Isoxaben and BAS 479 14H retention/loss from peat substrate of nursery plants

Weed management for nursery ornamental plants requires several applications of preemergence herbicides to control recurring weed emergence and to counter chemical dissipation and leaching losses. Herbicide losses from plant containers in runoff water may pose risks to surface and groundwater supplies. Sphagnum pear is a frequently used rooting medium. Limited information exists on the fate of herbicides applied to pear. The leaching of two commonly used chemicals in Europe by the containerized ornamental plant industry, isoxaben and BAS 479 14H, was measured. Herbicides were applied to 1-yr-old conifers (Juniperus communis, cv. Repanda [common juniper]) grown in pots containing sphagnum pear. The isoxaben-treated pots were placed on 1- by 1-m lysimeters that were buried in the center of replicated field plots. Pots were also placed in subirrigated sandbeds to determine herbicide dissipation and movement in irrigation water. With overhead irrigation, isoxaben had a half-life of 2 mo in the 0- to 5-cm depth of the pear container. More than 96% of applied isoxaben was recovered in the 0- to 5-cm depth. Less than 4% of the amount applied was found in the 5- to 10-cm depth, and none was detected in the 10- to 15-cm depth. No isoxaben residues were detected in water percolating through the field lysimeters. In subirrigated sandbeds, no isoxaben was detected in the water rising by capillary tension. Most of the applied isoxaben was found in the 0- to 5-cm layer of the pear container, where its half-life was also 2 mo. Similar results were observed in containers treated with BAS 479 14H, which had a half-life of 1.2 mo. The high organic matter content of the pear medium strongly sorbed both isoxaben and BAS 479 14H, and these herbicides remained primarily in the near-surface zone of the pear containers. No significant herbicide leaching or loss from the containers was found when subirrigated or irrigated by sprinkler.