Interfor said it would reduce output by at least 15% for the rest of 2024, increasing curtailments it made earlier this year amid tumbling demand and prices for two-by-fours.   Interfor, which owns sawmills across Canada, the U.S. South and in the Pacific Northwest, said it would reduce output by as much as 350 million board through December. The announcement gave a jolt to lumber prices, which added $23 per thousand board feet Friday to end at the highest price since May and nearly 20% above the July low.   "Lumber prices ...