Both Wicca and Witchcraft are highly individualized beliefs and practices. As such, there is little consistency in the answers you'll get to this question. Ask ten different pagans, and you'll get twelve different answers! Here's mine:
Most Wiccans call themselves Witches, but not all Witches consider themselves to be Wiccan.
Wicca is an earth-oriented religion that seeks to bring the practitioner (often self-described as a witch) to a deeper connection with Divinity, often portrayed as a duality of God and Goddess. Wiccans often (but not always) use techniques of magick to bring about needed change and spiritual attunement.
On the other hand, Witchcraft describes the practices of magick used by a witch to obtain what is needed in life: physical, emotional, and spiritual needs. Witchcraft is associated with spells, herbal remedies and potions, and other forms of magick.
Therefore, one can practice witchcraft (the techniques) without following the spiritual structure or form of Wicca (the religion).
~Flame RavenHawk