Disease Control Versus Leaf Health In Pyraclostrobin-Induced Yield Increases In Maize?.

The relative contributions of disease control and of changes in physiological processes in the leaf of maize (i.e. leaf health or leaf performance) induced by pyraclostrobin application are not fully understood and were the basis of these experiments.  In a series of experiments conducted in 2008 and 2009 we used different rates (from 0 to 150 g a.i. ha^-1) and times (V10, V15, and R1) of pyraclostrobin application to a grey leaf spot susceptible commercial maize hybrid (DKC60-18 YGPL), different locations (DeKalb, Champaign, and Dixon Springs), and in one instance inoculated with Gray leaf spot (GLS; Cercospora zeae-maydis), in order to achieve varying levels of disease pressure.  In all cases, pyraclostrobin application significantly lowered the level of leaf disease and resulted in late-season leaf greening, with the growth stage at the time of application having a larger effect than the application rate, and with V15 application tending to exhibit better leaf greening, and R1 application better disease control. Although variable in amount, grain yield was also increased at all sites and with all rates and application times (range of 0.5 to 0.8 Mg ha^-1, and was the result of more kernels per plant and heavier individual kernels.  In the inoculated experiment, GLS infection reduced photosynthetic competency, which could be partially ameliorated by the pyraclostrobin application. Collectively, our findings suggest that late-season leaf greening associated with pyraclostrobin application is an indirect consequence of a greater reproductive sink capacity, and implies that pyraclostrobin can increase maize grain yield by positively altering physiological processes in a manner that is independent of disease control.