Evaluation of prophylactic sprays on pest abundance, foliar damage and yield in winter wheat

Abstract

Producers in the Mid-Atlantic region of the United States often use prophylactic pesticide sprays in their fields to increase wheat (Triticum aestivum L.) yields regardless of disease or insect pest levels. This study was carried out at two sites during each of two field seasons to evaluate th-e effects of pesticide applications (fungicides and insecticide) on insect abundance, beneficial arthropods, foliar damage and grain yield in winter wheat. Insecticide applications reduced densities of cereal leaf beetle (CLB) and CLB damage of flag leaves at the Queenstown and aphid at the Upper Marlboro study site compared to controls during 2009 and 2011 field seasons, respectively. However, insecticide application also reduced arthropod predators at Queenstown in 2009. Fungicide applications reduced leaf spot severity symptoms at Queenstown in 2009 and both sites in 2011. Grain yield was negatively correlated with the percentage of severely damaged flag leaves during the 2009 growing season when diseases and insects pressure was greatest. Nevertheless, yield increase associated with application of pesticides (fungicides) was observed only at one out of four site–year combinations. Results from this study suggest that prophylactic sprays will not enhance wheat yields in the absence of high pest pressure.