Assessment of Kelp Extract Biostimulants on Tree Growth, Yield, and Fruit Quality in a Certified Organic Apple Orchard

Reduced tree vigor and fruit yield are common challenges experienced in organic apple (Malus xdomestica) production. Organic farmers commonly use natural biostimulants in their fertility program to supplement mineral nutrition. These materials are a poorly-defined group of products that are not plant fertilizers, but which when used in small quantities may improve plant growth or function. Two biostimulant materials extracted from the kelp Ascophyllum nodosum, Stimplex (TM) and Seacrop16 (TM), were assessed against a non-treated control over two seasons in 2009 and 2010 in a four year old certified organic apple orchard in South Burlington, Vermont. The objective of this study was to assess effects from application of Ascophyllum nodosum extracts (ANE) on tree growth, crop yield, and fruit quality. ANEs were applied at label rates seven times during each growing season to each of five replicates of the apple cultivars 'Ginger Gold', 'Honeycrisp', 'Liberty', 'Macoun', and 'Zestar!'. Treatments were applied in a completely randomized design to the same trees in both years. The majority of the data showed no effect from ANEs on tree growth, crop yield, and fruit quality. In one year, 'Ginger Gold' trees treated with Stimplex had increased tree growth over the non-treated control, but 'Macoun' trees treated with Stimplex had reduced canopy width in the same season. ANEs had little effect on assimilated mineral nutrients in foliage; however, Seacrop16 treated trees had reduced levels of some minerals. Trees treated with both ANE products showed reduced incidence of sunburn and frost rings on fruit in 2010.