Posts Tagged: strawberries
Strawberries, which generated $2.2 billion for California growers mainly on the coast in 2019, are sensitive to soilborne diseases. Strawberry plant roots infected by fungi are unable to take in nutrients and water, causing the leaves and stems to wilt. The diseases reduce fruit yields and eventually kill infected plants.
To protect the delicate plants from pathogens, strawberry growers fumigate the soil with pesticides such as chloropicrin and 1,3-dichloropropene before planting transplants. Due to the potential negative effects on the environment and human health, however, use of fumigants are highly regulated and developing non-fumigant alternatives has been a priority of the strawberry industry.
For a biological alternative to manage soilborne diseases in strawberries, Joji Muramoto, UC Cooperative Extension organic production specialist based at UC Santa Cruz, has received a $411,395 grant from USDA National Institute of Food and Agriculture to study the ability of other crops to suppress strawberry pathogens in the soil.
Verticillium wilt, caused by Verticillium dahliae, is a common soilborne disease that can be controlled with anaerobic soil disinfestation (ASD), a fermentation-based biological treatment using carbon sources such as rice bran under plastic mulch in moist soils for 3 to 5 weeks in autumn. About 2,000 acres of berry fields, mostly organic, were treated with ASD in California and Baja California, Mexico, in 2019.
In 2008-09, the diseases fusarium wilt, caused by Fusarium oxysporum f. sp. fragariae, and charcoal rot, caused by Macrophomina phaseolina, emerged in Southern California and now threaten strawberry plants throughout the state.
ASD isn't as effective against F. oxysporum and M. phaseolina unless it is applied in summer on the coast. As saprophytes, they feed not only on living plants, but also can colonize crop residues and rice bran especially at lower coastal temperatures in autumn. Treating fields on California's coast with ASD during summer is difficult because it competes with the vegetable production period.
Based on promising studies in Asia and other areas, Muramoto plans to test alliums – such as onion, bunch onion and leek – and a certain variety of wheat (Summit 515) to see if they will suppress F. oxysporum and M. phaseolina. His team will conduct a series of greenhouse and field trials and test these crops with and without ASD to compare the effects on soilborne pathogens.
“Studies have shown the potential of using allium crops to control Fusarium wilt, and Summit 515 wheat for charcoal rot,” Muramoto said. “Our goal is to examine the effectiveness of suppressive crops, optimize them for California strawberry production systems, and evaluate their economic feasibility for commercial use.”
“No single tactic is likely to replace fumigants,” he said. “Integration of multiple biological approaches such as crop rotation, ASD, and use of resistant strawberry varieties is a key to develop a successful non-fumigant-based soilborne disease management strategy for strawberries. This project is a part of such broader efforts.”
At the end of the three-year study, he plans to share the results at workshops, field days and webinars.
Rachael Goodhue, UC Davis professor of agricultural economics; Carol Shennan, UC Santa Cruz professor of environmental studies; and Peter Henry, USDA Agricultural Research Service plant pathologist, are co-principal investigators on the study with Muramoto.
Also collaborating on the project are Christopher Greer, UC Cooperative Extension integrated pest management area advisor in San Luis Obispo County; Oleg Daugovish, UCCE vegetable and strawberry advisor in Ventura County; Mark Bolda, UCCE director strawberry and cane berry advisor in Santa Cruz County; Jan Perez, food systems specialist, and Darryl Wong, farm research manager, at UC Santa Cruz Center for Agroecology and Sustainable Food Systems; Miguel Ramos of Ramos Farm; Agriculture and Land-Based Association (ALBA); Driscoll's; Naturipe; and The Oppenheimer Group.
Central Valley residents from Visalia to Sacramento look forward every year to the beginning of strawberry season in early April, when roadside strawberry stands operated by Hmong and Mien farmers open to the public.
These farms grow strawberry varieties such as Chandler and Camarosa that haven't traded flavor for shelf life – they don't ship or store well, but they are far sweeter than varieties usually sold in stores, and they reach their peak ripeness and flavor in the fields next to the strawberry stands.
