DOWNY MILDEW CONTROL IN GRAPES WITH METALAXYL

Abstract

Downy mildew (Plamopara viticola Berk. & Curt.) is a major disease in humid grape-growing areas potentially resulting in major crop loss. Tests were conducted in PA from 1990-1992 in two commercial vineyards to evaluate crop safety and downy mildew control in grapes (vitis sp. L.) with two metalaxyl-containing formulations compared to a standard program and untreated check. Four applications were made at 7-15 day intervals beginning when the shoots were 15-25 cm long using a handgun set to deliver 1870 l ha-1. In 1990, Ridomil MZ58WP (2.2 kg ha-1) applied prebloom followed by Ridomil Copper 70WP (1.1-2.2 kg ha-1) post bloom provided excellent control of downy mildew compared to Nova 40WP + mancozeb 80WP (0.28+3.3 kg ha-1). Twenty-four days after the last application, disease incidence and severity on the leaves was 100 and 67% in the check plants, respectively. The Ridomil-treated plants ranged from 6.7-16.7% and 1.7-10.7% while the Nova+manco-zeb-treated plants had 26.7 and 20% disease incidence and severity, respectively. The untreated check had 63% of its fruit infected compared to <1% in the Ridomil-treated and 6.7% in the Nova+mancozeb-treated plants. In 1991, no disease developed and disease control results in 1992 were similar to those observed in 1990. Little to no crop injury was observed in tests conducted from 1990-1992 on both copper-sensitive and copper-tolerant varieties.