WEEDSWhat are they?

Why are they in my yard and/or garden beds?What can I do about them?

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The University of Maryland Extension (UME) conducts the Maryland Master Gardener Program. The Master Gardener Program’s mission is to educate Maryland residents about safe, effective, and sustainable horticultural practices that build healthy gardens, landscapes, and communities.

It is the policy of the University of Maryland, College of Agriculture and Natural Resources, Maryland Agricultural Experiment Station, and University of Maryland Extension that all persons have equal opportunity and access to programs and facilities without regard to race, color, gender, religion, national origin, sexual orientation, age, marital or parental status, or disability. (Not all prohibited bases apply to all programs.)

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What is a weed?

A plant that Is growing where it’s not wanted Has nuisance characteristics Is considered unattractive

Hairy bittercress (Cardamine hirsute), cool season annual.BBC Gardeners' World Magazine

Common chickweed (Stellaria media), cool season annual. University of Maryland Extension

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Weeds are

Annual, biennial, perennial - Reproductive life cycle Warm season or cool season - Growth time Broadleaf or grasslike - Leaf type Flowers

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Annual Weeds

Dies at the end of the year

Seeds drop and scatter after plant flowers Well-adapted to survive and reproduce in annual crops Do not have any vegetative reproductive parts Easiest to control at the seedling stage

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Biennial Weeds

Two-year lifespan

First year: Seeds germinate and grow without flowering Second year: Produces flowers/fruit and seeds, grows vigorously, and

dies in the fall Most commonly found in no-till fields, pastures, and areas not mowed Easiest to control in the first year

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Perennial Weeds

May reproduce by seeds, roots, tubers (thick underground stems), or stolons (above-ground stems), rhizomes (below-ground stems)

Foliage may die back, but roots survive at end of growing season Can remain dormant until conditions are right for growth Most difficult to control due to multiple reproductive options and

persistence

Regrows year after year from the same root system

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Cool season weeds grow actively in spring and fall and often go dormant in winter

Warm season weeds grow mostly from June to September when soil is warm, and adapt well to hot, dry weather

Growth Time

Lesser celandine (Ranunculus ficaria), cool season perennial. University of Maryland Extension, Betty Marose INVASIVE

Common dandelion (Taraxacum officinale), warm season perennial, Nancy Martin

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Today, climate change is blurring the lines between seasons, and weeds are growing at unusual times. We may start seeing some weeds grow year round.

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Leaf types

Common lamb’s quarters (Chenopodium album), warm season annual. Michigan State University Extension

Large crabgrass (Digitaria sanguinalis), warm season annual. Betty Marose, University of Maryland Extension

Broadleaf Grasslike

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Broadleaf weeds

Characteristics of broadleaf weeds

• Wide leaves with a main central vein branching out to smaller veins

• No predominant shape or style of leaf• Annual, biennial, or perennial• Flowers singly or in clusters• Fibrous roots may comprise a single large taproot, a system

of fine roots, or both• Growth may be upright, close to the ground, or climbing• Stems may be round or square

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Broadleaf shapes

Common chickweed (Stellaria media), cool season annual, Karen Russ, Clemson Extension

Chicory (Cichorium intybus), perennial, Clemson University

White clover (Trifolium repens), perennial, Chris Evans, River to River CWMA, Bugwood.org

Dandelion (Taraxacum officinale), perennial, Betty Marose, University of Maryland Extension

Canada thistle (Cirsium arvense) flower (left), and foliage (above); perennial, Betty Marose, University of Maryland Extension INVASIVE

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Grasslike weedsCharacteristics of grasslike weeds

Closely resemble desirable grasses Fewer distinguishing characteristics More difficult to identify than broadleaf weeds Blades are long with parallel veins Stems are round and hollow Annual, perennial Similarity to lawn species limits control options, making perennial

grasslike weeds especially difficult to control in lawns

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Grasslike weeds

Japanese stiltgrass (Microstegium vimineum), warm season annual. Betty Marose, University of Maryland Extension

