Hope you are all enjoying the summer so far and keeping busy. Although, we’re about 2 months away from the Fall produce season, it’s never too early to begin thinking of IPM strategies you will be using to battle key insects next season. This includes keeping track of their typical activity during June, July, and August. Below is a short discussion detailing individual pests. 
 
Aphids:    The major aphid species that are important in produce crops each spring include green peach aphid, foxglove aphid and lettuce aphid.  These species are considered cool season pests and are biologically most active during the winter and spring when temperature average around (55-65 F). We do not find them on summer crops as the high temperatures prohibit their activity. They essentially become extinct each summer only to reappear in the fall to infest crops in Oct-Dec migrating into the desert via N-NW winds that occur after the monsoons.
 
Diamondback Moth (DBM):  Another key pest that disappears each summer but for a different reason than for aphids. The host range of DBM is limited to only brassica crop and plants. Although brassica weeds are common during the winter, they occur during the summer due to high temperatures and dry conditions. Thus, like aphids, DBM populations from the previous spring season become “extinct” during the summer when brassica crops and weeds are absent. They reappear each fall migrating in on high winds associated with tropical storms from Mexico, or arrive into the region on infested brassica transplants from California.
 
Whiteflies:       A resident pest that occurs year-round in the desert. As a warm season pest, whiteflies are most abundant on fall produce crops, and seldom a problem during the winter and spring. Peak abundance occurs during the summer months on cotton, and again in September and October on fall brassica, leafy vegetables and fall melons.  Thus, it is important to control whiteflies in cotton prior to defoliation to prevent large migrations onto fall produce crops. In addition, whiteflies can be found on several weeds such as purslane, goosefoot, ground cherry, and sunflowers. Sanitation in and around fields being prepped for fall plantings is important. Preventatively, growers should consider applying soil, system insecticides such as imidacloprid or Verimark to Fall produce crops.

Beet Armyworm (BAW):  A warm-season pest that occurs year-round in the desert. They tend to reach peak abundance twice a year. Generally, the most important peak is in September and October when weather is ideal for their development, flight activity and oviposition. A second peak occurs in late spring. Activity is generally light during the summer, occurring primarily in alfalfa crops. Although BAW is known to migrate in from the south via monsoon and tropical storms, resident populations annually occur in alfalfa during the summer. Thus, to minimize BAW in fall produce crops, thorough management of BAW can potentially minimize their movement onto Fall produce crops.  Weeds are also a source of BAW (purslane, goosefoot, sunflower and Russian thistle) so sanitation in and around fields is important.
 
Western Flower Thrips (WFT):  Also a resident pest that can be found in the desert year round. WFT is most abundant on lettuce in the late spring, but peaks in abundance on alfalfa, melons and cotton is May and June. During the late summer numbers drop dramatically where thrips can be found on melons and alfalfa and weeds like goosefoot and purslane. WFT slowly move into lettuce again in early fall and are least abundant during the winter.  Sanitation of weeds during the summer can help reduce thrips abundance moving into the fall crops and weeds.
 
For more information see:   Keeping Track of Major Produce Pests During the Summer

The situation on the Colorado River has not changed appreciably since last summer when the Bureau of Reclamation (BOR) made a bold announcement on 14 June 2022 with BoR Commissioner Camille C. Touton describing the need to make substantial reductions of 2 to 4 million acre-feet (MAF).    As Commission Touton described, the BOR has the authority to “act unilaterally to protect the system, and we will protect the system.” (Bureau of Reclamation, 28 June 2022).  She stated that the BOR was allowing the basin states 60 days to come up with a plan.  In the absence of a plan from the basin states, the BOR would be ready to take action.
 
Since June, the BOR has been engaging in discussions with the seven U.S. basin states that depend on the Colorado River to develop a plan for the reductions, and the anticipated decisions from the BOR have not materialized.
 
The basic arithmetic on the Colorado River is as follows:
 
16.5 MAF is currently the allocated amount of water budgeted with 7.5 MAF allocated to both the upper and lower basins, plus 1.5 MAF allocated to Mexico:
(7.5+7.5 MAF = 15 MAF U.S. + 1.5 MAF Mexico = 16.5 MAF total)
 
In the past two decades, the average annual flow of the Colorado River from 2000 - 2018 has been approximately 12.4 MAF, which is 16 % lower than the 1906-2017 average of 14.8 MAF/year.  Thus, we can see where the 4 MAF differential is determined.
 
A reduction of Colorado River water allocations from 16.5 MAF to 12 MAF represents a 27% reduction.  That is in line with the climate and hydrological reality we are dealing with.  That would be a huge reduction for the Colorado River basin and a painful experience for many entities in the desert Southwest.
 
On 16 August 2022, after the 60 days provided by Commissioner Touton had expired, U.S. Department of the Interior Deputy (DOI) Secretary Tommy Beaudreau with Assistant Secretary for Water and Science Tanya Trujillo announced that the 2023 Colorado River Operational Plan would move to Tier 2a reductions associated with the Drought Contingency Plan (DCP), which was ratified by the lower basin states in 2019 (Figure 1).

