Northern Light Auto

It is the beginning of burning from nitrogen toxicity, the leaves are waaay too green. Reduce the strength of your nutrients and/or the frequency of feeding. Autos do just fine on half strength nutrients. In soil you want a schedule of plain water, plain water, feed, plain water, plain water, feed - so that your plant is getting nutrients every 12 days roughly. If you have a "hot" soil mix, this would explain the burning too, but there is little you can do about that, except ride it out without feeding. Wind burn is rubbish and if it were root rot, the entire plant would be a lot more damaged. If you haven't got one, you will need a fan of some sort though, especially during flowering, otherwise bud rot might visit you. Hope this helps, Organoman.