Annual bluegrass (Poa annua), cool season annual. North Carolina State Extension

Golden bamboo (Phyllostachys aurea), perennial. James H. Miller, USDA Forest Service, bugwood.org

Bermuda grass (Cynodon dactylon), perennial. Betty Marose, University of Maryland Extension

Large crabgrass (Digitaria sanguinalis), warm season annual. Betty Marose, University of Maryland Extension

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Weed flowers

Broadleaf weeds Often have colorful flowers where the sizes and shapes vary Flowers can be very useful identification aids

Grasslike weeds Do not have showy or colorful flowers Leaf shapes are similar among species Look at their seed heads, growth habits, and vegetative features for

identification

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Weed flowers

Henbit (Lamium amplexicaule), cool season annual.Marylandbiodiversity.com

Purple deadnettle (Lamium purpureum), cool season annual. Marylandbiodiversity.com

Persian speedwell (Veronica spp), cool season annual . Emily StanleyGround ivy/creeping Charlie (Glechoma hederacea),

perennial. Betty Marose

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Why do I have weeds in my lawn/garden beds?

Weeds are common on all 485 million acres of US cropland and almost a billion acres of range and pastureland.

Maryland Farmland. Paul Goeringer, University of Maryland Extension

Source: https://extension.psu.edu, Penn State Extension

Bing.com

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Why are weeds so prevalent?Weeds characteristics

Abundant seed production Long-term survival of seed in soil Rapid growth once established Ability to spread via seeds, roots, tubers, stolons, rhizomes Ability to occupy inhospitable or disturbed areas

Carpetweed (Mollugo verticillate), warm season annual. University of Maryland Extension

Mugwort (Artemisia vulgaris), warm season perennial. University of Maryland Extension

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Seed production

Number of weed seeds produced by

Canada thistle (per stem) - 680Dandelion - 15,000Lamb’s quarters - 72,000Pigweed - 117,000Common mullein - 223,000

Source: University of Maryland Extension Master Gardener Handbook. Reprinted 2016. p.261

University of Wisconsin-Madison, Michael W. Clayton, Botany Department

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How long can seeds remain dormant?

Chickweed 10 yearsCanada thistle 10−20 yearsPigweed 20−40 yearsPurslane 40 yearsCurly dock 80 years

Source: University of Maryland Extension Master Gardener Handbook. Reprinted 2016. p.261

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Rapid Growth

One year’s seeds equals 7 years’ weeds

elm98 stock.adobe.com

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Weeds can grow in inhospitable areas

Common blue violet (Viola sororia), cool season perennial. Bill Hubick

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There are 250,000 species of plants worldwide, a little over 3%, 8,000 plants behave as weeds

Source: Penn State University Extension https://extension.psu.edu/introduction-to-weeds-what-are-weeds-and-why-do-we-care

Japanese stiltgrass, John M. Randall, the Nature Conservancy, Bugwood.org

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Let’s explore some common weeds

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Cool Season Annual WeedsDies at the end of the year

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Cool season annual weeds

Hairy bittercress (Cardamine hirsute). Betty Marose, University of Maryland Extension

Common chickweed (Stellaria media). Betty Marose, University of Maryland Extension

Common chickweed

• Smooth stems and leaves • Dense patches form in turf, landscape,

and vegetable gardens• Thrives in temperatures between 53° -

68°• Can have several generations a year

during cool wet seasons• Prefers thin, weak lawns • Found in drainage areas, yet can be

found in a wide range of soils and conditions

Hairy bittercress

• Favors shade and areas where lawn was cut too short

• Once in flower, seed capsules pop explosively

• Dense turf will prevent weed from establishing

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Cool season annual weeds Purple deadnettle

Member of the mint family Grows up to 16” tall Light purple flowers in early spring Seeds germinate in the early fall or

following spring Thrives in lawns that are mowed too short Healthy, dense lawn will prevent

establishment The name deadnettle is intended to

indicate that it will not sting you

Henbit

Member of the mint family Less than 12” tall Pink to purple flowers in spring Seeds germinate in early fall or following

early spring Establish where lawn is mowed too short Healthy, dense turf will prevent its

establishment Purple deadnettle (Lamium purpureum), cool season annual. Michigan State Extension (Wikimedia Commons)

Henbit (Lamium amplexicaule), cool season annual. Purdue University

Persian speedwell (Veronica persica), cool season annual,content.ces.ncsu.edu/persian-speedwell.com

Cool season annual weeds

Persian speedwell

Forms dense patches in early spring Low-growing with a fibrous root system Thrives in low-fertility soil Maintain healthy, dense turf that can compete Pull by hand to prevent infestation

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Speedwell (Veronica persica) was often included in fragrant bouquets of flowers that were given as farewell gifts with the warm words, “Speed well.”

