The interest in controlling soybean rust has spawned a related interest in the role of foliar applied fungicides for late-season disease control in soybeans.  Some people have gone as far to suggest that the application of foliar fungicides should be a routine management practice.  During the past two years, a total of fifteen on-farm research trials (9 in 2005 and 6 in 2006) were established in Wisconsin to measure the impact of fungicide applications on soybean health and productivity.  In addition, UW researchers established several small plot trials on outlying research farms. 

        Averaged over the fifteen on-farm trials, fungicide-treated soybeans responded with an overall 1.7 bushel per acre increase in yield (see graph).  To make a foliar fungicide application economically feasible, about a four bushel per acre increase is needed.  There were two situations where yield increases of 6.1 and 6.8 bushels per acre were obtained from the fungicide applications.  The problem is that there has not been one singular key factor that would predict whether a fungicide application would result in a positive economic return.

        One factor that may be involved is variety selection. In 2005, 22 of 123 soybean varieties in the UW soybean variety performance trial produced from 3.8 to 11.3 bushels per acre more when treated with a fungicide.  Results in Wisconsin and other states indicate that fungicides are more effective if applied at growth stage R3 (first pod stage) rather than at R1 or R2 (flowering).  The bottom line is that there is still more work to be done so that economic returns from foliar fungicides can be predicted.