Effects of Poa trivialis, Stellaria media and Rumex obtusifolius on the growth of Lolium perenne in the glasshouse

SUMMARY In glasshouse experiments shoot dry weight, leaf area and tiller number of Lolium perenne, cv. S. 24, were compared when grown in monoculture and in competition with Poa trivialis, Stellaria media or Rumex obtusifolius at a range of densities and for different time intervals. The results showed that S. media and R. obtusifolius were more competitive than P. trivialis. Competition effects with S. media and R. obtusifolius appeared between the 4 and 6 wk stage, coinciding with the production of the first S. 24 tillers. Spraying with 2,4‐D (0·84 kg acid equivalent/ha) for control of R. obtusifolius did not decrease grass yield whereas mecoprop (2·80 kg a.e./ha) for control of S. media damaged young L. perenne. It appeared that the optimum time for mecoprop treatment was between 4 and 6 wk after sowing when tillering had commenced. At this stage weed competition was only beginning and crop tolerance to the herbicide was adequate.