Providing a friendly environment for beneficial predators can also provide protection for your valuable crop. Benefits include a reduction on the reliance of chemicals, enhanced worker safety and increased plant quality.
A syrphid fly rests on cilantro, planted in an insectary plant installation to study the effect of such plants in luring beneficial organisms as an aid in pest control on nursery properties.
Photo courtesy of Robin Rosetta
“Nurseryscaping,” or the use of insectary plants, is an approach to crop production with a focus on enhancing the activity of beneficial organisms. It’s not necessarily a new concept, but it’s gaining momentum among growers who wish to try alternative methods to pest control in the field as well as in the greenhouse.
This emphasis on biological control, sometimes called bio-intensive pest management, is gaining attention for its potential to reduce pesticide use. It is thought that by providing food and habitat resources for beneficial agents, growers can attract and retain these allies. Encouraging natural enemy activity might reduce the fluctuations in pest populations and regulate insects and mites below damage thresholds.
Like any management strategy, nurseryscaping has its benefits and its challenges. The benefits of catering a feast for natural enemies may be many, including reduced pesticide costs, mitigating negative pesticide effects, improving worker safety, and increased plant quality. Complicating successful implementation in ornamental systems is the diverse range of plants, pests, natural enemies and production systems existing, and the limited research available directly from nursery production systems. One strategy to increase use of this ecological approach is to encourage more on-farm trials in nurseries and increase the dissemination of this information to and among growers.
Where—and how—to begin
Attracting and conserving natural enemies requires an understanding of their basic requirements for food and housing. Many biological control agents need supplies of nectar, pollen and host prey to sustain and increase their populations. By providing an extended season of floral resources, growers may increase the number and diversity of predators and parasitoids—insect parasites—within their systems.
The best way to begin is by thoroughly understanding the pest pressures on your specific crops. In a publication called “Farmscaping to Enhance Biological Control,” entomologist and IPM specialist Rex Dufour (Agriculture Specialist at the National Center for Appropriate Technology) suggests the following considerations in farmscaping design:
Examine the ecology of the pests and beneficials
Determine the most important key pests requiring management, identify their associated predators and parasites, and the primary food sources, habitat and other ecological requirements of both pests and beneficials.
Details are useful. How is the pest attracted to the crop? From where does the pest move into the crop? What is its behavior and life cycle? Similar information about the beneficials is important.
Predatory syrphid fly larva in an insectary planting at Oregon State University is evidence of the ability of these plants to lure beneficial insects as a means of pest control for ornamental plants in production.
Photo courtesy of Kirin Elliot, OSU
It is extremely useful to inventory key pests and beneficials in and around the crop or production system. Correct identification is critical and useful to shape the selection of plant resources. Determine which natural enemies attack which pests on which plants and when.
Dufour emphasizes the importance of knowing when things happen. When do the pests and their natural enemies appear? Noting flowering times on alternate plants can be helpful. These plant and key events like first bloom are called phenological indicators. What are the economic damage and action levels on the crop? When and for how long are food resources, such as nectar or alternate hosts or prey, available for beneficials? Where do pests and beneficials overwinter?
Growers can manipulate the habitat to reduce conditions favorable for the pest, such as eliminating overwintering sites or in-season refuges. Similarly, producing an environment conducive for natural enemy survival, such as additional floral resources, undisturbed areas for nesting and overwintering, can enhance the amount, diversity and effectiveness of beneficial agents. It’s also important to consider the economic costs—including ground preparation, planting and maintenance—before you begin.
Beneficial syrphid flies were attracted to insectary plants sited at Oregon State University trials.
Photo courtesy of Kirin Elliot, OSU
There are a variety of approaches to incorporating insectary plants into production systems. Insectary plantings can be added within the crop by interplanting strips or individual plants throughout the nursery. This concept has been utilized in some greenhouse and nursery systems by the use of banker plants that host nonproblematic pests. The alternative prey provide for the early establishment and consistent buildup of predators or parasitoids.
Planting strips or hedgerows can be incorporated along the perimeter of the nursery or the crop. Many retail and container nurseries already display plants in strips along the edge and entryway to their production sites, so the addition of specific insectary plants to these existing plantings may be relatively easy to integrate.
Insectary plantings can also involve the introduction of a cover crop between or throughout rows of plants. Some bareroot and ball and burlap plant production systems already utilize cover crops, and this might be expanded. An example of this is the use of buckwheat to act as a sink or trap crop for lygus pests in shade trees, and the use of slow-growing fescue species between plant rows to suppress weeds and reduce soil erosion and dust.
