Picture of yellow nutsedge

Family:

Sedge Family (Cyperaceae)

Other Names:

chufa, coco, cocosedge, earth almond, edible galinglae, edible nutgrass, ground almond, northern nutgrass, rush nut, tiger nut, watergrass, yellow nutgrass.

Origin and Distribution:

Yellow nutsedge is native to North America and Eurasia, but is found throughout the world. Although it is of subtropical origin, this species has spread north into temperate regions. Prior to 1950, is was found mostly in native habitats, but today it is considered one of the world’s worst weeds. Yellow nutsedge is especially troublesome in the northcentral and northeastern U.S. It is common throughout Ohio, where it occurs naturally in marshes and along riverbanks and lakeshores, and as a weed in cultivated fields, turf and gardens. It is especially common in poorly drained areas, but can tolerate upland sites as well. This species tolerates a wide range of soil types from sand to clay.

Plant Description:

Yellow nutsedge is an erect, grass-like perennial, characterized by its shiny yellowish-green leaves, triangular stem, golden-brown flower head and shallow rhizomes (horizontal underground stems) that produce many nut-like tubers. Young seedlings are often confused with grasses. This species reproduces primarily by tubers and less often by seeds. Rhizomes help to enlarge patches.

  • Root System:

    Yellow nutsedge forms a complex, shallow underground system composed of fine fibrous roots, thin scaly rhizomes (horizontal underground stems), hard spherical tubers and basal bulbs (swelled rhizome tips which produce stems and leaves). Roots are produced from rhizomes, tubers and basal bulbs. Two types of rhizomes are formed. Short rhizomes are produced from germinating tubers, and end in basal bulbs. Long wiry rhizomes are produced from basal bulbs, and can grow 2 to 8 inches long (sometimes up to 24 inches). Long rhizomes can end in either tubers or basal bulbs. Tubers (1/5 to 4/5 inch long) are white at first, turning brown and eventually black at maturity.

  • Stems:

    Stems (1/3 to 3 feet tall) are erect, hairless, unbranched and triangular in cross-section.

  • Leaves:

    The leaves are light yellowish-green (4 to 12 inches long or longer, 1/8 to 1/2 inch wide) with a prominent mid-vein, a waxy surface and a gradually tapering, pointed tip. Leaves are arranged in 3’s and form a sheath around the stem. Most leaves are produced toward the base of the plant. A set of 3 specialized leaves (bracts) (1 to 8 inches long, 1/8 to 1/2 inch wide) occurs just below the flower head.

  • Flowers:

    Inconspicuous flowers are arranged into numerous, flat, narrow, straw-colored clusters within a branched, umbrella-shaped flower head at the top of the stem

  • Fruits and Seeds:

    Fruits are oval, 3-angled, single-seeded, and yellowish brown.

Similar Species:

Small yellow nutsedge plants or young shoots are often confused with young annual grasses, but can be distinguished by triangular stems that are apparent if you roll the stem between your finger and thumb or look at the stem in cross section near the base of the plant. Grass stems are flat or round. A related species, purple nutsedge (Cyperus rotundus), can be distinguished from yellow nutsedge by its generally darker leaves and red-brown to purple flower clusters. Unlike yellow nutsedge, which produces tubers only at rhizome tips, purple nutsedge produces a chain of tubers along the length of the rhizome.

Biology:

Flowering occurs from July to September. Seed germination begins in May. Tuber germination typically begins as soil temperatures reach about 54 Farenheit degree (12 Celsius) (in May), and shoots continue to emerge through mid-July. Tuber formation begins in late July and continues through the rest of the growing season.

Yellow nutsedge reproduces and spreads primarily by tubers, which are the only structures (besides seeds) that can survive the winter. All foliage, rhizomes, roots and basal bulbs die with the first hard frost. Viable seeds are produced, but tend not to be an important means of reproduction since seedling survival is low. When a tuber germinates in the spring, several short rhizomes are formed, ending in a basal bulb near the soil surface. Basal bulbs generate stems and leaves above the ground and fibrous roots and long rhizomes in the soil. Long rhizomes produce basal bulbs or tubers at their tips (usually basal bulbs are produced early in the season and tubers late in the season as the day length shortens). Basal bulbs sprout immediately to form new shoots, roots and rhizomes, and rhizomes go on to produce more basal bulbs (which germinate immediately) and tubers. This process continues throughout the season. Tubers remain dormant over the winter, and many germinate the following spring. Most tubers remain viable for no more than 3 years (rarely 10 years). Basal bulbs are usually found 3/4 to 2 inches below the surface, and over 75% of tubers are formed within the top 6 inches of the soil. Shaded conditions severely limit tuber production. Tubers are easily spread by farm equipment and on crop transplants. Since rhizomes lack buds, new plants cannot be produced from rhizome fragments.

Yellow nutsedge is especially troublesome in agriculture because it is adapted to many crops and tillage systems. Some herbicides commonly used in corn and soybeans are not very effective on yellow nutsedge and serve only to eliminate other competing weeds, thus allowing yellow nutsedge to survive and spread. This species is also troublesome because it competes with crops for water, nutrients and light, and suppresses crop growth by producing toxic compounds in the soil (allelopathy). With high populations of yellow nutsedge, allelopathy can suppress the growth of young corn, soybean, and other crop plants. A density of about 10 yellow nutsedge plants per square foot reduces corn yields about 8%. Each plant can produce hundreds to thousands of tubers per season, and in densely infested fields, this adds up to 10 to 32 million tubers per acre. Rhizomes can penetrate potato tubers. Control of yellow nutsedge may be aided by improved drainage, crop rotation, several years of fallow, or shallow cultivation throughout the growing season (while tubers are sprouting) to prevent the formation of new tubers.

Toxicity:

None known.

Facts and Folklore:

  • The scientific name of yellow nutsedge means ‘abundant edible sedge’. Tubers have a mild, starchy taste, slightly reminiscent of almonds. Ancient wall paintings from Egypt indicate that this plant was cultivated as early as 400 BC. It is still grown in the Spanish-Mediterranean region, where tubers are used to make a nonalcoholic beverage

  • Pigs are reported to be very fond of the starchy tuber.

  • A Wisconsin field was reported to have up to 35,200,000 yellow nutsedge tubers per acre.

  • Four weedy varieties and one cultivated variety of yellow nutsedge are currently recognized.

