Experts tackle readers’ garden questions.
Q: I need help with nut grass. Is there any product out there to kill this problem weed? Numerous times, I have spent hours digging out (at least 10 inches deep) trying to remove it completely, only to have it appear again. I’m starting to see it in my lawn. What do you suggest?
Jeanette Garcia, Sacramento
Master gardener Rachel Tooker writes: Nutsedge, often referred to as nut grass, is a common weed in landscapes and gardens in the Central Valley. The plant thrives in waterlogged soil and its presence often indicates poor drainage (particularly an issue with clay soils), too frequent irrigation or leaky sprinklers. Once established, nutsedge will tolerate normal irrigation conditions or drought, making it even more difficult to eradicate.
This pesky weed also is prolific. One yellow nutsedge plant can produce 400 tubers in one year. One tuber can turn into 1,918 plants! That’s potentially 767,200 new plants from just one nutsedge.
The two most common species of nutsedge in California are yellow nutsedge (Cyperus esculentus) and purple nutsedge (C. rotundus). Yellow nutsedge grows throughout California, while purple nutsedge grows mostly in the southern part of the state.
Nutsedge is commonly referred to as nut grass because it resembles grass. However, nutsedge can be distinguished by its leaves, which are thicker and stiffer than grass, and are arranged in sets of three at the base compared to sets of two found in grass. If allowed to mature and flower, nutsedge will send up a triangular stem with three long, leaf-like bracts at the base of each flower head (flowers in yellow nutsedge are light brown).
Individual yellow nutsedge plants will spread to form a dense clump — sometimes ranging up to 10 feet or more in diameter. Nutsedge produces tubers on rhizomes (underground stems) that grow as deep as 8 to 14 inches below the soil surface, although most live in the top 6 inches of soil. The tubers are often referred to as “nuts” or “nutlets.” Buds on the tubers sprout and grow to form new plants.
Nutsedge can be controlled if cultivated at an early stage. Once established, a nutsedge infestation is extremely hard to manage. The best approach is to keep removing small nutsedge plants as soon as they crop up. If pursued diligently over time, the nutsedge population will slowly dwindle.
The best approach to managing nutsedge is a multipronged approach. First, remove small plants before they develop tubers (usually before they have developed five to six leaves). In summer, this will require patrolling the yard every two to three weeks. Remove as much of the plant as possible by digging down at least 8 to 14 inches. This will force the tuber to produce a new plant, draining its energy reserves over time. Tubers can resprout more than three times so it is important to keep at it.
Do not use a tiller, which will just scatter and spread the tubers. To remove nutsedge patches in turf, dig down at least 8 inches, refill with soil and then seed or sod the patch. Do not dispose of any soil or weeds in a compost bin.
Drying out the soil is more effective in controlling purple nutsedge than yellow nutsedge. However, being careful not to overwater an area will help establish less-optimal conditions for all nutsedge growth. Review watering practices and check for leaky irrigation heads. Because nutsedge does not grow well in low light, planting a tall, dense, groundcover or shrub may help shade out the weed.
A thick, nonwoven landscape fabric made from polypropylene polymers also can help suppress nutsedge growth. Do not use black plastic barriers which nutsedge can easily pierce. Cover the landscape fabric with mulch, but continue to monitor and remove any emerging young plants that grow through the mulch.
As a last resort, a chemical control can be considered. Administering herbicides must be properly timed and may require professional services. Glyphosate (commonly referred to as Roundup) is available to homeowners. However, it is only effective on young plants with up to four leaves before they produce tubers. If applied to mature plants, glyphosate will kill the leaves but not affect the tubers. Roundup Plus, a more powerful concentration that requires mixing, contains a higher percent of glyphosate, making it ideal for eradicating harder-to-kill weeds.
If the weeds have already been removed from the area, pre-emergent herbicides can be applied to prevent the germination or survival of weed seedlings. Great care is required when applying any chemical as it can damage other landscape plants. It is critical to always carefully read label instructions.
For more information on controlling nutsedge, check out the University of California, Integrated Pest Management Program, Pest Note 7432, “Nutsedge,” available free online at http://ipm.ucanr.edu/PMG/PESTNOTES/pn7432.html. For more information on using herbicides in landscapes, go to http://ipm.ucanr.edu/m/pn7441-7.html.
Rachel Tooker is a UC Cooperative Extension master gardener for Sacramento County.
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