The Online Tool for Helping Making Economic Decisions for the Use of Fungicide On Soybean.

Fungicide applications (FA) on soybean (Glycine max (L.) Merr. ) are common in Iowa due to small but often profitable yield responses (YR) observed, even when soybean leaf diseases are not visible. Because of large volatility in soybean prices observed over time, growers need a decision support system that would help them estimate the probability of economic return to FA. The objective of this study was to develop an online tool that would help estimate the potential economic benefits received from applications of Headline (Pyraclostrobin) on soybean.  We developed an online calculator using data collected from 282 on-farm replicated strip trials conducted across Iowa from 2005 to 2009. Each trial had three to 10 alternated strips applied with and without Headline. The strips received FA by ground or air, mostly at R3 soybean growth stage. Soybean yields were measured by combines equipped with yield monitors. Late-season color and near-infrared digital aerial imagery of the soybean canopy was used to verify treatment locations and identify possible application errors. Cumulative distribution densities of field-average YR to FA were used to estimate the probability of receiving a YR that was less or equal to the break-even YR estimated for a range of soybean prices and costs of FA. The calculator estimates 1) the break-even YR, 2) the probability of exceeding the direct cost of FA, 3) the expected average economic return based on a 5-yr median YR to FA, 4) a range in the expected average economic return, and 5) a number of years when FA would exceed the direct cost. The developed calculator enables growers to conduct they own economic and risk analyses before making decisions whether to apply or not apply a fungicide on soybean.