By now, you’re probably aware of reports of the Diamondback moth (DBM) outbreaks that Salinas has been experiencing for the past few months. I have spoken with coastal PCAs, growers and Industry reps who have described the situation as “awful” or “horrible”.  They basically can’t stop the DBM populations from infesting and damaging crops. Apparently in some Salinas growing areas, DBM have been very difficult to control, regardless of what insecticide products they’ve used. Based on these reports and images of damaged crops, it brings backs memories of the fall 2016/spring 2017 season in Yuma when we experienced our own DBM outbreak that was so destructive to local brassica crops.

The reason the Salinas outbreaks should be of concern to desert growers is the possibility that these “hard to control” DBM populations may be making their way into our cropping system on coastal brassica transplants. There are some early signs that this has already occurred. Since mid-September, local PCAs have indicated that they have found DBM larvae on transplants originating from Salinas nurseries, while there were no reports of DBM on directed-seed broccoli at that time. Furthermore, I have had no less than a half-dozen calls in the past 2-3 weeks from Yuma PCAs complaining that Verimark-treated transplants originating from California were infested with 3rd and 4th instar DBM larvae 10-12 days after transplanting.  Based on our local research, they should not be seeing DBM infestations like this until 25-30days.  This is a good indication that the Salinas DBM populations arriving on transplants have developed resistance to the diamide chemistry. What’s more concerning, I had a very seasoned PCA tell me last week that he was “having trouble with solid kills” of DBM on cauliflower and cabbage from the coast. Again, we don’t know how intensively these CA DBM populations have been exposed to the insecticide products we normally use.

So, what can you do as the fall season progresses. My first reaction has been: be very aggressive with your IPM program on any DBM found on California transplants. Don’t hesitate to initially hammer them with products like Radiant and Proclaim. These products have been the most efficacious against desert DBM for several years. Be sure to carefully monitor the infestations post-application to ensure that you’re picking up the DBM larvae following each spray as we don’t know the status of resistance of these CA DBM to products that normally work well for us. Because of the suspected resistance to the diamides, I strongly recommend you avoid using a foliar diamide (Coragen, Besiege, Exirel, Harvanta) until we learn more.  (Note:  Radiant, Proclaim and Harvanta are showing good efficacy against DBM larvae in our trials at YAC on direct-seeded broccoli and cabbage).  Remain vigilant in not allowing these populations to become established in your transplanted crops.  The last thing you need is these populations becoming entrenched in the desert this season and spread to locally grown brassica crops as the season progresses into the spring.  Remember, DBM population growth is enhanced under warm and dry weather and a La Nina winter has been forecasted by NOAA.  In the short term, the good news is the weather for early November is forecasted to be a bit below normal and that should help slow them down. Instead of cycling through a generation in 11-14days as they have been doing, it will likely take them closer to 21 days to complete a generation with the cooler weather. For more information on managing DBM see:   2024-25 Guidelines for Diamondback Moth Management in Desert Cole Crops.

The fact that we live in a harsh desert environment is being impressed upon us rather vigorously after more than two decades of severe drought.  Climatologists have marked the current drought as a megadrought and the worst experienced in the desert Southwest in more than 1,200 years.  We are living in unprecedented times in terms of water shortages on the Colorado River watershed and system (Figure 1) along with increasing demand for water from this river over the past several decades which is depleting the two giant reservoirs, Lakes Mead and Powell.  These conditions have resulted in the 2021 declaration by the U.S. Department of the Interior (DoI) and Bureau of Reclamation (BoR) for reductions in allocations from the Colorado River with Tier 1 restrictions associated with the Drought Contingency Plan (DCP, Table 1).

Figure 1. The Colorado River watershed that includes seven western U.S. states and 2
Mexican states, supports >40M people, >5.5M acres of farmland, and 22 Native American
tribes.  Source: USGS.

Table 1. Drought Contingency Plan reductions in Arizona’s allocation from the Colorado River.
FAS = feet above sea level; KAF = thousand acre-feet; MAF = million acre-feet

According to the DCP, Tier 1 requires a 512,000 acre-foot (AF) reduction in Arizona’s 2.8MAF annual allocation.  This reduction is primarily being taken from the agricultural irrigation districts associated with the Central Arizona Project (CAP), heavily 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 (Figures 1 and 2).  In response to the drought and the declining water supply in the Colorado River system, additional mitigation actions are being taken beyond the DCP reductions to further support the level of water in these storage reservoirs which have been steadily declining since 2000.  

Figure 2.  General outline of reductions in water allocations by general source associated
with the Drought Contingency Plan.

