I treat my tomatoes relatively sparingly with copper spray. At this point, my plants are still vigorous and producing well. My first frost generally doesn’t occur until at least Halloween, and often later. At what point do you stop spraying to battle fungal diseases?

Also, I don’t want excessive copper to build up in the soil. I mulch my beds with a thick layer of straw on top of newspaper, and at the end of the season it‘s all discarded along with the tomato plants. I assume that any copper runoff would be concentrated primarily in the mulch. Am I correct in that supposition?