My go to for preventive and also for treatment is liquid copper fungicide (Southern Ag). It is antifungal for both early and late blight, and other fungi, and it is antibacterial for speck and spot, as well as other bacteria. I have tried Daconil, but I admit I tend to start treating AFTER I get a problem started, and Daconil is best used as a preventive, as Carolyn said above. Additionally, it will clump and clog the sprayer if mixed with some things, such as liquid copper. Guess how I learned that?
I do use Neem, I buy 100% online, it also does insects, and fungi, not sure if it is bactericidal, but if you get mites, aphids, whiteflies, tomato suck bugs (horrible), thrips, etc, Neem is great stuff. You should be more disciplined than me, and immediately rinse out and flush your sprayer, or the neem will gunk it up with a gummy residue. Guess how I learned that?
I use 1 Tablespoon per gallon, with a squeeze of soap, and I keep agitating to remix it, it is strongly hydrophobic.
I have been using liquid copper from Southern Ag at rate of 1/2 tablespoon per gallon, which works great and still won't cause the new leafs to curl like stronger spray will, and I can mix that with 1/2 tablespoon per gallon of Permethrin 10% if I have stink bugs or Tomato Suck Bugs, or just add a squeeze of liquid dish soap if I have a soft bodied insect such as whiteflies, aphids thrips, soap ruptures the insects waxy bodies, and also clogs their spiracles so they cant breathe.
You can harvest the best day with all these.
If you use Permethrin you should wait until dusk so as not to harm bees, but it is the synthetic of pyrethrin which is derived from chrysanthemums. It also can be used for flea control in dogs and cats.