The situation on the Colorado River system and the responses have been changing rapidly.  On 3 May 2022 we learned that the BoR is holding back 480KAF from Lake Powell from the originally planned 7.48MAF release in fiscal year 2022.  Also, the BoR is also releasing an additional 500KAF from the Flaming Gorge reservoir on the Wyoming – Utah border.  Both steps are being taken to protect the hydroelectric power generation capacity of the Glen Canyon Dam (Lake Powell). If the lake falls to 3,490 ft. above sea level (FAS) at Glen Canyon Dam there would not be enough water to operate the generators in Glen Canyon Dam that provides power to the western electrical grid and serves as a primary source of electrical power to Wyoming, Utah, Colorado, New Mexico, Arizona, Nevada, and Nebraska. This is due to the placement of the penstocks that were built into the dam that provide water to the electrical generation turbines.  If the water level were to drop below the 3,490 FAS level it could cause cavitation and severe damage to the electrical turbines and the dam structure. The nearly 1MAF of extra water being held in Lake Powell behind the Glen Canyon Dam is intended to protect the electrical power generation and integrity of the dam.
 
So, this translates to nearly 480KAF less water moving through the Grand Canyon and into Lake Mead in FY22 and it puts the lower basin (the region below Lake Powell, Figure 1) one step closer to Tier 2 reductions.
 
The BoR periodically runs a series of model projections regarding the water levels at the dams for both Lakes Mead and Powell.  Results from these models recently projected future water levels at the dams for the end of calendar year (CY) 2022 and 2023.  For Lake Mead the end of CY 2022 projections include a most probable level of 1,049.37 FAS and the lowest probable level at 1,047.10 FAS.  These results project the need for a Tier 2a level declaration by the end of CY 2022.  
 
For the end of 2023, Lake Mead projections include a most probable level 1,035.63 FAS, which would trigger Tier 2b reductions in Colorado River water allocations to Arizona and a most probable minimum level of 1,020.63 FAS, which would necessitate Tier 3 reductions.
 
Due to the recent changes in river management plans that have been announced by the BoR associated with Lake Powell, these model projections for the end of CY 2022 and 2023 are probably high and probably project an overly optimistic condition.  But we can see that the probability of moving into the Tier 2a, 2b, and Tier 3 reductions are very likely to occur by the end of 2023, if not sooner.
 
The warnings of John Wesley Powell, the famous one-armed Civil War Veteran who first directed an expedition down the Colorado River and the Grand Canyon in 1869, are certainly very prescient in the face of the circumstances we are dealing with today.  In an address to the Montana Congressional Convention in 1889 he offered the following statement: “All the great values of this territory have ultimately to be measured to you in acre feet”.  That is incredibly prophetic and certainly true in the reality of conditions that we are dealing with on the Colorado River today.
 
Essentially what we have today on the Colorado River is a supply and demand problem.  Very simply, our demand and extractions from the Colorado River have been greater than the supply and what the river can provide.  As a result, the great reservoirs on the river system, the savings accounts so to speak, have been depleted.  We must come to grips with that reality and decide how the allocations of Colorado River water must be adjusted to bring them into an appropriate balance with the water we do have in the river.
 
The overall situation with the Colorado River offers some good news and some bad news for all of us depending on this water to live, work, and survive in this desert.  The average annual flow of the Colorado River between 2000 and 2018 has been approximately 12.4MAF, which is 16 % lower than the 1906-2017 average of 14.8MAF/year.  So, the good news is with the recognition that we have ~ 12MAF average annual flow in the Colorado River under these megadrought conditions.  The bad news is that the Colorado River system is budgeted for 16.5MAF of allocated water between the U.S. and Mexico.  Thus, there is a functional difference of >4MAF and the fact is that we must reconcile that difference and fast action is needed, much faster than our water governance systems normally operate.
 
Arizona agricultural is responsible for ~ 70% of the water diversions on the Colorado River and agriculture is taking the reductions now with Tier 1 and will carry much of the responsibility for the Tier 2 reductions.  How agriculture fares in this process of Colorado River management in response to the water shortages is critical for the future of Arizona agriculture and the overall complexion of life in the desert Southwest.
 
I believe agriculture will prevail, but a lot of hard work, difficult decisions, and changes are ahead of us in the near future.  Agriculture has some strong and effective groups working in this decision-making arena for water governance on the Colorado River and we need to be sure that practical agricultural considerations are being made in the process with both short and long-term implications.

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum,  is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult. 
 
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields. 
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting.  Wilting is followed by a yellowing of the leaves and finally necrosis.  The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time.  Affected plants that do not die are often stunted and have considerably reduced yields.  Under high inoculum pressure, seedlings may damp off as they emerge from the soil. 
 
 Initial infection of seedlings usually occurs from chlamydospores (resting structure)  that have overwintered in the soil.  Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge.  Infection may be enhanced by wounds or damage to the roots.  The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia.  Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen. 
 