Annual bluegrass (Poa annua), cool season annual, HGIC, University of Maryland Extension

Annual bluegrass

Native to Europe Favors cool, moist conditions,

compacted soil, close mowing, and high nitrogen levels

Avoid overwatering and overfertilizing with nitrogen (N)

Complete eradication is not practical The primary means of control in lawns

is to uproot by hand

.

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Warm Season Annual Weeds

Dies at the end of the year

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Crabgrass (Digitaria sanguinalis), warm season annual. Betty Marose, University of Maryland Extension

Crabgrass

Does not tolerate shade Thrives in thin or poor-quality turf Seeds grow once the soil consistently

reaches 55 degrees A single plant can produce 150,000

seeds Maintain a healthy, dense lawn to

prevent establishment Always mow lawn at 3” to 4” and

reseed bare spots

Warm season annual weed

Warm season annual weed

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Prostrate spurge (Euphorbia maculate), warm season annual. University of Maryland Extension

Prostrate spurge

Spreads by seed Low-growing plant with opposite

positioned small oval leaves Usually a red spot in the center of each

leaf Stem oozes a milky sap when broken Flowers from early summer through the

fall Maintain healthy, dense turf to prevent

establishment Hand pulling is recommended

.

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Warm season annual weed

Japanese stiltgrass INVASIVE

Bright green grass with silver hairs down the center of a short, bamboolike blade Seeds from mid-September through October and stay viable in the soil for years Seeks disturbed areas in sun or shade Tiny, sticky seeds cling to animals, shoes, and clothes and also are carried by water Seeds germinate in late winter or early spring before crabgrass Hand pulls easily Cut it back with a mower/string trimmer for larger areas in late summer After frost, foliage dies back in winter and turns a distinctive light tan color

Japanese stiltgrass infestation in a natural area. Leslie J. Mehrhoff, University of Connecticut, bugwood.org

Japanese stiltgrass (Microstegium vimineum), warm season annual. Betty Marose, University of Maryland Extension

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Japanese stiltgrass during the winter

Japanese stiltgrass, J. C. Neal, content.ces.ncsu.edu

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Warm season annual weedsLamb’s quarters INVASIVE

Dusty white coating on new growth and undersides of leaves

Thousands of tiny black seeds from one plant will remain viable for years

Hand pulling is recommended

Lamb’s quarters (Chenopodium album L). Missouristate.edu

Carpetweed (aka green carpetweed)

Small weed that covers large patches of ground in a short time

Able to climb over nearby plants and obstacles

Found in disturbed areas White flowers in the joint between

leaf and stem bloom from July to September

Control in late spring or early summer

Carpetweed (Mollugo verticillate), Green Carpetweed in Wicomico Co., Maryland (7/31/2016). Photo by Wayne Longbottom, marylandbiodiversityproject.com

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Warm season annual weed

Purslane (aka little hogweed)

Native to India and Persia

Found in landscapes and newly seeded lawns as well as sandy, nutrient-poor, and compacted soils

Drought tolerant

Thrives between bricks, and driveway cracks

Seeds germinate from late May through early August, and stay viable in the soil for 40 years

Ability to root, and spread through pieces of stem

Rototilling only increases the number of plants

Purslane (Portulaca oleracea), warm season annual. University of Maryland Extension

Purslane stem fragments form new roots. Guy Kyser, Regents of the University of California

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Warm season annual weed

Pigweed (Amaranthus retroflexus), Betty Marose, University of Maryland Extension

Rough pigweed, Luigi Rigananese, fs.fed.us

Pigweed (aka rough pigweed)

