The CIMIS stations measure all the weather variables necessary for calculating the atmospheric water demand and calculate ETo values at hourly and daily time-steps, which are then made publicly available for agricultural and urban irrigation management (photo by D. Zaccaria.)
In a recent presentation at the 2021 UC Davis Winter Grape Day, Daniele Zaccaria, UCCE agriculture water management specialist, evaluated the accuracy of Forecast Reference EvapoTranspiration (FRET) for prospective irrigation scheduling.
FRET ETo is a National Weather Service product. It was developed in 2008 collaboratively by UC Davis, the California Department of Water Resources and the National Weather Service to improve high-frequency irrigation management and encourage the adoption of ET-based scheduling for irrigation of agricultural and urban landscapes in California. FRET ETo forecasts are now available for one-, three-, five- and seven-day leads.
Zaccaria said that FRET ETo is a valid alternative to using near-real-time ETo data from the California Irrigation Management Information System (CIMIS) network and provides clear advantages for irrigation scheduling of specialty crops.
While ETo data from CIMIS are considered near real-time, they are retrospective, i.e., they refer to the previous time period when it comes to scheduling water deliveries to growers (for irrigation districts) and on-farm irrigation (for farmers). As such, when information from CIMIS is used, ETo data from the period just passed (one-day, three-day, one-week, two-week) are used for scheduling water deliveries to growers and/or irrigation applications for the next period ahead.
Visible are the rapid changes of the three-day and one-week cumulative ETo values for Napa Valley.
If growers use retrospective ETo data (CIMIS), they may run the risk of over-irrigating or under-irrigating crops during times/stages that may be sensitive for fruit yield and quality. The graphs below show rapid changes of the three-day and one-week cumulative ETo values for Napa Valley. As such, using the ETo from one week to quantify irrigation applications for the following week may lead to scheduling mistakes.
FRET forecasts all the weather variables (using the Global Forecast System, GFS) needed for the ETo equation except solar radiation (Rs). Rs is calculated from forecast daily fraction cloud cover (using the ratio of actual to potential sunshine hours, n/N) and extraterrestrial radiation (Ra), which is a function of latitude and day of the year (DOY).
The CIMIS stations measure all the weather variables necessary for calculating the atmospheric water demand and calculate ETo values at hourly and daily time-steps, which are then made publicly available for agricultural and urban irrigation management.
Zaccaria said the comparisons between FRET forecast ETo and CIMIS ETo calculated from observed weather variable showed good agreement for all the 15 selected station locations across California, which spanned from low to moderate to high ETo demand for all the considered months (June, July, August and September). The results also show that the seven-day ETo forecasts are nearly as good as the one-day ETo forecasts, while the three-day and five-day ETo forecasts are slightly better.
With all data together, Zaccaria said the correlations between FRET ETo and CIMIS ETo showed a Coefficient of Determination (R2) ranging between 0.9 and 1.0 (1.0 meaning perfect match between the variables being regressed) while the Root Mean Square Error (RMSE) was in most cases less than 0.04 inches per day (RMSE being a measure of the differences between the predicted and measured values.) The poorest results were obtained from the Imperial Valley station at Meloland, Torrey Pines in north coastal San Diego County and the Camino forest area in El Dorado County. A slight overestimation of 10% to 20% of forecast ETo versus CIMIS ETo were noted for Bishop’s mountain range site and the Oakville station in Napa Valley.
A lettuce field that tested positive for both INSV and Pythium in 2020. This is not a postharvest shot. The photo was taken at the time when the field should have been ready to harvest (photo by M. Zischke.)
Controlling host weeds and the disease vector are primary concerns for Salinas Valley lettuce growers as the reemergence of western flower thrips-vectored Impatiens Necrotic Spot Virus (INSV) has caused significant yield losses.
Mary Zischke, who leads an INSV task force created by Grower-Shipper Association of Central California, said the winter offseason for lettuce is a critical time to control host weeds.
INSV in lettuce causes necrotic patterns on the inner leaves of the plant as well as significant stunting. Zischke’s task force is identifying major research questions, examining treatment strategies and developing treatment efficacy levels. The task force is also building a grower education program specific to viral disease and is establishing a network for information sharing.
Lettuce is a key host for INSV during the lettuce production season, but during the winter when there are no lettuce fields, the virus survives in weedy host plants in a variety of habitats: roadsides, ditches, waste areas around equipment yards, and natural areas. Vineyards can also be habitat for INSV due to the presence of infected weed hosts.
Task force GAPS that are being recommended to growers and farm managers include disking harvested fields as soon as possible and aggressively managing weed hosts. That includes weeds in lettuce fields, other adjacent crops and border areas where possible.
Preferred weed hosts include hairy fleabane, annual sow thistle, common lambsquarter, purslane, field bindweed, malva, mare’s tail and nettleleaf goosefoot.
Little mallow, annual sow thistle and nettleleaf goosefoot are also common in vineyards and have relatively high levels of INSV, being good hosts for thrips, particularly when flowering.
