The only way to positively identify the problem with your Laurel is to bring a sample into the Extension office. My best guess is Phytophora root rot. This is a fungal disease that causes the roots not to be able to uptake water/nutrients properly and symptoms appear in the foliage of the plant. The disease is spread during cool wet springs and falls but the symptoms appear during stressed environmental conditions. It can remain in the soil for many years.
Culturally this occurs when the soil remains too wet due to too much rain/irrigation or poorly drained soils. Over mulching can also cause problems. Obviously, the other bushes are planted near the declining one-possibly the others have not been infected yet or that one small area has drainage problems. 
Check the bark around the soil line and see if it has a darkened discoloration.
In terms of chemical treatment, the Pest Management Guide only recommends using a fungicide with the active ingredient of Potassium salts of phosphorus. Read and follow all pesticide label instructions for use and safety.