Question: Yellow nutsedge is a recurring problem in my lawn. I have done some research and even used recommended herbicides, but I cannot seem to get rid of it. Do you have any suggestions?
Answer: Yellow nutsedge (Cyperus esculentus) is a common weed in lawns and ornamental beds, especially in moist or wet areas. It is easy to identify by its lighter yellow-green color and the fact that it usually grows faster than the surrounding lawn grasses. Yellow nutsedge also produces bristly, chestnut brown seedheads that resemble small bottlebrushes when it is not mowed. It is not a true grass, but a sedge, characterized by erect, triangular stems.
It can be difficult to control because it grows from underground tubers (also called nutlets) that provide a steady supply of carbohydrates. The top growth pulls up rather easily, but the tubers usually remain behind in the soil. If you pull it out relentlessly, you would eventually exhaust those carbohydrate reserves and get rid of it. However, it is likely to exhaust you or your patience before then!
Professional-use products such as Manage (halosulfuron) or Basagran (bentazon) provide the most satisfactory control and will not harm lawn grasses when used according to label directions. These products are not restricted use, but they are not usually available to home gardeners. Bentazon is sometimes sold to home gardeners as Monterey Nutsedge Nihilator. Manage is available in single-use packs from commercial turf supply dealers.
Timing is everything; these products are most effective on small plants. Label directions recommend applying Manage as soon as the weeds reach the three- to eight-leaf stage, prior to blooming. You often must reapply it six to 10 weeks later, once plants that have re-grown reach the same stage. You may even have to apply it again the next year.
Herbicides are much less effective after tubers form in late summer. Then it would be better to pull the weeds by hand and save the herbicide until spring.
It is also important to add a nonionic surfactant to your spray tank (one-third fluid ounce per gallon). These products help herbicides penetrate the waxy cuticle of weeds such as yellow nutsedge. Manage will not be nearly as effective if you do not use it because less herbicide will be absorbed.
Changing cultural practices can also help control hard-to-kill weeds. Have your soil tested to ensure that you are fertilizing properly and that your soil's pH is in the optimum 6.5-7.0 range that most grasses prefer. Be sure to water deeply and infrequently to help the grass develop a deep, extensive root system.
Because yellow nutsedge prefers a moist or wet environment, make sure the soil drains adequately in those areas. A quick test is to dig a hole 18-24 inches deep and fill it with water. Time how long it takes to drain. If it drains in an hour or two, drainage is not a problem. If it takes more than five or six hours, you have a drainage problem that may require French drains or other measures. Make sure that you are not overwatering that area.
Finally, raise your mowing height to 21/2 to 3 inches. If you cut it shorter, you reduce the lawn's root system and its ability to outgrow weeds of all kinds. Leaving your lawn a little taller makes for a healthier lawn and allows it to shade out competing weeds.
Send questions to Sandy Feather by e-mail at firstname.lastname@example.org or by regular mail c/o Penn State Cooperative Extension, 400 N. Lexington Ave., Pittsburgh 15208.