April 5, 2017
Marigold varieties like the African and French ones are known to control nematodes that infest plants.
Marigolds can be used as a cover crop or on a rotation basis as they produce a substance called alpha-terthienyl which can aid in the reduction of root-knot nematodes, lesion nematodes and other disease promoting organisms, such as fungi, bacteria, insects and some viruses.
This compound is nematicidal, insecticidal, antiviral, and cytotoxic. The presence of nematicidal compound alpha-terthienyl inhibits the hatching of nematode eggs, according to Dr S. Subramanian and K Poornima of the department of nematology at the Tamil Nadu Agricultural University.
The compound alpha-tertheinyl is only released by active, living marigold roots. Exposure to near-UV light inactivates alpha-tertheinyl when taken out of the soil, they said in a statement.
There is no benefit in changing a planting site with marigold extracts of homogenised plant parts. Marigold can be grown ahead of time as a cover crop to suppress nematodes before planting a susceptible crop like a vegetable.
To be an effective cover crop in nematode management, marigold should be planted at least two months before planting the vegetable, they said.
It must also be planted at the same site in which the vegetable is to be grown and planting of marigold should be dense to ensure the best nematode control.
For continuous effect, marigold must be grown every season before the actual crop is planted, because nematode populations will increase over a period in the presence of susceptible crops.
Inter-cropping marigold to reduce plant-parasitic nematodes does not appear to be as effective as under high density monoculture, they added. And not all marigold varieties control all types of nematodes.