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Yellow walnut covering a lawn and a softball field in the central PA. Photos: Peter Landschoot, Penn State

Yellow walnut (Cyperus esculentus) – sometimes also called nut grass – is a persistent weed problem on lawns, sports fields and golf courses. It thrives in damp, poorly drained soils and can remain in full sun and moderate shade. As an aggressive weed, it spreads through underground stems and tubers.

Many lawn managers and homeowners find the yellow color, rough texture, and rapid growth rate of turf stocks uncomfortable in the cool season, which also makes identification relatively easy. Stem bases typically show a reddish hue when the outer leaf sheaths are removed. It also has yellow nutsedge has angular, three-sided stems that can be recognized by holding and rotating the stem base between your thumb and forefinger.

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Yellow-green, coarse, shiny leaves from yellow walnut; reddish hue of the stem base; and triangular shape of the stem cross section. Photos: Peter Landschoot, Penn State

Fortunately, the yellow walnut can be controlled with good cultural practices and appropriate herbicides that are used at the right growth stage, which usually occurs in late spring or early summer. (This month is ideal). A new plant of several years is mainly made from knots on rhizomes and from tubers that can overwinter. Bulbs usually begin to form at the tips of the rhizomes in late June or early July. A single plant can produce multiple tubers that can rest in the soil one to several years before germination. Leaves and stems emerge in spring and grow quickly in warm weather in summer when the leaf growth of grasses slows down in the cool season. The leaves of the yellow nutshell die off in autumn after the first hard frost.

Cultural management

Yellow walnut is typically introduced through soil contaminated with tubers and rhizomes. Although there are no practical means of detecting reproductive structures in the soil, the use of soils from locations without a history of infestation can reduce the risk of contamination.

If only a few yellow nut plants infect a lawn, they can be removed by hand shortly after the leaves emerge in spring and before tubers form later in the growing season. Remove as much as possible from the underground part of the plants as broken plants can create new plants. Improving lawn density through fertilization, regular mowing, and the use of lawn grasses that are well adapted to the site conditions will help slow the spread of yellow walnut herb, but may not provide effective suppression once it has established itself.

Chemical control

The most effective control of yellow walnut herbicides is achieved when foliage is visible in the lawn and before the tubers start to ripen in mid to late summer. It is important to treat nutsedge before the tubers mature, as these underground structures can spawn many new plants in the following years. Herbicides are usually most effective in controlling nutsedge if mowing is restricted at least two to three days before and after application.

Herbicides characterized to control or suppress yellow walnut in cool season lawns include bentazone (Basagran T&O); Sulfentrazone and products containing sulfentrazone (Dismiss, Surepyc, Dismiss NXT, Solitare, Solitare WSL, Echelon 4SC, Q4 Plus, Foundation, Momentum 4-Score, SureZone, Surge and TZone SE); Halosulfuron-Methyl (Sedgehammer, Prosedge and Sedgemaster); Imazosulfuron (Celero); Mesotrione (toughness); and Dimethenamid-P (tower). A new herb herbicide, pyrimisulfan (Vexis) *, was recently launched.

Bentazon

Basagran T & O is a selective contact herbicide that contains bentazone, a photosynthesis inhibitor in susceptible weeds, as an active ingredient. This herbicide acts relatively quickly, with injury symptoms appearing on the walnut within five to seven days after treatment. Basagran T&O can be used on established Kentucky bluegrass, fescue, ryegrass and bentgrass to control yellow walnut and some weeds. Control can be improved by adding methylated seed oil or vegetable oil concentrate. A second application can be made seven to 10 days after the first application, if necessary, but at least 21 days after the first application for perennial ryegrass. Penn State trials show that Basagran T&O is effective in controlling yellow nuts with a single application of 0.75 fl oz of product per 1000 m². A leaf injury was observed with this product in perennial ryegrass in heat and drought stress situations.

Sulfentrazone and products containing sulfentrazone

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Yellow nutshell, treated with discharge three days after application. Photo: Peter Landschoot, Penn State

Dismiss and Surepyc are contact herbicides that are known to combat yellow walnut and contain 39.6% sulfentrazone as an active ingredient. In contrast to most systemic herbicides, Dismiss and Surepyc act very quickly. A recent Penn State trial showed marked yellow nut injury symptoms two days after application in early July, and treated plants were no longer visible 10 days after application. Both products can cause leaf injuries on some varieties of fine fescue, and neither product is marked for use on putting greens.

