I wouldn't let either a diluted OR full-strength solution sit for any nears as long as 20 minutes! Chlorine Bleach, which is what you want, will pretty much kill on contact. If you use a diluted solution, you won't do that much damage to the plants unless they get SPRAYED / SPLASHED with the 'stuff'. So, just cover them and let the 'residue' run off the plastic towards the perimeter.
How Chlorine Bleach causes damage to mold and mildew (ie., any 'green plant'), is explained at How Does Chlorine Bleach Work?. (Another, more technical explanation, is explained in Bleach Project.) In short, the chlorine causes a 'negative chemical reaction' that create the mold/mildew 'color', hence, killing them. So, splashing it on the ground is, pretty much, harmless to VISIBLE plantlife (but don't get that comfortable in this statement.) This is why chlorine is used in swimming pools to kill algea and such, as well as in public drinking water!
As for your 100 ft. trees, I'm sure your insurance company would have something to say about that, especially after one of them ends up in your living room. (Until then, they won't know BUT, if a tree were to fall as such, they may NOT insure you 'the next time'. Besides, who wants ANY of the 'inconveniences' that come with a 100 ft. tree landing on their house??! Maybe that's all your wife needs to hear. There's no place like home!) Yes, forget about the North side of the house, and it sounds like you have the have the front 'in check'.
I still say 'clean the trees up'. If the trees were 101' from the house, leave them alone. But if they're 99' from the house, well, some pruning needs to be done. My best to ya and hope this helps. Remember, please, not 20 minutes!