Characteristics and benefits of a systemic approach

Concerns over pesticide resistance, environmental and health hazards of pesticides, and declining profitability are not unique to weed management. Such problems have been recognized for several decades in the management of arthropod pests and plant pathogens and led in the 1960s and 1970s to development of the concept of integrated pest management (IPM). The IPM concept has never been fully implemented for managing weeds, but its useful ness in managing insects, mites, and plant pathogens calls attention to its potential for weeds.

As described by Bottrell (1979), IPM involves the concerted use of multiple tactics to suppress and kill pests and reduce crop damage to economically acceptable levels. Emphasis is placed on modifying habitat characteristics to reduce pest densities and promote crop health, conserving and releasing beneficial organisms that attack pests, and planting pest-resistant cultivars. Pesticides are used in IPM systems as therapeutic tools only when preventive practices fail to provide adequate control. If pesticide applications are deemed necessary, selective materials are applied in a manner that poses minimal risks to human health and the environment. A key component of IPM systems is timely farmer decision-making based on knowledge of (i) crop, pest, and natural enemy biology; (ii) pest abundance and distribution; (iii) impacts of environmental factors and farming practices on crop-pest-natural-enemy interactions; (iv) cost and income implications of different management options; and (v) human health and environmental impacts of different management options.

Multitactic, ecologically based, information-intensive pest management strategies are desirable for several reasons (Bottrell & Weil, 1995; Lewis et al., 1997). First, effective pest control can result from tactics whose individual impacts are weak, but whose cumulative impacts are strong. Second, risks of crop failure or serious loss can be reduced when the burden of crop protection is distributed across many tactics, and when information is available to allow rapid adjustments in management strategies. Third, the rate at which pests adapt or evolve resistance to a given management tactic can be decreased when the frequency of their exposure to that tactic is reduced. Fourth, environmental disruptions and threats to human health can be minimized as pesticide inputs are reduced. Finally, reductions in operating costs and increases in profitability can result from lowering the need for purchased inputs through better use of locally generated materials and site-specific knowledge.

How can transitions be made from conventional weed management systems toward more sustainable, ecologically based systems.? Bird et al. (1990) and MacRae et al. (1990) have described a general model that we find relevant for weed management in industrialized countries. It involves passage from heavy reliance on conventional herbicides through stages of improved efficiency of herbicide use, substitution of more benign inputs and practices for conventional herbicides, and finally system-level redesign to manipulate multiple ecological interactions, facilitate decision-making, and minimize reliance on purchased, nonrenewable inputs. Alternatively, for farmers in developing countries who are not yet fully reliant on herbicides, transitions toward ecological weed management systems may involve substantial agroecosystem redesign but lack intermediate stages of improved herbicide efficiency and input substitution. None the less, system redesign in developing countries is still likely to emphasize the improved use of multiple tactics, local biological resources, on-farm labor and knowledge, and skills for timely monitoring and decision-making.

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