The thrips on the hempy plants, where are the eggs being laid? Perlite is inert.
They don't lay eggs in the ground, lol, that's just where the second (third?) stage of life goes to pupate(?). The eggs are in your plants, where they'll be protected from everything short of incineration of their home.
You might find a few of their egg locations, if you are able to see tiny holes/slits in your plants. But you'll never find all of them. Therefore, plan to spray multiple times over two weeks or so. Might not be necessary, but they have the option of reproducing asexually, so it only takes one to create another 250 or so.