Fall is a great time to kill that bermudagrass hanging around where you want to plant (or expand) your vineyard.  The most effective way is to spray it with Glyphosate (RoundUp or similar product), fertilize the grass, wait for new growth, then spray it again.  That program usually takes care of bermudagrass pretty well.  Once it has been knocked back then the soil can be prepared for the vineyard.  This is a crucial step that is often forgotten or not done well enough.  Uncontrolled bermudagrass competing with young vines is not a good combination because the management strategies are more difficult — namely the use of grow tubes and careful, regular spraying.  Even then the grass will compete with the vines for important water and nutrient reserves in the soil.  Bermudagrass can also be allelopathic to other plants, meaning that the roots of the grass exude a chemical that inhibits the growth of a nearby plant thus making the environment more suitable for the grass and less for the other plant (your vines).  So, to sum up, bermudagrass = bad and now is a good time to get a handle on it.