Answer: What you refer to as nutgrass is actually yellow nutsedge (Cyperus esculentus), which may be the worst weed in Los Angeles. It is easily identifiable by its shiny leaf blades and hard, nutlike underground tubers. Complete eradication may not be possible. But there are some anti-nutsedge chemical products available at nurseries.
Make sure you follow label instructions precisely.
White stuff on the roses may be powdery mildew. Funginex is a good product for roses.
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