by Sanne Kure-Jensen

At different life stages, biocontrol insects eat other insects or pollen and nectar from flowers. As alternatives to using chemical pesticides, high tunnel and greenhouse growers may purchase and release biocontrol insects.

Successful pest management includes establishing a modest population of biocontrol insects or natural enemies before pest insect populations reach significant levels. Cheryl Frank Sullivan of the University of Vermont shared her experience nurturing habitat plantings to supply a steady food source as well as sites for refuge and reproduction for biocontrol insects in her workshop “Habitat Plants to Attract Natural Enemies into High Tunnel Crops” at the 2017 New England Vegetable & Fruit Conference.

“Habitat plantings are not the silver bullet for pest management in a high tunnel,” said Cheryl. “They are one of the tools in the toolbox.”

Cheryl recommended growers scout high tunnels and greenhouses regularly, looking for weak or diseased plants, insect infestations and their associated biocontrol levels and other issues. Growers should learn to tell insect friends from foes and teach insect identification to all staff. If there is a pest outbreak, growers need correct identification and magnitude of crop infestation to know which natural enemy or pest control technique would be most effective.

Establish a threshold for pest damage that requires action. Are a few chewed leaves okay? Have a plan and know who to call for help with pest management: a key staff person, a nearby grower, a Cooperative Extension agent or a pest expert.

Aphids can reduce crop yields and profitability for many high tunnel and greenhouse crops. Be sure to verify which type of aphid is present, and order the corresponding natural enemy appropriate for the crop, magnitude of infestation and time of year. Many natural enemies have a broad range of pests they will attack. Others are host specific and will only control certain insect species. Some natural enemies include:

  • Parasitic wasps
  • Predatory bugs such as the pirate bug Orius
  • Syrphid or hover fly maggots (larvae)
  • Lady beetles
  • Soldier beetles
  • Green lacewings
  • Spiders
  • Big eyed bugs
  • Assassin bugs
  • Damsel bugs

Successful pest managers establish and maintain a base level of natural pest enemies.

Cheryl and fellow researchers conducted tests in high tunnels in year-round production (tomatoes in summer, greens in winter) to see which plants were effective habitat plants for natural enemies. Some important qualities in a habitat plant are easy maintenance, wide temperature tolerance, low cost, non-invasive and not too attractive to pests. Plants evaluated were alyssum, marigolds, dill, borage, bean, viola and calendula. Their results showed beans, violas, borage and calendula tended to attract pests as well as natural enemies and could serve as indicator plants. Monitoring indicator plants could act as an early warning signal of rising pest populations.

The best habitat plants bloom year-round. Cheryl found alyssum to bloom almost year-round, is easy to produce and is inexpensive. Marigolds bloom spring through fall. Alyssum and marigolds need minimum maintenance and can be trimmed back once per season. Alyssum and marigolds transplants typically bloom six weeks from seeding and provide pollen, nectar and sometimes attracted pests for biocontrol insects. Beware aggressive, invasive or high maintenance plants. Do not let plants that readily self sow like borage go to seed and take over your high tunnel or greenhouse.

Cheryl recommended growers group two to eight blooming habitat plants per 1,000 feet of high tunnel or greenhouse space. Plants could be combined in a hanging basket or grouped at bed ends. Several plant groupings may be needed for adequate protection, depending on the size of high tunnels or greenhouses.

Cheryl advised growers to leave their high tunnel or greenhouse fallow for as long of a period of time they could spare between crops to help reduce aphid populations. Continuous growing allows for the carryover of pests and can lead to a steady increase in pest populations if left unchecked. It is important to remove debris between seasons. “Start clean to stay clean,” said Cheryl.

Learn more about IPM in high tunnels and greenhouses at Send questions to Cheryl Frank Sullivan, Greenhouse IPM Research Specialist and Lab Research Technician at the University of Vermont at or call 802.656.5434.