So here I am standing in a vineyard soaking up the sunshine and the brilliant field of yellow before me.  Mustard, the condiment that finds its way into many a dish and on bun alike paints another postcard for us in the Napa Valley.  The wild mustard is in full bloom throughout the vineyards.  This time of the year the vines themselves are catching a long winter nap but the mustard and other cover crops are growing …