State level data and not quite testing the exact logical statement in questions but an R2 of <2% for several tests would lead to a very reasonable hypothesis that May weather doesn’t matter much, at least in IL.

I can see how as you go father north planting date penalties would be more pronounced but it takes a lot of correlation to show up to be significant when you start at 1-2%.

What we all think we ‘know’ often just isn’t so when we examine the statistical record.


https://farmdocdaily.illinois.edu/2022/05/does-the-correlation-between-spring-and-summer-weather-explain-the-puzzling-results-on-late-planting-and-corn-yield.html