Emergence Timing and Recruitment of Volunteer Spring Wheat

Abstract

With the recent interest in genetically engineered (GE) wheat and the commercialization of novel-trait imidazolinone herbicide-resistant wheat in North America, volunteer wheat as a weed has also been the subject of renewed interest, specifically, its recruitment and persistence in annual cropping systems. The recruitment of seed from a wheat seedbank established the previous autumn was monitored in a flax crop at two field sites in southern Manitoba, Canada, in 2003 and 2004. Seeds of eight Canadian Western Hard Red spring wheat cultivars, which exhibit a range of preharvest sprouting-resistance characteristics, were broadcast and incorporated into the soil in the autumn at 500 seeds m−2. Tillage treatments consisted of autumn tillage only, and autumn and spring tillage. Recruitment the following spring occurred very early in terms of accumulated growing–degree days (base temperature of 0 C) but expressed as a proportion of total seeds broadcast was low and variable. Total cumulative emergence of wheat over all 4 site yr ranged from 0.9 to 13.1%, with an overall average of 4.3%. There was no relationship between preharvest sprouting-resistance characteristics and recruitment proportion, and no significant influence of tillage treatment on wheat recruitment. Wheat seed that did not recruit was rapidly degraded in the soil and did not persist for more than 12 mo. However, some emerged volunteer wheat plants escaped all control measures normally used in establishing and growing a typical flax crop, and these escaped volunteer wheat plants set viable seed. Therefore, results of this study indicate that efforts and attention should be directed toward achieving very high levels of volunteer wheat control in subsequent rotational crops and that reseeding by escaped volunteer wheat plants may be a more important persistence mechanism for spring wheat than multiyear soil seedbank persistence.