 

Figure 1.  Reductions in Colorado River allocations according to the 2007 Interim Guidelines, Minute 323, Lower Basin Drought Contingency Plan, and Binational Water Scarcity Contingency Plan.  Total volumes in thousand acre-feet (KAF) units.  Source: U.S Bureau of Reclamation.
 
The Tier 2a changes will require an additional 80 thousand acre-feet (KAF) being reduced from Arizona’s 2.8 MAF allocation of Colorado River water (Figure 1).  This will result in a 592 KAF total reduction from Arizona’s allocation, which includes the 512 KAF reduction for Arizona from Tier 1, that was first imposed in January 2022 (512 + 80KAF from Arizona = 592KAF, which is a 21% reduction in Arizona’s Colorado River allocation.  In addition, Tier 2a reductions include 25 KAF from Nevada, an 8% annual allotment reduction and 104 KAF, or 7% of Mexico’s annual allotment.  
 
The Tier 1 and Tier 2a reductions have wiped out the CAP allocations to the agricultural irrigation districts in central Arizona.  No water savings will be required for California in 2023 under these operating conditions.  If or when Tier 2b reductions are put in place California will take a 200 KAF reduction (Figure 1).
 
The developments and actions from the BOR and DOI since June have been basically “business as usual” since the DCP was already in place and the water levels in Lake Mead would warrant Tier2a or even Tier 2b reductions without any further actions on the part of the BOR or DOI.
 
In the 60 days following the June BOR announcement, the major agricultural districts on the lower Colorado River, including Arizona and California irrigation districts on the mainstem of the river, came together to form a coalition and develop a draft plan in response.  They presented a proposal to reduce nearly 1.0 MAF of irrigation water by agreeing to cut 1.0 AF/acre throughout the districts.  They were also seeking financial compensation of $1,500/acre, resulting in a total cost of nearly $1.4B to help farmers in these districts make changes and investments to achieve greater efficiencies with water allocated from the Colorado River.
 
This effort on the part of the lower Colorado River irrigation districts to develop this proposal in 60 days was substantial and remarkable in many ways.  Also, the state of Arizona has demonstrated a willingness to step up and contribute to the conservation needs of the Colorado River system by retaining more than 800 KAF behind Lake Mead in 2022.  In addition to the 512 KAF reduction required of Arizona from DCP Tier 1 reductions (Figure 1), the state of Arizona voluntarily contributed more than 300 KAF to leave in the river system.  That too was remarkable and quite impressive.
 
No other basin states have offered anything of substance other than suggestions that some other entity take the cuts in water allocations.  Thus, the collective efforts among basin states that Commissioner Touton was calling for in June have not materialized.
 
California has recently offered to leave 400 KAF in Lake Mead with the caveat that the state receives financial support for Salton Sea remediation.  However, to the best of my knowledge, California has not described what they would do for Salton Sea remediation.
 
The Gila River Indian Community (GRIC) has recently offered to 250 KAF of water under their control for the Colorado River system, with 125 KAF from their direct Colorado River allocation plus another 125 KAF of water they have stored in underground aquifers that they are willing to sell as part of deal offered.
 
On 28 October 2022, the DOI announced that the BOR will analyze the existing guidelines for operating the Hoover and Glen Canyon Dams for Lakes Mead and Powell, respectively.  This most recent announcement has generated a great deal of speculation with some observers suggesting that the DOI/BOR are ready to act soon.  Others are thinking that perhaps this will translate to another year of review and analysis on the part of the DOI and BOR.  
 
So, there are still a lot of questions and uncertainty coming from the federal entities with the Colorado River situation.  
 
Meanwhile, Mother Nature and the basic hydrology of the Colorado River basin is not changing or waiting for the feds or some great basin-wide coalition to come up with a plan.  We are still using water at a rate that is much greater than is being provided from precipitation in the watershed.  
 
What we have at stake is the Colorado River system as a water source that supports 40 M people in the Southwest, approximately 6.0 M acres of cropland, and 30 native American tribes among seven U.S. states and two states in Mexico.  If water levels fall too low in Lakes Powell and Mead, not only is there a lack of hydropower that can be generated but also large volumes of water cannot be moved to areas that need it, including agricultural districts.
 
This is a serious condition for desert agriculture in this region since more than 70% of the Colorado River's water is used for irrigation.  This water is used to irrigate 15% of the nation's farmland and produce 90% of the winter leafy green vegetables.  We have a lot at stake locally, regionally, and nationally.
 
Additional references:
 
Allhands, Joanna. Arizona Republic, 2 November 2022: https://www.azcentral.com/story/opinion/op-ed/joannaallhands/2022/11/02/federal-action-save-lake-mead-powell-colorado-river-too-late/8242368001/
 
Bureau of Reclamation, 28 June 2022 https://www.usbr.gov/ColoradoRiverBasin/
 
Charles, Dan. National Public Radio, 4 October 2022. 
https://laist.com/news/climate-environment/meet-the-california-farmers-awash-in-colorado-river-water-even-in-a-drought
 
Sanchez, Camryn. Arizona Capitol Times, 3 November 2022:  https://azcapitoltimes.com/news/2022/11/03/arizona-lawmakers-push-california-to-cut-water-usage/

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.

