Allelopathy is the inhibition of growth of a plant due to biomolecules released by another. It is the opposite of symbiotic mutualism. The biomolecules are called allelochemicals and are produced by some plants as secondary metabolites

Allelopathy in plants gives the organism a competitive advantage because the toxic chemical produced prevents other plants growing nearby and eliminates the competition for light, space, water, and nutrients in the soil.

all types of exploitation interactions. One species benefits from harming the other.

Part of the reason is due to inter-specific competition, and because they cause harm to others (allelopathy).

they don't "talk" per se, but can supposedly "communicate" chemically through the process of Allelopathy

see the related link