Last year my tomato plants were doing fine and then the bottom leaves
started turning yellow and it moved up the plants. I did not get many
tomatoes out of the deal

The same thing appears to be happening this year. I took a leaf to the
local garden center and they said aphids and sold me some poison dust
(Bonide?). I would prefer not to use it since it says that it's bad
for humans and pets, and my cats roam the backyard.

Is there anything else I can do? Is it likely that I have aphids? I
thought that I would see those but I don't see them anywhere.

Any suggestions appreciated.