How do you determine if fungicide application paid?

Corn Pest Beat: If you didn’t leave comparison strips, there are other ways to get a handle on this question. 
Oct 07, 2020
We sprayed fungicides on half our corn just after tasseling in 2020. We didn’t tell the custom operator to leave check strips. How do we tell if the fungicide paid or not? We’ve got one case with two fields with the same soil types near each other. It’s the same hybrid. We sprayed one and not the other. Could we compare yields from those two fields?
The Indiana certified crop advisers answering this question include Steve Gauck, regional agronomy manager for Beck’s, Greensburg; Andy Like, independent crops consultant, Vincennes; and Dan Ritter, agronomist with Corteva Agriscience, Rensselaer.
Gauck: You could compare the two fields that are similar to each other and it would give you an idea, but not necessarily the exact answer. Even fungicide strips in the same field can offer a lot of variation in some cases. So, getting your answer from the yield monitor can be difficult. Hopefully, you walked the fields and compared stalk strength and disease levels in the plants before harvest.
One way to compare, if you haven’t harvested those fields yet, would be to take a close look at the ears and compare kernel size and depth. If applying a fungicide gave you a larger kernel size and weight, and the corn is standing well and not slowing down your harvest, you can make a strong assumption that the fungicide made you money. It may have paid off in not only yield, but also in improved harvest efficiency.
Like: You can definitely compare the two fields. The comparison will not be perfect, but it should give you an idea of how the fungicide performed. After harvest, I would look at the yield maps and try to compare parts of the fields that have similar drainage and slope as well as similar soil types.
This comparison can be done with a number of different GIS software programs. If you don’t have access to a GIS program that can make these types of comparisons, your agronomist or seed dealer should be able to help. Once you have a valid comparison of yield, then you can put the numbers to it and see if the fungicide application paid or not.
Ritter: You could compare them. Obviously, you understand that check strips in the same field would be preferred. Compare the overall yields of treated versus untreated corn on your entire operation. Does that trend follow what you see in the two fields with the same hybrid?
Discuss this issue with your local crop advisers and find what they’re seeing for results in your area. They may have some local comparisons and tests they have been working on as well. Hopefully, with that information, you can make an informed decision.