The impact of sulfur on biological control of spider mites in Washington State vineyards and hop yards

Abstract

Data collected from field studies and experiments conducted in Washington State vineyards and hop yards during 2001-2005 indicate that the multiple use of sulfur as a tool to manage powdery mildew, has an adverse impact on biological control of spider mites. In vineyards there appears to be a positive correlation between the frequency of sulfur applications and spider mite population densities. Multiple (>4) applications of sulfur can result in spider mite population outbreaks requiring control. Similarly, in replicated vineyard and hop yard experiments, multiple applications of sulfur increased spider mite populations. Conversely, predatory mite (Phytoseiidae) populations are smaller in sulfur- exposed hops and grapes than in non-exposed plants, and it is likely that suppression of phytoseiid populations by multiple applications of sulfur contributes to spider mite population outbreaks in Washington State hops and grapes.