Malathion is pretty ugly... and I'm not sure it's the thrips causing your blossom drop. Have you seen the thrips recently? You can usually see them with a good magnifying glass or hand-lens.

Brandywine is notoriously finicky about setting fruit, particularly if it's the generic pink one. Too hot, not hot enough, not enough water, not old enough, a little too much humidity... it almost takes standing on one leg and reciting a limerick to get it to set. So just having blossom drop isn't an indication of thrip activity.

Look for the thrips, and don't spray unless you see them. Take out all the weeds in the garden area and as far out from it as you can, because weeds host them. Start flicking your Brandywine flowers, and don't use it as your indicator of how well things are setting -- use the other three, which are very reliable.

--Alison
who has noticed that the generic pink Brandywine is much less tolerant than the Sudduth strain for some reason -- Sudduth Brandywine has been setting in 100+ degree weather this week, where normal Brandywine would just fry.