  • An African variety called chufa (Cyperus esculentus var. sativas) is grown in the southeastern U.S. for its edible tubers.

  • Papyrus (Cyperus papyrus), a related species, grows 10 feet tall and was used in Ancient Egypt for making paper.

Yellow nutsedge, annual nutsedge, purple nutsedge, green kyllinga – these are just a few of the types of sedges that can be found in the US. Sedges grow across the entire world in the temperate to tropical zones. The scientific name for yellow nutsedge is cyperus esculentus, which loosely translates to edible nut, and refers to the tuber that grows on the roots of the plant. Some other names for yellow nutsedge is nut grass, chufa sedge, tiger nuts or earth almond. It is native to the Mediterranean and was cultivated in ancient Egypt for its tasty oil and rich tubers.

Yellow nutsedge can grow 8–30 inches tall and has an extensive underground network, roots, rhizomes, and tubers. The leaves are bright green with a prominent midrib and arise from the base of the plant. When looking at a cross section, the stem is triangular. The seed head is yellow-brown, golden, or straw colored.

Nutsedge was first introduced into the US as a possible vegetable crop in 1854. The cultivation of the plant dates to the Neolithic Age and it was thought to be the 3rd most ancient domesticated food. The tubers had medicinal qualities as well as a fumigant to sweeten clothes and homes. They can be ground up and mixed with honey as a good source of protein. They often called chufa or tiger nuts and are still available for purchase at many health food stores.

In less than 50 years, yellow nutsedge went from a possible cash crop to one of the worse weeds in the US. It quickly spread across the US from the southeast part of the country. Now, it is considered the 16th worst weed in the world. Its cousin, Purple Nutsedge, is rated as the worst weed in the world.

What Makes Yellow Nutsedge So Problematic?

One reason is the number of tubers and shoots that a single plant can produce. Research has shown that a single nutsedge plant planted in the spring can produce 1,900 shoots and 6,900 tubers in a single year (Tumbleson and Komedahl 1961). It can quickly crowd out other plants growing in the same area.

Most of the tubers are in the top 9 to 10 inches of soil. The tubers can remain viable for up to 10 years. During the housing boom that started after World War II, there was a good deal of top soil moved from one location to another as new housing developments sprouted up across the country. If there were yellow nutsedge tubers in that soil, the new location now had a new weed problem. Besides the tubers, one yellow nutsedge plant can also produce about 1,500 seeds.

The type of rooting that yellow nutsedge produces is called a rhizome. These rhizomes can produce several hundred daughter plants from the original plant within one year. This is in addition to producing hundreds of tubers at the end of each rhizome. These offspring can spread as far as 4 to 6 feet away from the original mother plant.

Yellow nutsedge grows best in moist to wet conditions and is tolerant of flooding. Highly irrigated lawns are more prone to swift expansion of a single yellow nutsedge plant. Allowing a lawn to dry out between watering can slow the pace of it spreading.

Cold weather can also help to keep yellow nutsedge under control. When soil temperatures drop to below 20˚ F, the tubers will die off, but those that are much farther down will remain viable. The plant is also somewhat shade tolerant.

There are several specialty herbicides that are used to control yellow nutsedge. Even with these products, the time it takes to get the plant under control can take 2 or 3 years. Considering how prolific yellow nutsedge can be, it is not surprising that it is an uphill battle to get this weed under control.

If your lawn has a problem with yellow nutsedge, contact your neighborhood lawn care professional at Spring-Green and have your lawn evaluated and put together a plan to help it improve. They will be happy to work with you to get Yellow nutsedge under control.

Yellow and Purple Nutsedge

Yellow and Purple Nutsedge

  • Erect stems that are triangular in shape.
  • Can grow to 30 inches tall with .5 inch wide blades.
  • Leaves are yellow-green in color in groups of three.
  • Reproduces from small pea sized tubers.
  • Prefers damp to wet soils.
  • The yellow variety has yellow seed heads, while the purple variety has purple seed heads.

Yellow and purple nutsedge are the two primary species found in lawns. They are often mistaken for grass, but have very noticeable differences making them easy to identify. Both types are perennials, but in cold winters can behave like annuals.

Weed Identification

The name comes from the tubers (or “nutlets”) it produces underground. The tubers are small organs that are used for energy storage and plant reproduction. The tubers develop along short rhizomes that grow just under the soil surface. These nutlets are the only part of the plant that survives cold winters. In frozen ground, every part of the plant, including the roots and rhizomes die. Only the tuber survives. This is where the plant behaves more like an annual than a perennial. The following year as temperatures warm, the tubers will sprout and begin new growth.

It has a shallow fibrous root system that prefers damp to wet soil. It will often start in poorly drained soils. Years with greater rainfall tend to be more favorable for nutsedge.

Both varieties have triangular shaped stems that grow upright and do not lay prostrate like grass. If left unmowed, they can reach 30 inches in height. If you were to cut the stem in half, you would clearly notice the triangular shape. This is in contrast to most other grasses that have round stems. Additionally, the seed head of yellow nutsedge is yellow, while the seed head of purple nutsedge is purple. However, if you mow regularly, you will probably never see the seed heads.

The leaves are produced in groups of three. The leaves of yellow nutsedge taper to a point gradually over the length of the blade. The blades of the purple variety taper abruptly near the tip. Lower leaves on the stem are the longest and arch outward with the tip touching the ground. The leaves farther up on the stem are shorter, becoming more upright in growth. The leaves have a waxy coating and has a prominent midrib down the center of the blade.

When plants reach maturity they will produce seed heads that have a star shaped pattern. However, the seed is not very viable. Only about 5 percent of the seed germinate, even in the best of conditions.

Reproduction from Tubers

Yellow Nutsedge will produce a small tuber, the size of a baby pea, at the end of a rhizome. Purple nutsedge will produce several tubers in a row along a single rhizome. These tubers grow within a few inches of the mother plant and are the primary method of plant reproduction. Each tuber can produce up to 3 new plants. As a result, you will often see plants growing in patches and will slowly spread outward.

Tubers will sprout as soil temperatures remain above 60 degrees and will continue to sprout throughout the summer. As each tuber sprouts, it develops into an individual plant with its own root and rhizome system. With each new plant, there will be even more tubers. While both are difficult to control, purple nutsedge can be more aggressive and harder to control due to the greater tuber production.

