Weed management: a need for ecological approaches - Ecological Management of Agricultural Weeds - page 4

(3) The composition of weed communities should be shifted toward less aggressive,
easier-to-manage species. Weed species differ in the amount ofdamage they
inflict on crops and the degree ofdifficulty they impose on crop manage-
ment and harvesting activities.Consequently,it is desirable to tip the
balance ofweed community composition from dominance by noxious
species toward a preponderance ofspecies that crops,livestock,and
farmers can better tolerate (Figure 1.1c).This can be achieved by selec-
tively and directly suppressing undesirable weed species while manipu-
lating environmental conditions to prevent their re-establishment
(Staver et al .,1995; Sheley,Svejcar & Maxwell,1996).Selective vegetation
management is particularly well suited to agroecosystems dominated by
perennial plants,such as orchards,pastures,and rangelands.
Other, broader objectives are also important for weed management
systems. Because farming is beset by uncertainties caused by variations in
prices, weather, and pests, farmers seek weed management systems that pre-
dictably and consistently suppress weeds and reduce risks of crop yield loss.
Convenience and profitability considerations lead farmers to seek weed man-
agement systems that use a desirable blend of labor, purchased inputs, and
management skills. Farmers also seek weed management systems that fit well
with other aspects of their farming system, such as crop sequence, tillage, and
residue management practices. Over the long term, weed management
systems are needed in which the number of effective management options
holds steady or increases, rather than decreases. Finally, weed management
systems need to protect environmental quality and human health.
What specific practices can be used to regulate weed density, limit the com-
petitive impact of weeds, and manipulate weed community composition in
ways that are compatible with broader, more systemic management objec-
tives?
Weed density can be reduced by using tillage practices and crop residues to
restrict the number of microsites at which weed seedling recruitment occurs
(see Chapters 4,5,and 7).Weed density can also be reduced by using tillage and
cultivation tools (see Chapter 4), biological control agents (see Chapter 8),
grazing livestock (see Chapter 9), and herbicides to kill or displace weed seeds,
vegetative propagules,seedlings,and mature plants.Monitoring and decision-
making are key components of managing weed density, and the development
and implementation of procedures for doing so are discussed in Chapter 3.
Weed competitive ability can be reduced by killing early-emerging cohorts
of weeds with herbicides or cultivation tools (see Chapter 4) and by choosing
particular crop densities, spatial arrangements, and genotypes to enhance
crop resource capture and competitive ability (see Chapter 6). Sequences and