al·le·lop·a·thy 
(ə-lē-lŏpə-thē, ăl′ə-)
(ə-lē-lŏpə-thē, ăl′ə-)n.
A usually negative effect on the growth or development of an organism of one species, caused by a chemical released by an organism of another species. Usually used of plants.
[Greek allēlōn, reciprocally (from allos, another; see al-1 in the Appendix of Indo-European roots) + -PATHY.]
al·le′lo·pathic (ə-lē′lə-păthĭk, ə-lĕl′ə-) adj.