In the past 20 years, the lake shores have exchanged any lingering memories of the past for a booming industry in the cultivation and sale of out-of-season vegetables like snow peas and trimmed beans, and cut flowers like roses and carnations — virtually all of them exported to distant markets in Europe. Paradoxically, the huge expansion of fancy food for export has come in a land that, because of sporadic drought and not-so-sporadic economic mismanagement, cannot grow enough of its own staple, corn.