As strawberry season opens this year, farmers are hoping that customers will still stop by the stands to pick up their fresh, seasonal strawberries, and also that they will observe 6-foot social distancing and other guidelines to reduce the spread of COVID-19. UC Cooperative Extension agricultural assistant Michael Yang and I were interviewed on a local news station to encourage Fresno residents to practice these guidelines while supporting local farmers.
To assist Fresno strawberry farmers, the UCCE small farms team in Fresno County developed, printed, and distributed signs for roadside strawberry stands reminding customers to observe social distancing and other safety practices, as well as guidelines for farm stands to reduce the spread of COVID-19. Versions of the signs were also developed for strawberry stands in Merced and Sacramento, as well as a general sign for local produce at any farm stand.
Signs and safety guidelines were printed with funding from the Western Extension Risk Management Education Center, and Michael Yang distributed large printed versions of the signs to all strawberry stands on the Fresno County Fruit Trail map in Fresno County. These materials have also been shared with UCCE small farms and food systems advisors as well as nonprofit and agency partners and county Agricultural Commissioner's offices, and they are available for printing on the UCCE Fresno strawberry website.
Slugs, snails, ants, aphids, spider mites and inclement weather conspire against strawberry growers harvesting perfect red berries to sell.
“Farming is hard work,” said Fam Lee, as she pulled a weed from a row of strawberry plants. Lee and her husband Nathan Punh are among about 60 Mien farmers in the Sacramento area who call on Margaret Lloyd, a UC Cooperative Extension advisor, for farming advice.
“Although we are not organic farmers, we always want to go with organic,” said Lee. “For example, we have slugs and ants, I asked Margaret if it's okay to put organic slug bait around the plant as long as it doesn't touch the berry. She said that's the best way to do. We work closely with our extension staff.”
In the Sacramento area, many of the Mien-owned farms are husband and wife teams. The typical couple farms an acre or two themselves, picking berries to sell the same day at a roadside stand, which provides the family's primary source of income.
“Many of them grew up on farms in Thailand or Laos growing vegetables or growing rice or soybeans,” said Lloyd, who serves small-scale farmers in Sacramento, Solano and Yolo counties. “A lot of them come from farming backgrounds so when they came to this country, they also sought out an agrarian lifestyle.”
Some Mien growers had never seen a strawberry before arriving in California, but chose the high-value crop to maximize returns on their small plots of land.
To help Mien growers develop successful strawberry farms, Lloyd updates them on regulations and shares growing tips at an annual extension meeting, visits them at their farms, and records videos demonstrating how to do things such as using compost to fertilize the crop.
“Because of language barriers, coming out to the farm regularly is a big part of the job,” said Lloyd, who partners with staff from the National Center for Appropriate Technology (NCAT) to assist Mien farmers.
“Once we're on the farm, we can communicate in-person more easily,” she said. “Often times it involves pest identification, so I'll show them how to use a hand lens and how to identify spider mites, aphids and lygus bugs, for example.”
“A lot of them have children who speak English fluently so if they don't speak English fluently, sometimes the children come out and help.”
For the past five years, Lee and Punh have been growing and selling strawberries at a farm stand on Bond Road, between Bader and Bradshaw, in Sacramento. They grow Albion, Chandler, Santa Rosa and Seascape – sweet, delicate varieties, some of which aren't found in supermarkets because the berries don't store and ship as well. They typically begin harvesting berries at the end of March and pick through July or August, depending on the weather. This year, the first berries were ruined by spring rain and frost.
Savvy consumers will ask for certain varieties by name, Lloyd said. “Chandler is well-loved by consumers for its delicate flesh and sweet flavor. Albion produces larger berries that are also very tasty.”
Because berries sold at the roadside stands are picked fresh daily, the farmers wait until berries are perfectly ripe before picking them.
Monday through Saturday, Lee begins harvesting her strawberries by hand at the break of dawn.
“We start at 5:45, the minute we can see, and we pick until 8 o'clock. That's our goal,” Lee said. “By 8:30, we want to open our stand and we sell until all the berries run out.”
Lee's parents often drive up from Alameda to help pick berries.
