Yes, GUMWEED is a Scrabble word!

Letter values in Scrabble US: G 2, U 1, M 3, W 4, E 1, E 1, D 2.

Is it a valid word?

GUMWEED is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any of various western American plants of the genus Grindelia having resinous leaves and stems formerly used medicinally; often poisonous to livestock

Also: gum plant.