Corn futures retreated after rising for the previous three sessions in a rebound from contract lows set on Monday. Both markets continued to face pressure from expectations for large US autumn harvests and mostly favourable crop weather in the world's biggest corn-producing country and second-largest soybean producer. "We're marching to a crop, and the weather looks non-threatening," said Don Roose, president of brokerage US Commodities. CBOT corn was down 3-3/4 cents at $4.20-1/4 a bushel. "While price weakness attracted opportunistic demand, a favourable weather outlook could well see lows tested again in the weeks ahead," Rabobank analysts said.