I have an established zoysia lawn that I need to get in better shape. It has its share of clover and other weeds in it. The weeds are especially bad under a large oak tree. I have not done a soil test. I have never put anything on it to control weeds, and I usually fertilize with triple 17 once or twice a season. Any suggestions to get this lawn looking better at a reasonable price? I am located in South Carolina, and do not have an irrigation system.