Weed management: a need for ecological approaches - Ecological Management of Agricultural Weeds - page 28

improve machinery and other components of their farming system, conduct
field day tours, exchange information with other farmers, and participate in
collaborative research projects with scientists at Iowa State University and
other institutions (Chapter 3) (Harp, 1996; Thompson, Thompson &
Thompson, 1998). Experiments conducted on the farm have shown that its
weed management system protects maize and soybean from weed competi-
tion as effectively as conventional herbicide-based systems (Exner,Thompson
& Thompson, 1996; Thompson, Thompson & Thompson, 1998). Production
costs on the farm are lower than for conventional farms in the area, but crop
yields are as high (National Research Council, 1989, pp.308-23).
Combinations of ecologically based weed management tactics are also
used effectively by certain farmers in the Canadian prairie provinces and the
American northern plains states. Matheson et al . (1991) and Hilander (1997)
described crop and livestock farms in the region that range from 400 to 1100
ha and operate profitably with little or no herbicide use. Insect herbivores
and mixed stocking of sheep with cattle are used to suppress perennial weeds
in grazing lands. In arable fields, weeds are managed through the use of
higher seeding rates,competitive crop varieties,pre- and post-emergence cul-
tivation, and crop rotation. Various annual crops (e.g., wheat, barley, oat,
lentil, pea, flax, buckwheat, and sunflower) are grown in sequence or in
mixture with perennial or biennial forage legumes (e.g., alfalfa and sweet
clover). In some cases, short-duration legumes (e.g., pea and lentil) are
included in rotations as green manures. Where possible, fall-sown crops are
alternated with spring-sown crops. As discussed in Chapter 7, sequences and
mixtures of diverse crops can help to prevent the proliferation of adapted
weed species by challenging them with complex sets of stress and mortality
factors.
Additional options have been proposed for ecological weed management
in the Canadian prairies and American northern plains.Derksen,Blackshaw &
Boyetchko (1996) suggested that increased use of residue-conserving tillage
techniques in concert with moderate use of herbicides may improve habitat
for insects,fungi,and bacteria that attack weed seeds and seedlings.The inves-
tigators noted that there is considerable potential to minimize herbicide use
in conservation tillage systems through improved use of crop rotations, com-
petitive cultivars, and crop densities and fertilizer placement strategies that
enhance crop competitive ability against weeds.
Lightfoot et al . (1989) described the use of the agroecosystem redesign
approach by a group of farmers and scientists in the Philippines seeking to
manage the perennial grass Imperata cylindrica. To begin the process, group
meetings and individual farm visits were used to facilitate discussions and