This past summer, Dylan asked if ammonium sulfate as a water conditioner (similar to what is used for prohexadione calcium and foliar-applied herbicides like glyphosate) impacts fungicide performance. Plant Pathology experts I reached out to did not know of data addressing this question. The results from a single study in 2025 are found here. There was a slight benefit in defoliation (less, suggesting greater protection from disease) when ammonium sulfate was used with four different fungicides. However, there was a slight yield reduction with ammonium sulfate. More research is needed to see if there is a real benefit or real negative with this approach.

2026 Fungicides and AMS