W. Bond et al., OPTIMUM WEED REMOVAL TIMING IN DRILLED SALAD ONIONS AND TRANSPLANTED BULB ONIONS GROWN IN ORGANIC AND CONVENTIONAL SYSTEMS, Biological agriculture & horticulture, 16(2), 1998, pp. 191-201
In field experiments with drilled salad onions, a single weeding made
at 4 weeks after 50% crop emergence was sufficient to prevent signific
ant yield loss due to weeds. Weed removal 5 or 6 weeks after 50% crop
emergence was generally unsuccessful in averting crop losses. It is we
ll known that the relative timing of crop and weed emergence is import
ant in determining the balance of crop-weed interactions. In the prese
nt experiments, the pattern of crop and weed emergence varied between
sites and years but the removal of early emerging weeds, at 4 weeks af
ter 50% crop emergence, avoided weed interference consistently. In the
transplanted bulb onion experiments, the crop began with an advantage
over the weeds, and a single weeding made at 5, 6 or 7 weeks after pl
anting was effective in preventing a reduction in yield. There was no
difference in response between crops grown organically and those grown
conventionally. Yield loss was due mainly to weed competition occurri
ng prior to handweeding or mechanical injury to the crop following lat
e or repeated weed removal. In the conventional crop, a single weeding
that removed inter-row weeds but left within-row weeds in place gave
yields little better than those of the unweeded crop.