David M. Kopec, Extension Turfgrass Specialist
Many turfed areas in Southern Arizona have 'the dreaded purple nutsedge -- scourge of the Southwest.' In the old days, farmers used to say, 'sell the farm' if you had lots of nutsedge. It doesn't take long for a little nutsedge to become a lot of nutsedge. Here's why!
Purple nutsedge (Cyperus rotundus) is a perennial plant with special underground growth structures that make it competitive in turfs. Purple nutsedge also has an upright growth habit and a faster vertical elongation rate the most turfgrasses. This allows it to grow on top of the turfgrass and capture more sunlight and thus make more food.
Purple nutsedge is a warm season weed. It is not a grass although sometimes it is called 'nutgrass.' In the spring underground tubers sprout rhizomes which reach the surface in the late spring. The tubers are food storage organs which contain food for up to 5-6 rhizomes which grow out of the 'eyes' of the tuber (just like a potato tuber). The tuber will release only one or two rhizomes at a time. Once the rhizome reaches the soil surface, it forms a special green shoot, called a vegetative bulbill. The bulbill swells at the base and unleashes two types of growth. (1) an upright shoot with the leaves that unfurl in a triangle (like an onion bulbill) and (2) a shallow underground runner which moves a few inches away from the 'mother bulbill.' This new runner re-establishes another bulbill with leaves and thus another plant. This occurs repeatedly in the spring and early summer. The result is an increased stand of nutsedge pants which came from only a few growing points from a few nutlets. Such a conservative tactic results in a 'profitable stand' of nutsedge -- from a weed stand point.
By the end of August, all these ?new? plants have been making enough food to now make new nutlets. The new nutlets will have 3-5 growing points for next year. One growing point on one nutlet can give rise to 10-15 plants per season. In a 'perennial stand of nutsedge', you can see where the 'staying power of nutsedge' comes from.
Chemical control programs are available to suppress nutsedge plant population, which will in turn eventually eliminate the weed from turf. Whatever chemical(s) you use, you must make repeat applications again and again and again until the nutlets are exhausted underground. Thus, it is a war of attrition. Chemical (or physical) eradication of the foliage triggers the nutlets to sprout new 'rhizomes' to reach the surface and establish new plants. This is why repeat applications are necessary once new foliage returns. You don't want to give the plants a chance to store enough food to make new nutlets. Thus, remove the foliage -- chemically. This forces the release of growing points from the nutlets and decreases the inventory of 'stored plants' in the soil. This war of attrition (repeat applications) can eventually result in the loss of nutsedge.
MSMA -- Repeat applications every 3-4 weeks of MSMA at 2.0 lbs. active ingredient per acre will burn back the foliage. This can result in some foliar burning of the bermudagrass as well, especially when a surfactant is used. Greater damage to the nutsedge occurs when a surfactant is used at 1/4 of 1% V/V. You can tank mix iron to minimize the damage.
IMAGE -- Image (imazaquin) has been around for 6-7 years and is active on purple nutsedge. The label rate is 0.5 lbs. ai/acre. It is absorbed both by the foliage and by the roots of nutsedge. Apply it during the morning and water it in with a normal irrigation that evening. In 14-18 days, the foliage will turn yellow and then brown. Regrowth occurs in about three weeks afterwards. Image can turn bermudagrass apple green for 3-5 days after application, then it returns to a dark green color. Image will eliminate all cool season turfgrasses, so say goodbye to any lingering overseed you may have.
TANK MIX -- I have seen a beneficial effect of tank mixing MSMA (2.0 lbs. ai/a) and Image (0.5 lb. ai/a). Burn down occurs quicker and suppression lasts longer than either one alone.
MANAGE -- Manage (halsulfuron) is a relatively new herbicide for control of both yellow and purple nutsedge. Manage is taken up by the foliage of nutsedge. So apply it in the morning and it will get absorbed by the end of the day. Manage burns the foliage quicker than Image and it seems to suppress regrowth for a longer period of time. Research has shown that Manage is translocated to the nutlets, but nutlets are not totally eliminated and regrowth will occur. Manage will not injure warm or cool season turfgrasses.
It's simply a war of attrition. You must repeatedly remove the foliage to force nutlets to release growing points and destroy that generations foliage.
Check the label for repeat intervals and allowances. You have enough flexibility with these three herbicides to have a season long rotation of 3-5 applications/season. In 3-4 seasons, you can eliminate nutsedge economically with spot applications to infested areas only.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.