Dismiss NXT contains sulfentrazone and a small amount of carfentrazone-ethyl (3.53%) and is marked with broad leaves to combat or suppress yellow walnut and some weeds. Solitars and Solitars WSL (Sulfentrazone and Quinclorac) are also featured to control or suppress yellow walnut and weed in most grassy grasses in the cool season. Echelon 4SC (sulfentrazone and prodiamine) is labeled for control after emergence or suppression of yellow walnut in lawns and for control before emergence in areas without farmland with bare soil. Users should be aware of the extended exposure restriction intervals after using Echelon 4SC due to the herbicidal activity of prodiamine before emergence. Some other sulfentrazone-containing products such as Foundation, Momentum 4-Score, SureZone, Surge and TZone SE have low concentrations of sulfentrazone and are only labeled to suppress yellow nuts.

Halogen sulfur methyl

Sedgehammer, Prosedge and Sedgemaster are herbicide products that contain the active ingredient halosulfuron-methyl, a sulfonylurea herbicide with systemic activity. These products are labeled for most cool grass lawn grasses. On the labels it is recommended to add a non-ionic surfactant with 0.25% v / v to the spray solution in order to optimally control the yellow nutshell. If necessary, another application can be made six to eight weeks after the initial application. Sedgehammer + is a special formulation that is premixed with a surfactant.

Sedgehammer, Prosedge and Sedgemaster are most effective when applied to nutsedge in the three- to eight-leaf stage. Although products containing halosulfuron methyl are very effective, they work slowly. In a study carried out in Penn State, injury symptoms did not appear until about a week after application of sedgehammer treatment, and complete dehydration occurred three weeks later. Although the active ingredient works slowly, it eventually migrates into the rhizomes and tubers and kills the entire plant. For best results, do not mow two to three days before or after application.

Imazosulfuron

Celero herbicide contains the active ingredient imazosulfuron, which belongs to the class of sulfonylurea herbicides and has a systemic effect in susceptible plants. This product is labeled for most cool grass lawn grasses and combats various types of sedge and some weeds. For optimal control, a non-ionic surfactant with 0.25% v / v must be added to the spray solution. Use should begin after nut plants have reached the three-leaf stage of growth. If yellow nuts are heavily infested, a second application can be made 21 days after the first treatment.

Mesotrione

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Heavy infestation of yellow walnut herb and stubbornly treated crab grass. Photo: Peter Landschoot, Penn State

Tenacity is a popular herbicide that fights stubborn weeds like bentgrass, nimblewill, crabgrass and yellow nutsedge with the active ingredient mesotrione. Persistence has systemic activity, but works somewhat slowly. Treatment effects include highly visible white plants, which in some cases may be undesirable. However, Tenacity has the advantage that it is safe on newly sown lawns (with the exception of fine fescue) and can provide some control before and after crab grass emergence. Therefore, this herbicide can be a good choice if young crab grass with walnut is present.

Toughness is marked for use on most cool season grasses. However, since it kills bentgrass, it must be used with care on golf courses. A second application two to three weeks after the first application may be necessary for complete control and optimal control. Apply Tenacity with a non-ionic surfactant. This herbicide not only fights yellow nuts and some grass weeds, but also fights or suppresses many broad-leaf weeds.

A recent trial at Penn State showed excellent control of yellow walnut infesting new Kentucky bluegrass using a single tenacity application at 8.0 fl oz per acre. Although the walnut and crab grass remained white for three to four weeks in the treated area, the weeds were killed and subsequent application was not required. No injury was observed on the Kentucky Bluegrass.

Dimethenamid-P

Tower is a pre-emergence herbicide that is used to control sedge and certain annual weeds of leaves and grass. The active ingredient of Tower is Dimethenamid-P and is only labeled for use on golf courses for grass grasses in the cool season. Applications should be applied to active growing of established lawn in the spring at soil temperatures of 55 ° F or higher.

Dr. Landschoot is a professor of Turfgrass Science at Penn State. Tanner Delvalle and Tim Abbey are extension educators at Penn State. You can find the original article here.

* DR. Landschoot has not worked with Vexis yet and therefore does not include it in this article. More information about Vexis can be found here.