Strange bug eating my Nellie Stevens Holly Tree
Greetings! Nellie Stevens Holly tree, approx 11 yrs old, 20 feet high, has black coating of junk on top of leaves, and slug-like creatures living on bottom side of leaves with whitish cocoons. Noticed one a few leaves last fall, now it's on two of my trees, same area/symptoms. Trees receive full light from 1pm to end of day; they are on the north side of my 2-story house. I've been spraying 1x/week for about 2 months with Bayer Advanced Disease Control (2.90% Tebuconazole), as it is systemic and will get into the plant. Still having issues. Overall the tree appears healthy. The outbreak is around the lower portion of the tree, from 2 feet to 5 feet off the ground (i.e. ring in the middle). What is this thing, and how do I get rid of it? See the two (2) attached photos for illustration. Leaves are 3.5" max length.
You are correct, this is a type of sucking insect called cottony camellia scale. You should immediately stop spraying the Bayer pesticide, which is only for diseases and will not help with your problem.
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. .
As the scale sucks plant juices, it excretes a sticky honeydew on the leaves beneath, and a sooty mold grows on it, causing a black coating on leaves.
Light infestations can be pruned out or oftentimes is controlled by beneficial insects.
If the infestation is heavy you can treat with a horticultural soap or oil in mid June when the crawlers are present. You can also treat in the dormant season with a dormant rate of horticulture oil.