Grows 2’ to 5’ tall Egg-shaped leaves, colored dull green to

reddish Small greenish flowers can produce up to

117,000 seeds per plant Seed production occurs from late summer

to fall until severe frost Thrives in sunny, fertile locations Hand pull before flowering occurs Can negatively affect grazing animals such

as cattle

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BiennialA plant taking two years to grow from seed to fruition and die

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Biennial weed

Common mullein (Verbascum thapsus), second year, Nancy Magnusson. Marylandbiodiversity.com

Common mullein first year, Dr. John Meed, Rutgers NJAES Cooperative Extension

Common mullein INVASIVE

Native to Europe, northern Africa, and Asia

Early America settlers crushed seeds of common mullein to stun fish in slow-moving water, making it easy to collect them

In two years, a single mullein seed can become a colony of see producing plants

The seed bank is long lived, making it difficult to eradicate established plants

To manage this weed avoid disturbing the soil where they grow and cut plants once the stalk clears the soil surface

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Biennial weedBull thistle INVASIVE

North American native, has pink to violet flowers about 1” to 1 ½” wide

Spreads entirely by burlike seeds that cling to animals, clothing, and machinery

Tap root in a juvenile plant is 28” long, rosette up to 3’ in diameter

Stem grows 2’ to 5’ tall

Sharp, long spines

Digging out the entire plant is the best control method, but mowing can effective

Bull thistle (Cirsium vulgare (Savi) Tenore ), Jim Brighton marylandbiodiversity.com

Bull thistle rosette, King County, Washington, kingcounty.gov

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Biennial weed

Musk thistle (Carduus nutans ssp leiophyllus). Richard Orr

Musk thistle rosette (Carduus nutans ssp leiophyllus), Loke T. Kok, Virginia Polytechnic Institute and State University, Bugwood.org

Musk thistle INVASIVE

Competes with grasses and other desirable plants, affecting commercial production of forage materials, such as hay

Adverse effects on both the quality and yield of forage reduces income from grazing areas

Cut thistle stalks close to the ground before the flower opens

Garlic mustard blooming in Washington Co., Maryland. Bill Hubick, marylandbiodiversityproject.com

Biennial weedGarlic mustard INVASIVE

Prefers shady forest and floodplains Rosettes have round to kidney-shaped

leaves 1’ to 4’ shoots form with triangular leaf

shape during the second year 4-petaled flowers produced on

terminal spikes Pull plants every year including the

roots until seed bank is exhausted (seeds viable in soil for 10 years)

Garlic mustard, one of our most notorious invasive species, in Anne Arundel Co., Maryland, marylandbiodiversityproject.com

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Biennial weed

Queen Anne’s lace (Daucus carota), Dan Small, marylandbiodiversity.com

Queen Anne’s lace rosette. Peter Dziuk, Minnesota Wildflowers

INVASIVE

Queen Anne’s lace, Queen Anne’s Co, Maryland, Wayne Longbottom, marylandbiodiversity.com

Queen Anne’s lace

AKA wild carrot Grows 1’ to 4’ tall Prefers full sun Flowers appear from

May to October with umbels (inflorescence that is made up of many short flower stalks which spread from a common point) 3” to 4” wide

Seeds released from midsummer to midwinter

Found on roadsides and old fields

Adaptable to variety of conditions

Grasp plant and pull entire root using a spade

Queen Anne’s lace, Chris Moorman, wrri.ncsu.edu

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Perennial weedsRegrow year after year from the same root system

Warm season perennials grow best between late spring and early fall.

