Agro‐ecology of onion couch ( Arrhenathemm elatius var. bulbosum (Willd.)).

SUMMARY This study investigates the performance of vegetative propagules of onion couch ( Arrhenatherum elatius var. bulbosum) of varying sizes during the crop growth cycle; especially trends in tiller and bulb production and crop yield loss. The results suggest that the earlier the crop canopy closes the more suppression it will exert on the bulb formation stage of onion couch and hence its future reproductive potential. The closed canopy provided by a dense crop cut short the bulb formation phase and forced onion couch to invest more in aerial tillers in order to compete and coexist with the taller tillers of the crop. An additive experimental design used here to predict the crop losses indicated that natural infestation of onion couch caused greater crop yield loss compared to artificially planted plots. It was found that, although the regrowth from large aggregates with densely packed bulb chains is reduced by correlative dominance and density dependent mortality, presence of such large aggregates can affect crop yield by interfering with the establishment of crop. The competitiveness and development pattern of onion couch suggests that the recent spread of the weed and the reported variable results of control measures is due to the recent shift in agricultural practices.