Here in PA we've found that applying almost any white powdery material
to brassicas from the time the coteledons appear repels flea beetles.
Depending on sopil tests, people may use wood ash, phosphate rock/bone
meal, lime, etc. The material must be reapplied to Brassicas after
overhead irrigation or rain.
This may fit better with crrent practice that row covers.
We've not tried it on potatoes or eggplant.