TARES (ζιζάνιον, G2429). Mentioned eight times in Matthew 13. Refers to a weed called darnel, which looks exactly like wheat in its young stages and, in fact, only the expert can distinguish some species of this darnel from the true wheat. Later on, the differences are remarkable. The farmer, however, cannot pull up the weed when it is almost fully grown without seriously damaging the true wheat plants which are growing alongside.
The darnel is an annual, Lolium temulentum, sometimes called the bearded darnel grass. It has far smaller seeds than wheat, and it is claimed that these seeds, when ground to flour, are poisonous, due perhaps to a particular fungus which develops in the seed itself. See Weeds.
International Standard Bible Encyclopedia (1915)
(zizania (Mt 13:25 ), margin "darnel"): Zizania is equivalent to Arabic zuwan, the name given to several varieties of darnel of which Lolium temulentum, the "bearded darnel," is the one most resembling wheat, and has been supposed to be degenerated wheat. On the near approach of harvest it is carefully weeded out from among the wheat by the women and children. Zuwan is commonly used as chickens’ food; it is not poisonous to human beings unless infected with the mold ergot.