The biology of autumn and spring emerging cleavers (Galium aparine) individuals

Field studies into the emergence patterns of cleavers (Galium aparine) popu lations and the biology of individuals emerging on different dates were und ertaken in autumn sown winter wheat crops. The emergence pattern study show ed that 7% of the total population emerged in the spring. The emergence pat tern of cleavers populations was variable both within and between populatio ns at the different sites. The vigour of cleavers individuals emerging late r was significantly reduced when compared to those emerging with the crop i n the autumn. However, later emerging individuals (after March 1(st)) were less sensitive to competition from the established crop than those of black -grass (Alopecurus myosuroides). Autumn emerging cleavers caused a 23% redu ction in yields, whilst the same density emerging in spring had no detectab le effect. Although spring emerging cleavers did not impact significantly o n the growth of the crop they produced up to 150 seeds/m(2) (at an average of 5.34 seeds/plant).