I've discovered small patches of scale on several of my small trees. I've sprayed with an insecticidal soap and tried to wipe as much of the scale off with a paper towel as possible. Will the insecticidal soap kill the scale by itself? I'm sure I haven't gotten all of the scale off, but I'm pretty sure all of it was sprayed.

An oil spray will be more effective than soap.

On the subject of Horticultural oils. Many members of this forum think that Ultra-Fine Horticultural oil is no longer available. Actually, it is still available, but it is now sold under the name Ultra Pure Horticulture Oil. As to the control of scale, soapy water will work, but it frequently takes repeated spraying. As Bonnie wrote above Horticultural Oils are a 100 times better in controlling scale, aphids, mites and white fly (especially eggs). - Millet 97