blueberry growth

Last year I turned out some old blueberry bushes which had been non-productive and replaced them with some old favourites that had served me well in the past.  The new bushes are still 'finding their feet' but the one that I have had for a number of years, Gold Traube, has produced just five little berries and a lot of top growth.  This growth looks different to the fruit bearing part of the bush.  I have had previous experience with 'Top Hat', which produced no fruit at all (over a number of years) but a lot of this strange growth.  Are bb bushes grown on a separate rootstock?  I am at a loss to know what to do.