Developing sustainable strategies for nutrient and pest management on small-acreage strawberry farms

Progress report for SW21-923

Project Type: Research and Education
Funds awarded in 2021: $349,736.00
Projected End Date: 03/31/2024
Host Institution Award ID: G313-21-W8612
Grant Recipient: Utah State University
Region: Western
State: Utah
Principal Investigator:
Dr. Jennifer Reeve
Utah State University
Co-Investigators:
Dr. Brent Black
Utah State University
Dr. Kynda Curtis
Utah State University
Dr. Robert Schaeffer
Utah State University
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Project Information

Summary:

Local strawberries are in high demand throughout the Intermountain West, but outdoor production to meet demand is risky due to late frosts which threaten yields. Previous research at Utah State University (USU) has shown that high tunnel strawberry production could potentially meet consumer demand and be highly profitable when compared to outdoor or low tunnel production. Despite grower interest, adoption of high tunnel strawberry production in the West is low due to uncertainties over cultivar performance and best management practices for soil fertility and diseases using organic methods. High tunnel growing conditions can promote grey mold (Botrytis cinerea) and powdery mildew (Podosphaera aphanis) epidemics, requiring weekly fungicide application, a practice that is not sustainable for small scale growers using organic or natural growing methods.

Compost is a cost-effective organic fertilizer with potential for enhancing disease suppression but yield response can vary due to challenges associated with predicting nutrient release and plant uptake, which often translates to growers over applying or eschewing the use of compost altogether. Indeed, our preliminary research has shown considerable variability in growth and nitrogen (N) uptake among strawberry cultivars when grown on slow-release organic sources of N like composts. Compost-mediated resistance can also be complemented through use of microbial biological control agents (mBCAs), which can be directly applied by growers or transferred to flowers by pollinators such as bumblebees. While strawberries are self-pollinating, pollinators and their foraging activity can have synergistic effects on grower outcomes through increasing berry size and yields, and by vectoring mBCAs.

This project will improve management options for sustainable strawberry production by harnessing synergies between season extension, cultivar identity, nutrient uptake on compost, and disease suppression by addressing the following objectives: 1) assess strawberry cultivars for nutrient uptake and growth on less readily available organic nutrient sources, 2) assess how mBCA effectiveness, both singly and in mixtures, varies with strawberry cultivar and compost use 3) evaluate use of bumblebee pollinators to enhance biological control and yield 4) assess market value and consumer preference for local strawberries, 5) improve grower and student understanding of high tunnel strawberry production through on-farm trials field days, training events, the development of new online resources and course material. The most promising cultivar/management combinations will be tested and showcased on five commercial farms, with results published in factsheets and videos. This research is unique in that it explores innovative and sustainable ways to solve common production problems. Recent data published by the National Agriculture Statistics Service shows strawberries are among the top selling organic crops. With improved management options, local farms could meet consumer demand, bolster local economies, and improve environmental impacts. The information generated will help growers to potentially transform their production systems, reduce or eliminate reliance on toxic chemicals, improve nutrient management and soil health, and meet market demand for local, sustainably produced strawberries.

Project Objectives:

The long-term goal of this project is to increase the production of strawberries for local markets, improve soil nutrient and disease management, and reduce reliance on purchased inputs through addressing the following specific, short-term objectives: 1) assess cultivars for nutrient uptake and growth on less readily available organic nutrient sources such as compost, 2) assess how mBCA effectiveness, both singly and in mixtures, varies with strawberry cultivar and compost use 3) explore the use of bee pollinators to enhance biological control and yield and 4) assess market value and customer preferences for local strawberries grown under various production schemes and 5) Improve grower and student understanding of high tunnel strawberry production through on-farm trials, field days, training events, the development of new online resources and course material.  Initial selection of cultivars and mBCAs occurred in the greenhouse and laboratory in year one, with a subset field tested at the USU Student Organic Farm in years one through three. The most promising cultivar and management combinations will be tested and demonstrated on five commercial farms in years two and three. Five commercial growers and one student farm manager will advise the project through twice yearly meetings throughout. Results will be showcased in Utah and five neighboring states through on-farm tours and workshops, and published in factsheets, videos, and peer-reviewed publications

Timeline:

If funded, we will begin screening cultivars in the greenhouse in April 2021 in time for plug plant production in July 2021. The first trials will be planted in early September 2021 and harvested in the spring of 2022. The second trials will commence in early April 2022 for harvest in the late summer and fall of 2022. A second round of trials will commence on the same schedule but starting in the fall of 2022 and spring of 2023.