Weed control is particularly important in the spring when thrips populations begin to increase. It is unclear how far thrips can move, but they rely heavily on the Salinas Valley winds for long-distance dispersal. Monitoring efforts showed that thrips are equally distributed in the wind column up to 10 feet high and have even been detected in moderate numbers at heights above 20 feet.
Zischke said a USDA Salinas monitoring program is in place to report thrips activity on a year-round basis.
Losses from INSV in 2020 exceeded $50 million. The INSV Task Force, composed of growers, PCA’s, the Grower-Shipper Association, the County Agricultural Commissioner and researchers, meets weekly to discuss ways of reducing the spread of INSV.
Palo Alto, CA – December 9, 2021– A&P Inphatec, a specialist developer of bacteriophages, announces the release of important new three-year commercial field trial data on the efficacy of XylPhi-PD™, the biologically-based reduction of Pierce’s disease (PD) in grapevines.
XylPhi-PD™ (EPA Reg. No. 93909-1) is EPA-registered and is commercially available through Wilbur-Ellis Agribusiness locations. XylPhi-PD™ is OMRI-listed and approved for use in organic production.
An early-order discount is currently available for XylPhi-PD (Early Order Program)
A Virtual Field Day (see video link below) was held in October 2021 at a leading commercial vineyard in Sonoma, California with a history of high PD. Field Trial Specialists Amy Ritchardson and Sarah Atwood (from Wilbur-Ellis and A&P Inphatec) walk the vineyard, perform visual disease assessments, and review results. XylPhi-PD reduced detectable Xylella fastidiosa by 55 percent, increased fruit yield by 17 percent and prevented new infections by 80 to 100 percent.
Additional information on XylPhi-PD and A&P Inphatec is available on www.inphatec.com
CDPR is looking at several different areas to determine the bounds of this new program, including what types of pesticides and application methods will require notification, who gets notified, how they get notified and how far in advance the notification will be required (photo courtesy Western Agricultural Processors Association.)
The environmental justice movement has hit a new threshold as the state legislature has now approved, and the Governor signed, a budget that includes $10 million for a new statewide notification system for pesticide application. The California Department of Pesticide Regulation (CDPR) has wasted no time in moving on the effort and has already held a series of focus group meetings to discuss the issue and begin developing the framework of the new program. This new effort will focus on advance notification of potential pesticide applications. While admitting that California already has the most robust pesticide regulatory program in the country, CDPR indicated in a recent meeting that these new notification requirements are a priority for Governor Gavin Newsom and CalEPA Secretary Jared Blumenfeld.
Existing Notification Requirements
There are some existing requirements already in place for advance notifications. Two counties, Monterey and Kern, already offer some form of advance notification, albeit very limited. In Monterey County, the public can sign up for email notifications for fumigation applications made within a quarter mile of one of ten designated schools. In Kern County, the county provides email notification to other growers surrounding a farm where a restricted use pesticide will be used.
For certain soil fumigants, including chloropicrin, metam sodium/potassium, dazomet and methyl bromide, notice of emergency response information must be provided to occupied residences and businesses within a specified distance of a buffer zone unless the applicator provides onsite monitoring. Also, if a beekeeper requests notification, they must be notified if a pesticide toxic to bees is to be applied at a site within one mile of an apiary. Finally, schools must be notified in advance of any pesticide application that will occur within a quarter mile of the school.
Three other states (Florida, Michigan and Maine) have some form of notification requirements; however, they are limited in scope and application. Florida provides a registry for persons requiring notifications, but they must reside in contiguous or adjacent property within a half mile of the application site. Michigan requires notification to someone with a physician diagnosed condition if they reside in property immediately adjacent or contiguous to the property being treated. Maine has a notification registry for applications within 250 feet, which can apply to even residential lawn treatments, and notification must occur within 6 to 14 days prior to the application.
Potential Requirements
With these new notification requirements, CDPR is looking at going way beyond any of these previous requirements or those in other states. In a recent series of focus group meetings, CDPR asked several questions in attempting to determine the bounds of this new program. CDPR is looking at several different areas, including looking at what types of pesticides and application methods will require notification, who gets notified, how they get notified and how far in advance the notification will be required.
By far, the biggest question is who gets notified. Concerns from the agricultural industry abound on this specific piece due to fears over environmental activism. The environmental justice community has been vocal that they want a countywide or statewide notification system where anyone can sign up for an email notification. Why would someone who does not live next to a field or orchard being treated want or need to know about an application unless they have an ulterior motive? One such incident happened in Monterey County where activists tried to stop a planned field fumigation after learning of the fumigation through the notification system.
Another area of concern is how broad CDPR applies this requirement. In the focus group meetings, CDPR asked if this should be limited to only restricted use materials or any pesticide. They also asked if this should apply to all types of application methods or focus on ones they consider to be the greatest risk for pesticide exposure, such as fumigations or aerial applications. Risk is a key question here as what is true risk? Just because a chemical is applied via helicopter or airplane does not mean it imposes a greater risk.
CDPR also asked how far in advance the notice should be made as well as how the notification should be made. Typical notifications are made 24 hours in advance, but CDPR is seeking guidance on whether there should be a shorter or longer notification period. As for how the notification is being made, CDPR is asking if the notification should be made with mail, email, fax or door hangers.