Studies have shown that these tubers will produce new plants even when buried 8 or more inches into the soil. This means that roto-tilling them into the soil will not kill the tubers, but could actually make things worse.

Cultural Practices

Like many other weeds, these plants are opportunistic, taking advantage of weaknesses in the lawn. The good things is that nutsedge does not compete well with a thick lawn. Therefore, producing a thick turf is the best defense against these and other weeds.

If you do find this weed growing in your lawn, it is best controlled when it is young. If you pull it up before tuber development occurs, you can probably control it. However, larger plants will usually break off at ground surface leaving the roots and tubers in place. Even if you were able to pull up larger plants, roots and all, the tubers are most likely to remain in the soil. Digging becomes an option, but only if you have gotten the entire root and all tubers.

Since nutsedge prefers damp or wet soils, it is frequently seen growing in poor drainage areas. If this is occurring in your lawn, it is important to correct the drainage problems. You may need to add soil to raise a low area, redirect runoff, etc. The key is to correct whatever is allowing the soil to remain excessively damp.

Chemical Control

Nutsedge cannot be controlled by traditional broadleaf weed herbicides. Since it is not a grass, but a member of the sedge family, it requires a different approach. Make sure the herbicide lists nutsedge on the label as one of the weeds it will control.

Look for a herbicide containing one of the following:

  • Ammonium Methanearsonate (AMA)
  • Disodium Methanearsonate (DSMA)
  • Monoammonium Methanearsonate (MAMA)
  • Monosodium Methanearsonate (MSMA)
  • Calcium Acid Methanearsonate (CAMA)

Use these products when plants are still young for the best results. You will probably have unsatisfactory results if you spray late in the season. Once the plants have hardened, they are less susceptible to herbicides and more difficult to control. Due to its waxy surface it is best to mix a “sticker/spreader” into the solution. You will find more information on Sticker/Spreaders below.

You can also use a non-selective herbicide such as glyphosate. Glyphosate is the active chemical in Round-Up, Rodeo, and similar grass and weed killers. Keep in mind that non-selective herbicides will kill all the grass it touches and not just weeds.

If you are unsure about what to use in your area, call your local county extension office. They should be familiar with the laws and products that work best where you live.

Since nutsedge has a waxy surface, the herbicide will roll off. The addition of a sticker/spreader will keep the herbicide on the plant and help with absorption. Some manufacturers will add a sticker/spreader to the formula and will be listed on the ingredients. If it is not already added, you can buy it in a small bottle and simply add the correct amount stated on the label. It can be poured directly into the sprayer along with the solution. Be sure to mix thoroughly.

Always read the labels and follow the directions carefully. Be sure to look at the Using Herbicides Safely Page for detailed information on how to safely handle, use and store herbicides and other chemicals. There is information on everything from protective clothing to how to read a label.

Crabgrass and Foxtails- Annual Grassy Weeds
Crabgrass and Foxtails are two major annual weeds that can cover your lawn. You will find detailed information on their growth habits and how to stop them before they even start.
Winter Annual Broadleaf Weeds
With each spring comes a surge of winter annual weeds. Here you will find valuable information about these difficult weeds including growth habits, photos, and measures that can be taken to control them.
Summer Annual Broadleaf Weeds
Many of the most problematic lawn weeds are annuals. Here you will find specific summer annual weed information, with weed names, photos and control methods.
Perennial Broadleaf Weed Identification Page 1
Click here for weed identification and control of common perennial lawn weeds. This page has detailed information on Canada Thistle, Mouseear Chickweed, White clover, Dandelion, Field Bindweed, Ground Ivy, and Common Mallow.
Perennial Broadleaf Weed Identification Page 2
Click here for perennial weed identification and control. You can find detailed information on Buckhorn Plantain, Broadleaf Plantain, Red Sorrel, Wild Violets, and Common Yarrow.
Wild Onions and Wild Garlic
Wild onions and wild garlic are common perennial lawn weeds. They are early season weeds that grow faster than the surrounding grass and can be a persistent problem. Find out how to get rid of them for good.
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Identify and Kill Nutsedge or Nutgrass in Lawns

Effective treatment and control of yellow and purple nutsedges calls for products designed to overcome the unique challenges of these difficult weeds. IMAGE Herbicide Consumer Concentrate Kills Nutsedge kills yellow and purple nutsedge in established lawns through a special ingredient that starves these weeds to death.

Available in a convenient ready-to-spray formula and an economical concentrate, IMAGE Herbicide Consumer Concentrate Kills Nutsedge delivers visible results in one to two weeks and kills weeds completely in three to five weeks. Used as directed, this product will not harm established warm-season lawn grasses, including Bermudagrass, Centipedegrass, St. Augustinegrass, Zoysiagrass and Buffalograss.*

For established cool-season lawn grasses, such as Kentucky bluegrass, tall and fine fescues, perennial ryegrass and rough bluegrass, IMAGE All-In-One Lawn Weed Killer begins working on contact to kill and control existing nutsedge. This convenient, ready-to-spray product provides visible results in three to seven days and kills yellow nutsedge within two to three weeks. Purple nutsedge may need repeat treatment every three to four weeks for effective control.

Treat nutsedge in summer lawns after turf greens up in spring and before winter dormancy sets in. Only treat while nutsedge and lawn grasses are both actively growing. Maximize your results by treating during late spring and early summer, when nutlets and seeds sprout and still have less than five to six leaves. This timing hits these young weeds at their most vulnerable and kills them before new nutlets start forming in mid to late summer.1,2

Purple Nutsedge Is An Invasive That Squeezes Out Native Grasses

Rhizomes and bulb-like nutlets branch out in all directions from this sedge. They easily detach if the plant is pulled from the ground.

By Les Harrison
Wakulla County Extension Director

The return of consistent warm weather to Wakulla County has many residents thinking about the state of their lawns. Mowing, fertilizing, weeding and patching bald spots are now the focus of homeowners and landscape maintenance professionals.

The choice of turf depends on the preferences and needs of the landscape’s owner. Bahiagrass, Bermudagrass, Centipede, Zoysia, and others selected for their particular traits and appearance.

However, there is one exotic “grass” not on any list of popular spring turf or ground covers. So of course this grass-like weed appears voluntarily and aggressively pushes the desired species to the brink of extinction if left unchecked.