Amino acid uptake measurements and mBCA leaf bioassays will commence in the fall of 2021 and will be completed within a year. Bumblebee trials will commence in the spring and late summer of 2022 to coincide with blossom and fruit set. A second round of bumblebee trials will commence in the spring and late summer of 2023. Economic field experiments will take place in 2022.

Grower advisory meetings will be held in October and March of each year. A high tunnel construction workshop will be held on the USU Student Organic Farm in August 2021. Five additional high tunnel construction and strawberry management workshops will be held in neighboring states in years two and three. Field days will be held in April or May in years two and three of the project. Post-program evaluations will be conducted on site or online directly after all field days, workshops etc. Follow-up surveys to asses producer adoption will be conducted one and two years after each program.

Data on yields, input costs and revenue will be collected from grower participants during each spring or fall planted trial. Data will be used to update an existing peer reviewed strawberry production budgets in the final year of the project. Outreach and journal articles will also be finalized in the final year of the project.Gantt chart

Cooperators

Click linked name(s) to expand/collapse or show everyone's info
  • Todd Burrows - Producer
  • Mark Cowley - Technical Advisor - Producer (Educator)
  • McKenzie Israelsen - Technical Advisor - Producer
  • Sara Patterson - Technical Advisor - Producer
  • Luke Petersen - Technical Advisor - Producer
  • Nate Stireman - Producer
  • Andrea Morgan - Producer
  • Merv Weeks - Producer

Research

Hypothesis:

We hypothesize that there is a positive relationship between growth and amino acid uptake on compost in the greenhouse and growth and productivity on compost in the field.

We hypothesize that more diverse mBCA treatments will be more effective at preventing disease than those that are less diverse and that strawberry plants grown on compost will be most responsive to mBCA treatment.

We hypothesize that use of bumble bees in high tunnels will have synergistic effects on strawberry health and yield quality.

Materials and methods:

Objective 1) Assess strawberry cultivars for nutrient uptake and growth on less readily available organic nutrient sources such as composts.

(i) Rationale and Hypotheses. We built on preliminary data already collected that suggests strawberry cultivars show considerable variability in growth on slow-release organic sources of N like compost (Figure 1; Reeve et al. 2017) and take up organic molecules such as amino acids directly (Reeve et al. 2008). We have been using greenhouse trials to select strawberries with extreme differences in growth on compost and confirm these results in high tunnels. We hypothesize that there is a positive relationship between growth and amino acid uptake on compost in the greenhouse and growth and productivity on compost in the field.

Strawberry data

Figure 1. Tissue nitrogen (N; percent), shoot dry weight, N use efficiency (NUE) and leaf chlorophyll in strawberry cultivars grown on compost with N-free vs complete nutrient solution. The line shows the 1:1 relationship between strawberry parameters grown on compost vs. complete nutrient solution. Points significantly above the line indicate cultivars that are more efficient at obtaining N from compost than from mineral sources.

