Effects of weed competition for different periods on the growth and yield of red beet

Abstract

SummaryIn four field experiments during 1968–70 annual weeds were removed by hand at different times from crops of red beet drilled at the end of April, and the effects on growth and yield determined. The presence of weeds at densities up to 1300/m2 during the first 4 weeks after 50% crop emergence did not affect yield if the crop was subsequently kept clean, and at low densities this period was extended. When 15–240 weeds/m2 remained throughout, yields of roots were reduced by 45–98%. Once competition began, fewer leaves were formed which were smaller, had a lower chlorophyll content and died more rapidly than those of the weed-free crop, but there was a considerable capacity for recovery after the weeds had been removed. It was only necessary to keep the crop clean for 2–4 weeks after 50% emergence; weeds that emerged after this were effectively suppressed by the crop. There was no ‘critical period’ of weed competition, and a single weeding at an appropriate time was sufficient to give a yield equal to that of beet which had been weed-free throughout.