As the week begins, we reflect on the great work of Dr. Martin Luther King, Jr.  Dr. King was known for his non-violent ways to promote civil rights and his use of civil disobedience. He was a strategist as he chose how and where to hold protests. His actions were instrumental in passage of the Civil Rights Act of 1964, Voting Rights Act of 1965 and the Fairy Housing Act of 1968. Sadly, his life was brutally cut short on April 4, 1968, at the age of 39. Although nothing can bring him back, there is an awe inspiring memorial in Washington D.C. to encourage all who visit to remain vigilant in working toward a more equitable Country, void of discrimination. I highly recommend viewing the memorial in daylight and at night.

"Injustice anywhere is a threat to justice everywhere. We are caught in an inescapable network of mutuality, tied in a single garment of destiny. Whatever affects one directly, affects all indirectly." Letter from Birmingham, Alabama jail, April 16, 1963. 

The rains continue to pummel California with snow amassing considerable amounts at elevation. Floods have closed roads, left mud and debris when waters recede and resulted in deaths. Many trees have lost limbs or completely come out of the ground. One newscaster this last week mentioned we were expecting ARBORgeddon since there were far more trees needing to be removed than arborists available to do the work. I talked with a cousin who said there were still trees on cars in a Sacramento neighborhood. The loss from these many storms has taken their toll physically as well as emotionally. Of course, a few days of sunshine (or at least no rain) will make for easier cleanup.  Let's keep the temperatures cool enough to keep the snow on the mountains at least until the rivers slow down. Our thoughts are with those who are managing the aftermath of storm related issues.

A mycologist's delight.

A mycologist's delight after recent rains.

Dr. Erik Porse joined ANR on Wednesday as our new director of the California Institute for Water Resources. We are excited to have a director with strong experience in science and policy. Erik's recent research with scientists and projects has addressed state and federal goals for safe drinking water, efficient urban water use, sustainable groundwater management, water reuse, beneficial uses of stormwater, and environmental finance. Stop by his office at our 2^nd Street Building in Davis and introduce yourself.

One of the highlights of last week was meeting with Food and Drug Administration Commissioner Dr. Califf and staff, and California Department of Food and Agriculture Secretary Ross and her staff to discuss how to implement soon to be released rules to make our food supply safer.  There are over 300,000 farmers who grow leafy green vegetables. California's share is 20,000 and our many trade organizations involved with leafy greens production are eager to begin work. It takes local people who are connected and trusted to translate regulations to growers for adoption. UC ANR Advisors are trusted, connected and practical. We bring the knowledge of the University of California into every county. We look forward to working with CDFA and FDA to help make our food supply even safer.

Maureen Ladley

A few years ago, I was in Reno overnight for work and wanted to save my delicious dinner leftovers for breakfast. But when I opened the mini refrigerator in my room, my first reaction was, "That feels too warm!" I did not save the leftovers and made alternative plans for breakfast. Since then, I've wondered how common an unsafe hotel refrigerator might be.

The pandemic delayed my research as travel was out of the question for a while. This year, I had the opportunity to test my question when I traveled up the coast from California to Washington and back home again on vacation. I stayed in a variety of places, perfect for my casual research project. My trusty refrigerator thermometer came with me. The results: mixed!

Of the five hotels I stayed in:

• One in-room refrigerator was too warm to store food safely overnight.
• Two were too cold. One was so cold, it froze the beverage I placed inside. Not optimal, but better than food poisoning!
• Two tested perfectly in the safe zone for food storage.

The score: One out of five refrigerators in my unscientific study was unsafe. One in five is not great odds.

The Ideal Refrigerator Temperature 

A temperature range of 33 F to 40 F is ideal. Refrigeration in this range slows the growth of microorganisms, including bacteria. Safe food-handling practices advise that food should be held for no more than two hours above 40 F. Keeping food overnight above that temperature could have serious consequences, meaning storing food in hotel refrigerators that are not 40^o F or below for more than two hours can have serious consequences.

Refrigerator temperature ranges: what's safe and what's not safe?

