Jayesh Samtani, Patricia Richardson, Baker Aljawasim, Guillaume Pilot, School of Plant and Environmental Sciences, Virginia Tech

In the past few years, there’s been an increased interest in the use of biostimulants for improved crop production. Biostimulants are materials that can promote plant growth when applied in amounts so small that they do not provide much nutrition. These are composed of different organisms, compounds or plant extracts; they include beneficial fungi and bacteria, humic and fulvic acid, seaweed extracts, and protein hydrolysates.

During the 2022-23 growing season we evaluated three different biostimulant products in annual hill strawberry plasticulture production. ‘Ruby June’ plants were transplanted on 24 Oct, 2022 on non-fumigated beds and were maintained as per grower standard practices. Treatments were as follows (i) no biostimulant (ii) preplant AminoSalmon (220 lb/A) applied during bed making (3) plugs dipped for 20 seconds in TerraGrow Liquid (TGL, 3ml/10 gal) prior to transplanting followed by a foliar spray and a drip application (20 fl. oz/A) at one (10/25/2022), fourteen (11/7) and thirty (11/21) days after transplanting, resuming monthly during spring (4/13/2023 and 5/11); and (iv) EZ-GRO 16-0-0 (3.5lb/A) drip application 14 days after transplanting (11/7) and every 14 days during fall (11/21 and 12/9), resuming during spring (4/13, 4/27, 5/11 and 5/25). All non-treatment irrigation valves were closed during treatment injection through the drip lines. After treatments were injected, the lines were flushed then these valves were closed, and the others opened to irrigate for the length of time used to inject treatments.

Preventative fungicide was applied as a foliar spray three times in the fall, beginning with Captan then rotating with Elevate and Thiram at the recommended rates. During the spring, Captan was applied twice, then rotated with Luna Sensation and Abound/Thiram due to high incidence of anthracnose fruit rot. Row covers (1.2 oz) were utilized once in the winter on 23 December to 3 January, then again in early spring from 14-22 March. Acramite miticide was applied twice on 21 December and 4 April. Weekly spring fertigation began on 27 March at the rate of 7lbN/acre. Tissue samples were collected on 4 April to determine fertilizer needs, prompting the addition of Epsom salts at 1.5lb S/acre to the fertigation regime on 20 April and 4 May. Ripe fruit was harvested beginning 31 March and continued twice a week until 16 June (Photo 1).

Photo 1. Study of the different biostimulant beds during the harvest season.

Fruit from each harvest was graded marketable and non-marketable (less than 10g, deformed, damaged or diseased) and weighed by category. Fruit size was estimated as g/fruit by weighing 10 marketable fruits weekly. Five marketable fruits were measured weekly for firmness using a penetrometer then stored at -20 °C for later analysis of pH and total soluble solids (°Brix) using a digital refractometer.

Result and discussion

For total yield and marketable yield, no treatment differences were found. However, the plots treated with TGL showed slight increases in the total and marketable yields compared to the other treatments and the untreated control (Fig. 1). The TGL product contains five different Bacillus species that typically protect the plant from harmful microbes and make nutrients available to plants, which may help to improve the total yield and markable yield. Although there were several diseases diagnosed during the season, such as anthracnose fruit rot (AFR), botrytis rot, and other diseases, the treatments did not affect the weight of diseased fruits per bed (data not shown). For strawberry fruits, quality, firmness, total soluble solids (TSS), and pH are important factors affecting fruit quality and customer acceptance, with sugars being the primary soluble metabolites impacting taste and ripeness. While fruit firmness and pH were not influenced by treatments, the application of both the amino salmon and EZ-GRO biostimulants significantly improved TSS values compared to the untreated control (Fig. 2).  In conclusion, during this first growing season, none of the biostimulant treatments stood out. We will be repeating this study with same treatments and adding two more biostimulant products, namely iQForte and PVent Microbial WP.

Figure 1. Effect of Amino Salmon, EZ-Gro, and TerraGrow Liquid on total yield. NTC (untreated control), Amino Salmon (preplant), EZ-Gro 16-0-0 at 3.5lb/A drip application, and TGL (TerraGrow Liquid at 20 fl. oz/acre foliar and drip). The total yield was calculated based on 12,432 plants/acre.
Figure 2. Effect of application of Amino Salmon, EZ-G, and TerraGrow Liquid on the total soluble solids (TSS). NTC (untreated control), Amino Salmon (preplant), EZ-Gro at 3.5lb/A drip application, and TGL (TerraGrow Liquid at 20 fl. oz/acre foliar and drip). The total yield was calculated based on 12,432 plants/acre.

Funding support.  USDA-NIFA VA-160194, Virginia Agricultural Council and industry sources.

Acknowledgments. The authors would like to thank Rob Holtz, Gabriel Kwesi Yeboah, Jacques F. Pouliquen, and Abigail Craige for assistance with field research.

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