I have a small plum tree about 3 years old and early this year it had a leaf curl problem. As a result, I had no fruit on it. I did spray with insecticide at that time. Where can I buy horticultural oil from?
Plum Leaf Curl
Certified GKH Gardening Expert
Horticulture oil can be purchased at most garden centers, greenhouses and even home improvement centers.
Neem Oil is a good option.
You can also general order these products and have them shipped to you. Just do a 'Google' search.
Here are a few links for you.