PinkLatina is right. Bugs dammit! Keep an eye on the other leaves, so no more bugs eat them up. They can be hardcore pests sometimes. Them, and animals. My first and only outdoor grow last year. I had a sweet Blach Haze plant about 5 weeks into flowering. I come back a week later to water, the whole plant is eaten up, completly stripped! There was nothing but a long stem sticking out of the ground. Good luck, keep us updated