Growth and development of feathertop Rhodes grass (Chloris virgata Sw.).

Feathertop Rhodes grass is an important summer weed in cotton systems. To measure the impact of time of emergence on growth and development of this weed, two glasshouse experiments were established in 2014 and 2015. Plantings commenced in October, and were repeated at four-weekly intervals. Each planting was grown for 24 weeks before above-ground biomass was harvested. Analyses were undertaken on plantings from October to April. There was a significant interaction between year and time of planting, so data was analysed separately for each year. Time of planting was significant (p <0.001) in relation to dry-weight biomass, maximum height, tiller production to anthesis, panicle production and panicle length. For the 2014 plantings, the October planting had the largest biomass (43.8 g), tiller number (15.4) and panicle number (41) than later plantings. The April planting had the lowest biomass (1.4 g) and grew, on average, to 22.6 cm compared to 141.7 cm for the November planting. Tiller production was lowest in late December plantings (3.0) and panicle production lowest in the February planting (7.8). Similarly for 2015, October plantings had the largest biomass (31.9 g) and grew taller at 139.2 cm, while the April plantings had the lowest biomass (1.1 g) and height (29.9 cm), but produced the highest number of tillers (11.3). Panicle production was greatest in March plantings (46.2) while November plantings produced the lowest number of tillers (2.8) and panicles (15.4). In both experiments seed production was greatest from October plantings (44 355 and 29 696 seeds, 2014 and 2015 respectively). This research shows feathertop Rhodes grass growth and development is influenced by time of emergence. Management efforts should focus on, but not be limited to, early emerging plants to minimise weed seed set and competition with cotton