WINNIPEG - The U.S. Commerce Department on Tuesday imposed a 3.94 per cent tariff against Canadian wheat exports, a much lower duty than Canadian trade officials expected. The preliminary duties are the result of a U.S. Commerce Department trade law investigation into Canadian exports of durum wheat and hard red spring wheat into U.S. markets. American trade officials and American farmers allege Canada unfairly subsidizes the exports by undercutting the price of U.S. wheat. In its decision, the Commerce Department says a preliminary investigation shows material damage to farmers from the Canadian imports. The Canadian Wheat Board controls the sale...