I have been working on a property that has one of nine cherry laurels in a row declining. They are well established shrubs, minimum 10 years old. The one in decline began with yellowing leaves that drop prematurely. I know Phytophthora root rot is common with laurels and have made sure the mulch is less than 2” deep and not piled around the crown. The soil is not heavy, but it is situated between the foundation and an asphalt driveway. My last inspection of the shrub I noticed what looked like gummosis and frass in large quantities around the trunk. Is this a borer, not root rot, issue? Or could it be both?
It is possible that the shrub was subject to root rot and peach tree borer but we cannot say for sure. Based on the photo this looks like peach tree borer symptoms. Decline and branch dieback is the most obvious symptom of borer activity. Gummosis with frass included at the root crown is a secondary symptom. There is no chemical control. We recommend removing the shrub.
Do not pile mulch high against Prunus stems because it appears to attract egg laying by this borer. Check the drainage in the area and make sure there are no downspouts dumping water in the area. Take a look at our blog on how to grow cherry laurels in the landscape