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Perennial weedBermuda grass (aka wiregrass)

Bermuda grass (Cynodon dactylon), warm season perennial, University of Maryland Extension

Originating in Africa (not Bermuda) Arrived in the U.S. in contaminated hay

or bedding when slaves were brought to America

Small infestations of Bermuda grass can be dug out, but all parts of the root must be removed since pieces of stolons(creeping stems, runners) can reroot

Machine tilling the live plant only worsens its spread

Grows best when irrigated Withhold water to dry the stems, then

machine–till or spade the area to bring up the rhizomes, allowing them to dry out

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Chicory

Favors open, well-drained, unmanaged areas Stalks grow up to 3”, and produce 1”

bright blue flowers that last for one day opening in the morning and closing as the sun becomes more intense Plant will grow after mowing, but not

after deep tilling Ground chicory root is sometimes

brewed with coffee or used as a coffeelike drink

Perennial weeds

Chicory (Cichorium intybus), warm season perennial, Betty Marose, University of Maryland Extension

Pokeweed

Grows 3 to 8 feet high. Lanceolate to egg-shaped, and often reddish

on underside leaves Stems are also reddish Seeds are dropped by birds into fields,

roadsides, fence rows. Thrives in deep, rich, gravelly soils Manually remove plants before flower

formation and seed production

Pokeweed (Phytolacea americana), warm season perennial,Betty Marose, University of Maryland Extension

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Perennial weeds

Ground ivy (Glenchoma hederacea). Betty Marose, University of Maryland Extension

Canada thistle (Cirsium arvense {Linnaeus} sopoli). University of Maryland Extension

Canada thistle INVASIVE

• Spreads by fleshy, creeping rhizomes (underground stems)

• Lavender disk flowers are followed by fluffy pappus (tuftlike appendage) capable of floating long distances by wind

• Each stem produces 680 seeds, which remain viable in soil from 10 to 20 years

• Plant favors barren, infertile areas• Root system holds huge energy reserves

in which tap roots send out side roots as deep as 3 feet. The plant can regenerate from a one-inch piece.

• Hand pulling is only possible with the youngest seedlings in moist, pliable soil

Ground Ivy (aka creeping Charlie)

Produces purplish-blue flowers Prefers damp shade but can tolerate full sun Reproduces mostly by stems that root at the

nodes Less common to reproduce by seeds When crushed or cut produces a minty smell Tilling and removing all plant debris

should eliminate this pesky weed In small areas, hand pulling is effective

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Perennial weedsLesser celandine (aka fig buttercup or pilewort)

Native to Europe. Brought to the U.S. as an ornamental Grows before trees leaf creating a dense carpet Prevents native ephemerals such as bloodroot and wild ginger from surviving Remove in small patches, be careful not to leave any tubers behind

May be misidentified as Marsh marigold

INVASIVE

Lesser celandine (Ranunculus ficaria), Jane Hill, marylandbiodiversity.com

Yellow Marsh marigold (Caltha palustris), marylandbiodiversity.com, Jim Stasz

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Wild violet

Found in thinning lawns Thrives in well-draining, moist shady sites rich in

organic matter Tolerates drought once established Produces purple, sometimes white, bicolored,

or speckled flowers in the spring Difficult to control Self-pollinating flower produced in the summer

below the leaves or underground Spreads by rhizomes (underground stems) and

by large quantities of seed Wild violet (Viola papilionacea). Betty Marose, University of Maryland Extension

Perennial weed

Without violets, there would be no fritillaries. This native plant is the larval food source for fritillary butterflies.

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Perennial weedMugwort INVASIVE

Has the leaf shape and aroma of a chrysanthemum.

Emerging in the spring, then flowering from July to late September

A single plant can produce up to 200,000 seeds that are dispersed largely by wind Major factor in its spread, is its production of

extensive rhizomes (underground stems), which produce new root systems

Problematic weed in commercial nurseries, since small root fragments can contaminate nursery stock

Never till this plant, as each root piece will create a new plant Hand pulling may eventually exhaust the root

system

If pulling isn’t practical, try smothering the plant under layers of newspapers covered with mulch

Mugwort (Artemisia vulgaris), warm season perennial. https://en.wikipedia.org/ wiki/Artemisia_vulgaris

Mugwort, marylandbiodiversity.com, photo by Bill Hubick

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Perennial weedWhite clover

Native to Eurasia, and North Africa

Prefers moist, well-drained soils in light shade

Tolerates full sun and dry soils Nitrogen-fixing plant, lessening the need to

fertilize the area

Complete eradication in lawns is not practical

Limit the spread by hand pulling Been growing in American lawns, fields, and

roadsides for a long time

White flowers attract pollinators

Good forage plant for livestock

White clover (Trifolium repons),cool season perennial, Bill Hubick, marylandbiodiversity.com

White clover closeup, USGS PWRC, Marylandbiodiversity.com

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Did you know . . .In the 1950s, clover was contained in lawn seed mixtures for its ability to enrich the soil and help the growth of turfgrass.

