I recently noticed a neighbors' tomato bed, maybe 4 large plants, totally free of blight. There was a lot of parsley growing around the base of these tomato plants. Just a coincidence?
Just a coincidence?
Probably -- blight is a fungal problem.
I suppose the parsley could have served as a sort of natural mulch, though, since there was a lot of it. Mulching helps prevent splashback of fungal spores onto the plants.
The short answer: No!