It is suggested that growers provide an extended season of floral resources. This can be accomplished by selecting plants that flower from the early season through the late season. Entomologist Whitney Cranshaw, professor and extension specialist in the Department of Bioagricultural Sciences and Pest Management at Colorado State University, Fort Collins, has reported good attraction of beneficials to the parsley family (Apiaceae); mustard family (Cruciferae—such as the early flowering basket-of-gold, Aurinia saxatilis) the mint family (Lamiaceae); and some members of Compositae (such as Achillea). Local growers usually have a good idea of plants in flower at various times of the season in their region.
In addition to flowering time, it’s critical to consider the floral structure of the plant. The design of the nectary—recessed and hidden, or shallow and easily available—also influences the beneficial fauna that utilize the flower for nectar and pollen. Readily accessible pollen and nectaries, such as those found in umbels of plants in the Apiaceae family or sunflowers or plants with extrafloral nectarines, such as vetch, are very attractive to many tiny parasitic wasps and predatory flies.
Some plants act as a sink or source of pest species of concern as well as natural enemies. Shade tree nurseries are familiar with the migration of thrips and lygus from nearby grass fields as they dry down or are harvested. Grasses might favor predatory beetles, but they might also allow food and cover for voles. You can also utilize a preferred host as a trap crop, such as the example of buckwheat for lygus.
The dispersal of the natural enemies away from the insectary plantings into the crop is desirable, but specific insect and mite immigration information can be difficult to obtain. Research has found that the effects from sweet alyssum flowers were noted 30 to 40 feet away from the plantings near lettuce fields. Sweet alyssum has a good reputation for attracting beneficials, with a ratio of 204 beneficials per pest, and it does not attract lygus bugs or aphids. Research in several planting systems in California indicated the rubidium (Rb) marked insects that fed in borders around farms, including lady beetles, lacewings, syrphid flies and parasitic wasps, moved 250 feet into adjacent crops.
Insectary or banker plants, such as this, ‘Black Pearl,’ pepper, have been used to lure beneficial insects to help protect ornamental grasses in production.
Photo courtesy of Hoffman Nursery Inc.
Growers can overcome some of the limitations of natural enemy dispersal by growing banker plants. Containerized plants or leaves from those plants that host non-crop pests attractive to beneficial insects can be moved as needed into the crop to augment control. Cindy McKenzie at USDA/ARS in Fort Pierce, Fla., and Lance Osborne at the University of Florida in Apopka, Fla., have looked at banker plants such as papaya and ornamental peppers that provide alternate prey for desirable natural enemies such as the parasitoid, Encarsia sophia, which will parasitize many whitefly species, and Amblyseius swirskii, a predatory mite that feeds on thrips and whiteflies.
Conservation of habitat
How would you feel if your home was constantly plowed under every three weeks? A stable habitat is beneficial for some natural enemies, such as ground beetles and many spiders. An example of this is shown in the impact of strip harvesting versus clear-cutting entire fields of alfalfa. Quantitative differences between the two harvesting methods show dramatic differences in the numbers of spiders per acre (1 million versus 105,000); 287,000 parasitic wasps versus 70,000; 205,000 lady beetle adults versus 46,000 and a roughly equivalent impact on their larvae, 232,000 versus 11,000. Beetle banks and uncultivated areas are two strategies designed to create a more favorable habitat for these types of allies.
Nurseryscaping involves the study of a dynamic and complex system, which can be made particularly difficult given the diversity in much of greenhouse and nursery production. This presents challenges requiring additional knowledge or management skills for growers. A systematic, research-oriented approach in planning habitat enhancement will improve the chances of a desirable outcome and reduce potential mistakes. Such efforts, implemented with a spirit of experimentation, determination and a good sense of humor, will likely benefit the grower in a better understanding of the ecology of pest management, no matter what the outcome of the experiment.
Robin Rosetta is associate professor and regional extension educator-integrated pest management for nursery production in the Department of Horticulture at Oregon State University’s North Willamette Research and Extension Centers in Aurora. She can be reached at firstname.lastname@example.org. For more information on the use of insectary plants and nurseryscaping, visit the Oregon State University’s Pacific Northwest IPM site at http://oregonstate.edu/dept/nurspest/Insectary_plants.htm, where you’ll find a considerable list of resources.