Lawn with white clover (Trifolium repens ), Kevin Frank, Michigan State University Extension

Source: https://extension.umd.edu/hgic/topics/lawns-and-microclover

White clover (Trifolium repens), Betty Marose, University of Maryland Extension

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Perennial weedCurly dock Favors nutrient-rich, heavy, damp soil, but also

adapts to dry, poor soil conditions

Generally found where overwatering occurs or in areas of standing water

Green flowering stalks form from a basal rosette and grow up to 3 feet tall, eventually turning rusty brown and lasting through winter. A single seed is enclosed in each reddish brown, three-sided fruit

One plant produces up to 60,000 seeds, which remain viable in the soil up to 80 years

Maintaining a healthy, dense lawn will compete and prevent weed establishment

May be poisonous to livestock if ingested in quantity

Curly dock rosette. (Rumex crispus),Michigan State University Curly dock (Rumex crispus), Betty Marose,

University of Maryland

Curly dock, (Rumex crispus), Nancy Martin, marylandbiodiverstiy.com

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Common plantain

Introduced from Europe

Found in lawns, roadside, compacted soil, vacant lots, and waste areas

Flower-covered stalks approximately 1’ tall

Seeds remain viable for up to 60 years

Hand pull before seeds emerge

Leaves were brewed in a tea to treat cough and dysentery or used as a poultice to treat blisters and insect stings

Perennial Weed

Common plantain (Plantago major). University of Maryland Extension

Common Plantain (Plantago major), Bill Hubrick, marylandbiodiversity.com

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Perennial weeds

Yellow nutsedge (Cyperus esculentus), perennial. University of Maryland Extension

Dandelion Warm season perennial Derives its name from the French dent de lion

meaning “tooth of the lion” Spread throughout the northern hemisphere Puritans found dandelions so useful they brought

them to settle in the new county Native Americans boiled dandelions in water to

treat kidney disease, swelling, skin problems, heartburn, and upset stomach.

Dandelion (Taraxacum officinale), perennial.learningherbs.com/remedies-recipes/dandelions/

Mow dandelions when they are flowering to prevent them from going to seed.

Warm season grasslike sedgespreads by offshoots as well as seeds

Seeks wet areas with poor drainage Digging out to remove the

underground nutlets helps prevent reoccurrence

Dense, healthy lawn will prevent weed establishment

Diverting water or improving drainage can help reduce infestation

Yellow nutsedge

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What perennial weed is pictured?

Eastern poison ivy (Toxicodendron radicans),Jonathan Sach , poison-ivy.org

Eastern poison ivy

• Deciduous, woody vine• The leaf is composed of three 2” to 4” long leaflets with the middle leaflet

having a longer stem than the two side leaflets• Climbing vines can have thick hairy stems• Seeds are spread by animals and birds that eat the fruit and by stems that

root• Invades landscapes, woodlands, and wetlands by creeping stems or

seeds; thrives under a variety of conditions and through all seasons• Contains urushiol that can produce a skin rash on contact at any time of

year• Sever vines growing up tree trunks to eliminate the flow of moisture from

roots Be very careful not to bring firewood into the house with poison ivy vines

attached

Never burn the plant as toxins can be inhaled in smoke

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To further test your knowledge, take the poison ivy quiz at poison-ivy.org

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Perennial weed

Eastern poison ivy, Josh Emm, marylandbiodiversity.com

Eastern poison ivy, Jonathan Sachs, poison-ivy.org

Eastern poison ivy, Jonathan Sachs, poison-ivy.org

Eastern poison ivy, Bill Hubick, marylandbiodiversity.org

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What to do with an unwanted plant?

