Green’s Dictionary of Slang

1. (Aus.) play on chicken n. (1a): the image is of a lure that attracts young women.

1914		Sport (Adelaide) 3 Apr. 5/4: What, wouldn’t Sandy bite, or didn’t he have any wheat in his pocket?
1914		Sport (Adelaide) 6 Nov. 5/5: Samm H., the whippet king, said he ran short of wheat — that is he went to the Baltic to get some for his chickens.

2. (drugs) marijuana.

1969		R.R. Lingeman Drugs from A to Z (1970).
1977		S.N. Pradhan Drug Abuse.
2001		ONDCP Street Terms 22: Wheat — Marijuana.