Purple nutsedge, Cyperus rotundus, grows from every possible sunny location with soil. This non-native plant is a rapidly spreading perennial which will take every opportunity to colonize new locations.

The identifier purple is in its name because there is a purple-tinged section of this sedge where it emerges from the ground. The plant is sometimes referred to as purple nut grass because of its long narrow leaves and its erect growth pattern originating from a nutlike basal bulb.

There are other sedges in Wakulla County, but only yellow nutsedge is identified by a specific color. It is sometimes called chufa and is a popular feed for wild turkeys, and turkey hunters.

The dark green, smooth leaves blend in easily with many turf grasses during the spring and summer. Beneath the soil’s surface and out of sight, the root system grows in every direction.

Purple nutsedge’s roots are a series of spreading rhizomes and tubers or bulbs identified as nutlets. Each nutlet sprouts a new bunch of grass-like leaves and continues growing the rhizomes.

The dense population of this sedge quickly crowds out most other plants, but especially turf and forage grasses. It can reach a height of 18 inches on its triangle shaped stem.

The root system’s design assures this plants continued success. If pulled, the rhizomes break off leaving a large number of nutlets to develop and emerge at a later date.

If plowed or tilled, the nutlets are detached and spread to new and inviting locations. Many times nutlets lodge in tillage equipment only to shake loose and deposited in un-colonized locations.

Most herbicides have little effect on this sedge’s hardy root system. Selected pre-emergent herbicides will prevent many of the nutlets from germinating in spring if properly applies.

Wakulla County’s sandy soils provide an ideal growing environment for purple nutsedge. The occasional periods of saturation from storms do not deter this plant’s rapid growth and expansion to new areas.

Purple nutsedge’s extreme competitive nature is a heavy consumer of plant nutrients. It robs rivals of important compounds necessary for their survival, and produces an allelopathic substance which is toxic to some plants.

Purple nutsedge is found in many locales in North America where the environment is hospitable to its growth. The autumn cool and shorter days send this exotic pest into dormancy, but the seeds of next year’s crop, and landscape problems, are just under the surface.

Just like desirable turf in north Florida, purple nutsedge will not grow in heavy shade. Typical of most weeds, it only grows where it is not wanted.

To learn more about purple nut sedge in Wakulla County contact the UF/IFAS Wakulla County Extension Office at 850-926-3931 or http://blogs.ifas.ufl.edu/wakullaco/.

by Les Harrison

Posted: April 6, 2017

Category: Invasive Species, Natural Resources

Tags: agriculture, Community, Environment, Extension, Farming, Florida, Garden, General Information, grow, growing, Horticulture, Landscape, Lawn & Garden, Les Harrison, Master Gardener, Natural Resources, Natural Wakulla, plants, vegetables, wakulla, Wakulla agriculture, Wakulla CED, Wakulla County, Wakulla County Extension, Wakulla Extension

Weed Profile: Yellow Nutsedge (Cyperus esculentus) and Purple Nutsedge (C. rotundus)

eOrganic author:

Dr. Mark Schonbeck, Virginia Association for Biological Farming

Abstract

Yellow nutsedge and purple nutsedge are grass-like perennial weeds that can cause severe losses in vegetable and row crops. Nutsedges grow during the frost-free season, spreading and propagating through an extensive underground network of rhizomes, bulbs, and small, starchy tubers or “nutlets.” Within a single growing season, one tuber can give rise to hundreds of shoots in a dense patch 3–6 feet across, and form over 1,000 new tubers.

Yellow nutsedge has bright green to yellow-green foliage, straw-colored or golden-yellow flower heads, and tubers borne singly at the tips of short rhizomes. It occurs throughout the United States and into southern Canada, and is most troublesome in moist or irrigated soils.

Purple nutsedge has dark green foliage, purple to red-brown flower heads, and tubers borne in chains along rhizomes. It is most troublesome in tropical and warm–temperate climates, including the southern United States and California.

Nutsedges are difficult to manage because of their large underground reserves, tolerance to cultivation and environmental stresses, and ability to penetrate mulches. To reduce heavy infestations, till when shoots first emerge in late spring, and repeat tillage to sever re-emerging shoots before they have 6 leaves. Soil solarization during summer can complement tillage in reducing the nutsedge population. Follow tillage or solarization with an aggressive summer cover crop to suppress nutsedge regrowth and replenish soil organic matter consumed by tillage.

To prevent light nutsedge infestations from worsening:

  • Time tillage and cultivation to disrupt nutsedge growth (late spring–early summer) and tuber formation (late summer).
  • Use tillage implements that bring rhizomes and tubers to the surface to dry out or freeze.
  • Design crop rotation to disrupt the nutsedge life cycle and facilitate timely tillage.
  • Grow competitive, shading crops during the frost-free season, such as bush bean, sweet potato, and summer cover crops.
  • Manage nutrients and moisture to favor the crop over nutsedge.
  • Run swine, poultry, or weeder geese in the field after crop harvest to consume nutsedge.

Introduction

The nutsedges are grass-like, colony-forming, perennial weeds that grow actively during the frost-free season, spread by rhizomes, and propagate from year to year by small, starchy tubers (sometimes called “nutlets,” which give the weeds their common name). Nutsedges, also called nutgrasses, are difficult to manage because of their tolerance to heat, drought, and flooding; their prolific underground vegetative reproduction; and their ability to regrow after cultivation and to penetrate most mulches.

Purple nutsedge causes serious losses to a wide range of crops in tropical, subtropical and warm–temperate regions—including the southern United States and California—and has been cited as the world’s most costly agricultural weed (Holm et al., 1991). Yellow nutsedge occurs throughout the United States and into Canada, and is a major weed in the Northeast (Else, 1996) and in irrigated crops in the Northwest (Ransom et al., 2009). The two species often occur together and are considered major weeds of vegetable production in the South (Webster, 2006).

Description and Identification

Nutsedges are grass-like plants in the sedge family (Cyperaceae) with narrow, linear, folded leaves 4–12 inches long by 0.1–0.4 inch wide. Nutsedges can be distinguished from true grasses by the 3-ranked arrangement of leaves (Fig. 1a), a simple leaf blade with no sheath or collar, and solid stems triangular in cross section. Grasses have round stems that are hollow in the internodes, and leaves in a 2-ranked arrangement showing distinct sheath, collar, and blade regions (Fig. 1b).