To extend the farm stand season, some Mien farmers supplement the strawberries with other berries, strawberry jam and vegetables. They grow blueberries and blackberries, tomatoes, peppers and green beans and sometimes specialty vegetables such as bittermelon.
“Growing strawberries isn't easy, but it's enjoyable work,” Lee said.
Lloyd has updated a map showing locations of about 60 strawberry stands in the Sacramento area at http://bit.ly/strawberrystands.
Micro-sprinklers in strawberries. Photo by Surendra Dara
Strawberry is an important commercial crop in California primarily grown on the Central Coast in Watsonville, Santa Maria, and Oxnard production areas. Strawberry crop requires 24-29” of irrigation water for a typical production season based on fall plantings. Irrigation is primarily administered through drip tapes installed under plastic mulch during bed preparation. In addition to the drip irrigation throughout the crop life, supplemental irrigation through overhead aluminum sprinklers is administered during the first few weeks after transplanting. Overhead irrigation is practiced to leach out salts from the root zone and to support the establishment of new transplants. Strawberries are sensitive to salinity and this supplemental irrigation is believed to reduce or prevent salt injury. In the Oxnard area, overhead aluminum sprinkler irrigation is considered very important to prevent dry conditions which could result from Santa Ana winds. However, overhead aluminum sprinkler irrigation requires a significant amount of water and can be an inefficient system. Evaporation, limited surface area for water penetration due to plastic mulch on the beds, and potential run off are some of the disadvantages associated with this overhead sprinkler system.
Water is an important resource for growing plants and it has become scarce due to epic drought conditions in California. Conserving water through improved irrigation practices is a critical area for maintaining acreage of a lucrative commodity such as strawberry. Micro-sprinklers, which are commonly used in orchard systems could offer an efficient alternative to conventional aluminum sprinklers. Micro-sprinklers, established on strawberry beds, can deliver water in a more targeted manner with minimum or no run off. They could also help modify the microclimate in the strawberry canopy and create humid conditions that discourage spider mite pest populations and promote predatory mites which are sensitive to dry conditions.
A study was conducted at Manzanita Berry Farms in Santa Maria during 2014-2015 production season to evaluate the potential of micro-sprinklers in strawberry production. Objectives of this study included i) conservation of irrigation resources without affecting strawberry plant growth and fruit yield, ii) impact on pest and predatory mite populations, and iii) impact on powdery mildew and botrytis fruit rot.
A block of strawberry (variety BG-6.3024 planted on 6 November, 2014) was divided into two parts with beds aligned from south to north direction. The west half of the block was assigned for micro-sprinklers and the east half for the grower standard with aluminum sprinklers. Each block had about 60 beds (about 306-365' long) and aluminum sprinklers were established in furrows every 40' (7-8 beds in between) while micro-sprinklers were established on every third bed. Micro-sprinklers were placed 16' apart (on every fourth bed) and had a 15' spacing within a bed. Within each treatment section six 20' long plots were marked to measure plant, pest, and disease parameters.
Installing micro-sprinkler system (Field crew at Manzanita Berry Farms, Santa Maria)
Micro-sprinkler (left) and grower standard with aluminum sprinklers (right) sections of the field
Data collection and results
Irrigation – Conventional sprinkler irrigation was made 14 times from 6 to 29 November, 2015 at a rate of 125 gallons per minute while micro-sprinkler irrigation was made 1-3 day interval at a rate of 40 gallons per minute using 35 PSI pressure. During this period, aluminum sprinklers delivered 120,000 gallons of water over 16 hours of total irrigation while micro-sprinklers delivered 81,600 over 34 hours of total irrigation. This translates to 32% of water saving in just 3 weeks and could be more in situations where overhead irrigation is administered for extended periods. Micro-sprinkler irrigation was continued for 15 min twice a week for the rest of the production period. Distribution uniformity could not be measured in grower standard treatment in this study, but it is believed to be between 50-60% at 70 PSI based on other studies. Distribution uniformity for the micro-sprinklers was 74% at 35 PSI when measured on 16 January, 2015. When electrical conductivity (EC) was measured on January 1 and February 1, 2015, it varied between 0.47 and 0.49 dS/m in grower standard treatment and was at 0.54 dS/m in micro-sprinkler treatment. Although EC in micro-sprinkler plots was significantly higher (P < 0.0007) than in grower standard plots, it was within the safe limit of 0.7 dS/m.