(ii) Approach. Twenty-nine commercial cultivars were obtained from nurseries (e.g. Nourse Farms, Whately, MA) and propagated according to Rowley (2010). Best and worst performers (as controls to test relationship between N uptake and performance in the field) from preliminary trials (Figure 1) were included. The most divergent cultivars were planted in high tunnels at the Student Organic Farm and four commercial farms (see below). Plug plants were grown with and without compost (Millers Inc, Hyrum UT) in 6” pots with 4 reps and analyzed in a completely randomized design with two treatments (cultivar, with/without compost). Compost treated plants were irrigated with N-free fertilizer, while control plants received regular soluble fertilizer. N mineralization was estimated in pots without plants maintained at field capacity with N-free fertilizer. All pots were leached four times over the course of the experiment with 300 ml water with leachate collected and analyzed for nitrate and ammonium (Lachat Instruments, Loveland CO). Leaf chlorophyll measurements were taken at the start and end of the experiment using a chlorophyll meter (Apogee Instruments, Logan UT). Plants were harvested after nine weeks, shoots and crown separated, and wet/dry weight and tissue N recorded. Amino acid uptake will be measured on eight best and worst performing cultivars on compost according to Reeve et al. (2008). Briefly, C14 labelled glycine and N15 labelled nitrate and ammonium are added to soil containing a rooted strawberry plant. The surface of the soil is sealed with wax to prevent atmospheric uptake and the plants placed in a vented manifold system. Glycine, nitrate, and ammonium uptake are determined after 24 hours.

Fall and spring plantings of strawberries grown with compost alone (Millers Inc, Hyrum UT) vs compost + soluble N fertilizer (fish emulsion on organic farms) were established on the USU Student Organic Farm and a total of six commercial farms in August/Sept 2021 and Feb/March 2022 and will be repeated in years two and three of the project. At the student farm, one 70 x 14ft tunnel was dedicated to fall and one to spring production and on farm trials were sized according to grower interest and available space. Eleven compost/cultivar treatment combinations (3ft. of bed per treatment with 12 plants per plot) with three replicate plots were established per high tunnel. Best performers selected in greenhouse trials as well as Chandler and Seascape that are expected to be poor were included to test the relationship between growth on compost and performance in the field. Optimum planting dates of September 1st for spring harvested berries and Feb 15th for fall harvested berries have been identified for a limited number of varieties. The on-farm fall plantings included two additional planting dates to optimize planting dates for a wider selection of locations and cultivars. Fertilizer was applied based on industry recommendations as a split plot at four locations.

Total and marketable berry yield, fruit size, plant growth, leaf chlorophyll, leaf N content and disease incidence will be measured. Soil health indicators (organic matter, microbial biomass, available soil nutrients, pH and EC) will be assessed each year at planting at 0-30 cm according to Gavlak (2003) and Anderson and Domsch (1978). Data from fall and spring plantings will be analyzed separately using a random complete block design with two factors (cultivar and compost) with harvest time as repeated measure. Additional replicated trials will be located on seven commercial farms using locally available compost. While it is anticipated that the data collected on these trials will also be of sufficient quality to support research and extension publications, the primary goal of the on-farm research is the hands-on training of early adopter growers and to facilitate robust economic analysis. The number of treatments deployed per site will depend on the space growers devote to the project, and on the objectives that best fit their farm operation (ex. spring vs. fall production system).

Objective 2) Assess how mBCA effectiveness, both singly and in mixtures, varies with strawberry cultivar and compost use.

(i) Rationale and Hypotheses. Application of mBCAs represents a sustainable alternative for disease control. To date, a handful of mBCAs have been screened for use in limiting powdery mildew (Podosphaera aphanis) and grey mold (Botrytis cinerea) development in strawberry (Sylla et al. 2013). Though single and paired species mBCA treatments demonstrate promise, they remain subpar to fungicides (Pertot et al. 2008; Silla et al. 2013). Increasingly, it is recognized that a positive relationship exists between microbial community diversity and resistance to pathogen invasion (Santhanam et al. 2015). Thus, we hypothesize that more diverse mBCA treatments will be more effective at preventing disease than those that are less diverse and that strawberry plants grown on compost will be most responsive to mBCA treatment.

