Hi Heraldo, Sounds like it could be rot. Lavenders originate from the Med. and like full sun and not overwatered. If warm and wet (humid) the bottom of the plant starts to go black and rots. The so called English lavenders are the hardiest. The French ( the ones with the little toorie on the top) are a wee bit more softer. If in pots let them dry out between watering. I am presuming that you did not cut nthem right back. You do this in April, and you dont cut into the old wood. Maybe Tbird will have more advice for you. Cheers Skylight