Agronomy Library > Soil Conservation

Weed Suppression of Alfalfa (Manitoba Weed Population Comparative Survey)
Author: P. D. Ominski, M. H. Entz, and N. Kenkel
Date Created: February 10, 1999
Last Reviewed: February 28, 2007

Document Source: Weed Science. 47 (3): 282 - 290 

A survey was conducted in Manitoba, Canada, in 1993 and 1994 to investigate weed populations in commercial cereal fields that had been preceded by either M. sativa (alfalfa) hay or cereal grain crops. A total of 117 fields were surveyed; approximately half from each field type.

- Principal component analysis indicated that the inclusion of M. sativa in crop rotations resulted in weed communities different from those of continuous cereal fields.

- Naturally occurring populations of wild oat (Avena fatua), Canada thistle (Cirsium arvense), wild mustard (Brassica kaber) and cleavers(Gallium aparine) were lower in cereal fields that had previously contained M. sativa than in cereal fields that had been preceded by a cereal crop.

- Lower field uniformity values for Canada thistle and wild oat indicated that these weeds were also more patchy in the M. sativa rotations. 

- Population differences between field types were non-significant for redroot pigweed (Amaranthus retroflexus), lamb's quarters (Chenopodium album) and green smartweed (Polygonum convolvulus), whereas populations of dandelion (Taraxacum officinale) and stinkweed (Thlaspi arvense) were greater in M. sativa/cereal fields than in continuous cereal crops. No consistent effect of field type on green foxtail (Setaria viridis) populations was observed.

These results show that M. sativa effectively suppressed some, but not all, of the weeds found in the study area. Including alfalfa hay crops in rotations can be part of an integrated weed management strategy for weeds such as wild oats, wild mustard and Canada thistle.