Cumulative volume of water delivered in micro-sprinkler and grower standard sections of the field. There was a saving of 38,400 gallons per acre in just about three weeks.
Yield – Total and marketable berry yield data were collected 2-3 times a week between 7 February and 12 June, 2015 for a total of 34 sampling dates. There was no significant difference in total or marketable berries (P > 0.05) when the seasonal averages for grower standard and micro-sprinkler plots were compared. During the observation period, 44,322 gr (97.7 lb) and 43,452 gr (95.8 lb) of marketable berries/plot were produced in grower standard and micro-sprinkler treatments, respectively.
Plots were covered with netting for exclusive harvest data collection.
Marketable berry yields per plot in micro-sprinkler and grower standard sections from February to June, 2015
Total strawberry yields (marketable and unmarketable) per plot during the study period.
Plant canopy and health– Growth was recorded by measuring the width of the plant canopy across and along the bed from 20 random plants per plot on the 6th of each month from January to March, 2015. Plant health was monitored at the same time by on a scale of 0 to 5 where 0 = dead, 1 = weak, 2 = moderate-low, 3 = moderate-high, 4 = good, and 5 = very good. Plants in micro-sprinkler treatment had significantly smaller canopy in January (P = 0.004) and February (P =0.0006), but caught up with the grower standard by March (P = 0.14). Plant health rating during this period also followed a similar trend, but the differences were significant only in February (P = 0.02).
Size of the plant canopy and plant health condition from January to March, 2015.
Both micro-sprinkler and grower standard plants look equally healthy and productive (Photo taken on 26 May, 2015)
Twospotted spider mite and predatory mite – One mid-tier leaflet was sampled from each of the 10 random plants within each plot and the number of eggs, nymphs, adult pest and predatory mites were counted using a mite brushing machine. Sampling was made once a month from February to April, 2015, but due to sparse numbers and uneven distribution useful data could not be obtained.
Powdery mildew– One trifoliate leaf from 20 random plants within each plot were collected and checked under microscope for mycelial growth and powdery mildew severity was rated on a 0 to 4 scale where 0 = absent, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, and 4 = 76-100% of leaf area with infection. Sampling was made on 15 April and 16 and 24 June, 2015. Powdery mildew severity was significantly less in micro-sprinkler treatment on 15 April (P = 0.009) and June 24 (P = 0.01).
Severity of powdery mildew on three observation dates.
Botrytis fruit rot – Berries harvested from each plot were kept at room temperature in plastic clamshell boxes and disease severity was measured 3 and 5 days after harvest using the 0 to 4 scale used for powdery mildew. Observations were made on 26 March, 13 April, 22 May, and 16 June, 2015. In general, botrytis fruit was less severe in micro-sprinkler treatment, but significant difference were seen 3 days after harvest for samples collected on 22 May and 16 June (P = 0.02).
Severity of botrytis fruit rot when observations were taken 3 and 5 days after harvest.
Micro-sprinkler system contributed to a significant reduction in overhead irrigation water without affecting the marketable berry yield. With less pressure required to deliver water through micro-sprinklers, they could also contribute to energy savings. EC value of below 0.7 dS/m suggests that micro-sprinklers were as effective as aluminum sprinklers in leaching out salts. Due to the lack of sufficient mite infestations, the benefit of micro-sprinklers in spider mite management could not be determined. Data also suggest that powdery mildew and botrytis fruit rot could be reduced by micro-sprinklers, but additional studies are required to confirm these preliminary observations. An initial estimate by the vendor suggests that equipment and handling costs of the micro-sprinklers are more or less similar to those of the aluminum sprinklers.
