Green’s Dictionary of Slang

1. to guard, to watch over.

1909

J. Ware Passing Eng. of the Victorian Era.

2. (US Und.) to arrest a group of criminals.

1927		‘Jargon of the Und.’ in DN V 449: Harvest, to arrest tramps.
1931		Irwin Amer. Tramp and Und. Sl. 96: Harvest.– To arrest or ‘gather in’ a criminal or suspect.