The efficacy and non-target impacts of an organic disease management system containing biostimulants compared with two sulfur-based systems on four apple cultivars in Vermont

isease 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 the target and non-target effects of an organic disease management system containing agricultural biostimulants compared to two sulfur-based systems on foliar and fruit diseases, pest and beneficial arthropods, tree growth, yield and fruit quality on four cultivars, 'Ginger Gold', 'Honeycrisp' and 'Liberty' and 'Zestar!'. Trees were arranged in a complete randomized design of five three-tree replications in a certified organic orchard. The two sulfur-based systems differed in the number of applications; in the third system, sulfur was replaced with biostimulants including pure neem oil, liquid fish, an activated microbial inoculant plus 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 per hectare which takes into account fruit yield and quality. In the higher fruit-bearing year of the study, it was estimated that the gross income per hectare of the biostimulant system would be significantly lower than the reduced-sulfur system and the full-sulfur system by at least...