The Maine University Extension office recommends sowing buckeye, wheat, oats or rye in the area where you would like to plant raspberries in the fall. Plow them into the soil after they have sprouted up, but before they go to seed in the spring. This increases the nutrients in the soil and can help with later weed control, according to this agency.
The Ohio State University Extension office recommends removing weeds from raspberries mechanically whenever possible. You can do this with a garden tiller in most instances. Use a lawn mower with a plow attachment to remove weeds between rows of bushes.
Place a layer of sawdust or hay around the raspberry plants after you have removed the weeds. This can keep new weeds from sprouting up while also retaining moisture. Make sure the soil is well-drained and not retaining water when you add mulch, as this can increase the possibility of disease in your raspberry plants.