Figure 1. (a) Yellow nutsedge, showing the characteristic 3-ranked leaf arrangement of the sedge family (Cyperaceae). (b) Weedy grasses with the 2-ranked leaf arrangement of true grasses (Poaceae). Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Individual flowers are small, inconspicuous, and borne in a cluster of spikes radiating 0.5–2 inches out from the top of the flower stalk, and subtended by a whorl of narrow, leaflike bracts (Fig. 2). Each flower forms a single-seeded dry fruit (achene) similar to grasses.

Nutsedges form complex underground networks of vegetative structures (Fig. 3), including basal bulbs from which the shoots arise; thin, wiry rhizomes; tubers; and a fibrous root system extending up to 4 feet deep. Tubers (nutlets) are about 0.4–0.8 inch long, scaly, whitish and succulent at first, turning firm and brown–black as they mature. The mature tuber is packed with starch and has 40–50% dry matter content (Holm et al., 1991).



Figure 3. (a) Yellow nutsedge tubers. (b) A chain of 4 purple nutsedge plants, consisting of a mother plant and two generations of daughter plants connected by rhizomes. Each plant arises from a small basal bulb. Photo credits: (a) Joseph M. DiTommaso, University of California-Davis, Bugwood.org. (b) Mark Schonbeck, Virginia Association for Biological Farming.

Yellow nutsedge is distinguished by its bright “spring-green” foliage (Fig. 4a); yellow, straw-colored, or golden inflorescence (Fig. 2a); and tubers borne singly at the ends of rhizomes. Purple nutsedge foliage is a darker green (Fig. 4b), the inflorescence is purplish to reddish-brown (Fig. 2b), and tubers are borne in chains, with individual tubers set 2–10 inches apart along the rhizome.



Figure 4. (a) Bright green foliage of yellow nutsedge. (b) Darker green foliage of purple nutsedge. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Life Cycle and Reproduction

Nutsedges reproduce primarily by tubers. In temperate regions, new growth begins after the spring frost date. A rhizome emerges from the tuber, grows toward the soil surface, and forms a basal bulb from which the shoot and fibrous roots emerge. Basal bulbs usually form within 3 inches of the soil surface, although purple nutsedge bulbs have been found at 4–8 inches (Hauser, 1962; Fig. 5). After several weeks’ shoot growth, new rhizomes grow laterally from basal bulbs, giving rise to new basal bulbs and shoots (daughter plants). The process continues for 2–4 months, during which a single overwintered tuber can give rise to a patch several feet across.

Figure 5. In this purple nutsedge infestation, most of the basal bulbs were found within 2 inches of the soil surface, with a few as deep as 4 inches. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Nutsedges generally bloom and begin to form new tubers about 7–8 weeks after initial shoot emergence. In temperate latitudes, tuber formation is triggered by shortening daylength in late summer and accelerates while aboveground growth rates decline (Hauser, 1962; Jordan-Molero and Stoller, 1978). Tubers develop throughout the top 6–10 inches of soil, and a few may occur at 12–18 inches (Tumbleson and Kommedahl, 1961; Holm et al., 1991). Foliage dies back with the first fall frost, and the weed overwinters as dormant tubers.

Yellow nutsedge reproduces most prolifically in cool–temperate climates. One yellow nutsedge tuber has given rise to 1,900 shoots and 6,900 new tubers within 1 year in Minnesota (Tumbleson and Kommedahl, 1961), and to 1,700–3,000 shoots and 19,000–20,000 tubers within 4 months in irrigated fields in Oregon (Ransom et al., 2009). Purple nutsedge multiplied several times faster than yellow nutsedge in a field trial in Georgia (Webster, 2005b), but the reverse was true in an outdoor container trial in Illinois (Jordan-Molero and Stoller, 1978).

Viable seeds are occasionally formed through cross pollination, especially in yellow nutsedge; however, seeds are not considered important in propagation of either weed (Holm et al., 1991).

Tuber Dormancy, Germination, and Dispersal

Newly mature nutsedge tubers are dormant. In yellow nutsedge, dormancy is broken over winter by chilling temperatures of 35–50°F (Holm et al., 1991; Stoller and Wax, 1973). Diurnally fluctuating temperatures with maxima near 85–95°F break tuber dormancy in purple nutsedge (Miles et al., 1996). Apical dominance regulates tuber sprouting in purple nutsedge tuber chains, so that the terminal tuber sprouts while the others remain dormant (Kawabata and Nishimoto, 2003). Individual tubers of either species can remain viable in the soil for several years.

Nutsedge tubers are spread to new locations in soil clinging to farm equipment and tires, and sometimes by animals or flood waters. In addition, tubers can occur in the soil or growing medium of potted plants, in compost and mulch, or as a contaminant in crop harvests.

Growth Habit, Environmental Tolerances, and Impact on Crops

Nutsedges have the C4 photosynthetic pathway, and thus grow rapidly in high temperature and high light conditions. Although the plants are low-growing (4–30 inches), they form dense stands that carpet the ground (Fig. 6), and can develop tremendous underground biomass. Heavy infestations can attain 4–9 tons dry weight per acre in the tubers alone (Tumbleson and Kommedahl, 1961; Holm et al., 1991). Large energy reserves in the tubers allow nutsedge to survive long periods of shade, drought, and flooding, and to tolerate repeated shoot removal by mowing or cultivation (Santos et al., 1997; Stoller and Wax, 1973).

Figure 6. A carpet of yellow nutsedge covers the ground in a home garden in Virginia. Photo Credit: Mark Schonbeck, Virginia Association for Biological Farming.

Nutsedge thrives under a wide range of conditions, although some species differences exist (Table 1). Yellow nutsedge is slightly less heat tolerant than purple nutsedge (Webster, 2003), but more tolerant to flooding, cold, and light shade. A heavy crop canopy suppresses nutsedge growth and tuber set (Santos et al., 1997; Jordan-Molero and Stoller, 1978), but existing tubers remain viable and sprout when the shade is removed (Holm et al., 1991). Tubers can be killed by heating to 122°F for 10–24 hours (Webster 2003), or desiccation to 15–24% moisture content (Holm et al., 1991). However, tubers located deeper than 2 inches in the soil are generally protected from lethal temperatures and dehydration.

