Operation witch hunt: conjuring eradication of the parasitic red witchweed plant with trickery and potions

Abstract

An integrated field trial was established near Mackay, Queensland, to test treatment efficacy for eradicating the parasitic weed, red witchweed (RWW) (Striga asiatica (L.) Kuntze). Treatments tackling the only known infestation of RWW in Australia include pre and post-emergent herbicides, catch crop, trap crop plants and fumigants. One thousand canisters containing 5800 seed sachets were buried to monitor seed bank decline over time. Each canister contained seed sachets buried at five depths. At six months posttreatment application, 100 canisters were exhumed and a further 100 will be exhumed annually, to evaluate RWW seed viability following annual treatment applications. This trial will determine the treatment options that are most effective at accelerating soil seed bank decline and preventing above-ground emergence of RWW. These results will govern the management strategies utilised within the RWW eradication program.
The six-month retrieval data showed encouraging trends. As seed burial depth increased from 0 cm to 50 cm deep, seed viability increased from 61 to 69%. Treatments utilising herbicides did not significantly differ from the control (maintaining bare ground) treatment (81% and 77% seed viability). The catch crop, sorghum, had the biggest reduction in seed viability (17%), followed by the fumigants, dazomat (38%) and ethylene (39%). Ethylene gas has been used with considerable success in the USA for accelerating soil seed bank decline. Our preliminary data indicate, through the use of a host (false or true) plant and soil fumigant, exhaustion of the soil seed bank is achievable within three to five years.