False cleavers and catchweed bedstraw are problematic weeds of field crops in high-latitude regions of the northern Great Plains of North America. The abundance of these species has been increasing in areas of greater tillage intensity and frequency. Field experiments were established over 4 site-yr in Manitoba, Canada, and results indicated that the recruitment of false cleavers and catchweed bedstraw was strongly promoted by a single shallow tillage operation with a sweep cultivator in the spring. Percent recruitment levels in 2001 (pooled over sites) were 17 and 46% for the untilled and tilled treatments, respectively. In 2002, the percent recruitment levels for the untilled and tilled treatments, respectively, were 28 and 38% for the Komarno site and 13 and 28% for the Petersfield site. Only a few and minor differences in microsite conditions (soil temperature, soil moisture, and bulk density) resulted from the single spring tillage pass. The single tillage pass caused a significant relocation of simulated seeds (plastic beads) to below the soil surface and deeper into the soil profile (2–4 cm). Mean bulk density and volumetric soil moisture increased significantly with soil depth. The results of this study suggest that the positive effect of tillage on cleavers recruitment was not due to the effect of tillage on microsite conditions per se. Rather, the vertical redistribution of seed by tillage moved these seeds to a place in which the microsite conditions differed from those on the surface and were more favorable for recruitment. False cleavers and catchweed bedstraw recruitment is clearly promoted by tillage (even minor tillage) under field conditions, and farmers might be able to limit recruitment by limiting spring tillage.

Nomenclature: False cleavers, Galium spurium L. GALSP; catchweed bedstraw, Galium aparine L. GALAP.