Effect of systemic inducing resistance and biostimulant materials on apple scab using a detached leaf bioassay

Abstract

A detached leaf bioassay was used to evaluate several systemic inducing resistance agents, a range of biostimulant products and a conventional triazole fungicide (myclobutanil) on apple scab (Venturia inaequalis) development under laboratory conditions. None of the biostimulant products (seaweed extract, betaine, molasses, humic acid, yucca extract, and plant hormone/vitamin complex) evaluated in this study inhibited germination of apple scab conidia, subsequent formation of appressoria or reduced leaf scab severity compared to water treated controls. All SIR agents used in this investigation (potassium phosphonate, potassium phosphite, harpin protein, salicylic acid, salicylic acid derivative) inhibited germination of apple scab conidia, subsequent formation of appressoria and reduced leaf scab severity. The synthetic fungicide myclobutanil resulted in the greatest levels of germination inhibition, reduced appressorium development and leaf scab severity. Results suggest application of an appropriate SIR product may provide a useful addition to existing methods of apple scab management; however, use of biostimulants as scab protectant compounds appears limited. ©2010 International Society of Arboriculture.