Stay Safe When You Travel

Here are three ideas to help you avoid problems when you travel:

1)     Measure. Take a refrigerator thermometer with you if you plan to use the in-room mini refrigerator. There's nothing like data to let you know the refrigerator is at the right temperature. Refrigerator thermometers are readily available at grocery and hardware stores, and online.

2)     Avoid. Consider not storing anything that might spoil in your hotel refrigerator if you do not know the temperature setting. Cooling sealed canned beverages would be fine. At worst, your beverage will not be as cool as you hoped, but because it's sealed, nothing will spoil.

3)     Take a quality cooler. Since I was driving, I took my cooler, one that holds appropriate temperatures for days. Traveling with a ready supply of ice, beverages and confidence that my groceries were held safely below 40 F was lovely. This solution is not for every trip, and of course, you need to replenish the ice as you go.

As you plan your future travel, I wish you a safe journey and a skeptical mindset on the safety of your hotel refrigerator for food storage.

Do you have any questions about safe food storage? You can find your local UC Master Food Preserver program or submit questions at http://mfp.ucanr.edu. You can also sign up to be notified of upcoming online food preservation classes.

As the drought continues on the central coast, growers are trying to utilize water as efficiently as possible to produce their crops.  Retaining and reusing sprinkler runoff, also referred to as tail water, can be an important strategy to increasing water conservation.  Also, retaining runoff prevents suspended sediments, pesticides and nutrients from impairing rivers and estuaries downstream of agricultural fields. 

Many ranches in the Salinas Valley have retention basins and infrastructure that can capture runoff and reuse tail water for irrigating crops.  Most growers use this water during the pre-germination or the germination stages to avoid food safety risks from microbial pathogens.    However, updates to the leafy green marketing agreement (LGMA) now require that water stored in open reservoirs and used for irrigating leafy greens maintain generic E. coli levels less than 10 MPN/100 ml. In most cases, tail water in open reservoirs will need to be treated with chlorine to achieve this low threshold for generic E. coli.  Fine sediments suspended in the tail water can greatly reduce the effectiveness of chlorine to control bacterial growth. 

Polyacrylamide (PAM), an inexpensive polymer molecule that has been used for controlling soil erosion in furrow irrigated fields since the early 1990s may be able to improve the efficacy of chlorine by reducing the suspended sediment concentration in sprinkler runoff. Additionally, if runoff is discharged from a ranch, treatment with PAM can greatly reduce the concentration of sediment-bound pesticides and nutrients that can degrade water quality downstream.   Past field trials that we conducted have shown that adding PAM to irrigation water at a low concentration (< 5 ppm) is an effective way to minimize erosion in sprinkler irrigated fields and remove suspended sediments from tail water.   However, for this strategy to be successful with sprinklers, we found that PAM must be injected continuously throughout each irrigation.  In other words, a single application of PAM cannot control suspended sediments in runoff during subsequent irrigations. 

New approaches to using PAM

Accurately injecting PAM into a pressurized irrigation system is not a simple process. Dry PAM powder becomes very gooey and viscous when moistened, and is almost impossible to uniformly dissolve into water.  Emulsified oil formulations of PAM that mix up uniformly in water are available but are more costly than dry PAM products and require sophisticated pumps to meter it into a pressurized irrigation system, as well as trained staff to assure that the application rate is accurate.   Another limitation of liquid PAM is that the mineral oil used to emulsify these products can be toxic to aquatic organisms.  In contrast, dry PAM is less than half the cost of liquid PAM and has been shown to have no toxicity to aquatic test organisms such as Hyalella azteca and Ceriodaphnia dubia, even at concentrations 20 times greater than would be typically used for treating irrigation water.   Hence, for these reasons, we have been developing and evaluating approaches of using dry PAM to control sediment in sprinkler runoff during the last several years. 