In the end, CDPR is committed to doing something. For the agricultural industry, the fight against our industry continues, and we must be involved to protect what we have. As stated in the beginning of this article, CDPR has acknowledged they have the most robust regulatory scheme on pesticides in the country. This will only make it tougher for farmers and easier for the anti-pesticide groups to attack our industry. There is no doubt that farmers must be careful with pesticide applications and follow all label requirements to the letter. But notifying people that do not live anywhere near where the pesticide application occurs does nothing to protect those that do.
Whether it is water, air quality, labor or pesticides, the California agricultural industry is once again under attack. Consider this article a ‘notification’ that we must stand up against overbearing and unnecessary regulations. When the time comes, be sure to weigh in and comment against these burdensome requirements that go beyond any scientifically justified reason.
We are blessed in California to have the ability to farm year-round. With over 400 commodities grown here, we are the fifth largest food producer in the world. In 2020, approximately 24,300,000 acres of farm operations were accounted for. Visiting with colleagues and other crop managers and consultants from across the nation, I am aware that agriculture in most states is very seasonal.
Limited crops and short growing seasons allow for agriculture producers to shut down and start thinking about next year’s crops.
Winter months are times to plan, repair equipment, prepare fields for next season and possibly take some time off. Not here in California or parts of Arizona. From October through February, many California and Arizona farmers are planting crops.
No Time Off
Crop planting in October may include crops such as artichoke, fennel, and sweet anise. In November, heavy hitters such as cauliflower and strawberry are started in the coastal areas of California. December brings time to plant asparagus, cabbage, carrot, kale, lettuce (head, leaf, romaine) and the popular spring mix. January, however, unlike much of the nation, brings plantings of bok choy, broccoli, cilantro, endive and escarole, Napa cabbage, onion green, peas, rappini and spinach. And the list goes on through February.
To ensure that nitrogen is available in the root zone of young plants, irrigation management should be optimized to limit nitrate movement below the root zone (photo by Marni Katz.)
So, what should growers be considering when deciding how, when and where to fertilize these crops? As with all crops at any given time, we need to understand plant nutrition. For annual crops, a plant’s nitrogen requirement is a function of its total N uptake and how efficiently it can access the available N in the soil. The nitrogen use efficiency depends on the crop type, soil type and how well irrigation, N application rates and timing match plant demand. For example, in general, we need to be aware N use efficiency will be lower with flood irrigation, on sandy soils, and when all N fertilizer has to be applied prior to planting. Cold, wet soils will limit availability and uptake by the plant. In today’s climate situation, we need to determine if adequate irrigation water will be available to us.
The crops are too numerous to go through detailed plans for every one of them. I am happy to say much of this information is available online through local university sources. Take time to look at what has been done on your individual crops. Some general guidelines on N application to consider: Most times, it is more efficient to split N applications than to apply the whole rate prior to planting. This is because most annual crops have a phase of slow early growth when they take up little N, which is followed by a period of rapid vegetative growth and N uptake. Consider that a small starter application at planting is sufficient to support early growth of many crops. High rates risk being leached during the early season. Side-dressing most or part of the N rate just before the rapid growth phase helps ensure that enough N will be present to meet plant demand.
Study the crop uptake curve and know the growth stages for each crop so you can be sure to have adequate N and other nutrients available at peak or critical demand stages.
If we just look at one single crop in more detail, such as lettuce, we can start understanding the multiple things we should be aware of.
Watch Preplan N
Pre-plant N applied in fall at bed listing is highly susceptible to leaching below the root zone by winter rain, and it has been found that lettuce receiving starter and side dress N outperformed lettuce that received a broadcast N application before seedbed preparation.
It would be wise to note that lettuce requires little N in the early phase of growth. Studies found that N uptake during the first month after planting represented no more than 20% of total uptake. As should always be the case, I highly advise using a current soil test to know where your N level is before applications. The optimal pre-plant application rate depends on residual soil nitrate N. When the residual nitrate N concentration exceeds 20 ppm, no pre-plant N application is required. When the residual soil nitrate N concentration is lower, a small application of 20 to 40 lbs./acre just before or at planting is sufficient to cover the early N needs. To ensure that N is available in the root zone of young plants, irrigation management should be optimized to limit nitrate movement below the root zone.
High application rates not only increase the risk of N losses, but may also damage seedlings. Studies in the Imperial Valley showed that pre-plant or starter ammonium N applications exceeding 50 to 60 lbs./acre may damage seedlings, resulting in uneven growth.
Interpretation of Test Results
Several studies carried out in commercial fields in the Salinas Valley found that no fertilizer N is necessary when the pre-side dress nitrate N level in the soil is above 20 mg/kg (= 20 ppm). A concentration of 20 ppm nitrate N in the top foot of soil equals approximately 80 lbs. N/acre. In the absence of leaching, this amount of N could supply a crop for at least two weeks, even at peak N demand. However, if you experience a heavy rainfall event or the have cold wet soil conditions this amount might turn out to be inadequate.
