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

Non-target impacts of agricultural biostimulants compared with sulfur-based fungicides on phytophagous mites on 'Zestar!' apple trees in a certified organic orchard in Vermont, USA

Authors:   A.L. Hazelrigg, L.P. Berkett, H.M. Darby, J.H. Görres, R.L. Parsons
Keywords:   integrated pest management, 'Zestar!', European red mite, two-spotted spider mite, sulfur, lime sulfur
DOI:   10.17660/ActaHortic.2016.1137.24
Abstract:
Growers and researchers are searching for suitable alternatives to sulfur-based fungicides for disease control in organic apple orchards. Agricultural biostimulants, used alone or in combination with fungicides, may offer new, low environmental-impact options for disease management. This two-year study evaluated the non-target or unintended effects of an organic disease management system containing agricultural biostimulants compared to two sulfur-based systems on phytophagous mite populations of the European red mite, Panonychus ulmi and two-spotted spider mite, Tetranychus urticae on 'Zestar!' trees in a certified organic orchard. The impacts of the three systems on the incidence of foliar and fruit diseases, pest and beneficial arthropods and impacts on tree growth, fruit quality and fruit yield on 4 cultivars are reported elsewhere in this publication. This mite study examined the non-target effects of the three organic disease management systems (OMS) only on the cultivar 'Zestar!', yet used the same orchard, experimental design plus the same materials and timing of the OMS applications as used in the other two studies previously reported. Leaf samples were evaluated for the number of motile phytophagous mites approximately every 14 days from July 1 through August 26 in 2003 and 2014. Although not always significantly different from the sulfur-based systems, when there were differences, the biostimulant system had fewer mites per leaf than one or both of the sulfur-based systems in both years. The difference in the number of sulfur sprays did not have a major effect on the mite populations. This research documents that the biostimulant system, which represents a novel management system for Vermont organic apple orchards, did not result in increased phytophagous mite populations and potentially may offer beneficial suppression compared to sulfur-based management systems. Before adoption in commercial orchards, the efficacy of the agricultural biostimulants on important diseases, in addition to the non-target effects on insects, tree growth, yield, fruit quality and potential gross income must be considered.

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