Chris Martinez and rest of the field crew, Manzanita Berry Farms, Santa Maria after transplanting
Acknowledgements: Thanks to Dave Peck, Manzanita Berry Farms for his collaboration, Chris Martinez for his field assistance, Manzanita field crew for help with planting, irrigation, and yield data collection, Danilu Ramirez, Fritz Light, and Tamas Zold for their technical assistance, and RDO Water and Netafim for partial funding of the study.
Dara. S. K. 2012. Salt injury in strawberries. UCCE eNewsletter, Strawberries and Vegetables. //ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=6820
Efficacy of botanical, chemical, and microbial pesticides on twospotted spider mites and their impact on predatory mites
Twospotted spider mite, Tetranychus urticae Koch is a major pest of strawberries in California. Spider mite damage reduces plant vigor and contributes to yield loss. Twospotted spider mites are typically found on the lower side of the leaf and form webbing at higher population levels.
Damage: Spider mites cause damage by puncturing the epidermis with their mouthparts and sucking the plant juices. Death of plant cells appears as yellow mottling during initial stages and as feeding continues, damaged areas coalesce and result in scarring, bronzing, and drying out of leaf tissue. This reduces the photosynthetic ability of the plant and thus its growth and vigor. If left uncontrolled, damage leads to stunted plant growth or eventual death. Damage symptoms are unique in Benicia variety where upper leaf surface corresponding to spider mite feeding on the lower side, shows purplish coloration.
Yellowing, scarring, bronzing, and drying of infested foliage and stunting of plants. (Photo by Surendra Dara)
Biology: Life cycle includes egg, larva, protonymph, deutonymph, and adult stages. Females lay an average of 100 eggs in 10 days. Eggs are round, initially translucent and turn whitish as they mature. Larvae have three pairs of legs and nymphal stages have four pairs of legs. Males are wedge-shaped and about 0.3 mm long. Females are oval, 0.4-0.5 long, and have a single dark spot on either side of their body. At 85-90 oF, life cycle can be completed in 7-8 days.
Life stages of twospotted spider mite (Photo by Surendra Dara)
Management: Growers typically rely on biological and chemical control options for managing twospotted spider mites in strawberries. Type I specialist Phytoseiulus persimilis Athias-Henriot, Type II specialists Neoseiulus fallacis (Garmin), N. californicus (McGregor), Galendromus occidentalis (Nesbitt), and Type III generalist Amblyseius andersoni (Chant) are common predatory mites that attack twospotted spider mites. Releasing one or more species of predatory mites is a popular practice in strawberry production. Abamectin, acequinocyl, bifenazate, etoxazole, fenbutatin-oxide, fenpyroximate, hexythiazox, and spiromesifen are the most commonly used chemical miticides according to pesticide use reports of the California Department of Pesticide Regulation. Chemical miticide use shows a 2% increase in the Watsonville-Salinas area, an 82% increase in the Santa Maria area, and a 125% increase in the Oxnard areas from 2009 to 2013. There is a continued need for identifying effective chemical and non-chemical miticides to manage twospotted spider mite in strawberries.
A small plot field study was conducted in 2013 at Manzanita Berry Farms in Santa Maria to evaluate the efficacy of various botanical, chemical, and microbial pesticides. Treatments included bifenazate (Acramite 50 WS at 1 lb/ac), abamectin (Agri-Mek SC at 4.29 fl oz/ac), entomopathogenic fungus Beauveria bassiana (BotaniGard ES at a lower label rate of 1 qrt/ac) + bifenazate (Acramite 50 WS at the lowest label rate of 0.75 lb/ac), rosemary and cotton seed oil (Eco-Mite at 1% concentration), fenpyroximate (Fujimite 5 EC at 2 pt/ac), fenpyroximate (Fujimite XLO at 2 pt/ac), Chromobacterium subtsugae strain PRAA4-1 (Grandevo at 2 lb/ac), Burkholderia sp. strain A396 (Venerate XC at 2 gal/ac), and cyflumetofen (Nealta SC at 13.7 fl oz/ac). A spray volume of 150 gal/acre was used with 0.25% non-ionic surfactant except for the treatment with B. bassiana, where an organo-silicon surfactant was used. Each treatment had a 15' long strawberry bed and treatments were replicated in randomized complete block design. Treatments were applied using a CO2 pressurized backpack sprayer twice at weekly intervals and eggs and mobile stages of twospotted spider mites and predatory mites were sampled 3 and 7 days after each application. On each sampling date, 10 mid-tier leaflets were collected from 10 random plants within each plot and mites were collected using a mite brushing machine and counted under microscope. Data were analyzed using analysis of variance and significant means were separated using Tukey's HSD test.
