Germination biology of liverseedgrass (Urochloa panicoides) and its response to postemergence herbicides in Australian conditions

Abstract

Liverseedgrass (Urochloa panicoides P. Beauv.) is one of the most important summer grass weed species in the eastern cropping system of Australia. Experiments were conducted to evaluate the effects of temperature, salt stress, water stress, burial depth, and sorghum crop residue load on germination and emergence of U. panicoides and the performance of postemergence herbicides on this weed species. The optimal germination temperature regimes for U. panicoides were 30/20 C and 35/25 C (alternating day/night temperatures) but seeds also germinated at temperatures occurring in winter, spring, and autumn seasons in Australia (15/5, 20/10, and 25/15 C). A concentration of 48 mM sodium chloride and -0.27 MPa osmotic potential inhibited 50% germination of U. panicoides, indicating that this weed species is not salt and drought tolerant at germination. The maximum germination was obtained for the surface seeds and a burial depth of 1.9 cm inhibited 50% emergence. No seedlings emerged from 12 cm depth but about 3% of seedlings emerged from 8 cm. The addition of sorghum residue amounts up to 8000 kg ha-1 to the soil surface stimulated its emergence compared with the no-residue treatment, suggesting that conservation agriculture will promote the emergence of U. panicoides. Several postemergence herbicides were found to be effective in controlling this weed species, especially when applied at an early stage. Information obtained from this study will help to develop effective and sustainable control measures for U. panicoides and other weed species with similar germination requirements.