Answer: Scale insects have hard outer shells which makes them practically unaffected by insect sprays. The sprays are effective against the newly emerging juveniles because they haven't yet developed the hard outer shells. The spray you used probably wiped out the next generation of scales, if they were present. To kill the adults, smother them by using a horticultural oil during the winter. Apply the oil in late winter, when air temperatures are above 40F. Be sure to thoroughly spray the trunk plus all branches and twigs. One treatment should be sufficient. As with all pesticide products, read the label carefully and apply according to label directions.
Q&A Library Searching Tips