Looking in my notes from 8/18/16
Amy tells me about the chemical from Brewer that kills nut grass (from C. Brewer)
https://www.google.com/search?q=what+kills+nut+grass
https://www.google.com/search?q=what+kills+nut+grass+hawaii
This is the article I was looking for. It's from the College of Tropical Agriculture & Human Resources from the University of Hawaii
Apparently the nutgrass in Hawaii is purple nutsedge.
Purple nutsedge (Cyperus rotundus), commonly known as nutgrass in Hawaii, is one of the world’s most serious weeds. In addition to being unsightly in gardens, lawns, and landscapes, nutgrass can compete with garden crops or landscape plants and restrict their establishment and growth.
Because its growth is severely restricted by shade, most other weeds and many larger crop or landscape plants can eventually dominate nutgrass, but they seldom can completely suppress it, and it will almost always persist if not controlled. Nutgrass grows most rapidly in full sunlight when adequate water and nutrients are available. It becomes more serious when allowed to grow without competition from other plants for light, water, and nutrients. This can occur when annual weeds are removed, crops are harvested, or the soil is cultivated for new plantings.
Left undisturbed, nutgrass will spread by growing laterally underground, several yards each year.
[not good!]
Tuber dormancy is perhaps the most important of the adaptations that enable nutgrass to persist. Dormancy prevents tubers in the soil from sprouting all at once, so a potential reservoir for new plants is maintained. This is the reason you will find nutgrass emerging after you thought you controlled it with herbicide or by weeding.
When hand-weeding, the wiry connections between tubers make them easier to remove than if the connections have been severed by soil cultivation. The tuber or basal bulb of an emerged shoot must be removed to control nutgrass. Clipping the topgrowth is ineffective, and an inch or so of new growth will emerge the following day. Patient gardeners can dig up and remove tubers from the soil and greatly reduce the nutgrass population.
Herbicides
There are effective herbicides for nutgrass control. One of the most effective is glyphosate (Roundup®), because it will kill the underground tubers connected to the leaves. Timing of the Roundup application, however, is crucial for effective control. Spraying newly emerged nutgrass plants is not the most effective method. It is best to apply Roundup 2–3 months after the initial emergence of nutgrass.
One way to do this is to allow nutgrass to grow while raising a crop that takes 2–3 months to mature. During this time, weed once or twice to remove annual weeds that may outgrow nutgrass and the crop. After harvesting the crop, and while the nutgrass is still growing well, apply Roundup following the label directions, then wait 1 or 2 weeks (or longer) before preparing the soil for the next planting. Many crops can be planted into the treated area, but be sure to read and follow directions on the Roundup label.
This procedure kills nearly all new tubers connected to the emerged nutgrass shoots, as well as the original tubers that sprouted. The nutgrass population in the next crop will be greatly reduced, but it is unlikely that this procedure will kill all the nutgrass, because tubers that are dormant or are not connected to above-ground leaves are not affected by the herbicide application. When nutgrass again becomes a serious problem, this procedure can be repeated.
Roundup can also be used as a spot treatment or directed spray to nutgrass growing beneath trees, including many fruit trees and landscape plants that are listed on its label. Special care must be taken to avoid getting Roundup spray or drift on green bark or foliage of any desirable trees, shrubs, or groundcovers.
In turfgrass, Manage® and Image® or a combination of Image and MSMA can provide effective control of nutgrass. Do not apply MSMA to St. Augustinegrass or centipedegrass. A single application of Manage, Image, or Image and MSMA usually controls an existing stand of nutgrass growing in turf. However, a few weeks later, new nutgrass shoots will emerge, arising from dormant tubers that were not connected to nutgrass shoots when the herbicide application was made. The new stand of nutgrass must be treated to prevent new tubers from repopulating the soil. However, it is best to wait 21 /2–3 months between herbicide applications to allow more nutgrass shoots to emerge before reapplication.
In any herbicide control program for nutgrass, it is important not to allow the weed to grow untreated for longer than three months, because most nutgrass shoots die naturally after three months. Once the nutgrass shoot dies, there is no living connection to the tubers, and many of them escape the herbicide treatment to serve as a source of re-infestation. This reserve can last for two years or longer. Thus, in order to effectively reduce the nutgrass tuber population in the soil, herbicides must be reapplied about every three months for about two years.
***
[OK, weed and spray every three months for two years.]