Nutsedges often first appear in wet areas and may indicate poor drainage or overirrigation (Fig. 7); however, once established, the weed can persist in normal to dry conditions (Russ and Burgess, 2009). Yet, some farmers who use organic inputs and judicious tillage to improve soil tilth and drainage have observed a decrease in yellow nutsedge populations as soil quality improves (Josh Hardin, farmer in Arkansas, pers. commun.; Charles Maloney, farmer in Virginia, pers. commun.).

Figure 7. Yellow nutsedge growing vigorously in wet, poorly drained soil with low organic matter. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Nutsedges compete aggressively against warm-weather crops for moisture and nutrients (Fig. 8). Cool-season crops planted in fall escape nutsedge competition, as the weed enters dormancy at this time of year (McGiffen et al., 1997). In tropical regions, purple nutsedge can inflict severe losses on crops many times its height, including sugarcane and coffee (Holm et al., 1991). In field trials in the low desert of California, purple nutsedge was very hard to control with cultivation and crop rotation—causing 80-95% crop losses in winter broccoli—while yellow nutsedge had little effect on broccoli yield (Wang et al., 2008). Purple nutsedge is less aggressive near the northern edge of its range (e.g., North Carolina), where seasonal cold limits its growth. Yellow nutsedge is most troublesome in temperate, high-moisture soils, and in irrigated crops maintained at a high water potential, such as onion or rice (Ransom et al., 2009).

Figure 8. Severe infestation of purple nutsedge in cotton. Photo credit: Charles T. Bryson, USDA Agricultural Research Service, Bugwood.org.

Nutsedges also affect crops by releasing allelopathic (growth-inhibiting) substances (Drost and Droll, 1980; Friedman and Horowitz, 1971); by hosting root-knot nematodes (Schroeder et al., 1997); and by damaging root crops as rhizomes pierce the edible portion. A heavy infestation of yellow nutsedge in potato can render every potato in the field unmarketable (Holm et al., 1991).

In Oregon field trials, yellow nutsedge responded only slightly to nitrogen (Ransom et al., 2009), and good soil fertility apparently increased crop vigor relative to this weed in the northeastern United States (Mohler and DiTommaso, unpublished). In the southern United States, purple and yellow nutsedge compete more aggressively against vegetable crops at higher fertilizer N rates (Morales-Payan et al., 1997; Santos et al., 1998). High soil moisture levels have been reported to intensify purple nutsedge competition against cotton (Cinco-Castro and McCloskey, 1997) and to stimulate yellow nutsedge growth and propagation (Ransom et al., 2009).

Shading by crops such as bush snap bean, potato, sweet potato, and sweet corn can curb nutsedge growth and tuber set, and crop competition has been cited as a nutsedge management tactic (Keeley and Thullen, 1978; McGiffen et al., 1997; Neeser et al., 1997; William, 1976; William and Warren, 1975). A few crops may retard nutsedge growth by allelopathy, including sorghum (Cheema et al., 2004), rye (Mohler and DiTommaso, unpublished), and sweet potato (Neeser et al., 1997).

The sharp, pointed shoots of nutsedge readily emerge through organic mulches, and can puncture opaque plastic mulches (Webster, 2005a) (Fig. 9). Black plastic slowed the spread of yellow nutsedge by about 50% in field trials in Georgia, but doubled the spread of purple nutsedge, which responded to soil warming under the film (Webster, 2005b). However, in the low desert of southeastern California, a black plastic film sufficiently raised temperatures throughout the top 6 inches of the soil profile to kill nutsedge tubers and rhizomes, thus providing a substantial measure of control (Wang et al., 2008). Nutsedge shoots emerging under clear or translucent films become trapped because their leaves open in response to light before the growing point can puncture the film (Patterson, 1998). The trapped foliage is often heat-killed, whereas tubers are weakened but rarely killed.

Figure 9. Nutsedge has penetrated the plastic film mulch and is interfering with the pepper crop. Photo credit: Theodore Webster, Agricultural Research Service, Bugwood.org.

Table 1. A Comparison of Yellow Nutsedge and Purple Nutsedge

Yellow Nutsedge Purple Nutsedge
TOP GROWTH Yellow-green to bright green; 8–24 inches (36 maximum) Dark green; 4–18 inches (30 maximum)
FLOWER HEAD Yellow, gold, or straw-colored Purplish to reddish-brown
SEEDS Viable if outcrossed Mostly non-viable
TUBERS Borne singly at ends of rhizomes; edible, pleasant flavor (chuffa) Borne in chains on rhizomes; bitter and hard
TUBER DORMANCY Broken by chilling (35-50°F) over winter Broken by heat (95°F), fluctuating temperatures, or release of apical dominance when tuber chains break
RANGE IN NORTH AMERICA Throughout United States into Canada Mostly southern half of United States
MOST AGGRESSIVE REGIONS Temperate region, irrigated fields Tropical or subtropical regions
ABILITY TO PENETRATE ORGANIC MULCH Very high Very high
ABILITY TO PENETRATE BLACK PLASTIC Moderate (mulch slows spread) Very high (mulch stimulates spread)
ABILITY TO PENETRATE CLEAR PLASTIC Low (leaves open and are trapped) Low (leaves open and are trapped)
DROUGHT TOLERANCE Moderate to high Very high
HEAT TOLERANCE High Very high
FLOODING TOLERANCE Very high (thrives in wet soil) High (goes dormant)
COLD TOLERANCE Moderate (tubers ~20°F) Low (all parts frost tender)
SHADE TOLERANCE Low–moderate Low (shoots die back, tubers persist)
NUTRIENT RESPONSE Variable (low in cool climates) High (more aggressive at high N)

Nutsedge populations show significant variation across their geographic range (Holm et al., 1991), and unusually robust strains of both species have been reported in California (Tayyar et al., 2003) and Brazil (William, 1976). This suggests that nutsedges can undergo genetic adaptation to climate, soil, or production practices—possibly through occasional sexual reproduction, genetic recombination, and selection.

Management

Organic growers have been advised to avoid fields infested with nutsedge (Bangarwa et al., 2008). However, in the real world, organic vegetable growers must often cope with these weeds. To maximize chances of doing so successfully, growers should:

  • Identify the nutsedge species, learn its strengths and vulnerabilities (Table 1), and plan accordingly.
  • Use an integrated strategy that combines multiple preventive and control measures.
  • Bring heavy infestations under control before attempting organic production, especially summer vegetables and perennial crops.
  • Be vigilant and proactive to keep small populations from exploding.

