How can you eliminate tall grass from raspberry bushes?

Smother the grass out with newspaper.

I'm with Janet! Choke out the unwanted grass by covering it with layers of newspaper and mulch. Good luck!

my father always burned the grass first thing in spring.

Pulling out as much as you possibly can, then mulch - heavily! Grass is hard to eliminate.

There are "dreaded chemical" weed killers that are formulated to kill grass in flower beds that will not harm your raspberry bushes. I've used them to kill dallis grass invading my roses. Beware home brew remedys that do more harm than good.

If weeds were taking over my patch I would dig up the raspberry plants and separate the weeds from the roots and replant the berries. Especially if the plants were old enough to need refreshing. I've started a small leafed Sedum ground cover in my berry patch for weed control.