"Blight" is a dificult term to diagnose. You could have fungal, insect or nutrient/pH issues. Using neem oil is an insect problem treatment, but (no offense meant) are you sure it's insects?
Orggrwr is right. Need pictures and better descriptions to even make a guess.
"Blight in my dirt"? Tell me you didn't put a shovel full of yard dirt into your indoor grow pot! That introduces insect eggs and fungal spores! (Assuming indoors - outdoors totally different.) I would get past this grow, clean everything with a 50/50 water/bleach solution and start over with a sterile grow medium.
Read! GWE has tons of excellent tutorials.
Geometry Dash Full: A successful grow is a planned grow. Too many newer growers think dirt, pot, seed = big frosty nugs. It is almost that simple with the proper techniques. But, that knowledge takes a few grows and making the necessary mistakes to learn from. Keep trying. You'll get there.