How allelopathic effect control pests in marigold?

Allelopathy is the ability of an organism to produce chemicals that are toxic to other organisms. Marigold roots release the chemical alpha-terthienyl, one of the most toxic naturally occurring compounds. This compound is nematicidal, insecticidal, antiviral, and cytotoxic. The presence of alpha-terthienyl inhibits the hatching of nematode eggs. However, if in a field setting, it is unclear if marigolds producing alpha-terthienyl inhibit development because of the alpha-terthienyl itself or because marigolds are a non-host for certain nematodes.