The sustainability of conservation tillage is dependent on the extent
of changes in weed community composition, the usage of herbicides, and
the development of integrated weed management (IWM) strategies, inclu
ding biological weed control. The objective of this paper is to review
research on conservation tillage and weed management in light of thes
e factors. Recent Canadian research has found that changes in weed com
munities due to the adoption of conservation tillage are not necessari
ly those expected and were not consistant by species, location, or yea
r. Changes reflected the use of different selection pressures, such as
different crop rotations and herbicides, within the studies to a grea
ter extent than weed life cycle groupings. Therefore, research that de
termines the reasons for change or the lack of change in weed communit
ies is required to provide the scientific basis for the development of
IWM strategies. Documented herbicide usage in conservation tillage va
ries from less than to more than conventional-tillage systems. Potenti
al to reduce herbicide usage in conservation-tillage systems exists: F
urthermore, the herbicides used in western Canada are different from t
hose causing ground water contamination in the United States, are less
volatile, and are used at lower rates. The presence of surface crop r
esidues in conservation tillage may provide a unique environment for c
lassical and inundative biological control agents. Some insects, fungi
, and bacteria have the potential to survive to a greater extent in un
disturbed plant residues. Residue management and conservation tillage
systems are evolving in Canada. Research must keep pace by providing w
eed management strategies that enchance the sustainability of these sy
stems.