Comment by 9rx

> You only want to apply expensive fungicide when there is a fungus problem. That means someone needs to go out to the field and check

Nah. If you can see that you have tar spot, you are already too late. To be able to selectively apply fungicide, someone needs to model the world around them to determine the probability of an oncoming problem. That is something that these computer models are theoretically quite well suited for. Although common wisdom says that fungicide applications on corn will always, at very least, return the cost of it, so you will likely just apply it anyway.