***
Here's another article (now that I know it's purple nutsedge)
Hand Weeding
Pull on a pair of garden gloves, and remove the purple nutsedge by hand, a method of control that works best with limited nutsedge invasions. Grasp each weed shoot at its base, and pull gently upward, being careful to also remove the bulb at the base of each shoot. If you find the uprooting process difficult, lightly water the area, as moist soil makes weed removal easier. For the best results, pull up purple nutsedge before it has five leaves -- plants that are this young don't have a fully developed root and tuber system and are easier to eliminate.
Spray With Chemicals
One of the quickest and least labor-intensive options for eradicating purple nutsedge is the application of a nonselective, glyphosate-based herbicide, such as any of the Roundup ready-to-use herbicide sprays. Wait eight to 12 weeks after the purple nutsedge has started growing; this ensures adequate foliage surface area to absorb the herbicide. Then, mist all exposed surfaces of the nutsedge with the glyphosate spray. This nonselective herbicide chemical will kill all parts of the weed, including its underground tubers.
***
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 the 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 only will 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.
[8 to 14 inches!]
Chemical Control
Few herbicides are effective at controlling nutsedge, either because of a lack of selectivity to other plants or a lack of uptake. For herbicides that are suitable, apply them when they’ll be most effective (Table 1). Most herbicides aren’t effective against tubers.
This is an interesting table.
Roundup is glyphosate and should be applied to young plant and is available to home gardener
Certainty (what Amy uses) is sulfosulfuron and also should be applied to young plant but not available to home gardener
[What about the Ortho Nutsedge Killer? It's sulfentrazone which is not listed in the table.
According to this study, sulfentrazone provided 60% for sulfosulfuron. Trifloxysulfuron was equally effective as sulfosulfuron. Trifloxysulfuron-sodium is Monument, also not available to home gardener.]
The only nonselective postemergent herbicide currently available to help control nutsedge in the home landscape is glyphosate (e.g. Roundup) or glyphosate with nonaoic acid (Roundup Plus). This herbicide requires repeated applications, and its use will result only in limited suppression of these weeds.
Many people mistakenly use glyphosate on fully grown plants to try to kill the tubers. Unfortunately, when tubers are mature the herbicide usually doesn’t move from the leaves to the tubers, leaving them unaffected. Instead, apply glyphosate when the plants are young, actively growing, and haven’t recently been mowed or cut.
Selective Postemergent Herbicides
Postemergent herbicides that have some selectivity, particularly in turf, are halosulfuron (Sedgehammer) and MSMA. These herbicides move through the plant rapidly, but to be effective, you must apply them to nutsedges before the fifth-leaf stage, when the plant is still building energy reserves by drawing energy from its leaves to the newly forming tubers. After this stage, this translocation to the tubers slows down or ceases, and the herbicide will kill only the above-ground portion of the plant, leaving the tubers unaffected.
[maybe I should try Sedgehammer, but check out this video]
Halosulfuron is used in such minute amounts the manufacturer markets it in premeasured, water-soluble bags. Follow all label directions for optimal control of nutsedge, and be sure to add a nonionic surfactant to the spray solution. MSMA is more effective on yellow than on purple nutsedge. Other herbicides available to professionals for use on turf include trifloxysulfuron-sodium (Monument) and sulfosulfuron (Certainty). Be sure to read the label carefully, as these products will injure some turf species.
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Here's Mike's answer. Not sure who this Mike is, but he's from You Bet Your Garden
My good buddy Howard Garrett, a long-time organic advocate in Texas, had a great bit about this weed on his "Dirt Doctor" website recently. "There is only one guaranteed, foolproof method to completely kill nutgrass," he recounts: "First, dig out every tiny piece of the plant including the seeds and nutlets. Make sure you sift the soil through a mesh screen. Dump the collected material on the driveway and burn it. Sweep up all the ashes and seal in a concrete box. Drive to the coast and dump the sealed box 20 miles off shore."
Now, because it does grow so much faster than grass, this nutty weed gives its location away easily. So yes, burning the top growth repeatedly with a flame weeder (or smothering it with an herbicidal soap spray or attacking it with a vinegar based herbicide) will force the underground tubers to resprout and use up a great deal of their energy; one soil scientist says up to 60%. Thus, repeated attacks on the top will eventually starve the underground tubers. But while some sources say that four attacks on the above ground growth (wait until at least six new leaves are showing) will do it, others say it takes a dozen.
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