The influence of soilless growing media on the movement and longevity of the herbicide dimethenamid-P

Pine bark based soilless growing media dominates substrates use in containerized plant production in the ornamental industry. Due to high organic matter content coupled with limited cation exchange capacity (CEC), surface area, and bulk density, the time period herbicides can provide weed control within soilless media combinations may vary. Limited information exists in scientific literature about the interaction of soilless growing media with herbicides. Dimethenamid-P was recently registered by BASF for control of annual grasses, broadleaf weeds, and sedges in containerized ornamentals. A study was conducted to examine dimethenamid-P chemical behavior for two soilless media, pine bark alone, and a commercial mix containing pine bark. Data indicated that dimethenamid-P was not detected in the leachate from these materials. Bioassay data indicated that dimethenamid-P grown in the pine bark mix provided significant control of common lambsquarters (Chenopodium album) and tall fescue (Festuca arundinacea) for 6 weeks after treatment.