Prevention and Early Detection

If nutsedge is present in your region but not yet on your farm, avoid importing it! Ensure that nursery stock, topsoil, compost, manure, and mulch materials are free from nutsedge plants or tubers before buying them. Thoroughly clean borrowed or rented field equipment before bringing it onto the farm. If just one or two fields on the farm have nutsedge, avoid spreading it to other fields by carefully cleaning tools, equipment, vehicle tires, and footwear immediately after working infested fields.

Nutsedge outbreaks often begin in poorly drained, compacted areas within crop fields. Improve drainage and soil quality in such areas by subsoiling, cover cropping (include “biodrilling” cover crops like tillage radish, sorghum-sudangrass, and sweetclover), adding organic matter, and adopting conservation tillage and controlled traffic practices to minimize compaction.

Monitor fields regularly and act promptly at first sighting of nutsedge. Small, local infestations can be eradicated by digging out all plants, rhizomes, and tubers. Dig at least 10 inches deep and 10 inches beyond the perimeter of the patch (Russ and Burgess, 2009).

Tillage and Cultivation

Timely repeated tillage is the main organic strategy for reducing a heavy nutsedge infestation. Begin tilling in late spring after shoots have emerged but before they can form new rhizomes or daughter plants. Till 6–8 inches deep to break tuber dormancy. Deplete rhizomes and tubers by tilling or cultivating again whenever emerging shoots have at least 3 but not more than 6 leaves (Mohler and DiTommaso, unpublished; Russ and Burgess, 2009); this may require cultivating every 2–3 weeks (Fig. 10). If practical, work deep enough to sever basal bulbs from their root systems (William, 1976).

Figure 10. Purple nutsedge regrowth photographed 13 days after initial tillage. Cultivate now. The small shoots on the right have drawn down underground reserves to their low point, whereas the larger plant to the left has already begun to rebuild below-ground biomass. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Be aware that tillage, especially rotary tillage, can spread a localized infestation by moving tubers around in the soil. This is particularly true when the soil is wet and liable to cling to tines or plowshares, thereby facilitating long-distance transport of tubers. Whenever practical, till or cultivate for nutsedge control when the soil is dry enough to leave implement tines clean (Russ and Burgess, 2009). To be safe, powerwash or otherwise clean the implement before leaving an infested field.

Use a field cultivator or similar implement to bring rhizomes and tubers to the surface, thereby exposing them to desiccation or freezing. Several passes during dry weather can significantly reduce the population (Tumbleson and Kommedahl, 1961; Mohler and DiTommaso, unpublished).

Control nutsedge that emerges in crops by cultivating whenever emerging weeds have 3–6 leaves. An economic analysis of nutsedge control strategies for vegetable production in southern California showed net returns for multiple cultivations > summer solarization > spring and summer smother crops (Wang et al., 2009). Till promptly after a spring vegetable harvest or immediately prior to a midsummer vegetable planting to knock the weed back before it can propagate.

Soil solarization

In very hot and sunny climates such as the desert southwest region of the United States, soil solarization during late June to early August (when solar radiation and temperatures are near maximum) can significantly reduce a nutsedge infestation. In Florida, solarization with clear plastic does not kill most purple nutsedge tubers; however, it causes daily pulses of high temperature that break tuber dormancy. Tubers are gradually weakened when emerging shoots open under the clear film, become trapped, and are heat-killed (Chase et al., 1999). Because tuber dormancy is a major factor in nutsedge persistence, solarization can be an important component of the control strategy.

Till or cultivate to remove existing nutsedge top growth, stimulate additional tuber sprouting, and prepare a smooth surface. Lay clear or translucent plastic film, and leave in place for 3–6 weeks during late June through early August when solar radiation and air temperatures are near their maximum. To ensure effective heating of the soil profile, be sure the soil is moist—irrigate before laying plastic if necessary—and the film fits tightly and evenly over the soil surface. After solarization, cultivate to remove emerging nutsedge regrowth when it reaches the 3–6 leaf stage.

Crop Competition, Crop Rotation, and Cover Crops

Exploit the two weaknesses of nutsedges: their short stature and shade intolerance. Design crop rotations and production systems to maximize crop competition against weeds during the frost-free growing season. Choose vigorous, adapted varieties of heavy-canopy crops like potato, bush bean, and sweet potato; and tall crops like sweet corn or trellised tomato. Canadian potato growers have found that growing a potato variety with particularly heavy foliage (‘Kennebec’) can substantially reduce yellow nutsedge populations in the following season, compared to fields with less-competitive varieties (‘Katahdan’ or ‘Irish Cobbler’) (Mulligan and Junkins, 1976).

Choose optimum planting dates so that crops are not subjected to growth-retarding cold or other stresses. Use crop row spacing and orientation that promotes canopy closure (except for crops in which this would increase the risk of fungal diseases), or effective shading of alleys.

Design crop rotation and select planting dates so that the late spring flush of nutsedge either emerges beneath a dense crop canopy (such as a winter or spring cover crop like rye/vetch, or oats /field peas), or can be knocked out by tillage after harvest of an early spring vegetable like spinach or salad greens. Similarly, disrupt the onset of tuber production in late summer, either by providing heavy shade (such as snap bean or sweet potato at full vegetative growth), or through tillage after a midsummer vegetable harvest.

Follow spring vegetables with an aggressive, fast-growing, summer cover crop that will shade out emerging nutsedge. Use optimal seeding rates and methods to maximize cover crop weed suppression. Buckwheat closes canopy rapidly and can provide excellent weed suppression during brief (30–50 day) fallow periods in frost-free, moderately warm weather. For longer fallow or hotter conditions, combine a tall grass (sudangrass, sorghum-sudangrass hybrid, or pearl millet) with a heavy-canopy summer legume (cowpea, forage soybean, velvetbean, or lablab bean) for maximum competition. In fields with nutsedge populations too heavy to allow successful production of summer vegetables, grow high biomass summer cover crops and follow with cool-season vegetables in fall, winter, or early spring, when nutsedge is dormant.

No-till methods of terminating cover crops can enhance soil quality and suppress annual weeds; however, this technique should not be attempted until nutsedge has been eliminated from the field.

The allelopathic potential of rye, sorghum-sudangrass, and sweet potato may contribute to nutsedge suppression and should be considered in designing the rotation. However, do not rely on allelopathy alone to control these weeds.

