LATE BLIGHT CONTROL ALTERNATIVES FOR ORGANIC POTATO GROWERS

Abstract

SUMMARY Organic potato production is a flourishing sector of the British Columbia food industry and acreage dedicated to that crop is increasing. Late blight (Phytophthora infestans (Mont.) de Bary) is one of the largest production risks of the region's potato growers and has the potential to cause substantial economic losses. Consequently, prevention of foliar epidemics leads to weekly application of an arsenal of fungicides by the conventional growers. On the other hand, only one product, a formulation of copper hydroxide (Parasol WP), provides late blight protection for organic growers. The need for alternatives to copper led to testing of alternative, biological controls for the disease. This study tested two OMRI-listed, natural products, Actinovate SP® and Sonata®, alone or in combinations with each other and/or Parasol WP. The study consisted of six treatments: 1) Parasol sprayed, 2) Actinovate SP sprayed in rotation with Sonata 3) Actinovate SP sprayed 4) Actinovate SP sprayed in rotation with Parasol WP 5) Sonata sprayed 6) Sonata sprayed in rotation with Parasol WP, and 7) untreated (water) Control. Plots were treated weekly and leaves with active late blight lesions were introduced to plots. Late blight incidence and severity was assessed weekly. At harvest, tubers were assessed for yield and infection by P. infestans. Disease incidence on the last scoring date reached 29% in the Parasol/Parasol treatment, versus 52% of plants in the untreated Control