Japanese maple scale is another armored scale creep found on many trees and shrubs, but most oftern on Japanese maples and dogwoods. These insect creeps feed directly on trunks and limbs. Over time they can contribute to tree stress and cause branched death and overall tree decline.
Scale insects go through several life stages. The crawler phase is when immature insects leave their shells, called tests, and feed on the tree. This is when scales insects are most vulnerable to treatment. The crawler phase for Japanese maple scale is fast approaching.
To learn more check out this site: http://ipmnet.umd.edu/nursery/docs/JapaneseMapleScale-UMD2011.pdf