Understanding your crop and its response to soil temperature and moisture conditions might avoid a poor yield. N treatment technologies can help to hold the nutrients in position near the root zone for longer periods. This could help mitigate stress conditions and help the crop rebound from adverse climate conditions. Again, seek information from your crop consultant about current technology available. It might come in the form of seed treatment or a direct treatment or additive to the nutrient added to promote nitrogen use efficiency. There are nitrogen fertilizer manager technologies that will let you increase nutrient availability over longer periods in season. It can help protect from losses by stabilizing your N and allowing for less loss by volatilization, nitrification and denitrification.
After reading your soil report, you find that the nitrate N concentration in the soil is below 20 ppm, and adding only enough N to increase soil-available nitrate N to 20 ppm is needed. Contact your local crop advisor for more information. You may need or benefit from a second opinion on the sample interpretations.
As you can plainly see, a lot more goes into nutrient management than just applying a rule of thumb amount of nutrients to the soil or plant. Fall is upon us now, so prepare your fields. Study your crop needs and keep a close eye on field and weather conditions. Use your Crop Advisors and Extension experts and pay attention to current releases of technology by reading web-based and printed articles that could improve not only your yield but crop quality.
Older DBM larvae will chew holes in mature leaves, which is especially damaging to cabbage. Later, as the larvae and the crop mature, there is the potential for damage to the crowns of broccoli and cauliflower (all photos by Surendra Dara, UCCE.)
The Diamondback Moth (DBM, Plutella xylostella) is not a new insect pest by any means, but it has the capability to damage or destroy crops of tremendous value in a short time, and keeping up with viable management tactics can be a real challenge. This insect is present wherever cole crops (cabbage, broccoli, Brussels sprouts, etc.) are grown throughout the world. It can be a serious pest in canola, and while it does not prefer non-cruciferae crops, it has shown the capability to feed on other plant types, including legumes. Perhaps its most diabolical attribute is its ability to have up to 12 or more generations in a year, which gives them the potential to quickly become resistant to insecticides used against them.
Biology
The adult DBM is a small grayish moth that, when its wings are folded at rest, have dark markings, giving it the “diamondback” moniker. Eggs are deposited singly and are visible without a hand lens once a scout’s eyes have been trained to look for them. The larvae are a translucent green with spots and are easily distinguished from other caterpillars by their behavior of falling from plant surfaces when disturbed, often hanging from a silken thread. The larvae go through four instars before cocooning themselves to a leaf or stem to pupate into adults.
Damage and Control
Damage from DBM varies according to the age of the crop. Transplants carrying the eggs of DBM may be an initial source of infestation, but the adults are also known to travel long distances to find host plants. Young seedlings and transplants may have their growing tip chewed off, effectively killing or stunting the plant. Young larvae will strip off the outside layer of leaf tissue, leaving a “window pane” effect and harming the development of the crop. Older larvae will chew holes in mature leaves, which is especially damaging to cabbage. Later, as the larvae and the crop mature, there is the potential for damage to the crowns of broccoli and cauliflower, and larvae will burrow into maturing Brussels sprouts and cabbage heads. Reports have come from central Mexico, where a large amount of broccoli and other cole crops are grown, that up to 80% of a crop can be lost to diamondback moth damage. Should the genetics for diamide resistance become persistent for DBM, that mode of action which is the most recent may be rendered non-viable, and there are few modes of action other than peptides (Spear-Lep) coming online.
Diamondback moth prefers to feed on cole crops, such as Brussels sprouts shown here.
Control of diamondback moth relies mostly on the use of insecticides. There are no cole crops that have been modified to carry the Bacillus thuringiensis protein gene(s) that protects other crops, and for that matter, DBM has shown the ability to become resistant to Bt. There are natural enemies of diamondback moth, but they cannot be relied on to prevent economic damage to a crop. Insecticide resistance is a serious concern as DBM is capable of developing resistance to just about anything thrown at it, including the newest modes of action. Several companies have developed pheromone dispensers to disrupt mating of diamondback moth, and this is a potentially powerful tool to consider in a DBM management plan. An areawide management plan may prove difficult because of the adult’s ability to spread quickly and their ability to use weed species, especially mustards, as non-crop hosts.
Management Plan
A diamondback moth management plan should account for protection of seedlings/transplants by using a soil drench insecticide at planting and by inspecting plants for presence of DBM eggs. If cyazypyr was used at planting, be sure to note that so it or another member of that class (diamide) is not used again for seven to eight weeks.
Pheromone traps will alert a scout to the presence of DBM but will not be an indication of how severe the population could get or the correct timing for an application. Once the crop becomes established, twice-weekly scouting looking for eggs and early damage becomes necessary.
Rotation of insecticide modes of action is absolutely needed, taking into account the re-entry and pre-harvest intervals for each product. Bt insecticides (DiPel, Javelin, Xentari) are still considered effective unless otherwise noted by the local Extension office. The advantages of Bt are that it is non-toxic to anything except caterpillars and can be used close to harvest. The drawbacks are that they have a very short residual, do not have any effect on adults and cannot penetrate behind wrapper leaves where DBM larvae have burrowed to. It is also true of the newer chemistries that their modes of action target larvae only and will not control adult moths. Through diligence and effective treatments, damage from diamondback moth can be minimized.
