Knowledge, science, and practice in ecological weed management: farmer–extensionist–scientist interactions - Ecological Management of Agricultural Weeds - page 109

recently participation (Roling, 1988, pp. 36-62). Interfaces between knowl-
edge communities, however, are just as often characterized by gaps, disconti-
nuities, and differences, precisely because they represent the point of contact
between communities with contrasting objectives and procedures for gener-
ating knowledge (Long & Villareal, 1994). These discontinuities may be sig-
nificant when indigenous farm communities interface with government
extension services staffed with urban-born technicians who have limited field
experience, not an uncommon situation in Africa, Asia, and Latin America.
Cultural and class prejudices, mutual lack of respect, and divergent interests
in such cases may produce reinforcing negative images and limit productive
interaction. Even when farmers, extensionists, and scientists have a common
culture and similar preferences in crop technology, each sector uses different
portions of the total pool of weed management knowledge. For example, as
shown in the case study from Iowa in this chapter, the three communities
often disagree about which knowledge is more relevant and about which
themes need further attention.
Fortunately, just as knowledge communities change internally based on
the social interactions among their groups and individuals, the way they
interface also changes. To reduce crop losses to weeds and the costs of weed
control, effective work at the interface between farmers, extension, and
research is crucial (Engel, 1997, pp. 21-44). Both the nature of weeds and the
demands of decision-making in crop production indicate directions for more
effective interactions among farmers, extensionists, and scientists.
Weed patchiness and uncertainty: the challenge to
improving weed management
Weeds in a crop field are distributed irregularly, with patches of high
density as well as patches with few weeds (Cardina,Johnson & Sparrow,1997).
Spatially these patches may be relatively stable from year to year, a product of
localized seed rain, a relatively immobile seed bank, the clonal spread of vege-
tatively propagated weeds, and the patchiness of the soil environment
(Colbach, Forcella & Johnson, 2000).
Although many weed species may be present in a field, only a limited
number are important for crop management (Johnson et al ., 1995). Each of
these species has a defined life cycle with a relatively defined phenology
around which weed and crop management practices are usually organized.
This patchiness of weeds presents difficulties for monitoring and record-
ing weed abundance and composition at the field and farm scale. Weeds
reduce crop losses at the scale of individual crop plants. Control practices,