Treating pressurized irrigation water with PAM

The first method that we describe in this article uses an applicator to dissolve dry PAM into pressurized irrigation water.   The applicator consists of cartridges filled with PAM granules that insert into a series of cylindrical chambers (Fig. 1).  A small pump can be used to divert a portion of the irrigation water from the mainline into the inlet of the applicator.  PAM slowly releases from the cartridges (Fig. 2) as irrigation water streams through the space between the cartridges and the outer walls of the chambers.  Vanes surrounding the cartridges increase turbulence of the flowing water to maximize the dissolution of PAM.  The treated water then returns into the main line of the irrigation system where it distributes into the field through the sprinkler system.

Fig. 1. Field trials evaluated a prototype PAM applicator in sprinkler irrigated lettuce

Fig 2. PAM cartridge with static mixing elements.

Field-testing the dry PAM applicator

Field-testing of the prototype PAM applicator was conducted in commercial lettuce fields during 2020 and 2021.  Each field test occurred during the germination phase of the crop (5 to 6 consecutive irrigations) using overhead sprinklers.  The fields were divided into untreated, and PAM treated areas, where the PAM treated plots ranged from 1.9 to 4.2 acres.  Soil textures at the sites varied from loam to sandy loam.  A portion of the flow in the main lines was diverted through the PAM applicator.  Flowmeters were used to measure the flow rate in the mainline and the inlet of the applicator.   Another flowmeter monitored the volume of water applied in an adjacent untreated plot. 

Table 1. Description of PAM field trials conducted in 2020 and 2021

Flumes were installed 30 ft from the far end of the fields to measure run-off volume in the PAM treated and the untreated plots during the irrigations (Fig. 3).  A stilling well and float mechanism were used to measure the height of the water in the flume.  A datalogger recorded the height of the water in the flume and converted it to a flowrate using a calibration curve.   The datalogger also automated sampling of run-off into collection containers using a peristaltic pump.  Composite samples of run-off were collected from the plots during 5 to 6 irrigation events and analyzed for turbidity, pH, electrical conductivity, suspended sediments, total nitrogen (N), nitrate-N, total phosphate (P) and orthophosphate at the UC Davis analytical laboratory.

Fig. 3. Flume and peristaltic pumping system used to monitor run-off volume and automatically collect run-off samples from test plots in a commercial lettuce field.

 Results of field tests

The average concentration of suspended sediments in the untreated sprinkler runoff ranged from 466 to 1256 milligrams per liter (mg/L) during each trial (Table 2).   Results of these field trials demonstrated that pretreating the irrigation water with the PAM applicator could reduce the concentration of suspended sediments carried in sprinkler runoff by 85% to 95%, depending on the soil type.  The average reduction in suspended sediment concentration in the runoff was 90% across all trials.  Turbidity of the runoff in the PAM treated plots was also reduced by an average of 95% across all sites (Fig. 4, Table 3). Runoff volume in the PAM treatment was reduced by an average of 26%, but the reduction in runoff volume varied from 8% to 67% depending on the site characteristics (Table 3).   

Table 2. Average effect of PAM on suspended sediments transported in sprinkler runoff and sediment loss for field trials conducted during 2020 and 2021.

Fig. 4. Sprinkler run-off from PAM treated (left) and untreated (right) plots in a commercial romaine lettuce field. Run-off is flowing through flumes positioned at the lower end of the plots.

Table 3. Average effect of PAM on volume and turbidity of sprinkler runoff for field trials conducted during 2020 and 2021.

Total and soluble phosphorus were reduced by an average of 65% and 14% respectively in the PAM plots compared to the untreated controls in the two trials conducted in 2021 (data not presented).  Total nitrogen and nitrate nitrogen concentration in runoff from the PAM treated plots were not reduced compared to the untreated plots. 

The combined effects of reduced runoff volume and suspended sediment concentration under the PAM treatment resulted in less loss of soil from these fields (Table 2).  Soil erosion was reduced by an average of 93% compared to the untreated control, varying from 89% to 96% reduction in erosion among field sites.  Cumulative losses of sediment during the germination phases of the crop were reduced from an average of 76 lbs per acre in the untreated plots to 5 lbs per acre in the PAM treated plots.  The sediment lost in the untreated plots would equate to 15 tons for a 200-acre ranch that was planted with 2 crops of vegetables per season.  This estimate is only for the germination phase of the crop and so total losses of sediment could be much higher for crops irrigated with sprinklers until harvest.     

