Determine if fungicides gave return on investment

Soybean Pest Beat: Make valid yield comparisons in the field and accurate financial comparisons in the office. 
Sep 06, 2022
I applied a fungicide on some soybean fields, an insecticide on a few, and both on some. How can I tell once I get yield results if any of it was worth the investment?
The panel of Indiana certified crop advisers answering this question includes Shaun Casteel, Purdue Extension soybean specialist, West Lafayette; Steve Gauck, regional agronomy manager for Beck’s, Greensburg; Andy Like, agronomist with Evansville AgriSelect LLC, Vincennes; and Dan Ritter, central region agronomist with Dairyland Seed, Rensselaer.
Casteel: The best way to determine if foliar applications of a fungicide, insecticide or a combination are worth the investment is to leave untreated strips for comparison. Then, you can compare yields in those strips with the yield monitor, or you can harvest the strip and weigh it with a weigh wagon or grain cart with load cells. The next best version is to leave an untreated section of the field for comparison.
If you didn’t leave any strips or sections untreated, try and compare fields similar in planting date, variety and soil type that do and do not have the application of fungicide, insecticide or the combination. If you’re able to find similar fields except for the foliar application, compare the single application of fungicide or insecticide with another field that has both. Determine if it was one component that had the greatest impact on yield.
Understand that it is very difficult to determine if it’s worth the investment without having untreated or different treatments in the same field. Proceed with caution. Plan for untreated strips or at least sections next year to make direct comparisons.
Gauck: Did you leave check strips? Ideally, this is the best way each year to determine if a treatment worked. Before harvest, walk fields and look for differences in treatment. Things such as diseases or insect damage will be visible. If you find something, see if it is in the entire field or only in spots that were not treated.
After you get yield data, look at comparisons in yield to similar fields with similar planting dates, rainfall, varieties and soil types. Make comparisons between fields that were treated and those that were not treated.
Like: An analysis that looks at yield vs. cost of application would help see if the investment had a positive return. In addition to looking at input cost, figure out the value of soybeans you ran down making the application, plus cost per acre to apply. Keep in mind that insect and disease pressure vary from year to year, so this year’s outcomes do not necessarily predict the best outcome next year.
Ritter: As much as feasible, compare similar environments. Eliminate as many variables as possible in evaluating the fields’ performances. Look at similar planting dates, location, soils, varieties and cropping history. As best you can, look at just effects of inputs added and not another factor.
For return on investment, run a simple budget on all aspects. Consider costs of application, labor, product and application damage vs. added yield. Some operators have issues with harvest timing and fungicide on soybeans — they believe applying a fungicide delays harvest. This may be a factor to consider. However, the purpose of the fungicide was to keep the plant healthy, alive and functioning longer in the first place to deliver more yield.