The battle for the Dawson: can sunn hemp be cotton's underground hero?

Abstract

Sunn hemp (Crotalaria juncea) has been used overseas as a cover crop for nematode suppression and nitrogen fixation. This legume has not been readily available in Australia until recently when AGF seeds were granted import approval for planting seed in 2022. Reniform nematodes (Rotylenchulus reniformis) are a serious pest of cotton and were first detected in the Dawson Valley in 2012. This pest has caused considerable yield loss with the only control measure having been crop rotation with non-host species like sorghum. However, the forfeiture of a cotton crop to accommodate a low value summer grain crop that provides temporary relief for 1-2 seasons at best on high value irrigation country is uneconomic. Recent research has explored the use of sunn hemp as a short-term cover crop, grown between cotton crops for nematode suppression. This may become part of an integrated farming system that could also include future cotton varieties with resistance to reniform nematodes. This presentation will introduce you to Sunn hemp and share the results of recent research in CQ where it has successfully suppressed nematodes resulting in improved cotton yield. Finally, the talk will also consider its potential to be utilised as a dual-purpose cover crop in warm regions for the purpose of pest suppression, nitrogen fixation and soil health.