I am beginning to think that it may not be the copper that effectively works in cases where you have lots of rains. It may have got to do with your sealer, the Nufilm. Through time, these fungi would have developed resistance already, like in our case here, copper don’t work as effectively like before. The most important factor, thinking out loud here, maybe is that when you have a coating of Nufilm that is rainproof or have some waterproof properties, it actually has prevented the spores from spreading by trapping them in. If copper has indeed killed them, even if the spores has spread, there would have been no need for Nufilm because the dead spores shouldn’t germinate on the leaves when they break out. The fact that you needed Nufilm to be effective may not be due to copper but due to the Nufilm itself. Just my thoughts on this. One way to test this is to apply Nufilm without copper. Or you can mix Nufilm with my Italian salad dressing recipe sprayed right after hydrogen peroxide to trap the peracetic acid that was formed for a much longer time.