News
Marigold Magic: A Natural Solution for Thrips Management
February 19, 2025
Managing thrips populations can be a persistent challenge for greenhouse growers, but an innovative guardian plant strategy using marigolds offers a simple, cost-effective solution. AFE-funded research from our Thrips and Botrytis Campaign has shown that yellow marigolds are highly attractive to western flower thrips, often drawing them out of crops two weeks earlier than traditional monitoring methods like sticky cards. By integrating marigolds into pest management programs, growers can lure thrips away from their crops and even further target them with other biocontrols before they become a serious problem.
All of this information and more is available online for free in both English and Spanish at AFE’s Thrips and Botrytis Research Library.
Key Takeaways:
- Yellow marigolds are very attractive to western flower thrips.
- They are ideal guardian plants because they are easy to grow and bloom within 1 month.
- Thrips are often found 2 weeks earlier on marigolds than on yellow sticky cards.
- Marigolds can lure thrips out of the crop plants, where they can be managed with various biological control agents. If thrips populations can be reduced early in the season, they may not become a serious problem later.
How it Works:
- The guardian plant strategy uses an Attract, Sustain, and Kill approach.
- Flowering marigolds attract thrips out of the crop. A slow-release sachet containing predatory mites (Neoseiulus cucumeris) is attached to the marigold to attack thrips adults and immatures on the foliage.
- A millet-based granular formulation of Beauveria bassiana (the isolate in BotaniGard® products) can be mixed into the top layer of potting soil to control thrips pupae for a period of at least 12 weeks. This fungus grows in the soil and creates a fungal mat that infects the immature thrips as they descend to pupate.
- The key to success is to get the flowering marigolds into the crop early, before thrips populations begin to build. Growers must be proactive when using biological control and guardian plants are an easy low-cost way to start early.
- Guardian plants should be placed every 1,000 sq. ft., raised a few inches above the crop. To be effective, they must be introduced early before thrips populations begin to build. They provide prolonged thrips suppression for at least 2-3 months and are a low-cost pest management solution.
Guardian Hedges:
- In warmer climates, where there is a constant source of thrips from outside, the guardian plant concept could be extended to incorporate plant hedges around the greenhouse. These plant hedges contain a variety of annuals that attract thrips, beneficial insects, and pollinators.
- Habitat hedges should be regularly monitored for thrips populations. If damaging levels are detected, targeted chemical treatment can be applied.
For a deeper dive into marigold guardian plants, check out our webinars in both English and Spanish on our YouTube channel, and and explore additional articles on this topic at endowment.org/tb.
