• It is estimated that 1.5 maf/year is lost due to evaporation and system loss.
• Thus, the 4 maf/year target reduction that has been identified by the BoR is basically the difference between the 16.5 maf/year allocated versus the 12.4 maf/year average flow in the first two decades of this century.

 
Some notable progress is being made for conservation of Colorado River water with agreements among lower basin states and tribes that will conserve more than 1.5maf/year through 2026.  For example, California water agencies have recently agreed to conserve up to 643,000 acre-feet/year through 2025.  The Quechan Indian Tribe has reached an agreement with federal water managers to save up to 39,000 acre-feet/year through 2025.  Arizona has agreed to conserve up to 348.00 acre-feet/year through 2026.  All these temporary agreements are being supported with federal funding.
 
With agriculture responsible for 70% of the diversions on the Colorado River, these negotiations are extremely important for the future of agriculture in this region and our capacity to support high population densities that are now common and rapidly growing.
 
These types of negotiations are certainly challenging in dealing with a limited water supply and a lot of demand.  There are many competing interests involved.  Yet, we are confident that the representatives we have will be able to work this out and come to a set of functional agreements.

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. 

Time flies. February is right around the corner and that means it is farm equipment/ag trade show season. Upcoming regional events include the World Ag Expo, Tulare, CA, February 13-15, the Southwest Ag Summit, Yuma, AZ, February 20-22, and AgroBaja, Mexicali, Mexico, March 7-10.  If you are interested in the latest ag tech and farm machinery, all are outstanding events and well worth attending. For more information, click on the links below.

Fig. 1. Upcoming farm equipment/ag trade show events: World Ag Expo, Tulare,
CA, February 13-15, 2024 theSouthwest Ag Summit, Yuma, AZ, February 20-
22,2024 and AgroBaja, Mexicali, Mexico, March 7-10, 2024.

Before making decisions for weed control it’s imperative to have a proper identification of the plant species. There are two names for plants:
The common name, which is a name that people come up with in a certain region to describe a particular weed and it varies by region and therefore can be confusing. Then we have an exact scientific name for each species that is based in the binomial nomenclature system started by Carl Linnaeus in 1753. This binomial (or two term) system includes the genus and the species, which is used worldwide¹.
 
Some very close species from the same family can be controlled by the same product but occasionally their herbicidal susceptibility varies. Such is the case of Chenopodium murale (goosefoot) and Chenopodium album (lambsquarter) two very close and similar species. A product like Pursuit (Imazethapyr) has good activity on goosefoot but can’t control lambsquarters. With accurate identification in a mixed population, you would be able to determine what strategy to use or select the herbicide that would control both species. 
 
There are about 75 weeds most common in Arizona and are included in the PCA² study guide, but many other species could be introduced to the State and complicate our crop production systems. Two great tools for weed identification are the books “An Illustrated Guide to Arizona Weeds” that lists 172 species, and “Weeds of California and Other Western States” which has at least one photograph of 735 weeds.
Another weed identification tool is the book “Weeds of the West”.
Additionally, there are many phone applications that can be used as identification tools such as “id weeds”, “PlantNet”, “PictureThis”, “iNaturalist”, “Seek”, “PlantSnap” and “LeafSnap”. When we have problems with weed ID we contact the UA herbarium.
Thank you for sending samples for Weed ID to the IPM Team it is always a learning experience.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 7, Apr 3, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts remain  at low levels  in all areas, well below average for this time of year. 
 
Beet armyworm:          
Trap increased areawide; about average compared to previous years.
 
Cabbage looper:           
Cabbage looper counts increased to seasonal highs; above average for this time of season.
 
Diamondback moth:       
DBM moth counts increased in most areas. About average for this time of the year.
 
Whitefly:                      
Adult movement negligible, average for late winter. 
 
Thrips:                          
Thrips adult counts increased in most areas. Below average compared with previous years.
 
Aphids:                         
Aphid movement decreased in all areas; below average for late-March.
 
Leafminers:                   
Adults remain low in most locations, average for March.