Supporting Natural Enemies in a Biocontrol Program

At Costa Farms, a company known for the houseplants, annuals, and perennials that company employees grow and supply across the U.S., Michelle Opela, the IPM Manager, uses a support plant system as part of the greenhouse biocontrol program.

Banker plants are one type of biocontrol support system. They are mini-rearing systems used to provide a continuous supply of natural enemies. In one banker plant system, a monocot like winter wheat is grown and infested with bird cherry-oat aphids; these aphids only affect monocots. Most vegetables are dicots, except sweet corn, and are not hosts for bird cherry-oat aphids. The winter wheat plants can be covered with bird cherry-oat aphids, and these aphids will not move to nearby vegetable plants. Aphid-infested winter wheat plants are placed in a greenhouse, and parasitoid wasps are released.

Parasitoid wasps are a natural enemy of aphids. There are many species of parasitoid wasps. We have commonly used Aphidium colemani, which parasitizes green peach and melon aphids. The female wasp lays a single egg in the body of an aphid. A single female wasp can lay over 300 eggs, which means she can parasitize many aphids. Once the larva hatches from the egg, it feeds on the organs of the aphid until it emerges as a wasp by cutting a hole in the aphid exoskeleton. The aphid is dead by this point, and all that remains is the "shell" of its body called an aphid mummy. Emerged female wasps lay eggs in more aphids continuing the cycle.

Another way to support natural enemies is to grow flowering plants that attract pests and natural enemies by providing pollen, nectar, and refuge.

We recently completed a 3-year experiment focused on using habitat plants in a biocontrol program to manage aphids in high tunnels. In the spring/summer, we planted alyssum, dill, borage, beans, and marigolds; in the fall/winter, we planted alyssum, viola, calendula, bean, and marigold. We tracked the types and numbers of pests and natural enemies on the plants. We found alyssum to attract many natural enemies and have the added advantage of growing in our high tunnels year-round.

Habitat plants, such as alyssum, promote the establishment of natural enemies and encourage them to come in from outside the high tunnels. They provide pollen and nectar to the adults of several natural enemies that require floral resources to reproduce. They can also attract pests/hosts. Use caution to ensure habitat plant systems are not attracting too many unwanted pests that can infest the cash crop. Scouting routinely helps to avoid this occurring.

At Costa Farms, Michelle set up pots of alyssum and a purple-leaved ornamental pepper and placed them throughout the greenhouses to support natural enemies. These plants support released natural enemies by providing pollen, nectar, and shelter.

Whatever method is used, success when using a biocontrol program relies heavily on finding the problem before pests reach damaging levels. Early intervention is crucial to release natural enemies so they can become established at the onset of an issue. Monitoring pests and natural enemies after making releases is essential to determine if the natural enemies are working, additional releases are needed, or an insecticide application is warranted.