With the produce season essentially finished, it’s time to begin thinking about insect management in melons. Spring melon crops are rapidly growing, and so are insect pest populations. Cabbage loopers and leafminers are becoming evident in some areas, and PCAs should start ramping up their monitoring and sampling. More importantly, whitely populations are quietly becoming abundant on the spring melons of all sizes. Adults can easily be found on recently planted melons located at the Yuma Ag Center, and reports from local PCAs suggest that adult populations are beginning to show up on older plantings. As temperatures increase and crops/weeds mature, avoidance of excessive feeding from whitefly nymphs should be the primary concern on all melon types. Although CYSDV does occur in later spring melons, it is rarely yield limiting. But honeydew and sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability is whiteflies are not adequately controlled.  Our research has shown that to prevent fruit yield and quality losses on spring melons, a foliar insecticide treatment should be applied on threshold; that is, when average adult numbers exceed 2 per leaf when averaged across an entire melon field. At this level of adult abundance, immature populations are beginning to colonize. Timing sprays based on the adult threshold has been shown to significantly reduce the chance of yield / quality losses during spring harvests.  This threshold applies for the use of recommended IGRs (Courier, Knack, Cormoran, and Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion), neonicotinoid-like compounds (Sivanto prime and Transform), diamides, (Exirel and Minecto Pro) and the feeding disruptors (PQZ and Sefina).  For more information on whitefly management and available insecticides, go to these documents on Insect Management on Spring Melons: Whiteflies and Whitefly Control Chart-Spring Melons -2024. Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine bee safety of a product before making an application in a melon field.  If applications are necessary during bloom, only apply a product that is considered bee safe (e.g., PQZ, Sefina, Sivanto, Assail). We also recommend that insecticides only be applied when honeybees are not actively working in the field (e.g. 10:00 pm – 3: 00 am).

The Colorado River Compact of 1922 was formally negotiated among the basin states (Figure 1) to define how much water from the Colorado River can be used by each state on an annual basis. In 2007, basin states negotiated interim guidelines to deal with Colorado River water shortages and determine the reductions for each state depending on the elevation of water in Lake Mead. Another series of agreements have included Colorado River water allocations to Mexico.
 
After more than 20 years of drought, reduced flows in the Colorado River are now resulting in some serious steps to arrest the decline of the major storage reservoirs, Lakes Powell and Mead. The Drought Contingency Plan (DCP) Authorization Act was agreed to by the lower basin states (Nevada, California, and Arizona) and signed into law on 16 April 2019.  Participation from Mexico was determined through a U.S. – Mexico agreement.  The DCP outlines a process, dependent upon triggers related to the water level in Lake Mead that is intended to protect the Colorado River system through voluntary reductions and increased conservation. Similarly, there is an Upper Basin DCP involving Colorado, New Mexico, Utah, and Wyoming.  The lower basin DCP will extend through the end of 2026 and consists of increasing reductions in Colorado River use in Tiers 1, 2a, 2b, and 3 at Lake Mead elevation levels of 1,075; 1,050; 1,045; and 1,025 ft. above sea level, respectively.
 
With the water level in Lake Mead below 1,075 ft. above sea level, the Tier 1 water allocation reductions have been called into action by the Bureau of Reclamation beginning in January 2022.  
Arizona will suffer the biggest cuts because it agreed in the 1960s to take the lowest priority among the Lower Basin states.  According to the DCP, Tier 1 requires a 512,000 acre-foot (AF) reduction in Arizona’s 2.8M AF annual allocation.  This reduction is primarily being taken from the agricultural irrigation districts associated with the Central Arizona Project (CAP), primarily impacting agricultural areas in Pinal County.  It is important to note that urban/metropolitan and tribal water allocations are not reduced in Tier 1 conditions.
 
Even with the DCP reductions, there are still valid concerns regarding the rate of decline of Lakes Mead and Powell with a continuation of existing weather patterns.  As a result, representatives from Nevada, California, and Arizona have been working on an additional plan to provide further reductions of water use from the Colorado River with a goal of achieving an additional 500,000 AF to leave in Lake Mead.  This would serve to nearly double the conservation of Colorado River water and further reduce the rate of decline in Lake Mead.  For California, this would mean they will take water reductions prior to reaching DCP levels that would trigger their mandatory cuts.
 
This new proposal is being referred to as the “500+ Plan” and it would be entirely voluntary among entities in the lower basin states to participate.  It is estimated that $100M will be needed to implement this plan for further reductions in Colorado River water allocations from the three lower basin states.  For example, this plan would include payments to farmers for fallowing land to save water.  The water agencies from these three states are working to find the money to support this effort and Arizona has pledged $40M to support the plan.  California and Nevada have the plan under review for funding and additional funding could possibly come from the federal government to make this work.
 
In the past two decades, the flow of water in the Colorado River has declined nearly 20% below the 20th century average.  As a result, extractions from the Colorado River have exceeded inputs and in time this catches up with us.  These plans are important for everyone living in the desert Southwest with a dependence on the Colorado River.  Therefore, all steps to conserve this valuable source of water are critical.  In Arizona, approximately 70% of the water is diverted to agriculture and our efforts to provide good stewardship and management of our water resources are always important and increasingly so under these circumstances.
 
Reference:
Colorado River Drought Contingency Plan: Arizona Implementation. Central Arizona Project
https://library.cap-az.com/documents/departments/planning/colorado-river-programs/CAP-FactSheet-DCP.pdf

Figure1. The Colorado River watershed of seven western U.S. states and 2 Mexican states.  Source: USGS.

This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches between bed centers. All other water 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. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

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Herbicide Chemigation Injecting products through irrigation systems is an old technique. It was first used with fertilizers but is now used with pesticides as well. The first herbicide that was chemigated was EPTC (Eptam) in the early 1960’s. Chemigation is generally simple, cost effective and can be done when the field is too wet for equipment operation. Off target drift is minimized and those herbicides that require incorporation into the soil are incorporated at the same time as application. Disadvantages are that sprinklers are designed to apply large volumes of water over several hours and days. It works well for water and fertilizer because any ununiformed is masked by the volume and time it takes to apply them. With herbicides we might be applying only a few ounces per acre and if they are applied in less than an hour or if it is windy ununiform applications can result. Probably the major disadvantage is that sprinkler pipe must be in the field. The pipe commonly has been removed when postemergence applications are made. Most of the common soil applied preemergence herbicides including Prowl,Treflan, Dacthal, Eptam and others can be chemigated. Some of the postemergence, foliar herbicides including Buctril/Maestro, Goaltender, Clethodim, Sencor, Diuron, Dual, Prometyrn and others are also registered for chemigation. This is surprising because you would expect them to be washed off with the water, but they work well and some work better when chemigated. Chemigations typically require lower rates so check the label for rates.

Area wide Insect Trapping Network 
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts are down areawide and average for this time of year. 
 
Beet armyworm:         
Trap counts decreased in most locations; about average compared to previous years.
 
Cabbage looper:         
Cabbage looper counts increased in most traps and about average for this time of season.
 
Diamondback moth:      
DBM moths continue to increase in all areas. Below average for this time of the year.
 
Whitefly:                      
Adult movement negligible, typical for early January. 
 
Thrips:                           
Thrips adult counts beginning to decreased in the past 2 weeks, likely in response to rainfall in late December. Currently, numbers are about average compared with previous years.
 
Aphids:                       
Aphid movement increased significantly in the past two weeks, particularly in North Yuma and Gila Valleys. Well above average for early January.
 
Leafminers:                  
Adults decreased in most locations, but above average for January.