that looks like a chemical burn.......flush your dirt/potters with tap water

I bet the water that comes out of the bottom of your potter will be brown/yellow from salt build up from fertilizers

Flush the plant/root system until the water comes out clear

Also if your transplant into a larger potter, right before you cut your lights you will have healther plants/ buds

I have found that using 1/2 of what the directions call for when using veg and bud fertilizers reduce the chances of chemical burns and allows you to use the fertilizer more