Chemical and trade names used in this article do not constitute a recommendation. Consult a crop advisor, extension agent or manufacturer representative for more information.
The navel orangeworm (NOW) continues to be public enemy #1 for most almond growers in California. Current efforts using the sterile insect technique and future efforts with new technologies could benefit from an areawide approach. In simple terms, this strategy coordinates control efforts over relatively wide areas in which hosts of a given pest are grown. These programs have proven successful in a number of crop systems, including pink bollworm in cotton, codling moth in apples and screw worm in cattle.
Shortly after I arrived in Bakersfield, Calif. in 2002 to start an entomology research program for Paramount Farming (which later became Wonderful Orchards), it was apparent that NOW could benefit from such a program because of the importance of sanitation, the need for good spray timing and the recent demonstration of mating disruption as an effective management tool. Having directed two such areawide projects in apples and pears for codling moth management during my tenure with USDA-ARS in Yakima, Wash., I approached the National Program staff of USDA-ARS to explore the possibility of funding such a program for NOW. The funding was ultimately approved in 2007, and Joel Siegel of the Parlier Station was chosen to administer the NOW Areawide Project, which began in 2008 and continued to 2012. For the purpose of this project, the definition of areawide was expanded to a statewide focus on nut crops. Researchers from UC, USDA-ARS and the private sector were enlisted to perform research seeking new knowledge and solutions to several questions. Meanwhile, Wonderful Orchards (WO) had taken the initiative to start two separate 2,500-acre NOW Areawide projects (Lost Hills in 2006 and Santa Fe in 2007) to complement the individual research projects funded by the USDA.
The USDA funding for the NOW Areawide Project amounted to $3.5 million over five years and funded a myriad of projects. Research on NOW flourished during this period (2008-12), and included research directly funded through the Areawide project, co-funded with the Almond Board of California and independent work. In all, over 25 peer-reviewed scientific papers were published during this period, expanding our knowledge and improving our ability to manage NOW substantially. Among the topics were identification of the minor components of the NOW sex pheromone (allowing development of an attractive lure for monitoring), spray coverage improvement, discovery of a new kairomone attractant, multiple studies on aspects of NOW monitoring and relationships among trapping options, variable development rate of NOW on the same and different diets, spray timing and efficacy of insecticide programs, duration of control for commonly used NOW insecticides and relative efficacy of NOW insecticides.
In addition, WO self-funded two areawide projects (Lost Hills and Santa Fe) and related research projects investigating NOW, including insecticide program efficacy, spray coverage characterization and improvement, NOW monitoring and new lure development, predictive NOW damage modeling, bifenthrin resistance in NOW moths, mating disruption and NOW dynamics.
A list of publications and patents associated with the USDA-ARS NOW AW-IPM program can be found at github.com/ChuckBV/Y2008_to_2012_navel_orangeworm_areawide.
Results from the Areawide Sites
The combination of mating disruption (MD) and insecticides resulted in the lowest NOW damage (Higbee and Burks 2021).
One of the major outcomes of the Lost Hills Project (2006-15) was the demonstration that MD supplemented with two hull split sprays resulted in lower NOW damage than MD alone or the insecticide program alone (Fig. 1). All treatment areas received identical sanitation, nutrition and secondary pest inputs. The project site covered 2,500 contiguous acres and was planted in 1996 with Nonpareil, Monterrey, Sonora, Fritz, Carmel, Wood Colony and Price, with a relatively small area that included Ruby and Butte. Treatment areas were rotated each year of the study such that the insecticide-only treatment was situated on either the north or south end to minimize pheromone drift from NOW MD areas. The NOW insecticide program in all years consisted of two applications of methoxyfenozide (Intrepid), one spray directed at the first flight (typically in April) and one spray targeting the second flight (typically in late June/early July.) Aerosol dispensers were used as the pheromone source.
Figure 1. The combination of insecticides and NOW MD (both) achieved the lowest levels of NOW damage in eight out of ten years compared to insecticides (Chem) or MD alone in the Lost Hills Areawide Project (Higbee and Burks 2021).
NOW MD and sanitation could stand alone with increased monitoring effort. (Rosenheim et al, JEE, 2017)
The idea that NOW MD along with sanitation could stand alone, with sufficient monitoring efforts that provided the confidence to make a “no-spray” decision, was validated in the Santa Fe Areawide Project (2007-12). The site chosen was a historical hot spot, largely due to very large trees that were difficult to sanitize adequately. This project was made up of two large ranch units; R370 was planted in 1990 with Nonpareil, Price, Butte and Sonora for a total of 950 ac and R371 was planted in 1993 with these same varieties plus Monterey, Carmel, Fritz, Price, less than 100 ac of Padre and Mission for a total of 1,700 acres. All treatment areas received identical sanitation and secondary pest inputs. These two ranch units were divided by a two-lane highway.
