This is Green foxtail. To distinguish Green foxtail from Yellow or Giant, look at the upper surface of the leaf blade near the stem:

• Green- smooth surface.
• Yellow-a few prominent, kinky hairs.
• Giant-fine short hairs covering the entire upper surface of the blade.

The seed heads are distinctly different:

• Yellow- smallest, and is yellow or orangish-yellow.
• Giant- much larger and often curls over.
• Green- in between the two others in length, and sometimes will confuse you by curling over like Giant foxtail.

Both Green and Giant foxtail are green until mature, when they turn slightly yellow to brown.