(ii) Approach. mBCA treatments [single, paired, or consortia (i.e., three species)] were tested for their efficacy against mildew and mold. The subset of best and worst performing cultivars identified in Obj. 1 were used for this assay, grown on and off compost. To test efficacy, we used a detached strawberry leaf disc bioassay, following Sylla et al. (2013). Briefly, leaf discs (1 cm diameter, N = 30 per mBCA treatment and cultivar/soil combination) were sourced from plug plants, grown as above, and treated with mBCA suspensions (~1 × 107 CFU ml−1). The Control treatment consisted of leaf discs dipped in sterile Ringer solution. Treated discs were incubated at 25°C (65% RH), with an alternating 12 hr. light/dark photoperiod. After 24 hr., leaf discs were inoculated with P. aphanis or B. cinerea conidia and incubated to allow for pathogen development. Leaf discs were processed to determine levels of conidia production, using microscopy and a Thoma counting chamber to determine the number of conidia per cm2 of leaf. The following mBCAs were tested: Aureobasidium pullulans, Bacillus subtilis, Metarhizium anisopliae and Streptomyces globisporus. These species were chosen as they have demonstrated potential for suppressing mold and mildew (Sylla et al. 2013; Kim et al. 2019), are effectively dispersed by pollinators (Dedej et al. 2004; Kapongo et al. 2008; Russell et al. 2019), and to a degree (a subset of listed species), are commercially available to growers. mBCA treatments include the following possible species compositions (14 total: four one-species communities, six two-species communities and four three-species communities) drawn from the four-species pool. These in-vitro assays will be used to inform cultivar and mBCA treatments for field trials (Obj. 3).  

Objective 3) Evaluate use of bee pollinators to enhance biological control and yield.

(i) Rationale and Hypotheses. Cross-pollination can significantly enhance strawberry yields, fruit quality, shelf-life, and commercial value (Klatt et al. 2014; Wietzke et al. 2018; MacInnis and Forrest 2019). Moreover, pollinators (e.g., bumble bees) naturally disperse microbes among flowers and can vector with considerable success (Yu and Sutton 1997; Kapongo et al. 2008; Russell et al. 2019). We hypothesize that use of bumble bees in high tunnels will have synergistic effects on strawberry health and yield quality.

(ii) Approach. Assessment of bee effectiveness for biocontrol, yield enhancement, and how this varies with soil background, will be tested through cage trials, performed in two high tunnels at the USU Student Organic Farm in years 2 and 3 of the project. Commercial bumble bee colonies (Bombus impatiens, Biobest Group) will be obtained and fitted with an mBCA inoculum dispenser (Yu and Sutton 1997; Al-mazra’awi 2004). Each cage (i.e., treatment) will contain 32 strawberry plants. The RCBD experiment will be replicated 4 times. Treatments will consist of control treatment with neither inoculum nor bees, mBCA inoculum sprayed alone, bees alone, and mBCA inoculum + bees. Cultivar performance data (Obj. 1), plus results from Obj. 2, will inform the identity of mBCA/cultivar combination tested initially. Half of the plants will be treated with either control or compost-amended soil as in Obj. 1.

After establishing caged arrays, we will introduce colonies to allow for bee foraging and dispersal of mBCA inoculum. Following a three-day period of bee activity, flowers and leaves of eight randomly selected plants per soil treatment will be artificially inoculated with either mildew or mold conidia. After six days, leaf and flower samples will be harvested for disease assessment, with mBCA dispenser removed from colonies. After each tissue-sampling, remaining inoculum will be dried and weighed to determine the amount delivered. Finally, we will assess fruit yield and quality by measuring fruit production, mass, shape (length:diameter ratio), soluble solids, titratable acidity and total phenolic compounds.

Objective 4) Assess market value and consumer preference for local strawberries.

One project graduate student will work with growers starting in year two to collect information to revise and update previously-published cost of production budgets (Maughan et al., 2014). Pricing estimates will be based on current local pricing of strawberry cultivars produced collected from the USU farmers’ market and dining outlets (e.g., Luke’s Café), the Cache Valley Gardeners Market, Ogden and Salt Lake City farmers markets and also through interviews with local chefs and retail outlets. Cost estimates will be based on inputs used during study trials and those provided by local vendors. Cost of production budgets will be used to educate growers on production and marketing methods at Extension field days, workshops, webinars, and online. These budgets provide growers will good estimates of the potential profitability (by cultivar and production methods) of strawberries under reduced chemical and organic production systems, thus enabling growers to better assess and adopt study recommendations.

