With local temperatures expected to increase in the next few weeks, insect activity should also start to pick up. Even though worm pressure has been light in the field for the past month or so, it would be wise to keep an eye out for corn earworm (CEW).  In the past, unusually high CEW abundance has occurred on late head lettuce, particularly in the Dome/Wellton areas.  Our areawide trap catches show that moth counts have been nearly bottomed out for some time.  However, we did see an increase in CEW trap captures in Roll and Dome Valley last week (>1 moth/trap/night).  This is above normal for early February (see Areawide Trap Network) and could be the calm before the storm. In the spring seasons where lettuce was heavily infested with larvae (i.e., 2014-2015), trap catches started to increase in early February and peaked by mid-March. These increased trap numbers should be used as an early indicator that moths are actively flying at night at higher abundance and PCAs should start to scout more aggressively for eggs and larvae.  CEW can be very damaging in spring crops once head formation begins; larvae will usually bore into the head 1-2 days upon hatching.  Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera larvae, rendering the heads unmarketable.  If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, control of larvae with currently available insecticides is not possible. 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, it would be a good idea to treat at regular spray intervals (~ 7days). The UA nominal threshold for CEW in head lettuce from early heading to harvest is 1-2 larvae / 100 plants. Essentially, you find one, you spray.  Repeated insecticide treatments may be required to maintain low population levels near harvest.  Most contact insecticides recommended for Lep larvae are active against CEW. Furthermore, the addition of a pyrethroid with thrips, aphid and/or fungicide sprays may be cheap insurance against larvae infesting heads as you approach harvest. For more information on CEW management and control recommendations see Corn Earworm Management on Desert Produce and the 2024 Lep Control Chart.

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.

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.

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.

Table 1. Palmer amaranth population at various dates throughout the growing season following cultivation and/or spray application in 2020 and 2021.

 

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

 Areawide Insect Trapping Network   VegIPM Update, Vol. 15, No. 16, Aug 7, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased areawide; about average to previous years.
 
Beet armyworm:        
BAW moth counts decreased; comparable to previous summers.
 
Cabbage looper:         
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:     
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                     
Adult movement continues to decrease, average for this time of the year.
 
Thrips:                          
Thrips adult activity continues to decline, average for early August.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                   
Adult activity declining and below average for early August.