- Additional Plants: herbs, ornamentals
- Education and Training: on-farm/ranch research, participatory research
- Pest Management: biological control, field monitoring/scouting, integrated pest management, traps
Thrips damage greenhouse plants by chewing on the foliage and 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 propose to evaluate marigolds as trap plants for thrips both outside and inside the greenhouse. Thrips will be physically removed from the greenhouse by removing infested marigolds. Marigolds in bloom appear to be ideal trap plants for thrips because they are easy to grow, fast to bloom, and inexpensive, they are often blamed for producing thrips. However, it appears that they are excellent at attracting and retaining immigrating thrips, much like the trap chrysanthemums used in large Canadian greenhouses to trap thrips away from the vegetative chrysanthemum crops. Additionally, we will create marigold trap station signage to promote the grower’s use of sustainable practices. If successful, the marigold trap method will be an easy and inexpensive way to keep migrating thrips off greenhouse crops. Minimal thrips in the crop will greatly reduce the need for pesticide use, and at the same time make it more feasible for natural enemies to suppress the thrips that are there.
Project objectives from proposal:
In summer 2008, Bakers Acres of North Lansing placed one 4-inch pot with a single marigold plant on each bench in their herb greenhouse to attract thrips away from their herbs. Their scout, Michelle Ten Eyck estimated that when a marigold plant had 20 thrips, it was time to remove that trap plant from the greenhouse and replace it with a fresh marigold plant. Plants were removed before the thrips could reproduce on the plant and spread to the adjacent crop. Michelle consistently found many more thrips on the marigolds than on the adjacent plants, which she wants to document this year. The thrips catches on the sticky cards were half that of 2007, albeit still quite high, but the growers were satisfied with the low thrips numbers on their herbs.
Trap cropping is a traditional method of pest management that relies on a pest being more attracted to a trap crop than to the commercial crop. A successful trap crop arrests the flight and dispersal of the pest that it has attracted. For pests that aggregate in response to visual and olfactory cues, the trap crop combines attraction with arrestment. Trap cropping has been successfully used commercially in the United States for striped cucumber beetle, lygus bug, and aphids on papaya (Shelton and Badenes-Perez. 2006).
Very large Canadian greenhouses now use chrysanthemums to trap thrips out of their crops, and then discard the plants with the thrips on them. This practice is based on the following research. Buitenhuis and Shipp (2006) observed that flowering stage chrysanthemums were more attractive to thrips than the vegetative, bud and crack-bud stages of chrysanthemums up to a distance of 36 feet. In some of the work, they elevated the trap plants above the rest of the crop. The trap plants were more likely to trap dispersing thrips than resident thrips. Their observations suggested that once thrips have settled onto a plant, they are less likely to move away from that plant. In previous research, female thrips were more likely to be attracted to, settle on, and colonize healthy chrysanthemum flowers than aged flowers. They also dispersed at higher rates from aged flowers than from healthy flowers (Rhiands and Shipp, 2003).
Marigolds have an effect on thrips similar to that of chrysanthemums. In addition, they are much easier to grow and are less expensive. The Bakers Acres’ 2008 use of marigolds as a superior attractant for thrips in herbs is backed by 3 years of data on the numbers of thrips on marigolds in Habitat Plant Systems (research funded by NESARE in 2005, 2006, and 2007). University of Vermont researchers Margaret Skinner and Cheryl Frank are currently investigating marigolds as habitat and banker plants for natural enemies. While these habitat systems can (in theory) support excellent season-long biological control, we must know the appropriate threshold to determine when to carry the marigolds and the thrips out of the greenhouse.
We propose to evaluate and document the use of marigolds as a trap plant 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 roll 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.