Responses to defoliation and fertiliser, corm development and chemical control of onion grass (Romulea rosea) in the Mediterranean environment of southern Australia

Abstract

Background

Onion grass (Romulea rosea) is a common weed that infests native and improved pastures in the Mediterranean environments of southern Australia. It is a very challenging weed to control due to its distinctive growth and survival mechanisms involving corms.

Methods

Three glasshouse experiments were conducted in Australia to investigate the response of onion grass to defoliation and fertiliser application, the development and growth of onion grass corms and the chemical control of the weed in winter and spring.

Results

Defoliating consistently to 1 cm above ground reduced corm weight by 84% compared with the control. Medium or high fertiliser application did not increase herbage mass of onion grass compared with the nonfertilised treatment. The corm weight of onion grass declined from Weeks 1 to 8 after emergence, remained at 53–60 mg dry matter (DM) corm⁻¹ from Weeks 8 to 19 and then declined on average to 37 mg DM corm⁻¹ up to Week 26 after emergence. New corms started to develop at Week 6 after emergence. A small proportion of the onion grass plants (7.5%) developed multiple new corms (3–6 corms) from a single old corm. The most effective herbicide control was a winter application of metsulfuron methyl or imazamox as an alternative product to protect clover.

Conclusions

This study has identified the growth and development patterns of onion grass corms, how the plant responded to defoliation and fertiliser application and effective chemical control of this weed. These findings have significant practical implications for the improvement of onion grass-infested pastures.