Biology Reference
In-Depth Information
varying crop sowing date (Clayton et al. 2004), or by varying the date of crop har-
vest (Harker et al. 2003b). Almost any other method that introduces diversity into
cropping systems can reduce the prevalence and impact of a relatively few domi-
nant weed species. Therefore, crop diversity can be temporal (varied planting and
harvest dates), spatial where different species are grown in the same space but at
different times (variable life cycles), or by growing different crop species at the
same time and in the same space (intercropping).
8.7
System Approach Vs. Single Components
It is important to recognize that any single practice will not be adequate for long-term
weed management. Successful crop managers combine a variety of weed management
practices both in time and in space. For example, combining early herbicide application
with a competitive canola cultivar and higher-than-normal seeding rate not only reduced
weed biomass and variability, but also improved crop yield (Harker et al. 2003a). When
combining several optimal practices, a major goal should be the promotion of crop
health. Healthy and early developing crop canopies limit weed invasion (Harker et al.
2005), because they exploit weed vulnerability to low light and altered light quality
(Mohler 2001) and pre-empt nutrient and soil moisture resource availability. Overall,
annual weed invasions can be managed when two or more related cropping principles
are used in combination: in this case, rotational diversity and crop health.
Beck (2006) reminds us that 'Successful crop production, regardless of the methods
used, is a careful piecing together of numerous components into a system. Simply replac-
ing one component with another is seldom successful'. Focusing on crop health and
competitiveness will lead producers to adopt a tool kit of management practices that
includes sanitation to limit weed seed spread, low-disturbance seeding (maintaining crop
residues), higher crop seed rates, relatively narrow row spacing, optimum fertilizer place-
ment, and diverse crop rotations. For example, the simple practice of increasing crop seed
rates consistently reduces weed competition and improves herbicide performance
(Blackshaw et al. 2006; Mohler 2001), and is a very effective form of biological weed
control (Blackshaw et al. 2000; Harker et al. 2005). Seeding crops at relatively high rates
can also increase weed economic threshold values, and thus reduce the need for herbicide
application (O'Donovan et al. 2005). Poor fertility can reduce crop health to the degree
that all of the tools employed for pest management are negated. Similarly, disease and
insect management are also important for weed management because of their impact on
crop health and competitiveness. It may be that the best weed management approach for
a weakly competitive crop such as pea (
Pisum sativum
L.) is to ensure that optimal prac-
tices are combined to limit weed seed production in the crop grown before pea.
ICM exploits synergies that are possible when technologies are combined with
natural resources for sustainable and profitable crop production. Crop management
solutions can be so urgent that
quick-fix
remedies seem imperative. In response,
research and extension personnel have often stressed single tools (usually a techno-
logical input such as a herbicide). However, crop management challenges are the