Consumer preferences and willingness to pay for successful strawberry cultivars and production systems will be evaluated through economic field experiments conducted with Northern Utah residents. Experiments will include blind sensory analysis of strawberry cultivars followed by a survey including choice sets to determine consumer preferences and willingness-to-pay (WTP) based on strawberry product pricing, strawberry sensory and production attributes, as well as consumer psychographics and demographics (Barnes et al. 2014; Bosworth et al. 2015; Drugova et al. 2020). Field experiments will be conducted at farmers’ markets (Logan, Ogden, and Salt Lake City), the USU campus, and local retail outlets. Market viability studies such as these are an important part of understanding consumer interest in new products/production methods such that product pricing, attributes, sales venues, and promotional messages are appropriate for the target market(s), which are also identified through this analysis. A study on consumer interest and WTP for eco-friendly and organic peaches found that reduced chemical and eco-friendly production methods are valued by consumers in Northern Utah (Curtis et al., 2020).

 

Research results and discussion:

 

Objective 1) Assess strawberry cultivars for nutrient uptake and growth on less readily available organic nutrient sources such as composts

The growth of twenty-nine commercial strawberry cultivars were compared on compost versus commercial fertilizer in the greenhouse. Many of the cultivars of interest were already sold out for the season by the time funding was awarded for this project so we based our initial selection on availability. As with our preliminary findings considerable variation in growth on compost between cultivars was found Fig. 2). There was broad agreement between the results of our preliminary trials and follow-up trials with more vigorous plants producing more biomass in both sets of trials. Unlike previous trials however, all cultivars performed much worse on compost which may be attributed to year-to-year variability in the compost used. The exception was Monterey but given that very little growth occurred on conventional fertilizer for this cultivar, this is likely an anomaly. Given this and the fact that many of the cultivars we were interested in were already sold out at the commencement of the study in spring of 2021, we decided to conduct a second round of greenhouse trials in the fall of 2022. Amino acid uptake experiments will be delayed until after the second round of greenhouse trials have been completed.

Fig. 2.  Change in biomass between initial and final plant weights when grown on conventional fertilizer vs. compost. Unlike previous experiments all cultivars performed much worse on compost than conventional fertilizer. We attribute this to differences in compost quality.

Sub-selections of the 29 cultivars were planted in high tunnels at the USU student Organic Farm and six commercial farms in August and September of 2021 and February and March 2022 for spring and fall production respectively. Selections were made to include representatives from the best and worst performers from the greenhouse trials in addition to other cultivars of interest to our grower cooperators. Compost was applied across all cultivars where needed based on soil test results. The USU plantings and plantings on two commercial farms included a second treatment with and without supplemental fertilizer. Plant survival, number of crowns, runners and leaf chlorophyl were recorded. Total and marketable yield data will be collected on fall plantings this spring.

Preliminary results from high tunnels show considerable variability in plant growth and leaf chlorophyll between cultivars as well as considerable site to site variation. At the student farm, Allstar, Galleta, AC Valley, Seascape and Camerosa were our top ranked cultivars while an aggregated ranking for our commercial farm collaborators were quite different with Sparkle, Honeoye, Mayflower, Allstar and Malwina doing best so far. We had some poor establishment, especially on our commercial farms which we contribute to a combination of a high degree of variability between cultivars in the degree of root development of the plug plants at planting, poor soil health, high temperatures at planting and grower inexperience. One farm in particular had very high soil salinity and poor soil structure and even though they were actively working to address the problems through leaching and organic matter inputs, the majority of the cultivar showed symptoms of salt burn. Two cultivars that seemed relatively unaffected were Camerosa and Mara des Bois, although Mara des Bois performed very poorly at other locations due to high symptoms of iron chlorosis. Going into our second year, we plan to provide several additional weeks for plug plant establishment, and we are actively working with our collaborators to improve soil conditions and management experience of strawberry.

