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

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 commercial cultivars were obtained from nurseries (e.g. Nourse Farms, Whately, MA). Eleven cultivars were propagated according to Rowley (2010) and planted in high-tunnels at the USU Student Organic Farm and four commercial farms in the fall of 2022. Eleven cultivars were planted directly in high tunnels at the USU Student Organic farm and on three commercial farms in the spring of 2023 and harvested in the spring and fall of that year. The trials were replanted in the fall of 2023 and spring of 2024 due to problems associated with extreme cold followed by flooding. A total of four commercial farms plus the USU student farm participated in the trials. A third greenhouse experiment was conducted in the summer of 23 as follows. Plug plants of six cultivars 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 twice weekly with 100 ml water with leachate collected and analyzed for nitrate and ammonium (Lachat Instruments, Loveland CO). Leaf chlorophyll measurements were taken at the end of the experiment using a chlorophyll meter (Apogee Instruments, Logan UT). Plants were harvested after eight 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 (Millers Inc, Hyrum UT) with and without soluble N fertilizer (fish emulsion on organic farms) were established on the USU Student Organic Farm and four commercial farms in August/Sept 2023 and Feb/March 2024. One 70 x 14ft tunnel was dedicated to fall and one to spring production at the student farm and on farm trials were sized according to grower interest and available space. Eleven compost/cultivar treatment combinations (3ft. of bed per treatment with 6 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. Compost was applied across all cultivars where needed based on soil test results. The USU plantings and plantings included a second treatment with and without supplemental fertilizer. Plant survival, number of crowns, runners and leaf chlorophyl were recorded. Total and marketable berry yield, fruit size, plant growth, leaf chlorophyll, leaf N content and disease incidence were measured on the spring planted trials. Soil health indicators (organic matter, microbial biomass, available soil nutrients, pH and EC) were assessed at two points during the growing cycle 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.

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 (single, Aureobasidium pullulans) effectiveness against grey mold (Botrytis cinerea) will continue to be evaluated across cultivars. The focus on A. pullulans has been dictated by commercial availability of the mBCA for producers, as well as prior work showing its effectiveness against pathogens, including strawberry (Sylla et al. 2013; Iqbal et al. 2022). We are also focusing on grey mold, as powdery mildew has been less of a concern to date in our trials, and we wish to ensure post-harvest health of our berries for market. To test efficacy, we will perform a detached strawberry leaf disk bioassay, following Sylla et al. (2013). Briefly, leaf disks [1 cm diameter, N = 30 per treatment (mBCA or control) per cultivar] will be sourced from leaves of strawberry mother plants grown in the greenhouse for plug plant production. The control treatment will consist of leaf disks dipped in sterile Ringer solution, while the mBCA-treated disks will be treated at a density of ~1 x 10⁷ CFU/mL. Treated disks will be incubated at 25°C (65% RH), with an alternating 12 hr. light/dark photoperiod. After 24 hr, leaf disks will be challenged with B. cinerea conidia and incubated to allow for pathogen development. Leaf disks will be processed to determine levels of conidia production, using microscopy and a Thoma counting chamber to determine the number of conidia per cm² of leaf. These data will extend our previous dataset on cultivar-dependent performance of Aureobasidium, which has been performed with each round of cultivars purchased in spring for evaluation. A complementary assay will also be performed with leaf material stemming from the planted trials of cultivars grown on and off compost, to determine how Aureobasidium and compost-addition may interact to affect mold resistance.

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 a tunnel at the USU Student Organic Farm. Commercial bumble bee colonies (Bombus impatiens, Biobest Group) will be obtained and fitted with an mBCA inoculum dispenser, following Yu and Sutton 1997; Al-mazra’awi (2004). Each cage (i.e., treatment) will contain18 strawberry plants. The RCBD experiment will be replicated 4 times. Treatments consist of control treatment with neither inoculum nor bees, mBCA inoculum sprayed alone, bees alone, and mBCA inoculum + bees. Three cultivars (AC Valley, Chandler, Galetta) were selected for this experiment and half of the plants were treated with either control or compost-amended soil as in Obj. 1.

After establishing caged arrays, we will introduce the 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 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.

A graduate student will work with growers in year three to collect information to revise and update previously published cost of production budgets (Maughan et al., 2014). Pricing estimates are 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 are 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).