Yellow Nutsedge (watergrass to most) are common weeds in landscapes, gardens and lawns. They thrive in waterlogged soil, and their presence often indicates drainage is poor, irrigation is too frequent, or sprinklers are leaky. Once established, however, they will tolerate normal irrigation conditions or drought.
Although nutsedges resemble grasses and often are referred to as “nutgrass” or “watergrass”, they aren’t grasses but are true sedges. Their leaves are thicker and stiffer than most grasses and are arranged in sets of three at their base; grass leaves grow across from each other in sets of two. Nutsedge stems are solid, and in cross section they are triangular; grass stems are hollow and round, and in cross section they are almost flat or oval.
Yellow nutsedges produce tubers, which are incorrectly called “nuts” or “nutlets”, thus the origin of their common name. The plants produce these tubers on rhizomes, or 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 and eventually form patches that can range up to 10 feet or more in diameter.
Yellow nutsedges are perennial plants. Their leaves and flowering stalks generally die back in fall as temperatures decrease, but tubers and rhizomes survive in the soil and sprout the following spring once soil temperatures remain higher than 43°F.
The majority of tubers occur in the top 6 inches of soil where they can survive for 1 to 3 years. In field crops, research indicates most nutsedges sprout from tubers, and seeds don’t contribute much to the spread of the plant; however, no work has been done to examine the role of seed in the spread of nutsedge.
Nutsedges are a problem in lawns because they grow faster, have a more upright growth habit, and are a lighter green color than most grass species, resulting in a nonuniform turf. In gardens and landscapes, nutsedges will emerge through bark or rock mulches in shrub planting and vegetable and flower beds throughout the growing season.
Tubers are key to nutsedge survival. If you can limit production of tubers, you’ll eventually control the nutsedge itself.
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, the plant hasn’t formed new tubers yet. Removing as much of the plant as possible will force the tuber 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 the nutsedge will have to use 60% of its reserves to develop the first plant and 20% for the second. However, mature tubers can resprout more than 3 times. Even though these newer sprouts start out weaker than previous ones, plants can develop from them and produce new tubers unless you remove them.
The best way to remove small plants is to pull them up by hand or to hand hoe. If you hoe, be sure to dig down at least 8 to 14 inches to remove the entire plant. Using a tiller to destroy mature plants will only spread the infestation, because it will move the tubers around in the soil. However, repeated tillings of small areas before the plants have 6 leaves will reduce populations. If you find nutsedge in small patches in your turf, dig out the patch down to at least 8 inches deep, refill, and then seed or sod the patch.
Few herbicides are effective at controlling nutsedge, either because of a lack of selectivity to other plants or a lack of uptake.
The Above article is courtesy of http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7432.html