Workshop Home

A New Tool for Measuring the Resilience of IPM Systems --
The PAMS Diversity Index

- Harold Coble
The cost-effectiveness and sustainability of an Integrated Pest Management (IPM) system depends on its capacity to maintain pest populations below economic damage thresholds across varying, often unpredictable circumstances. Systems must be resilient across a wide range of weather, pest pressure and agronomic conditions. In addition, they must perform well over time by continuously undermining the ability of pests to adapt to their environment and the tactics used to manage them.

Ecological theory suggests and field experience confirms that IPM systems based on a diversity of control tactics are the most resilient because of redundancy in the system. In a system where a single tactic is relied on for control, growers are vulnerable when, for whatever reason, the tactic breaks down. Row crop farmers who use cultivation alone for weed management must be able to get equipment into fields at the right time to assure no yield loss to weeds. Others, relying on preemergence herbicides, depend on certain weather conditions to activate the chemicals and to maintain season-long control. Regardless of the tactic, there are combinations of weather, agronomic conditions, and pest pressure that are likely to lead to problems. The best way to assure cost-effective management across all conditions is to build redundant mechanisms of control into biointensive, prevention-based IPM systems.

Farmers understand the importance of having many options available for managing pest populations. In the past, especially in systems largely reliant on pesticides, farmers have generally applied different pesticide-based options sequentially. As the effectiveness of one chemical decreases, other materials are chosen and incorporated into management systems. While new options are drawn upon, the systems remain largely one-dimensional and vulnerable to future problems.

As reliance shifts from treatment with chemicals to prevention of pest pressure through management of biological interactions, farmers will need to utilize several control options simultaneously. Greater redundancy in control mechanisms will be needed because genetic and biological control mechanisms are driven by crop and species interactions, which are in turn a function of the competitive balance between different pests, their natural enemies, and the stage and vigor of crop growth. Variable weather and other exogenous factors can often have profound impacts on pest and beneficial organism population dynamics. For this reason, growers who wish to avoid a return to sole reliance on pesticides must build into systems a greater diversity of preventive control tactics, and when problems begin to emerge, they must activate a greater number of control tactics. Pesticides used to suppress populations must be chosen and applied in ways that avoid adverse impacts on beneficial organisms.

Recent developments in the Midwest highlight a new concern - the ability of pests to adapt and develop resistance to a cultural practice, in this case crop rotation. Beginning in the mid-1980s some farmers reported corn rootworm feeding damage in fields planted to corn which had previously produced soybeans. For forty years, this simple cultural practice had been relied on almost exclusively in managing a major, widely dispersed pest. But in the mid-1980s a strain of the western corn rootworm changed its behavior patterns and gained the ability or inclination to oviposite in near-by soybean, undermining the effectiveness of two-year corn-soybean crop rotations.

This change in pest behavior has led to a shift in management strategies and a dramatic increase in soil-applied insecticide use in corn in the eastern Corn Belt over the last two years. While there are several effective chemicals registered for control of corn rootworm, many factors may undermine their longer-run efficacy or availability, especially if they are now relied upon as a sole control tactic. Resistance is a major concern across all classes of registered insecticides, and the environmental consequences of widespread reliance on insecticides may prove significant enough to trigger regulatory restrictions.

As Midwestern row crop farmers adapt their IPM systems to respond to this new challenge, a premium should be placed on system innovations that diversify the tactics in place. The goal should be a system that will manage corn rootworms successfully over time without the need for a major increase in pesticide use. Highlighting the essential characteristics of such systems is a major challenge in measuring IPM system adoption and performance. Elucidating the necessary ingredients of sustainable IPM systems will help specialists and growers predict when current management systems are becoming vulnerable. It will also help in choosing the best ways to diversify and stabilize systems, including identification of high-priority research and education needs.

Gaining such insights is a critical challenge for USDA as it develops and refines methods to measure IPM adoption. A key goal is finding better ways to measure and track IPM system resiliency as a function of system diversity and capacity to adapt to changing circumstances. With the help of such a measurement system, specialists should be able to predict which IPM systems or parts of systems are at risk of failure before major management failures occur, triggering the need for costly and environmentally disruptive interventions. In addition, measures of system diversity may be an appropriate means to highlight research priorities and measure progress toward the attainment of the Administration's 75 percent IPM adoption goal.

Measuring IPM System Diversity

IPM systems are comprised of four complimentary strategies: prevention, avoidance, monitoring, and suppression (the PAMS approach). Within each of these strategies, multiple tactics may be identified, some of which may be applicable only to certain cropping systems while others may be broadly applicable. In all crops and circumstances though, an IPM system should include at least some tactics within each of these four strategies.

The concept of using a "diversity of control tactics" index as an indicator of IPM system resiliency arose during the June 12-13, 1998, Integrated Pest Management Measurement Systems Workshop held in Chicago, Illinois. The meeting was sponsored by the American Farmland Trust, the U. S. EPA, and the World Wildlife Fund.

Much work is needed to refine the idea and determine how existing and future NASS survey data, and other information at varying levels of aggregation, can be used to develop viable empirical measures of IPM system diversity. One approach would be to -

  1. Determine the maximum potential diversity of any IPM system by listing all viable tactics within each of the four major components;

  2. Develop a method to quantify the diversity of measures within each PAMS component taking into account the intensity of reliance on each tactic; and

  3. Use a matrix or equation to then combine the diversity of tactics in each of the four PAMS components into a single measure of system diversity.
Another option would be to assign preventive practice points to various tactics reflecting the degree to which each practice contributes to system diversity or reduced reliance on pesticides. The intensity with which a tactic is used could then be used to adjust the basic point value established for each tactic. This would allow qualitative ranking of practices both within and across PAMS components.

A key variable in measuring system diversity is the intensity with which certain tactics are relied upon in a given PAMS component. For instance, most four-year crop rotations should be assigned a higher intensity value than a two-year rotation. A farmer using cultivation should receive higher intensity scores for more passes with a tillage tool.

In the suppression component, a method will be needed to capture both the intensity of pesticide use, measured by pounds applied and the inherent toxicity of active ingredients, as well as the degree of diversity in farmers' selection of pesticides. The more narrow a farmer's selection of pesticides, the more toxic the materials, and/or the more pounds applied, the higher the estimate of reliance on pesticides as a method of suppression.

The method to measure IPM system diversity will be refined through consultation with a wide range of experts. The diversity index value for a system used on a given field will be determined by measuring the tactics used, the relative share of the control burden borne by each PAMS component, and the degree of potential resiliency in the system.

Such an index could be a valuable measurement tool at all levels and stages of IPM adoption. It could be applied on an area-wide scale such as a river basin or for crop-specific IPM systems. The diversity index is compatible with the IPM continuum and would be a valuable indicator to help monitor progress along the continuum.