Agriculture Reference
In-Depth Information
represented within these management categories (Letourneau and Goldstein 2001). Organic
farms had a more diverse arthropod fauna than conventional farms, with the average for five
30-s vacuum samples per farm yielding about 40 arthropod morphospecies in conventional
tomato and 66 morphospecies in organically managed tomato. Natural enemies (parasitoids
plus predators) were almost twice as abundant on organic compared to conventional farms.
Conventional tomato fields received seven times as many insecticide sprays as organic
fields (Letourneau and Goldstein 2001), and the application frequency, spectrum of toxicity
and persistence of pesticides was inversely associated with some of the prominent natural
enemies. Fields managed with cover crops or annual weeds over the winter wet season had at
least a magnitude higher abundance of these parasitoids and f flea beetles than did fields that
were kept in bare fallow (no vegetation). Vegetative fallow practices, which maintained vegeta-
tive cover during the wet season, may have perennialised the crop habitat to allow continuity
of certain arthropod populations through the year. Natural enemies are often enhanced in
perennial crop habitats and in vegetative fallow compared to annual crops disrupted by bare
fallow (Honek 1997). However, insecticide treatments could disrupt the potential stability
gained by local vegetational cover. In general, practices used more often on organic farms,
such as cover cropping and low intensity pesticide treatments, were associated with increases
in parasitic wasps (primary source of variability among farms) and more predators.
Clearly, the avoidance of synthetic insecticides and fungicides in organic tomato produc-
tion did not reduce yields by the predicted 36% (Agricultural Issues Center 1988). Indeed, in
both the SAFS experiment and the field surveys, there were no significant differences in pest
damage between CNV and ORG treatments. Arthropod communities were not monitored in
the SAFS experiment, but substantially different arthropod community profiles in ORG v.
CNV farmers' fields (species diversity of herbivores and abundance and species diversity of
natural enemies) suggested that natural biological control on ORG farms may be compensat-
ing for pesticide inputs in CNV operations. Whereas specific management practices and land-
scape characteristics of ORG and CNV farms were associated with abundance patterns of
specific pests and natural enemies, these management schemes were generally robust to
variable pest control challenges on individual farms.
Conclusions
For any given combination of crop, location, labour and capital availability conditions there
are potentially several optimum crop protection strategies. Different crop production or pro-
tection strategies include schedule-based prevention, integrated pest management, organic,
traditional, biodynamic, biological or ecological practices. Alternative strategies may rely on
fundamentally different conceptual approaches, yet also function as viable suites of best man-
agement practices for crop production. Andow and Hidaka (1989) demonstrated the idea of
such 'syndromes of production' using Shizen and conventional rice farming management
schemes, and show that qualitatively different sets of integrated practices can produce favoura-
ble outcomes in terms of yields and profit. We suggest here that for most conventional crop
production systems in most locales, viable alternatives, including organic agricultural schemes,
either already are in practice or are possible. To support and develop alternative crop protec-
tion schemes that are economically, socially and environmentally sustainable, alternative lines
of research, price supports, agricultural policies, and land-use practices may need to be
embraced. To optimise crop protection in organic agriculture, research should be geared to
defining and accessing suites of crop production materials and practices that work in concert
as a favourable production syndrome (
sensu
Andow and Hidaka 1989). We suggest four key
research areas for crop protection improvement in organic agriculture.
