Greenhouse Canada

Marigolds shown to deter whiteflies

April 15, 2019  By Dan Nosowitz Modern Farmer

In the long lore of gardeners, the marigold is thought to do something to help tomatoes avoid pests. New research finds that it isn’t just lore.

Researchers from Newcastle University tested marigolds to see exactly what kinds of gaseous chemicals were released by the plants. The most notable of those compounds was limonene, also the major component of the oil in citrus peels.

In a couple of greenhouse trials, they discovered that pots of marigolds do in fact deter whiteflies, small insects that are usually found on the underside of plant leaves. When marigolds were nearby, the whiteflies significantly reduces their number.


Another experiment, published in the same article, found that adding an “emergency” marigold has only a minimal effect. But the researchers also created a limonene dispenser, a little bit like an air freshener, that spat out nice citrusy limonene. That dispenser turned out to be much more capable of reducing whitefly populations, even when they’ve been allowed to build up. | READ MORE

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