I have used Neem oil on the leaves one time and there is a large amount of leaves that look like they are being eaten. I do see some black spots but not as many. It is not affecting new growth, just the older leaves. Should I continue to use the Neem oil? Also, I have ants that are running up and down the tree. I have used a three-in-one fertilizer that is supposed to take care of this. How long before this takes effect?
Nectarine Leaf Problems
Certified GKH Gardening Expert
It sounds like your tree still has an aphid or mealy bug infestation judging by the presence of ants and black sooty mold. Neem oil kills only pests present on the day they are sprayed, so applications may need to be repeated - I would continue to use the neem oil. When applying neem oil, be sure to spray the leaves thoroughly.
For more information on aphid and mealy bug control and neem oil, please visit the following links: