The only symptom of neem overapplication that I have ever encountered is a darkening of the leaves- they go DARK green and translucent. It's from suffocation.
Yellow spots don't sound particularly like anything to do with the neem.
stinkyattic Reviewed by stinkyattic on . Has anyone experienced this?!??! Last night I brought two three foot sativas in five gal pots from my backyard to my grow closet, located in my garage. Prior to placing them in the then-dark closet (I am starting them at 12:12 immediately) I sprayed them with some neem oil. This was at 10:00 PM, and my 400W HPS came on at 6:30 AM this morning. I checked the plants around 1:00 PM today, and many of the fan leaves had dull yellowish spots on them. I looked with a 5x glass, and couldn't really see too much in the way of pests. Rating: 5