Oregon's Swanson Group is implementing production curtailments with immediate effect, citing deteriorating market conditions.  The group's stud mill in Roseburg will curtail production by 30%, while its Glendale sawmill will reduce output by 20%, the report said.  Swanson Group Inc., along with its subsidiaries, is engaged in manufacturing, marketing, and selling forest products for residential and industrial applications. It offers various wood products, including Doug Fir dimension lumber products, structural plywood panels and specialty plywood products, veneer and residual products, and green and dry studs ...