white powdery substance on cherry laurel branches
We just noticed that the branches of some of our Otto Luken cherry laurels are covered with a white powdery substance...(maybe scale?) They actually looked like they had been painted white. Some leaves have turned yellow and there is some die back. I did recently wash off the branches with soapy water and a soft brush. As you can see from the picture I didn't get it all. Should I work at this some more? Is there anything else I should do at this time of year? Would using a systemic product be helpful? The shurbs are about 16 years old and 6' wide by 3' tall and receive full sun from late morning on.
Montgomery County Maryland
This is white prunicola scale (WPA.) WPS is a sucking insect that sucks plant cell contents from twigs and branches. This can cause dieback, which is usually preceded by leaf yellowing and premature leaf drop. If the infestation is heavy, you may want to remove the shrub. If the other laurel shrub nearby are stressed, they can be susceptible to the scale.
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. If the infestation is light, 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