Weed control and response of transplanted uhaloa in the presence of two pre-emergence herbicides applied at the time of planting

The Hawaii Statewide Noxious Invasive Pest Program (SNIPP) and associated storm water management plans provide statutory justification for increased use of native plants along the State of Hawaii transportation corridors. The demand for native plants exceeds the availability of plant materials or seed. To produce seed stock and ensure seed lot purity, establishment protocols for weed control must first be defined. Uhaloa (Waltheria indica), a native Hawaiian broadleaf shrub has been identified for increased roadside usage, thus will be the focus of this research. Weed control during the establishment phase of uhaloa is essential for optimising establishment success. In this study, the efficacy and phytotoxicity of the pre-emergence herbicides oxadiazon and indaziflam, applied over uhaloa transplants, were evaluated. Crop and weed response to granular oxadiazon at 2.24 kg ai ha-1 and 4.48 kg ai ha-1 and flowable indaziflam at 24 g ai ha-1 and 49 g ai ha-1 were determined. Unacceptable uhaloa injury with both rates of indaziflam was recorded. Oxadiazon provided excellent broad-spectrum weed control with acceptable injury to uhaloa.