Yes, TARWEEDS is a Scrabble word!

Letter values in Scrabble US: T 1, A 1, R 1, W 4, E 1, E 1, D 2, S 1.

Is it a valid word?

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

any of various resinous glandular plants of the genus Madia; of western North and South America
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.