Weed Management Strategies for Organically Grown Flax (Linum usitatissimum).
Sarah Carlson1, Mary H. Wiedenhoeft2, and Margaret Smith1. (1) Iowa State University, 1537 Agronomy Hall, Ames, IA 50011-1010, (2) 1126D Agronomy Hall, Iowa State Univ., Ames, IA 50011-1010
Demand for certified organic flax (Linum usitatissimum) grown in the upper Midwestern U.S. has increased due to a rise in consumer demand for food products rich in omega-III oil and due to the recent construction of a certified organic oilseed expelling facility in northwestern Iowa. Challenges exist to raising organic flax in the upper Midwest due to competition from weeds and limited information about weed management strategies for organic farmers. Weeds can negatively impact flax yield and re-populate the soil seed bank, increasing weed pressure in organic crop rotations. Seven weed managment strategies for flax were compared in 2005 and 2006 at two locations in Iowa. Treatments, categorized as either biological, mechanical or chemical, included: drilled flax (no underseeding); drilled flax + brodcased red clover (Trifolium pretense)(16 kg ha -1); drilled flax + broadcasted alfalfa (Medicago sativa)(18 ka ha -1); drilled flax + broadcasted grass/legume mix (orchardgrass (Dactylis glomerata) 2.2 kg ha -1, timothy (Phleum pretense) 3.4. kg ha -1, red clover 4.5 kg ha -1 and alfalfa 4.5 kg ha -1); drilled flax + Sethoxidym (Poast) and MPCA (Rhomene) MCPA herbicides; broadcasted flax; and flax cross drilled at half rates at 30° angles in two directions. Flax was planted in early April at 56 kg ha -1. Flax was harvested when plots contained 95% dark brown bolls at each location during late July. Flax grain yield, total percent oil, treatment biomass dry weight, and weed biomass dry weight were measured to assess: 1. Which weed managment strategy will control weeds the best in flax? 2. How damaging are weeds on flax grain yield and total percent oil? Results from 2005 indicated that weed competition reduced yields and percent oil only for the broadcast treatment.