Q. I spoke to you about my patch of Bermudagrass at one of your classes. You said that Bermudagrass could be controlled just by letting a fescue lawn shade the soil. Can I really get my Bermudagrass under control simply by mowing higher? Winter fescue lawn with dormant bermudagrass now obvious. Invasion of bermudagrass is because sprinklers cannot irrigate a triangular patch of grass efficiently. Under irrigation = bermudagrass in the hot desert. A. No, you cannot control existing Bermudagrass in a lawn just by letting the fescue grow taller. I think I was misunderstood. Once you have a fescue lawn established, by keeping the soil shaded you will reduce and possibly eliminate Bermudagrass from getting started. This is what I intended to be heard.             Bermudagrass cannot survive in shade. By keeping the soil surface shaded by a healthy lawn, Bermudagrass will be discouraged. Bermudagrass invades a home lawn where lawns are mowed too short or damaged, thus eliminating shade on the soil surface. Typical places where it invades include around sprinkler heads and the edges of the lawn near concrete. Both of these places are where line trimmers are frequently used to keep grass shorter.             It also invades damaged areas due to under irrigation, disease or insects. Once established in the lawn, Bermudagrass is nearly impossible to eliminate without renovating the entire lawn. This would mean fertilizing, watering and mowing the lawn to get it as healthy as possible and then killing it with Roundup.             This is best done in the fall around mid-September to mid-October. About 10 days after the Roundup application or applications, the lawn can be mowed extremely short, power raked until you see bare soil and reseeded directly into the dying or dead lawn.             The key to eliminating the Bermudagrass will be getting a thorough kill with the Roundup before replanting. Spray once, mow in two days and spray again going 90 degrees to the first spray to get good coverage and a better kill.