Summary

The dry PAM applicator that we field tested showed promise for greatly reducing soil erosion, as well as helping improve water quality.   Presumably, by removing the sediment from the tail water, less chlorine would be required for controlling microbial pathogens.   The six-unit PAM applicator tested in this study can treat up to 500 gpm.  The applicator would need more mixing units to treat all the flow from a typical agricultural well in the Salinas Valley (flow rates of 1000 to 1500 gpm).  To see a video showing runoff from PAM treated and untreated field plots during a sprinkler irrigation, follow this link.  The second part of this article will discuss an additional method to use dry PAM to treat irrigation runoff.  This second approach uses an applicator that directly treats runoff in drainage ditches.

Acknowledgments:  We greatly appreciate assistance in fabricating the prototype PAM applicators from RayFab. This project was funded by the California Leafy Green Research Board.

After attending UC ANR's Science for Citrus Health webinars, over 50% of participating citrus professionals say they intend to adopt actions related to psyllid management. These practices can help safeguard abundant, healthy food for all Californians.

The Issue

Huanglongbing?  Never heard of it? Why should I care? Maybe you need to learn more?

Huanglongbing, HLB, a bacterial disease of citrus also called Greening Disease, is spread by the Asian Citrus Psyllid. It causes the citrus fruits to be deformed and taste salty and bitter. HLB was first reported over a century ago in southern China. But why is it a problem for U.S. citrus? Diseases don't “respect” country borders and in 1998 the psyllid and the disease arrived in Florida in the early 2000's. Because there is no cure, damage caused in the largest orange producing state was extensive. By 2019, citrus production decreased in Florida by 74%. Despite federal bans on interstate movement of host plants, the psyllid did not abide by those rules!   

And the disease also easily spreads from state to state. The first tree with HLB in California was found in 2012 in Los Angeles County. Then the question became, even though millions of research dollars were being spent, is there progress toward a cure?  What could be done in California to slow the spread?  Much was learned in Florida's battle and much is being learned through research. But it is hard for growers, the media, and the public to understand how that information might be used in California.

How UC Delivers

To address this information gap, Cooperative Extension Specialist Beth Grafton Cardwell and I started Science for Citrus Health (SCH) in 2015. It is designed to spread in lay language information about research aimed at understanding and combating HLB. SCH is now a cooperative effort with individuals from California, Florida and Texas, involving many activities.

These included developing Snapshots, short, two-page pieces on HLB research, written in lay language, posted on the SCH website, on Instagram, and disseminated at citrus meetings. In total, 45 Snapshots have been written, focusing on five themes related to detection, disease and psyllid management and the tools being used. Another resource for educational efforts is a large PowerPoint slide set, covering genetics, as well as regulatory and consumer issues. Recently efforts expanded, owing to grad students and postdocs, to include a YouTube channel on HLB and a popular podcast series that focuses on HLB researchers, their approaches and their career stories. Another effort involves translating citrus information and Snapshots into Spanish to reach Hispanic growers and workers in the citrus industry. In 2021, five informational webinars were convened on topics, such as ACP and HLB Management, the use of particle films to manage HLB, and citrus thrips. A recent webinar on the biology and management of ACP was presented in Spanish. These webinars attracted international audiences of up to 300 people.

The Impact

Post-meeting polls from UC ANR's Science for Citrus Health webinars indicated that more than 50% of attendees would implement at least one new practice they learned at the session. Research from the University of Florida has shown that the application of particle film screens, for example, has the potential to reduce ACP populations by more than 80% compared to monthly insecticide treatments, thereby contributing to UC ANR's public value of safeguarding abundant, healthy food for all Californians. Creation and proliferation of SCH efforts, providing information on research efforts focused on HLB, is an important educational resource for citrus growers, the media and industry. Another resource provides slides and educational materials to be used by educators for presentations to these groups, and the public. These newly created educational resources, some in Spanish, are unparalleled on other citrus sites.

Huanglongbing Illustration. Credit: Barbara Alonso