The general rule is that mosquitos need a pool of water the size of a bottle cap, and it needs to be there for at least a week. Good luck, and good hunting.
Just to be clear, my recommendation is to mitigate both man-made and natural breeding sites. Fortunately mosquito dunks don't harm other species.
So do I, but mosquitos are usually a problem for people who live close to nature. And then you'll have lakes, puddles, ditches, swamps, etc. But maybe I'm wrong and mosquitos don't fly that far, as another commenter here mentioned.
I will certainly try the mosquito dunks as you advise. Hope they can help.
I do. That's where I put the dunks.
Lakes are usually okay as long as they have minnows or other mosquito-eating fish, but puddles and ditches are the places I focus on.
Fortunately I'm not near a real swamp, but I do have some swampy areas. I break each dunk into quarters and toss 1-3 per puddle, depending on size and funkiness. The package optimistically says four weeks, but I have my phone remind me every three. Good luck!