Agriculture Reference
In-Depth Information
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Weed management: a need for ecological
approaches
Introduction
Agriculture is the process of managing plant communities to obtain
useful materials from the small set of species we call crops. Weeds comprise
the “other” set of plant species found in agroecosystems. Although they are
not intentionally sown, weed species are well adapted to environments domi-
nated by humans and have been associated with crop production since the
origins of agriculture (Harlan, 1992, pp.83-99).
The ecological role of weeds can be seen in very different ways, depending
on one's perspective. Most commonly, weeds are perceived as unwanted
intruders into agroecosystems that compete for limited resources,reduce crop
yields, and force the use of large amounts of human labor and technology to
prevent even greater crop losses. In developing countries, farmers may spend
25 to 120 days hand-weeding a hectare of cropland (Akobundu,1991),yet still
lose a quarter of the potential yield to weed competition (Parker & Fryer,
1975). In the USA, where farmers annually spend $6 billion on herbicides,
tillage, and cultivation for weed control (Chandler, 1991), crop losses due to
weed infestation currently exceed $4 billion per year (Bridges & Anderson,
1992).
At the other end of the spectrum, weeds can be viewed as valuable agroeco-
system components that provide services complementing those obtained
from crops. In India (Alstrom, 1990, pp. 25-9) and Mexico (Bye, 1981; Mapes,
Basurto & Bye, 1997), farmers consume
Amaranthus
,
Brassica
, and
Chenopodium
species as nutritious foods before crop species are ready to harvest. In western
Rajasthan, yields of sesame and pearl millet can be increased by allowing the
crops to grow in association with the leguminous weed
Indigofera cordifolia
(Bhandari & Sen, 1979)
.
Certain weeds may limit insect damage to crops by
interfering with pest movement or by providing habitat for natural enemies
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