There are four basic types of soft scale - I found Hemispherical soft scale on one of my shrubs, and there are also Brown, Black and Green Shield varieties. Soft scale has one of nature’s stranger life cycles.
The thing that makes soft scales so interesting is that they are mobile only as infants. The initial development stage, or instar, has functional legs, whereas the adults are attached to the inside of a shell, where they feed and lay eggs pretty continuously, until the weather gets too cold or the host plant dies.
In the photo above, you can see a large number of established Hemispherical soft scales. They suck sap from the twigs and leaves of the plant and then excrete a sugary honeydew that ants love. In fact, heavy ant traffic was what notified me of this very subtle, but potentially deadly infestation. As it was, I had to remove several branches.
The problem with infestations such as these is that the excreted honeydew provides a perfect growth medium for fungal and bacterial populations. As ants collect the honeydew and move from plant to plant, they can quickly spread disease throughout your garden.
To avoid the use of chemical treatment against soft scale, regularly monitoring woody plants and stripping the vermin from twigs and leaves by hand are your best bet. You can also use sticky barriers around the trunks of trees and shrubs to prevent the mobile first instars from establishing themselves on your plants.
You can grow a surprising amount of food in your own yard. Ask me how!