Figure 2 summarizes Nonpareil damage as measured from truckload samples delivered to the processor. This project was managed as a demonstration of what could be achieved with NOW MD combined with sanitation and increased monitoring over large areas. In the initial year of the project (2007), an aggressive insecticide program consisting of a spring application of Intrepid (April), a first hull split spray of Lorsban + Intrepid (late June) and a second hull split spray in late July consisting of bifenthrin (Brigade). This insecticide program was applied to both ranches, while in addition, R370 received NOW MD using aerosol dispensers. The resulting NOW damage in 2007 was much lower in both ranches relative to 2006, the addition of MD in R370 contributing to an even greater reduction than insecticides alone. NOW MD was used over the entire project in for the remainder of the project. The following two years, 2008 and 2009, the only insecticide applications for NOW applied (based on monitoring data) were to a hotspot of 360 acres in 2008 and borders in 2009. In the final three years of the project (2010-11), monitoring indicated no need for NOW insecticides, and damage remained at about 1% or less.
Figure 2. Processor grade samples from the Nonpareil variety in the Santa Fe Areawide Project from 2002 through 2012. The project began in 2007 with a combination of insecticides + NOW MD and with increased monitoring efforts, reduced NOW insecticide use over the following two years, then managed NOW with MD (and sanitation) only over the final three years of the project.
One MD aerosol dispenser per acre was effective at low to moderate NOW populations (Higbee and Burks 2021).
Another interesting study conducted in the Lost Hills Project from 2008-11 was the comparison of aerosol mating disruption at two different dispenser densities, with or without insecticide, was compared to insecticide treatment alone. There were five treatments: 1) insecticide treatment without mating disruption; 2) one mating disruption dispenser per acre without insecticide; 3) one mating disruption dispenser per acre with insecticide; 4) two mating disruption dispensers per ac without insecticide; and 5) two mating disruption dispensers per acre with insecticide. The two replicates of the no-mating disruption insecticide treatment were placed adjacent to each other and rotated each year at either the north or south end of the site to minimize the effect of the mating disruption treatments on the insecticide only treatment blocks.
Final Thoughts
These projects demonstrated that with sufficient monitoring, NOW could be managed optimally over time with the possibility of eliminating insecticide use directed at NOW. The results solidified the viability of NOW MD as a management tool and provided information on how to monitor and interpret collected data to make management decisions. Although precise damage thresholds were not developed, a predictive model incorporating various trap data and early split evaluations was developed that explained over 50% of the variation observed in NP damage. While it is difficult to make precise predictions, the best predictors are a combination of 1) adult female captures in almond-meal baited traps during the 3rd flight, and 2) infestation of the early split nuts.
Certainly, additional work has and will be done to optimize MD systems. These include passive MD dispenser systems, additional attractants for use as monitoring tools, precise dispensing of the sex pheromone, and the impact of the addition of minor sex pheromone components to MD formulations on disruption of communication between male and female moths. As more research addresses how to use MD most efficiently, it should ease and increase the adoption of this technology.
If you ask tomato growers in the northern San Joaquin Valley what the most seen disease in 2021 is, beet curly top virus (BCTV) is the one that stands out. Undoubtedly, we have seen an exceptionally high incidence of BCTV on processing tomatoes vectored by the beet leafhopper (BLH). From April to July, most farm calls were about the curly top virus infestations in tomato fields in San Joaquin and Stanislaus counties. Not only in the northern San Joaquin Valley, similarly alarming reports also came from the southern San Joaquin and lower Sacramento Valleys. The unusually high incidence of BCTV in the Central Valley seems to be associated with drought, which likely has caused an earlier withering of the vegetations on the foothill that led to the earlier migration of BLH down the valley.
The Vector: Beet Leafhopper
BLH, Circulifer tenellus (Baker), has a typical leafhopper wedge-shaped body with tapering posterior. An adult BLH is approximately 1/8-inch long and has a distinct and broad head with a rounded anterior margin (Fig. 1). The adult BLH body color varies from olive green to light tan, with small dark-brown and black markings. Although BLH is believed to have originated in the Mediterranean region, its presence in North America has been reported for over a century ago. In the U.S., it is considered a serious pest of several crops in semi-arid and arid areas of the southeastern and western states, including Colorado, Washington, Oregon, Utah, Idaho, Arizona and California.
Figure 1. Beet leafhopper adult (source: G. Oldfield, USDA; bugwood.org.)
BLH has multiple generations per season, with up to five generations reported in California. BLH has numerous weed and crop hosts that are common in the Central Valley. Adult leafhoppers overwinter in the foothills. As the temperature warms up in February and March, the overwintered females lay eggs in various early weed hosts, such as pepperweed and desert Indian wheat in the foothills, and complete the first generation (and partial second generation in some years) before the vegetation dries. The first-generation nymphs acquire BCTV through direct feeding on the infected early season weed hosts, and the newly emerged virus-carrying adults migrate down to the valley.
