- Agronomic: potatoes
- Education and Training: extension, on-farm/ranch research
- Farm Business Management: whole farm planning
- Natural Resources/Environment: biodiversity, habitat enhancement
- Pest Management: biological control
- Production Systems: agroecosystems, holistic management
- Sustainable Communities: partnerships
A comparison of carabid beetle assemblages between grassy field margin habitats and potatoes found that these predators of crop pests were more abundant and diverse in grassy habitats. At broader scales beetle communities in landscapes that included large amounts of natural habitat were not as dominated by common crop species as those sampled from agricultural landscapes. Predation on green peach aphids in potatoes also increased as the amount of natural area within 1 km increased. These results suggest that conservation of natural areas adjacent to crops may enhance biological control of crop pests by natural enemies.
In the last 50 years agriculture has dramatically increased yields and the ability to support an ever-increasing human population. However, this increased capacity has relied in large part on significant human inputs including synthetic fertilizers and pesticides. This intensification of agriculture has come at a significant cost. For example, declines in biodiversity have been linked to modern farming practices. This erosion of biodiversity has resulted in the disruption of ecosystem services, such as natural pest suppression by arthropod predators and parasitoids (natural enemies) (Altieri, 1999). Our ability to increase the long-term sustainability of our agricultural practices will be dependent on our ability to modify farming practices so that natural pest control makes high external inputs of pesticides unnecessary. Increasing the amount of natural land surrounding crop fields, a form of “conservation” biological control, may be one way to enhance natural pest control.
Natural areas adjacent to crops (such as grassy field margins) may enhance pest control because they can provide important resources needed by natural enemies that are not available within the disturbed, simplified environment of crop fields (Wratten et al., 1998). This has shown to be the case in many instances and has led to the adoption of “habitat management” strategies as a form of conservation biological control (Landis et al., 2000). For example, “beetle banks” are perennial grassy strips added to fields that enhance predatory ground beetle (carabid) abundance and diversity. These predators then disperse into adjacent crops and consume insect pests such as aphids. (Wratten et al., 1998; Collins et al., 2002).
In addition, a number of studies have found that natural enemy populations are influenced by the abundance and diversity of natural habitats at scales much larger than individual farms and their immediately adjacent lands (Elliot et al., 2002; Menalled et al., 2003; see Tscharntke & Brandl, 2004 for other examples). For example, parasitism by natural enemies of pests of oilseed rape shows a strong positive correlation with the amount of natural habitat present within 1.5 km of the crop (Thies & Tscharntke, 1999; Thies et al., 2003). These findings suggest that large-scale, cooperative habitat management efforts by growers may be more effective than uncoordinated, individual efforts.
A unique opportunity to use natural areas to enhance biological control for insect pests now exists in Wisconsin. Potato growers in the state have recently adopted an intensive bio-IPM program that has reduced pesticide applications by 20% through the use of economic thresholds and pest monitoring tactics. In addition to this, a number of growers have also begun restoring natural habitats adjacent to fields. Growers are currently seeking advice on how to restore natural habitats so as to increase biodiversity on their lands. However, the current state of knowledge is inadequate to understand the role that natural habitats play in agricultural landscapes and the spatial scales at which they enhance pest control. We do not understand the degree to which pest control can be enhanced by conserving natural areas. Furthermore, it is unclear whether growers should focus on conserving habitats immediately adjacent to fields (“field margin” habitats) or at a landscape (kilometer) scale to enhance pest control. The research described here aimed to determine if natural habitats (created or naturally-occurring) influence native biodiversity of natural enemies and if this diversity results in improved pest control. We also conducted research at a variety of spatial scales to determine the scale at which habitat conservation should be practiced. Filling in these important knowledge gaps will be needed in order to make conservation biological control a more reliable and effective strategy.
The goal of our research was to determine whether grassy field margin habitats adjacent to potato fields (Objective 1) and natural areas in the broader landscape (Objective 2) support natural enemies that control potato pests. Grassy field margin habitats are found along the edges of field access roads and ditches and in the corners of fields where irrigation pivots cannot reach. Plant communities vary widely in these areas but are dominated by grasses ranging from non-natives like smooth brome grass, Bromis inermis, to native prairie grasses like big bluestem, Andropogon gerardii. Examining natural enemy communities in these areas enabled us to contrast results at a small spatial scale (crop and adjacent habitat) with larger, landscape-scale analyses (crop and habitats within kilometers distance) to provide information on the scales at which conservation biological control tactics are effective. Thus, our research was designed to determine: (1) whether conservation of natural areas can improve biological control and (2) the scales at which such strategies are effective.
Towards these ends, our research was designed to meet the following objectives and test their associated hypotheses:
Objective 1: Evaluate the role that grassy field margins play in supporting populations of natural enemies that control potato pests.
Hypothesis 1: We hypothesized that grassy field margins serve as reservoirs of a diverse and abundant natural enemy assemblage that can control potato pests. Thus, we expected that natural enemies are more abundant and diverse in grassy field margins compared to crops.
Objective 2: Ascertain if the amount of natural habitat in the landscape surrounding fields influences predation on insect pests in potatoes.
Hypothesis 2: We hypothesized that a greater abundance and diversity of natural enemies in fields surrounded by extensive natural habitat results in increased pest suppression within these fields.