Question
We have a very old large white willow on the edge of the lake in front of our home. Recently Ive notice a build up of a black scaley substance building up on the long leaf stems. The entire tree has it. when you touch it comes off on your hand as if the dark scale is full of a redish purple liquid. It remeind me of a scale very common in ficus trees, but smaller and more concentrated? Any idea what this might be and if I need worry about it. Is the tree in any danger? Is this something that will die off with the coming frost and winter?  

Answer
Hi there. Sounds like you already know what the problem is.

Scale is tiny parasitic insects that adhere to plants and live off the plant抯 sap. They look like bumps and are often mistaken for a disease. There are some 7,000 species of scale insects, varying greatly in color, shape and size, usually ranging from 1/16 - 1/8 inch.
Scale is usually divided into 2 groups: soft scale and armored scale. Soft scale is covered with a protective waxy substance and is somewhat easier to kill than armored scale, which secrete a hard shell over their bodies for cover. Mealy bugs are also part of the scale family.
Scale eggs are laid under the female抯 body. They are called crawlers when they first hatch, because the nymphs have legs at this point and crawl off to find their own spot to attach and feed. Control measures are most effective during the crawler stage.
Different species favor different plants. Plants frequently infested with scale include: Euonymus, magnolia and fruit trees and shrubs
Control of Scale
Outdoor Plants:
  1.Treat with dormant oil in late spring, just before the leaves  unfurl. Scale can overwinter as nymphs or eggs tucked away in tree bark.
       2.You can also treat the tree with the insecticide product available for home use: Bayer Advanced Garden?Tree and Shrub Insect Control.
For additional treatment options, contact a local professional arborist.
Caution: read all label instructions before using any pesticide, avoid skin
contact, and store pesticides  where children cannot reach them.