I agree "foxtailing" can be caused by light stress (too close/far) overfeeding or strain, a 'sativa' dominant strain will have more tendancy to foxtail then an 'indica' genetics wise! Check the bottom buds on the plant and if all are foxtailing then it gives you a pretty good assurance it's genetic, IF, it just effects to top colas then it's more than likely due to light or feed stress, happy growing