Question: Every summer when the weather turns hot, my lawn is covered with yellow nutsedge. In the past, we’ve tried renovating the entire lawn—tilling, raking, and replanting—but to no avail. Is there any solution short of replacing the top six inches of soil in my lawn?
– Bethpage, NY
Answer: Yellow nutsedge (Cyperus esculentus) is an herbaceous perennial weed that goes dormant in the fall and regrows from underground tubers. Nutsedge thrives in full sun and moist soil, and unfortunately a single plant can produce thousands of tubers that can remain dormant for years.
Keeping nutsedge out of a lawn in the first place involves keeping the grass healthy and vigorous, with careful attention to pH, fertilizer, and regular mowing, but an infestation such as yours is best adressed with an herbicide. You have a choice of three ostemergence herbicides, all suited to cool-season lawns: bentazon (Hi-Yield Basagran), halosulfuron (Manage), and methanearsonate (Daconate).
Follow the directions for each herbicide exactly. In general, the soil should be moist and the nutsedge actively growing.