The migrating adults feed or probe on summer weed hosts such as Russian thistle, London rocket, annual saltbush, goosefoot, lamb’s quarters, pepperweed, filaree, redroot pigweed, etc., and cultivated plants such as sugar beet, bean and tomato. Several leafhopper generations are produced before the maturity of the weeds or crop harvest. The leafhopper populations from the summer generations can transmit the curly top virus to the host crops, such as processing tomatoes, and produce disease. Unfortunately, there are no processing tomato commercial varieties that are resistant to BCTV. In 2021, due to unusually dry springtime, likely BLH migration to the valley occurred early, which might have contributed to the increased BLH abundance and curly top disease incidence in tomatoes.
Vector and Virus Interaction: Disease Transmission
BCTV is taxonomically in the genus of Curtovirus within the family of Geminiviridae, containing a single-stranded circular DNA. BCTV is currently known to be only vectored by BLH and has over 300 host plant species in the western U.S. The virus must be inoculated from diseased to healthy plants by BLH feeding. So, there is no risk of disease spread from one plant to another without the insect vector involved. The mechanism of virus transmission by BLH is called circulative persistence transmission.
The leafhopper ingests the virus from the phloem of the infected plant. The virus circulates through the insect blood (hemolymph) and finally reaches the insect’s salivary gland. When the insect feed on the healthy plant, the virus passes down to the healthy plant through saliva. The virus circulates within the insect body but does not multiply. The virus-infected BLH is an efficient vector and can transmit BCTV within a minute of feeding as it has a ready-to-go virus load in its salivary gland. On the other hand, once a healthy leafhopper picks up the virus from a diseased plant, it takes about four hours for that leafhopper to be infective (i.e., incubation period). Also, infected leafhoppers cannot transmit the virus through the egg to their progenies.
Figure 2. Diseased plants emerge in multiple rows (marked in yellow boxes) inside a processing tomato field. Note the western foothills in the background (photos by J. Rijal.)
Since BLH probe and feed on multiple hosts that appear in their flight path indiscriminately, the degree of disease incidence varies among tomato fields. Although it seems that field margins or isolated plants with exposed soils are more vulnerable, we did see clusters of infected plants in the middle of tomato fields (Fig. 2). Once fed and inoculated by BLH, tomato plants begin to exhibit purpling of veins and stunting within two weeks (Fig. 3). After infection with BCTV, younger plants usually die, while plants infected at a later stage may survive, but premature green fruits, if any, will turn red (Fig. 4). Regarding the yield loss, a field with a BCTV incidence below 5% may still reduce productivity if several diseased plants emerge next to each other in multiple rows (Fig. 5).
Figure 3. Tomato plants infected with BCTV exhibit purpling of veins and stunting (photo by Z. Wang.)
Field infestations over 10% are more likely to cause significant yield losses. CDFA has an active statewide control program by applying insecticide to the western foothills using a threshold (treatable if the sweep net sampling produced a minimum of eight BLH per sweep.) However, the sporadic occurrence of BCTV and likely presence of the population below the treatment threshold makes the control sometimes challenging as there might be a lot of areas left out without treatments due to the mild leafhopper populations based on that sweep net sampling. Eliminating host weeds before transplanting and during the season as well as delaying tomato planting are usually tried. Insecticide application to control the BLH population may reduce disease spread even though infested plants will not recover. More detailed information can be found at ipm.ucanr.edu/agriculture/tomato/Beet-Leafhopper/, ipm.ucanr.edu/agriculture/tomato/Curly-Top/, and cdfa.ca.gov/plant/IPC/curlytopvirus/ctv_weekly_reports.htm.
Figure 4. Premature fruit of a diseased plant turns red (photo by J. Rijal.)Figure 5. Single diseased plant is typically compensated by the healthy “neighbors” (top), while several infested plants in a row are likely to cause yield losses (bottom) (photos by Z. Wang.)
Collaborated Study with California Tomato Research Institute
With the California Tomato Research Institute (CTRI) funding support and in collaboration with the CDFA’s BCTV Control Program, we began a research project to monitor BLH population dynamics and BCTV incidence in processing tomato fields. To monitor BLH activity, we set up yellow sticky traps on 4-ft-tall metal posts at 10 different locations near 22 processing tomato fields along the highway-33 corridor in Stanislaus County (Figs. 6 and 7). The gross acreage of the monitored tomato fields is 2,180 acres. During the study, we replaced sticky traps biweekly and took sweep net samples monthly. By inspecting collected traps and sweep net samples, we submitted all suspicious BLH together with diseased tomato tissues to the CDFA-Integrated Pest Control and UC Davis for laboratory confirmation prior to estimating BLH population and BCTV incidence at each monitored location (Fig. 8). As fields are being harvested, we will work closely with growers to estimate the potential yield loss. Besides the 22 monitored fields, eight additional tomato fields which were not part of the study were also reported for BCTV infection by growers or their PCAs.
Figure 6. Locations of the 10 sites where yellow sticky traps were installed (LOC = Location).Figure 7. Yellow sticky traps were set up representing different locations with various vegetations near prospective processing tomato fields in March 2021 (photos by Z. Wang.)Figure 8. Suspicious BLH were sorted from sweep net and sticky trap samples and saved in vials filled with alcohol before submitting them for laboratory identification (photos by Z. Wang.)
