Cotton futures rose the most in five months on mounting concern that adverse weather will slash output in the U.S., the world’s biggest exporter.

Conditions in Texas, the biggest U.S. producer, range from “abnormally dry” to “exceptional” drought, the most-severe ranking on the U.S. Drought Monitor. Cotton futures for December delivery, the contract with the highest open interest, rose 8.1 percent last week.

“Everyone was waiting to see what would happen with the weather and production, and the news wasn’t good,” said Mike Stevens, an independent trader in Mandeville, Louisiana. “This is a critical period, and it looks like we have weak supply.”

Cotton for December delivery rose the exchange limit of 6 cents, or 4.6 percent, to settle at $1.355 a pound at 2:37 p.m. on ICE Futures U.S. in New York. That’s the biggest gain for a most-active contract since Dec. 3.

The markets were closed yesterday for a U.S. holiday.