Last month, we investigated the use of applying steam to the soil to control weeds in baby leaf spinach. In the study, we utilized the prototype steam applicator described in previous UA Veg IPM articles to inject steam into the soil prior to planting. The concept is to heat the soil to levels sufficient to kill soilborne pathogens and weed seeds (140 °F > 20 minutes). The device is principally comprised of a 35 BHP steam generator mounted on an elongated bed shaper (Fig. 1). The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper. After cooling (<1 day), the crop is planted into the disinfested soil. 
In the trial, the unit was configured so that one of the unit’s narrow-bed bed shapers (42” wide) was outfitted with fourteen steam injection shanks positioned to inject steam in the soil at a depth of about 2” (Fig. 2). Seven of the injectors were in a rank towards the front of the bed shaper with each injector spaced about 3.5” apart. A second rank of 7 injectors, also spaced 3.5” apart, was positioned in-line with the first rank towards the rear of the bed shaper. The steam applicator was underpowered to treat the entire 22” wide bedtop as the machine was designed to treat two, 4” wide bands of soil (8” total). As a consequence, travel speed was slow, 0.15 mph, to ensure target temperatures were met. 
Results showed that steam treatment provided outstanding weed control of nearly 100% (Table 1, Fig. 3). The predominant species at the site were nettleleaf goosefoot and common purslane. This is a very impressive result however work rates were low (0.05 ac/hr) and fuel use/cost was high ($1,000/ac).
This was our first trial investigating the use of soil applied steam to control weeds in high density crops and think these operational parameters can be significantly improved. As stated previously, the unit was equipped with a steam generator with insufficient steam generation capacity. Equipping the device with a higher powered steam generator so that two beds can be treated at the same time would double the work rate. Also, steam was injected at a depth of 2” and at a travel speed was such that the amount of steam applied was adequate to control essentially all (100%) of the weeds. It is logical that shallower treatment depths and faster travel speeds could be utilized and still provide adequate control. Finally, it is estimated that travel speed can be at least doubled by operating the device when initial soil temperatures are high (>120 °F) as compared to this study where soil temperatures were relatively low (90 °F) since much less heat energy is needed to raise soil temperatures to target levels. If travel speed were doubled and two beds were treated during a pass, work rate would be improved to 0.21 ac/hr and fuel costs would be about $500/ac. These numbers are much more reasonable and show potential if high levels of weed control can be maintained. Over the next couple of months and throughout the summer, we plan to investigate these and other ways to improve the efficiency of steam application.

Acknowledgements
This work is supported by the Arizona Specialty Crop Block Grant Program and the Crop Production and Pest Management grant no. 2021-70006-35761 /project accession no. 1027435 from USDA-NIFA. We appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Fig. 1. Band-steam applicator principally comprising a 35 BHP steam generator mounted on a bed-shaper applicator sled.


Fig. 2. Steam applicator sled a) top view and b) bottom view.

Table 1. Weed density and control with steam in baby leaf spinach trial.
Treatment	Weed Density	Weed Control
	(#/ft2)	(%)
Steam	0.05	99.4
Untreated	8.23	---

Fig. 3. Weed control with steam in spinach. Steam was applied to the soil at a 2” depth via shank injection prior to planting (a) and untreated control (b).

The IPM team has received questions about how to evaluate possible crop injury from herbicides that were applied in previous seasons. As we know residual soil activity is very useful when we needed but we must be very careful when the following crop is sensitive. Potential injury is affected by soil type, watering methods, weather, tillage, organic matter, or the combination of these factors.
The following is a chart that “Minimum Recroping Interval” contains the rotational crop interval and soil persistence of herbicides for the major crops and herbicides used in the desert. You can find this chart in the PCA Study Guide Section VI-26.

During 2014-2018 we ran an HPLC (High Pressure Liquid Chromatograph) in our Lab at the Ag. Center to quantify soil and plant herbicide residues free of charge.  Currently we don’t have this equipment available so, we helped growers and PCAs evaluate potential herbicide injury using our greenhouses at the Yuma Ag Center (YAC). A basic bioassay can be done just by growing sensitive plants in pots containing soil from the field in question. Even though bioassays are often done with plants that are sensitive to the herbicide used, it is reasonable to use the crop and variety that will be planted. 
Also, it is very important to collect small amounts (top 2-4 inches) from several areas of the field. Herbicide concentrations often changes within fields, so separate samples should be collected and labeled to indicate which block they come from. 
We are also doing some field evaluations right now with bensulide and metolachlor in spinach at the UA YAC to answer some of your questions and results will be shared soon in this newsletter. If you have a suggestion or herbicide injury test or bioassay you want to run, please contact us at AZVegIPM-Team@email.arizona.edu.

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