Hi..Recently a Basil plant of mine was infested with scale insects so I had to dispose it .. Might have spread to some of the other plants.. I have isolated them.. Though what is the best was to treat this (a more organic approach)
First clean up the plant by manually scraping off as many scale as you can reach. Use a an old toothbrush, a wooden stick, fingernails, whatever.
Second, spray the plant with a horticultural soap or oil to smother the remaining scale. You can use neem oil, but the 'oil' is the important part, not the 'neem'.
Third, repeat the first two steps as needed.
The leaves that are sprayed should not be eaten, even though soaps and oils are not very toxic.
However, if you eradicate the scale, the new growth on the plant will be free of both scale and soap/oil residue.