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management. 

Herbicide resistant Palmer amaranth is becoming increasingly problematic in Arizona cotton production. Cultivation is an effective way to control the pest, but standard cultivators do not remove in-row weeds. Finger weeders are an in-row weeding tool made from flexible rubber. Pairs are centered on the seed row and overlapped slightly to remove in-row weeds. In a two-year study, Dotray et al. (2021) evaluated the use of finger weeders for controlling in-row weeds in cotton at the Texas A&M research station in Lubbock, TX. In the study, a cultivator configuration developed by organic cotton grower Carl Pepper, Lubbock, TX was utilized. The device uses 34” wide, shallow pitched sweeps followed by finger weeders mounted on a spring-loaded arm (40” row spacing) (Fig. 1). 
In the trials, use of finger weeders was compared to standard tillage, and an XtendFlex system where multiple herbicides were applied throughout the growing season (trifluralin – preplant incorporated; prometryn – preemergence; dicamba, S-metolachlor, glyphosate – early postemergence; dicamba, dimethenamid, and glyphosate second post emergence application). Six cultivations and two spray applications were made each year as dictated by weed pressure. Weed counts were recorded following cultivation and/or herbicide application on the dates indicated in Table 1. Hand weeding operations were performed twice during the season to control weed escapes. 
The results were very promising. Control of Palmer amaranth with finger weeders was as good as chemical control using the XtendFlex system and significantly better than standard tillage. The authors also reported 95% in-row weed control when Palmer amaranth was ≤ 3 inches, and about 50% when plants were 3-4 inches tall. Crop injury due to cultivation was minimal, even in seedling cotton (1-3 leaf).
Some observations that are key to making the setup successful are that: 1) sweep blades are oriented such that the end of the sweep is pointed towards the crop row rather than away from it. This facilitates fracturing of soil toward the crop row making it easier for the finger weeders to loosen in-row soil and at a deeper depth, and 2) small diameter (9”) finger weeders made from relatively firm, yet flexible rubber are used and oriented at a steep angle. This configuration promotes soil penetration and loosening in firm soil.

A video of the device canhere or by clicking on the image below.

References

Dotray, P.A., Keeling, J.W., & Russell, K.R. 2021. Precision cultivation with finger weeder systems. Project No. 20-190 Final Report. Cary, N.C: Cotton Inc.

Acknowledgments
T
hanks are extended to Peter Dotray, Wayne Keeling and Kyle Russell, Texas A&M University for sharing their project findings. Credit and thanks are also extended to Kyle R. Russell, Texas A&M University, for recording and sharing images and video. 
Project funding provided by Cotton Inc. Their support is greatly appreciated.

Fig. 1. Cultivator configuration used in Texas A&M studies investigating the use of finger weeders and wide sweeps to control in-row and between-row weeds in cotton. Cultivator design and setup credit: Carl Pepper, Lubbock, TX.

Fig. 2. Video of finger weeders and wide sweeps operating in seedling cotton to control in-row and between-row Palmer Amaranth. Video credit: Kyle R. Russel, Texas A&M University. Cultivator design and setup credit: Carl Pepper, Lubbock, TX. Click here to see the video.

Hairy fleabane is a summer annual weed from the Asteraceae family and occasional biennial in our area found in cultivated areas and citrus orchards, alfalfa fields, roadsides and ditch banks, landscapes and around buildings. The seedlings are oval to egg shaped and very similar in size (~0.4-0.8mm) to horseweed (Conyza canadiensis), which makes it very hard to distinguish one from the other in the field. 
Hairy fleabane grows about 4 feet, branches from the bottom and leaves are pubescent also stems are covered with stiff hairs. The growth habits of horseweed (marestail) are different in that they grow up to 10 feet tall and branches from the upper half of the plant.
You can find Fleabane flowering right now in the Yuma area especially the Yuma Mesa. The IPM Team has received calls from our friends PCAs and growers stating that the Fleabane survives the application of Glyphosate, which has been reported for both conyzas. So, we got some trials in progress looking for options to control Fleabane as well as other weeds that have shown tolerance to Roundup such as White sweet clover or malva in different crops.
The results from the evaluations will be shared in this newsletter.

Reference:
1. UC/IPM Retrieved from http://ipm.ucanr.edu/PMG/WEEDS/hairy_fleabane.html

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth light in the past 2 weeks, below average for the beginning of the produce season.
 
Beet armyworm:          
Trap counts increasing in all locations, about average for early September.
 
Cabbage looper:           
Cabbage looper numbers remained low consistent with early September.
 
Diamondback moth:      
DBM moths not active in any trap since June; expected this time of the year.
 
Whitefly:                       
Adult movement increased in the past week, above average for early September. 
 
Thrips:                           
Thrips adults light 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 early September.