Yellow nutsedge (Cyperus esculentus) is a common, persistent and troublesome weed in lawns and landscapes in Nebraska.  This is especially true from Kearney east into Iowa.  Yellow nutsedge thrives in waterlogged soil and its presence often indicates that drainage is poor, irrigation frequency/quantity is excessive, or sprinklers/valves are damaged and leaking.  Once this tenacious weed becomes established, they can survive and persist with no irrigation and have been documented to survive prolonged drought.  More than 150 sedge species can be found in Nebraska, however none are as problematic as yellow nutsedge in lawns and gardens.  This plant is not isolated to Nebraska.  It has been documented in 48 of the 50 states, including Alaska, and several Canadian provinces.  Yellow nutsedge is a species capable of tolerating extremes in temperature and precipitation, but is generally found in lower elevations.  This article will describe basic biology of this persistent pest and on-going work at UNL to identify strategies for management and control.

IDENTIFICATION

Although yellow nutsedge is often referred to as "yellow nutgrass," and the leaves resemble those of a grass, it is not a grass but a true sedge.  The leaves are thicker and more rigid than most grasses and are arranged in sets of three at the base, whereas grass leaves are opposite in sets of two.  Nutsedge stems are solid, and when looked at in a cross section, they are triangular; grass stems are hollow and round, and in cross section they are almost flat or oval.  One of the common reference for identification of sedges is "sedges have edges."  By rolling the stem between your fingers the triangular "edge" of the stem is easily recognized.

Yellow nutsedge reproduces by underground storage organs called tuber, which are incorrectly called "nuts" or "nutlets," thus the origin of its common name.  These tubers are produced on rhizomes (underground stems) that grow as deep as 8 to 14 inches below the soil surface.  Buds on the tubers sprout and grow to form new plants; thus individual nutsedge plants eventually form patches that can range up to 10 feet  or more in diameter.  Yellow nutsedge produces round, smooth, brown or black tubers that are approximately 1/2 inch at maturity.  Only one tuber is formed at the end of a rhizome.  Tubers of yellow nutsedge have a pleasant almond taste.  It has been estimated that, if planted in a pure stand, yellow nutsedge would produce approximately the same yield as potato.

LIFE CYCLE

Yellow nutsedge is a perennial plant.  The leaves and flowering stalks die back in the fall as temperatures decrease, but tubers survive in the soil and sprout the following spring when soil temperatures remain above 43^o F for yellow nutsedge.  The majority of tubers can be found in the top 6 inches of soil where they can survive for 1 to 3 years.  In field crops research indicates that most plants sprout from tubers, and seeds do not contribute much, if any, to the spread of nutsedge.

DAMAGE

Yellow nutsedge is a problem in lawns because of accelerated growth during the summer months, a more upright growth habit, and a lighter green color than most grass species, resulting in a non-uniform turf.  In gardens and landscapes, it will emerge through bark or rock mulches and landscape fabric, in shrub plantings and vegetable and flower beds throughout the growing season.

MANAGEMENT

The online publication (heep://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7432.html) provides the following management suggestions for yellow nutsedge:

"Tubers are key to yellow nutsedge survival.  If you can limit production of the tubers, then the nutsedge will eventually be controlled.  To limit tuber production, remove small nutsedge plants before they have 5 to 6 leaves; in summer this is about every 2 to 3 weeks.  Up to this stage, new tubers have not yet formed.  By removing as much of the plant as possible, the tuber will be forced to produce a new plant, drawing its energy reserves from tuber production to the production of new leaves.  Continually removing shoots eventually depletes the energy reserves in the tuber because 60% of the reserves are used to develop the first plant and 20% for the second.  However, mature tubers can resprout as many as 10 to 12 times.  Even though these newer sprouts start out weaker than the previous one, they will gradually resupply the tubers' energy reserves unless they are removed.

The best way to remove small plant is to pull them up by hand or to hand-hoe.  If you hoe, be sure to dig deeply (at least 8 to 14 inches) to remove the whole plant.  Using a tiller to destroy mature plants will only spread the infestation because it moves the tubers around in the soil.  However, repeated tilling of small areas before the plants have 6 leaves will reduce populations.  Many people mistakenly use systemic herbicides such as glyphosate to try to kill the tubers after the plant is fully grown.  Unfortunately, when tubers are mature, there is little translocation of the herbicide from the leaves to the tubers, thus tubers are not affected.  If nutsedge is found in small patches in turf, it may be best to dig out the patch at least 8 inches deep, refill, and then seed or sod the patch."

Other cultural practices that have been shown to be effective include shading.  Nutsedge does not grow well in shade.  In the lawn, raising the mowing height may suppress growth and deplete tuber reserves.  Planting larger shrubs and perennials in landscape beds will achieve the same result.  Proper timing of mulch applications at the proper depth will also suppress nutsedge growth.

Obviously cultural practices should be the first line of defense in any weed control strategy.  While hand weeding may be a viable option for a retiree with lots of time on their hands, it is not practical on a commercial or large scale turf and landscape installation.

Data from recent studies at UNL indicate that any removal or eradication strategy post emergence, including hand weeding and herbicide applications are most successful if done prior to the longest day of the year (June 21).  This has also been documented in studies in Louisiana and Indiana.  Current recommendations from UNL include SedgeHammer from post emergence control.  More recently chemicals have been identified that have good to excellent pre-emergence control of yellow nutsedge.  Dismiss (sulfentrazone) and Echelon (Dismiss and prodiamine) and Tenacity (mesotrione) to a limited extent, have documented pre-emergence activity on yellow nutsedge based on results from Dr. Peter Dernoeden at the University of Maryland. 

We now have products which offer multiple strategies for controlling/suppressing yellow nutsedge.  Early post control is excellent with SedgeHammer.  However, spraying after June 21 with any systemic product often results in stimulation of the daughter tubers and will result in the need for additional applications.  Contact products such as Dismiss do not appear to release the dormancy of the daughter tubers, but these tubers will germinate the following spring or summer.