In NW Europe a major limitation to the yield of sugarbeet is development of the foliage canopy in May and June, too late to capture much of the available solar energy. This problem could be solved if the crop was sown during autumn so that the seedlings survived the winter and developed a large leaf canopy in early spring. This has led to a search for mechanisms to control flowering so that plants remain vegetative after the winter. However, there has been no serious attempt to estimate the effect of advanced canopy development on the likelihood of water stress. This study has used a combination of modelling of growth to predict yield of rainfed crops and an analysis of the literature to examine the likely consequences for pest and disease incidence if autumn sowing could be achieved without bolters. Compared to spring sowing, a potential yield advantage averaging 26% could be achieved, but this is likely to be overturned by any one of several beet-specific pathogens. For example, beet yellows virus would become more difficult to control and this has the potential to halve yield. Downy and powdery mildew and beet cyst nematode would be more expensive to control. The change from spring to autumn sowing would not allow harvest to be significantly earlier; this would be prevented by dry, strong soil conditions. Nevertheless, the increased emphasis on autumn work on arable farms would be costly.