Evaluation of organic products to control blueberry rust

Blueberry rust, caused by Pucciniastrum minimum, is spread primarily by urediniospores and causes lesions on foliage and fruit. Options to enable organic growers in Australia to control blueberry rust are limited, with alternatives to conventional fungicides and copper being sought. This paper presents results of two glasshouse experiments with pot-grown blueberries (inoculated with urediniospores) and two field experiments in a commercial orchard, to assess the efficacy of a range of products, using a highly susceptible cultivar. Seven products with some known ability to inhibit rust pathogens were compared to a conventional fungicide (mancozeb) and copper, at a range of rates. These included the biological control Serenade® Opti® (Bacillus amyloliquefaciens), Intervene® (fungal-derived polyoxin-D), Eco-carb® Plus, Stim-phos®, Aminogro®, Eco-oil®, and Anolyte (electrolysed water). Low levels of disease were obtained in the glasshouse experiments, but there was some significant difference between treatments for rust severity and incidence. As there was no evidence of phytotoxicity, field experiments were conducted with all products (except Stim-phos® as it was not commercially available at the time). Field experiments showed that products could reduce blueberry rust disease in some situations, but the most repeatable result was with Intervene®. Intervene® reduced the area under disease progress curve (AUDPC) value by approximately 20 % and 25 % compared to the poorest performing treatments in field experiment 1 and 2 respectively. While none of the products trialled led to control of blueberry rust, Intervene® provided the most repeatable suppression, with no impact on fruit bloom.