My silver maple has anthracnose and I had an arborist drop by to confirm. She had mentioned she could spray with neem oil. While I was out of the house, they sprayed the tree, but I see no signs [visual/odor] that the tree had been sprayed. Should neem oil leave some signs on the leaves, as I smell or see nothing?
Certified GKH Gardening Expert
It does not have too much in the way of smell, and because it works systemically from within the tree, not very much is needed to control any pests. It is normally sprayed on in a watered down solution to cover the plant and then the water evaporates, while the neem oil is absorbed into the tree. It is very possible that you would see nothing on the tree if it had had a few hours to dry.
While it is primarily used as an insecticide, it is also an excellent fungicide, so it is effective against anthacnose, which is a fungus. Neem oil is an all round, near perfect spray for plants as it combats a wide variety of problems.