Scale on Mountain Laurel
I was told that the white powdery substance on my Mountain Laurels is Scale. I purchased Horticultural Oil and have sprayed the shrubbery twice. Both shrubbery are about fifteen years old. Last Spring the leaves were pale green. Any suggestions on what I can do to nurse them back to better health?
This looks like white prunicola scale on cherry laurel. This is a sucking insect which can cause dieback. In general when shrubs are stressed due to poor planting techniques, poor site conditions, and environmental issues, they can be susceptible to insect and disease issues.
Make sure the shrubs are not planted too deeply. Deep planting causes bark deterioration at the soil line which will eventually kill the plant. Cherry laurels grow best in partial shade in a well drained soil. Check the drainage in the area (they do not like wet soils and poor drainage), make sure mulch is no thicker than two inches in depth, and keep away from the base of the shrub. Boring insects can be attracted to excessive mulch around the base of plants.
Here is some information on control. Prune out any dead or dying branches. You can scrub off the white scales with a soft brush.
You will have to check for crawlers starting in May (there may be three generations and they are salmon colored) before you spray. Wrap some of the branches with double-sided sticky tape to monitor for crawlers. When you see the crawlers, spray with a summer rate of horticultural oil. Follow all label directions. Do not spray when temperatures are in the high '80s in hot weather. https://extension.umd.edu/hgic/armored-and-soft-scales-trees-and-shrubs