Yes, your Nellie Stevens holly has scale. This particular scale is called cottony camellia scale. This species of scale infests many different shrubs. They lay white cottony ovisacs (eggmasses) on the undersides of leaves in May. Crawlers hatch through June and remain on the undersides of the leaves through winter. Heavy infestations in the spring may cause the leaves to turn light green. A fungus called sooty mold is also associated with the scale. Sooty mold grows on the honeydew the scale produces and causes a black coating on leaves. Light infestations can be pruned out or oftentimes is controlled by beneficial insects. If the infestation is heavy treat with a horticultural oil now while the crawlers are present. You can also treat in the dormant season with a dormant rate of horticulture oil.

dr

Thanks for the help. So when applying the oil does one do just the underside of the leaves and should the application be before a certain time in the spring/summer if applying at this time?
Thanks again

You need to target the undersides of the leaves with the spray. You time the spray to when the crawlers are out which begins in June and are there through the summer. Use a summer rate or growing rate of horticultural oil according to the label directions.