Objective 2) Assess how mBCA effectiveness, both singly and in mixtures, varies with strawberry cultivar and compost use

In Year 1, mBCA effectiveness against mold was screened for in a subset (N = 11) of cultivars available. Given limitations on the number of plants available for each cultivar, we limited our mBCA screening to a single microbial species, the basidiomycete fungus Aureobasidium pullulans. Our reasoning for choosing this sole species is that it 1) has documented success as an mBCA against an array of plant pathogens, including those that affect strawberry, and 2) it is commercially available (Blossom Protect, Westbridge Agricultural Products), thus easily accessible for growers for use in high tunnels. In our preliminary screening with these 11 cultivars, the general trend was for A. pullulans to suppress mold growth, nearly completely. The only exception was Mara du Bois, which still experienced considerable mold growth when challenged with the pathogen following mBCA treatment. This cultivar also displayed the least resistance against mold in the control treatment (water spray), experiencing nearly two-fold higher growth than other cultivars screened. Finally, among control plants, cultivars AC Wendy and Chandler exhibited high levels of resistance.

Going into the second year, we plan to complete our screening of mBCAs (alone and in mixtures) across all cultivars for both mold and mildew. As plug-plant production protocols are refined and additional plant material becomes available, we will also address our subobjective on how disease suppression outcomes are mediated by soil type. With such information in hand, we can inform selection of mBCA/cultivar combinations for continued research with bumble bee pollinators (Objective 3).

Objective 3) Evaluate use of bee pollinators to enhance biological control and yield

Evaluation of bee pollinators as vectors of mBCAs and their potential to synergize yield outcomes will begin in Year 2 of the grant. As we continue to evaluate mBCA and cultivar combinations, we can inform selection of candidates for our bumble bee trials. This work will begin in Fall 2022.

Fig. 3 Microbial biocontrol agent (mBCA) to grey mold. Grey mold suppression was excellent on all cultivars selected except Mara des Bois.

Objective 4) Assess market value and consumer preference for local strawberries

A graduate student has been identified to conduct this work and will attend a professional development school at MSU in late May to learn the choice task set up and modeling that we will need to do. Data collection will start in year 2 of the project.

 

Participation Summary
6 Producers participating in research

Research Outcomes

No research outcomes

Education and Outreach

22 Consultations
6 On-farm demonstrations
2 Online trainings
4 Webinars / talks / presentations
1 Workshop field days
1 Other educational activities: We held a session specifically on berry management at the Utah Urban and Small Farms Conference in which this project was featured in one presentation and invited speaker from Oregon State also presented her work on small farm strawberry prodution.

Participation Summary:

3 Ag professionals participated
Education and outreach methods and analyses:

Outreach on the project is on track. We held a grower advisory meeting where we discussed general strawberry production methods and invited input on initial cultivar selections and interest in preliminary planting date trials. Four out of five of our producers opted to participate in the preliminary trials and we have since recruited an additional two commercial farmers, Ranui Gardens in Hoytsville, Utah and Weeks Berries in Paradise, Utah who joined the trials planted this spring. In addition we completed four site visits per farm to assist with plot establishment, initial assessment and to answer any questions.

Initial results were showcased at the Utah Urban and Small Farms Conference on 24 February 2022 and a subsequent USFC Season Extension Field Day held on 24 Mar 22. The Utah Urban and Small Farms Conference Data featured an invited presentation by Clare Sullivan from Oregon State University on her work on small farm strawberry production, also funded by WSARE. Our initial results were also shared as part of a virtual season extension workshop sponsored by Wasatch County Extension on 18 March 2022.

 

Summary of Outreach activities/presentations.

Presentations to date:

24 Feb 22  Strawberry management systems for Utah. Utah Berry Growers Association Meeting. Utah Urban and Small Farms Conference, (Virtual, 89 in attendance).

18 Mar 22 Tunnel design, temperature management and fruit crop options for Utah. Season Extension Workshop, USU Extension Wasatch County, (virtual, 55 in attendance)

24 Mar 22 Strawberry management in high tunnels. Season Extension Field Day for the Urban and Small Farms Conference, Greenville Farm (60 in-person attendance). 

Upcoming:

6 June 22 Strawberry high tunnel management research from Utah. Western Montana Research and Extension Center, Corvallis, MT.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.