(Jared Strong/Iowa Capital Dispatch)OMAHA — High interest rates, along with weak farm commodity prices and equipment sales, helped push a regional “rural mainstreet” economic index tracked by Omaha’s Creighton University to below growth neutral for the 10th month in a row. The Rural Mainstreet Index is based on a monthly survey of bank chief executives in 10 states including Nebraska, targeting about 200 rural communities with an average populat…