Seasonal and site variability in the tolerance of wheat cultivars to interference from Lolium rigidum

The ability of crop cultivars to maintain yield in the presence of weeds was examined at a number of locations and in successive years. It was found that the magnitude of yield advantages from particular cultivars differed considerably between years and locations. Moreover, there was little correlation between competitiveness at different sites within a year or in different years within a location. Only one cultivar out of 17 in the Western Australian experiments was consistently a good competitor; two cultivars were consistently poor. The former may be of use in breeding for competitiveness, whereas the latter should clearly be avoided in weedy situations. Several cultivars were among the most tolerant at three sites but competed poorly at any one site. It is argued that this makes the provision of advice for farmers difficult. More attention needs to be given to agronomic ways of making a given cultivar more competitive.