V5 through V7 fungicide applications to corn are generally promoted “in addition to” the more common VT-R1 stage applications, not “instead of.”  However, V5 through V7 fungicide applications are also regarded as a way to expand the fungicide market for fields where the VT-R1 applications could not readily take place, or where there is unwillingness to pay the aerial application fee.  Although significant yield improvement from the V5-V7 fungicide has been inconsistent and yield improvement is seldom as great as with VT-R1 applications, we sometimes see positive results from this practice in fields having multiple risk factors (see list below). 

2015 fungicide trials from Iowa State University indicated that a V5 to V7 fungicide application by itself, was of little value in these trials.   However, a V5 to V7 application, followed by a VT-R1 application provided greater benefits than the VT-R1 application alone, when fungicides were applied to a moderately susceptible corn hybrid during a season where conditions favored disease development.

The benefits often claimed for V5 through V7 fungicide applications to corn include: yield improvement, improved season-long plant health, ability to make ground applications where aerial applications may not be possible, potential to apply fungicides in tank mixes with herbicides which saves trips and application costs.

The following list of risk factors may be of assistance in selecting situations in which a V5-V7 fungicide application is most likely to be of benefit.  The more risk factors, the more likely will be the benefits from the fungicide application.  In particular, there has been some evidence that the early corn fungicide applications may have greatest value where there is a history of early season diseases, such as anthracnose.  We are aware that development of fungicide resistance is always a risk with a higher frequency of fungicide applications, so unnecessary fungicide application is discouraged.

Risk Factors – (Support timely fungicide application.)