Live Thrips Traps: Using Inexpensive Marigolds to Draw Thrips Away from Greenhouse Crops
Thrips damage greenhouse plants by chewing on the foliage & flowers and deforming new growth. Since this damage causes serious economic losses, growers are anxious to control thrips with any means possible, usually with pesticides that are now giving diminishing control. In response to pesticide resistance, combined with growing interest in sustainable agriculture, some growers are using natural enemies to suppress thrips populations. One barrier to success with natural enemies is that sometimes there are massive immigrations of thrips into the greenhouse from mature outdoor crops, which creates too many thrips for natural enemies to suppress in the greenhouse.
In collaboration with a New York grower and a Pennsylvania grower, we evaluated marigolds as a Guardian Plant for thrips both outside and inside the greenhouse. Guardian Plants act as traps for pests and habitat sites beneficial predators and parasites of those pests. Marigolds in bloom appear to be ideal trap plants for thrips because they are easy to grow, fast to bloom, and inexpensive. At Peace Tree Farm in Pennsylvania, grower Joe Volpe observed that marigold plants directly adjacent to the greenhouse vents served as an extreme filter for thrips, reducing the numbers of thrips detected inside the greenhouse to very low levels in comparison to the numbers of thrips coming in the vents. The marigolds also served as host to the beneficial thrips predator, Orius.
At Bakers Acres, in New York, we observed clean crops adjacent to individual marigold plants with abundant thrips. When those plants became too infested, they were removed from the greenhouse, along with the thrips. Several tests were ruined by bad weather and similar disruptions. We plan to repeat those trials in the summer of 2010.
Though marigolds are often blamed for producing thrips, it appears that they are excellent at attracting and retaining immigrating thrips. Both Peace Tree Farm and Bakers Acres physically removed thrips from the greenhouses by removing heavily infested marigolds. Pesticides for thrips were not necessary at either site.
For the Guardian Plant trap method to be successful, we must determine the appropriate threshold to know when to carry the marigolds and the thrips out of the greenhouse. We proposed to evaluate and document the use of marigolds as trap plants for the removal of thrips from a greenhouse crop in 4 ways:
1) Evaluate the level to which thrips will settle onto trap plants outside of the greenhouse.
2) Evaluate the ability of marigolds to attract and retain thrips that have entered the greenhouse, and demonstrate the level of thrips removal from the greenhouse.
3) Compare numbers of thrips caught on marigold plants that are elevated 4 inches above the crop with marigolds that are at the same level as the surrounding plants.
4) Compare the number of thrips that are supplied by stressed or wilting marigolds with the number that are supplied by similarly infested plants with ample water in an empty greenhouse.
Our ultimate goal is to support the development of Guardian Plant Systems that serve as concentrated microcosms of pests and natural enemies, which growers can then use to detect and assess the presence and ratios of pests and natural enemies in their greenhouses. In their role as indicator plants, habitat plants, banker plants, and trap plants, the Guardian Plant System can serve as an important tool to enable growers to increase their understanding and use of biological controls.
This study was designed to test whether or not marigolds can be used as Guardian Plants to trap thrips away from greenhouse crops. At the Pennsylvania site, our 2009 work found that marigolds are able to filter thrips coming into greenhouses through air vents. There were 2 to 7 times as many thrips per flower on the vent side marigolds in comparison to marigold in pots on the ground. The marigolds also served as predation sites for the beneficial thrips predator, Orius. Thrips counts within the greenhouse at the Pennsylvania site were extremely low and no pesticide treatments for thrips were required.
The New York site experiments will be repeated in 2010. We lost one portion of the study at Bakers Acres that compared of the number of thrips that are supplied by stressed or wilting marigolds to the number that are supplied by plants with ample water when “water-deprived” marigolds got rained on after heavy winds removed the greenhouse covering. Though the mixed herb crop with the marigold Guardians did not require any pesticide treatments for thrips, there was a problem with keeping the yellow sticky cards at the busy greenhouse entrance from being knocked to the ground. The sticky card data is necessary to assess the ability of the marigolds to act as a filter for incoming thrips at the greenhouse entrance.
Impacts and Contributions/Outcomes
The 2009 work demonstrated that marigolds can serve as Guardian Plants by pulling thrips away from crops and supporting the reproduction of the thrips predator Orius. The results have been shared with the public in the following articles and presentations:
Newsletter Article: IPM Labs Research at Bakers Acres: Third Year of Guardian Plant Trials (Fall 2009) Michelle Ten Eyck & Carol Glenister, Baker Acres Newsletter, North Lansing, NY.
Powerpoint Presentation: Guardian Plants to Assure & Evaluate Natural Enemy Survival, Reproduction, and Effectiveness (September 12, 2009) Biological Control in the Greenhouse, Putting it All Together, UMass and Univ. CT Coop Extension, Tolland, CT
Guardian Plants Protecting Our Crops (October 10, 2009) Bakers Acres Apple Fest, Tabletop Display & Banner, North Lansing, NY