Low-Level Copper Plus Chitosan Applications Provide Protection Against Late Blight of Potato

Abstract

The organic grower can manage potato late blight, caused by Phytophthora infestans (Mont.) de Bary, with natural copper compounds such as copper sulfate pentahydrate, copper oxide, or copper hydroxide. However, recent environmental concerns about copper residues by the USDA's National Organic Program indicate a need to control late blight with reduced copper levels. This report describes a strategy for disease control using lower levels of copper sulfate pentahydrate in combination with a chitosan sticker and complexing agent. In excised leaf assays, this combination provided moderate control of late blight and protection against copper-related leaf yellowing at copper levels approximately 40 fold lower than those recommended for a commercial fungicide with copper hydroxide as the active ingredient. Accepted for publication 23 February 2006. Published 6 April 2006.