Question
My maples had oyster scale a few years now.I sprayed them twice,but the scale is still there.Is their anything else I can do to them.

Answer
I would try using a product called Bayer Advanced Tree and Shrub Insect control. This is applied to the soil around the tree and the roots take it up to the twigs and branches and when the scale insects suck the plant juices they are killed. Imidacloprid (Bayer Advanced  Tree & Shrub Insect Control Concentrate) is applied as a drench around the root zone of infested plants. This water soluble insecticide is taken up by the roots and transported throughout the plant where it is ingested by sap feeding insects. This provides a means to suppress scales without reliance on sprays. This product may need to be applied in the fall to control spring crawlers.

You did not say where you were located so IF the maples have started turning there I would wait until spring--as the buds start to un fold and apply the Bayer product. At that time of year the roots a carrying the sap up at a faster rate to aid in the leaf formation.

Here is a web link to this product check with your local garden type store for it.

http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect