Of DOW JONES NEWSWIRES MOSCOW (Dow Jones)--Russian Prime Minister Vladimir Putin banned grain exports for the rest of the year amid severe heat and drought that has kindled fires throughout the country, sending U.S. wheat futures toward their highest open in nearly two years. September wheat on the Chicago Board of Trade finished the overnight trading session up the daily, exchange-imposed limit of 60 cents at $7.85 3/4 a bushel, an 8.3% increase from .