Oxadiazon, Oryzalin, and Oxyfluorfen Residues in Container Plant Nurseries

Abstract

Ronstar® and Rout® are two of the most common and effective preemergent herbicides used by the nursery industry. However, there is some uncertainty as to what happens to the chemicals in nurseries that are recycling their runoff water. The fate of the chemicals has been studied in two nurseries that are completely dependent on recycled water. Negligible amounts were found in the recycled irrigation water. Most of each herbicide remained where it was applied, either close to the top in the substrate, or on the surface of the growing area, for periods of ≈4 months. Five months after application, <10% of oryzalin remained vs. ≈30% of the oxyfluorfen and oxadiazon. Less residue was produced if oxadiazon was applied when the pots were packed together after potting up, compared to application to spaced pots in the standing area. These herbicides are of low mammalian toxicity, and the main hazard is from contamination on the standing area after application, and from the top layer of substrate. To minimize any risk, we recommend that the herbicides be applied before the plants are spaced out on the growing area, and that staff handling the pots take suitable precautions, and in particular avoid inserting their unprotected hands into the top of the mix. Chemical names used: 2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one (oxadiazon); 4-(dipropylamino)-3,5,-dinitrobenzenesulfonamide (oryzalin); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trichloromethyl)benzene (oxyfluorfen); tritium-labelled [N-(4-chloro-2-fluoro-S-(propargyloxy)-phenyl]-3,4,5,6-tetrahydrophthalimide [3H]THP.