Pre-treatment counts were not available due to a technical issue, so comparisons were made for pest and predatory mite counts after each spray application and the post-treatment period as a whole. Compared to untreated control, treated plots had fewer spider mites throughout the observation period, but the pest suppression was not statistically significant (P > 0.05, Table 1). When the percent reduction in treatments relative to untreated control was compared, rosemary+cotton seed oil, fenpyroximate EC, and B. bassiana+bifenzate had relatively higher reduction in mobile stages while Burkholderia sp., rosemary+cotton seed oil, and cyflumetofen had a higher reduction in eggs after the first spray application (Fig. 1A). Reduction in mobile stages following the second spray was the highest in cyflumetofen followed by bifenzate, rosemary+cotton seed oil, fenpyroximate XLO, and EC (Fig. 1B). After the second spray, the highest reduction in eggs was seen in fenpyroximate EC followed by Burkholderia sp., cyflumetofen, rosemary+cotton seed oil, and B. bassiana+bifenzate. In general, rosemary+cotton seed oil treatment did a better job of reducing egg and mobile stages after both applications followed by Burkholderia sp., cyflumetofen, and fenpyroximate EC (Fig. 1C).
Table 1. Number of eggs or mobile stages (mean+SE) of twospotted spider mite 3 and 7 days after first and second spray treatment along with post-treatment average.
Fig. 1. Percent reduction in eggs and mobile stages of twospotted spider mites in different treatments compared to untreated control after first (A), second (B), and both spray applications (C).
There were no statistically significant differences in predatory mite populations among treatments except in mobile numbers on 7 days after the first spray (P = 0.0046, Table 2). Plots that were treated with Burkholderia sp. and cyflumetofen had a relatively higher number of predatory mites and bifenzate and abamectin had lower numbers, in general.
Table 2. Number of eggs or mobile stages (mean+SE) of predatory mites 3 and 7 days after first and second spray treatment along with post-treatment average.
Although treatment differences were not statistically significant, this study demonstrates the efficacy of various botanical, chemical, and microbial pesticides against twospotted spider mites and their safety to predatory mites. Results show the potential of non-chemical alternatives, which can be used in rotation with chemical pesticides for a sound IPM program.
General IPM recommendations:
- Obtain transplants from a clean source to avoid early spider mite infestations, which could lead to season long problems in production fields.
- Periodically scout the fields to evaluate infestation levels and make appropriate management decisions.
- Rotate chemicals among different modes of action groups and consider botanical and microbial control options to reduce the risk of resistance development.
- Understand the dietary preferences and environmental requirements of different species of predatory mites and release the right species appropriate for the situation.
- Avoid water stress for plants as spider mites thrive when plants are under stress.
- Excessive nitrogen fertilization encourages spider mite population build up, so optimize fertilizer input.
Acknowledgments: Thanks to Dave Peck, Manzanita Berry Farms, Santa Maria for his collaboration, pesticide industry partners for the financial support, and Sumanth and Suchitra Dara for their technical assistance with mite brushing.
Blecker, S. 2015. Pesticide use trends in strawberries. Presentation at Santa Maria Strawberry Field Day. http://cesantabarbara.ucanr.edu/files/213517.pdf
Dara, S. K. 2014. Managing spider mites in California strawberries. UCCE eNewsletter Strawberries and Vegetables. //ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13943
Dara, S. K. 2014. Predatory mites for managing spider mites on strawberries. UCCE eNewsletter Strawberries and Vegetables. //ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=14065
Hoffland, E., M. Dicke, W. V. Tintelen, H. Dijkman, and M.L.V. Beusichem. 2000. Nitrogen availability and defense of tomato against two-spotted spider mite. J. Chemical Ecol. 26: 2697-2711.