Soil, Nutrient, and Moisture Management

Use slow-release organic fertilizers and in-row drip irrigation to deliver moisture and nutrients preferentially to the crop. Sidedress faster-release N materials to heavy feeders when the crops are established and entering their rapid growth phase. Avoid overapplying N and overwatering. Rotate crops that require frequent irrigation to maintain high soil water potential with crops that thrive in drier conditions.

Pest Management – Nematodes

If root-knot nematodes or other pest nematodes for which nutsedge can be a host are present, it is especially important to reduce nutsedge populations to low levels before attempting production of susceptible crops. Nutsedges do not suffer ill effects from the nematode (Schroeder et al., 1997), and the two together put crops in double jeopardy. Building soil organic matter and soil life diversity can help combat pest nematodes.

Nutsedge Removal by Livestock and Poultry

Consider using swine, hens, or weeder geese to consume nutsedge. Laying hens confined in small fenced areas (up to 50 ft by 50 ft for one chicken coop or chicken tractor) at densities equivalent to 480 birds per acre have been reported to clean up a heavy nutsedge infestation in one season. Weeder geese at 8 to 16 birds per acre have significantly reduced nutsedge competition in cotton (Mayton et al., 1945). Swine will root out and consume nutsedge tubers (Ohio State University), and 60-75 hogs have been reported to remove purple nutsedge tubers from a 2.5 acre field in one day in India (Open Source for Weed Assessment in Lowland Paddy Fields).

Remember that USDA certified organic production requires at least a 120-day interval between incorporation of livestock or poultry manure and harvest of any food crops that might have exposure to soil or soil splash; and a 90-day interval for food crops not exposed to soil, such as tree fruit and sweet corn. Remove livestock, poultry, or geese from the field and incorporate droppings at the suitable time prior to organic food crop production to protect food safety and meet USDA Organic requirements. A good time to use livestock or poultry for nutsedge control is immediately after cash crop harvest and before planting a cover crop.

Mowing

Mowing is less effective against nutsedge than tillage and cultivation, yet it may be warranted where tillage is not practical, such as in alleys between trellised tomato rows. Cut top growth as close to the ground as possible with a push mower or weed whacker. Mow before tuber set (mid-late summer), and repeat as needed to keep the weed from propagating.

Mulching

Mulching is generally ineffective against nutsedge. Do not use opaque synthetic mulch in fields with moderate to high nutsedge populations. In addition to causing yield losses, nutsedge growing through plastic film or landscape fabrics can complicate end-of-season plastic removal.

Multiple, Integrated Tactics

None of the above measures alone will bring a significant nutsedge problem under control. Use a multi-component, integrated strategy. For example, follow an early vegetable harvest with one or more tillage passes to disrupt emerging nutsedge, solarize in June or July, then follow with an aggressive summer cover crop. When nutsedge populations decline sufficiently to allow summer vegetable production, combine vigorous, locally-adapted varieties with best management of water, nutrients, and pest nematodes, as well as timely cultivation to maximize the crop’s advantage over nutsedge.

References and Citations

Biology: Yellow nutsedge (Cyperus esculentus), also known as chufa (chufa is a non-weedy variety that is used for wildlife food plots and is not a cold hardy weed like yellow nutsedge), nutgrass, or watergrass, is a troublesome, difficult-to-control perennial weed found throughout the United States. It is important to understand that yellow nutsedge is not a grass or a broadleaf weed, but a sedge; which is crucial when determining effective control strategies. It establishes by rhizomes, which form tubers (called nutlets) that are capable of surviving in the soil for periods of up to ten years. These nutlets, as well as viable seed, sprout and establish from May until the end of July. Reproduction by tubers can be very prolific. A trial in Minnesota found that one nutsedge tuber produced 1,900 shoots and 6,900 tubers within one year (Tumbelson and Kommedahl, 1961)!

Figure 1. Yellow nutsedge has a brown seed head. Photo by Aaron Patton.Figure 2. Yellow nutsedge has triangular stems. Photo by Kyle DanielFigure 3. Infestation of yellow nutsedge. Photo by Aaron Patton.

Identification: Yellow nutsedge can be identified by solid, triangular-shaped stems which are be easily determined by rolling the stem back and forth between fingertips. Yellow nutsedge leaves have a prominent mid-rib and are arranged in threes which also help to distinguish it from grasses. Leaves are a light green to yellowish in color, have a shiny/waxy appearance, and have a long leaf-tip tapered to a sharp point. While many grasses have hairs on the leaf blades, such as crabgrass or bermudagrass, yellow nutsedge leaves and stems are completely smooth, which accentuates the shininess of the leaves. Though it seldom forms in areas of mowed turf, yellow nutsedge produces golden to brown colored seedheads (short spikelets) from July to September. It is often mistaken for purple nutsedge; however, purple nutsedge has dark green leaves that quickly taper to a blunter tip, and produces reddish brown to purple seedheads (spikelets). Additionally, purple nutsedge develops tubers along the entire length of rhizomes where yellow nutsedge only produces tubers at rhizome tips.

Cultural control: The best method of cultural control is prevention by inspecting new soil prior to bringing into the landscape. For sites that have existing nutsedge, improving drainage and reducing compaction can aide in reducing populations.

Figure 4. Triangular stems of yellow nutsedge. Photo by Aaron Patton.Figure 5. Rhizomes beneath the soil surface of yellow nutsedge. Photo by Aaron Patton.Figure 6. Purple nutsedge has a more rounded tip (left) than yellow nutsedge (right). Photo by Aaron Patton.

Biological control: None known for specific use in yellow nutsedge.

Chemical control: Yellow nutsedge is a difficult-to-control weed that may require multiple herbicide applications. The most effective time to kill and prevent tuber production is while plants are small in the late spring and early summer. The most effective postemergence herbicides on yellow nutsedge include halosulfuron-methyl (Sedgehammer), clopyralid (Lontrel), metsulfuron (Manor, Ally, others), bentazon (Basagran T/O), and sulfentrazone (Dismiss).

Figure 7. The growth habit of yellow nutsedge is a three leaf arrangement. Photo by Aaron Patton.

Purdue Bulletin on yellow Nutsedge:

Reference in this publication to any specific commercial product, process, or service, or the use of any trade, firm, or corporation name is for general informational purposes only and does not constitute an endorsement, recommendation, or certification of any kind by Purdue University. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer

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