Current results indicated that of all the 10 monitored sites (22 fields), six sites, including 14 tomato fields, were identified to have a BCTV incidence of 5% to 10%. The disease incidence levels of 0% to 5% and >10% were found in the remaining eight monitoring fields. For the additional infested fields reported by growers and PCAs, three, four, and one fields had estimated 0% to 5%, 5% to 10% and >10% BCTV, respectively. The complete results of this study will be reported later in the year.
Management practices to improve soil health, develop alternative water supplies and reduce water demand will be sought by team members with a goal of continued production of agriculture crops, including grapes, vegetables and almonds (photo by Julie R. Johnson.)
Climate change adaptation management strategies to ensure a future for irrigated agriculture are under development by a team of UC Davis researchers.
Isaya Kisekka, UC Davis professor in agrohydrology and irrigation, is leading the team of climate, plant and soil scientists, along with hydrologists, engineers and economists. They will work with groundwater sustainability agencies to develop tools and data to enhance water management at the farm and groundwater basins scales. The practices, models and tools developed could be used by growers, policy makers, irrigation districts, coalitions and GSAs to address effects of extreme climate events.
Part of the five-year project includes looking into aquifer systems in California’s Central Valley, central Arizona and the lower Rio Grande basin in New Mexico. These regions have all experienced unprecedented overdraft.
The negative effects of overdrafting groundwater basins, Kisekka said, is the lowering of groundwater levels, subsidence and deterioration of groundwater quality.
Management practices to improve soil health, develop alternative water supplies and reduce water demand will be sought by team members with a goal of continued production of agriculture crops, including grapes, vegetables and almonds.
The project team will also establish education and extension resources to inform the public about the importance of agriculture.
While the depletion of groundwater supplies, among other factors, puts major pressure on agricultural operations in the southwest region, Kisekka said he hopes the management practices and tools that will be developed during this project will help improve production and resource sustainability and make the region more resilient to climate change. UC Davis will establish the Agricultural Water Center of Excellence as part of the $10 million grant from the USDA’s National Institute of Food and Agriculture.
UC Davis’ Center for Excellence will also have the capacity to support agricultural water research, education and extension activities at collaborating institutions.
“We hope at the end of the day we can still grow food in California and the southwest in general without drying out our groundwater aquifers. We have to learn to adapt to climate change. We may not be able to stop it, but we can learn to adapt,” Kisekka said.
Researchers from UC Berkeley, UCANR, Stanford, CSU Fresno, University of Arizona, New Mexico State University, USDA-ARS and Water Management and Conservation Research in Maricopa, Ariz. along with the USDA Climate Hub are participants in this project.
Identification of weeds is necessary for weed management in tomatoes because it influences management decisions. UC IPM guidelines suggest twice-a-year weed surveys in each field after the crop is planted but before weeding and just before harvest (photo by A. Vinchesi-Vahl.)
Controlling weeds in processing tomato fields is vital to achieving good yields. Effective weed management involves crop rotation, field preparation, sanitation, irrigation management and use of effective herbicides.
In a UCCE webinar on IPM in vegetable crops, Farm Advisor Amber Vinchesi-Vahl also stressed the importance of several cultural practices, including field sanitation to prevent the spread of weeds and disease pathogens in fields.
Identification of weeds is necessary for weed management in tomatoes because it influences management decisions. UC IPM guidelines suggest twice-a-year weed surveys in each field after the crop is planted but before weeding and just before harvest.
Common weeds found in Sacramento Valley processing tomato fields are field bindweed, nightshades, nutsedge and broomrape. Broomrape, a root parasite, is a growing problem in California processing tomato production. At high densities, this weed can greatly reduce yields or result in crop failure. Branched broomrape is an “A-list” noxious weed by CDFA. Discovery of broomrape in a California tomato field leads to quarantine and crop destruction without harvest, resulting in significant economic loss to growers. Vinchesi-Vahl said the short-term goal with this weed is to minimize spread to other fields.
Crop rotations change the environment in a field, reducing weed pressure. Rotations into alfalfa, corn, wheat, cotton or rice are recommended. Rotation into potatoes, peppers or eggplant crops is not recommended. Other options for weed control in processing tomatoes include field sanitation, pre irrigation to germinate weed seeds, herbicide use and fumigation. Shifting planting dates to allow for weed germination is also helpful.
Although the use of transplants gives tomatoes a head start on weeds, pressure can mount during the growing season. Preventing weeds from going to seed, keeping canal banks free of weeds and avoiding moving weed seeds into fields on equipment can reduce weed pressure. Keeping bed tops dry with drip irrigation or using alternate furrow irrigation to prevent overly wet conditions are also good practices.
Vinchesi-Vahl said two in-row cultivator trials have been done to evaluate weed control, costs and time using mechanical cultivators. The trials in Colusa and Merced counties sought to compare in-row mechanical and robotic weeders to grower-standard practice and post-emergence herbicides. The Robovator, a robotic tool with automatic camera vision, provided good weed control, but also caused crop damage in the 2020 and 2021 trials. The finger weeder provided excellent weed control in 2020 and moderate control in 2021.
