witch grass

1. An annual North American grass (Panicum capillare) having branching, purplish panicles.
2. See couch grass.

[Probably alteration of QUITCH GRASS.]

The noun has 2 meanings:

Meaning #1: North American grass with slender brushy panicles; often a weed on cultivated land
  Synonyms: witchgrass, old witchgrass, old witch grass, tumble grass, Panicum capillare

Meaning #2: European grass spreading rapidly by creeping rhizomes; naturalized in North America as a weed
  Synonyms: dog grass, couch grass, quackgrass, quack grass, quick grass, witchgrass, Agropyron repens