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ISHS Acta Horticulturae 1137: International Symposium on Innovation in Integrated and Organic Horticulture (INNOHORT)

Assessment of agricultural biostimulants compared with sulfur-based fungicides on diseases, tree growth, fruit yield and quality on three cultivars in a certified organic apple orchard in Vermont, ME, USA

Authors:   A.L. Hazelrigg, L.P. Berkett, H.M. Darby, J.H. Görres, R.L. Parsons
Keywords:   apple scab, rust disease, integrated pest management, 'Ginger Gold', 'Honeycrisp', 'Liberty'
DOI:   10.17660/ActaHortic.2016.1137.22
Disease management in organic apple orchards in Vermont is focused on controlling diseases with sulfur fungicides. The objective of this two-year study was to evaluate both the efficacy and the non-target or unintended effects of an organic disease management system containing agricultural biostimulants compared to two sulfur-based systems on foliar and fruit diseases, tree growth, yield and fruit quality. Trees were arranged in a completely randomized design of five three-tree replications of the cultivars 'Ginger Gold', 'Honeycrisp' and 'Liberty' in a certified organic orchard. The two sulfur-based systems differed in the number of applications; in the third system, sulfur was replaced with tank-mixed biostimulants including pure neem oil, liquid fish, an activated microbial inoculant, and equisetum and stinging nettle teas. Each biostimulant application also included kelp meal, unsulfured organic molasses and yucca extract emulsifier. The biostimulant system did not successfully manage apple scab and rust diseases as well as the sulfur-based fungicide systems, and had variable results with other diseases. No differences were observed among the three systems in tree growth parameters; however, the length of the study may not have been sufficient to determine effects. Differences in the incidence of disease among the three systems were reflected in extrapolated figures for gross income ha-1, which takes into account fruit yield and quality. In the higher fruit-bearing year of the study, it was estimated that the gross income ha-1 of the biostimulant system would be significantly lower than the reduced-sulfur system and the full-sulfur system by at least 5,800 and 12,000 USD, respectively. It is estimated that the full-sulfur system would have generated approximately 6,500 USD more gross income ha-1 than the reduced-sulfur system suggesting the number of sulfur sprays can influence fruit quality and income.

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