For the first time, scientists have uncovered the marigold's natural weapon to ward off the whitefly pest (which has a devastating effect on tomatoes).
Researchers from the Institute of Natural and Applied Sciences at Newcastle University conducted a study to find the natural enemy of the whitefly in many places to prove what farmers have known for generations.
The researchers, who published their findings in the journal PLOS ONE, identified limonene released by marigolds as the main ingredient that repels tomato whitefly.
The findings of the study have the potential to pave the way for the development of safer and cheaper alternatives to pesticides.
Since Limonene repels the whitefly without killing it, it does not cause resistance in the use of the chemical and does not affect the quality of the product. All it takes to deter whiteflies is to scatter marigolds in tomato fields or hang small containers of limonene on tomato plants so the scent can diffuse through the tomato leaves.
In fact, Dr. The research team, led by Colin Tosh and Niall Conboy, has shown that it may be possible to develop a product such as an air freshener containing pure limonene that can be hung in glasshouses to confuse whiteflies.
Newcastle University PhD Student Niall said, "We spoke to many farmers who know that marigolds are effective at protecting tomatoes against whitefly, but it has never been scientifically tested."
“We found that the chemical released in the highest amount from marigold was limonene. This is exciting because limonene is cheap, non-harmful and much less risky than pesticides.”
“Most pesticides are sprayed on crops. This not only kills the targeted pest, it kills absolutely everything, including the pest's natural enemies."
Limonene makes up about 90% of the oil in citrus peel and is often found in household fragrances and mosquito repellents.
Dr. Tosh said: “Limonene indoors and outdoors, you can make a huge impact against whiteflies in your garden by planting marigolds around tomatoes or using pure limonene peels. Another important benefit of using limonene is that it is not only safe for bees, it is also a source of nectar for bees, which is vital for pollination.”
“Alternative methods of whitefly control that can reduce pesticide use and bring greater plant and animal diversity to horticultural crops should be welcomed.”
The researchers conducted two large greenhouse trials. Working with French marigolds in the first experiment, they found that the repellent effect worked and marigolds were an effective companion plant for keeping whiteflies away from tomato plants.
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For the second trial, the team used a machine that allowed them to analyze the gas and volatile chemicals emitted by the facilities. In this way, they were able to determine which chemical was released from marigolds. They also determined that marigolds interspersed with other complementary herbs that whiteflies dislike did not increase or decrease the repellent effect. This means that not only marigolds but also non-host plants of whiteflies can repel them.
A Worldwide Pest
Whitefly adults are tiny, moth-like insects that feed on plant sap. They cause serious crop losses in a number of crops by promoting the spread of several plant viruses and the growth of mold on the plant.
Direct feeding from both adults and larvae results in very high honeydew secretion. The nectar secretion covering the leaves reduces the photosynthetic capacity of the plant and renders the fruit unmarketable.
The team's next work will focus on developing the triple mix that will repel the three big pests of tomato - whitefly, spider mites and thrips.
In the longer term, the researchers aim to publish an herbal guide to the problems of horticultural crops as an alternative to pesticides.
What is Limonene?
It is one of the most abundant terpenes in cannabis and can be found in concentrations as high as 16% of the essential oil fraction. The ubiquitous limonene in citrus peel is a monoterpene commonly used in perfumes, household cleaners, foods, and medicines. Limonene has numerous medicinal benefits that have been demonstrated in human and animal studies.
Limonene is among some vegetable essential oils that have been found to have antioxidant and anticancer properties. This is why Limonene has been recommended as an excellent dietary source for cancer prevention.
The anxiolytic effects in the mouse maze model were comparable to diazepam but not antagonized by flumazenil, implying a non-benzodiazepine mechanism. This is in contrast to previous results that also showed antidepressant activity via the 5-HT1A receptor pathway. Limonene has anti-inflammatory effects in models of osteoarthritis and asthma. Many modes of anticancer activity were observed, including chemoprevention. Limonene is also metabolized into peryl alcohol, which has been the subject of many cancer studies.