Ask Mr. Smarty Plants

We are sorry to hear about the problems you are having. Since we had never heard of putting rock filled cylinders in to help roots "breathe," and are not plant pathologists, we will just have to revert to telling you what we know about Prunus caroliniana (Cherry laurel), and try to go from there to discover the problem and hopefully, a solution. First, from our Native Plant Database page on this plant, all of which you can read by following the above link:

Growing Conditions

Water Use: Medium
Light Requirement: Sun , Part Shade
Soil Moisture: Moist
Cold Tolerant: yes
Soil Description: Moist, deep, loamy, well-drained soils. Clay Loam, Medium Loam, Sandy Loam, Sandy
Conditions Comments: Likes the moist, well-drained soils of its natural range. Prolonged saturation can cause root rot, particularly in clay soils. Shallow, nutrient-poor, rocky soils can cause chlorosis and heat stress.

You will note that the preferred soils are deep, loamy, well-drained soils. Most of the soils in Central Texas are alkaline clay. The soils east of us have more sand and are more acidic. The biggest problem could easily be the drainage or the lack thereof, which might have been helped by mixing the soil in which the cherry laurel was planted with some compost. The issue of chlorosis mentioned in the Growing Conditions above can also be blamed on drainage. Please see this previous Mr. Smarty Plants answer on the problems caused by our soils.

We suspect that these native plants are getting more attention than they need. Watering too much can have invited the fungus, as well as compacting the soil so that the nutrients in the soil were not available to the rootlets. Mulching the root area will help protect from heat and cold, and the mulch will decompose to add more compost to the soil. When you water, push the hose down in the soil and let it dribble slowly until water comes to the surface. Don't water by sprinkler-the water on the bark and leaves can invite disease. We may not have the ideal soils for these plants, so if they don't pull out, we suggest researching replacements in our Native Plant Database, checking to make sure they are native to this area and tolerant of our soils.