Plot size can influence yield benefits from fungicides on corn

Use of foliar fungicides on corn has increased over the last decade. Part of the reason for this increase is due to physiological benefits on plants from QoI (strobilurin) containing fungicides. However, there remains controversy over how significant yield and economic benefits are from strobilurin fungicides. A potential source of this controversy might be explained by experimental plot size. To better understand grower-relevant yield benefits from fungicides, three hundred and fourteen commercial-strip trials (8.1 ha fungicide treated and 8.1 ha untreated) were conducted on growers' farms across four years, and twenty-five small plot (37.2 m2 or less) trials were conducted across the corn belt in 2010. Yield benefits from fungicides were much greater in the commercial-strip trials than in the small plot trials. In 2011, twenty-six large plot trials (ranging from 557 to 1394 m2), were established with efforts made to reduce border and alley effects. Two corn hybrids were evaluated at each of the 26 trial locations, and the results indicated that corn yield benefits from Quadris® fungicide (a solo formulation containing 22.9% azoxystrobin) applied at the V4-V8 growth stage, Quilt Xcel® fungicide (a premix formulation containing 13.5% azoxystrobin and 11.7% propiconazole) applied at the R1 growth stage, or a combination of the two, provided yield benefits similar to those from the commercial-strip trials. The financial gain/loss from the use of fungicides was determined. Using the highest cost estimates for fungicide and applications, Quilt Xcel fungicide applied at the R1 growth stage provided estimated yield benefits of $105, $219, $241, and $278/ha ($19, $65, $74, and $89/A) over the untreated checks in the commercial-strip trials conducted in 2009, 2010, 2012, and 2013, respectively. The average economic benefit to growers over the four year period was $211 ± 37/ha ($62 ± $15/A). Variability in economic benefit not only includes costs associated with fungicides but also includes annual commodity price, disease pressure, and location effects. This study supports the hypothesis that plot size influences assessment of yield effects of fungicides. Yield responses from the small plot, large plot, and commercial-strip trials resulted in increases of 378 kg/Ha (6 Bu/A), 701 kg/Ha (11 Bu/A), and 1132 kg/Ha (18 Bu/A) over the untreated, respectively.