Success begins with asking the right questions

Do you believe this plant is a weed?

Where is the plant growing? lawn or garden

What type of leaf does the plant have? broad or grassylike

When did you first see the plant growing? cool or warm?

Are there any flowers on the plant?

Have you recently had a soil test?

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Beneficial properties of weeds

Enrich organic content of soil through repeated cycles of growth and death

Loosen compacted soils

Control erosion by stabilizing soil

Improve water quality

Provide habitat and food for wildlife and microbes

Supply ingredients for dyes, food, and medicinal remedies

Indicate the nutritional balance of soil

Common mullein (Verbascum thapsus).Ohio Weed Guide, Ohio State University

White clover (Trifolium repens), perennial, Betty Marose, University of Maryland

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Weeds are an indicator of soil fertility and pH

• Crabgrass or dandelions indicate poor soil that's low in calcium

• Henbit or lamb’s quarters indicate high nitrogen

• Common mullein indicates acidic soil with low fertility

• Plantain indicates compacted acidic soil with low fertility

• Purslane indicates rich soil, high in phosphorus

• Queen Anne’s lace indicates poor, dry alkaline soil

Maintain the correct pH for turf and plantsA pH of 6.0 to 7.0 is right for most home gardeners

Acid Soils have a pH below 7 and alkaline soils have a pH above 7

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The negative impact of weeds may include

Competing with desirable plants for light, water, nutrients, and space

Reducing the quality and quantity of flowers, fruits, and vegetables by crowding out the desirable plants

Acting as hosts to plant pathogens, e.g. Verticillium wilt (fungal disease)

Inhibiting growth of beneficial plants through the release of a chemical compound into the environment also know as allelopathy

University of Connecticut, IPM

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Weed control is a long-term commitmentGardening is a balancing act between weeds and wonders.

Carol Stocker in Organic Gardener

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Weed Control in the Home Landscape

One can never eliminate all weeds. Control may be possible with some weeds. Each gardener must choose which weeds to target and which to tolerate.

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Integrated weed management

Weed management requires multiple approaches falling under two broad headings: Prevention and Suppression.

Prevention involves excluding weeds from entering the landscape.Suppression is employed after a weed has become established, and may involve one or all of the following approaches: Cultural methods Mechanical methods Biologic methods Chemical methods

Start with prevention, then move to suppression using cultural and mechanical approaches before considering other methods.

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PreventionYour first line of defense

The best way to control weeds is not to allow them to become established in the first place.

Use weed-free seeds, soil, and mulchBuy from trusted sources Identify and remove weeds before planting nursery purchasesMaintain clean equipment to avoid transporting weeds

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Suppression: Cultural practicesFor your lawn

Perform a soil test to determine whether your soil’s pH supports your type of grass. A pH of 6.0 to 7.0 is ideal Apply grass seed in early fall if planting cool season grasses (tall fescue,

Kentucky bluegrass, perennial ryegrass, fine fescue, creeping fescue). Overseed bare and thin areas of lawn in the spring to increase lawn

density. This will help to prevent weeds from getting established and spreading Use high-quality grass seed appropriate to your climate, light conditions

(sun, shade, or mixed), soil moisture, and foot traffic Choose grass seed blends that have the best chance of surviving periods

of drought and local diseases READ the label, which identifies the varieties of grass seed in the mixture

and the percentage of weed seed allowed. Avoid blends with weed content above 0.5 percent

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Suppression: Cultural practicesFor your gardens

Plant the right plant in the right place Consider light, moisture, and available

space before you plantMaintain healthy, vigorous plants by

regularly checking for pests and diseases, taking prompt remedial action when necessary Apply 2 to 3 inches of mulch, shredded

leaves, or compost, preferably in spring when ground is moistWhen planting a vegetable garden, rotate

your crops for soil nutrient replenishment

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Suppression: Cultural practicesFor lawn and gardens

Maintain the correct pH for turf and plants• A pH of 6.0 to 7.0 is right for most home gardeners

Fertilize at the proper time when plants are actively growing, never when the plant is preparing for dormancy

Suppression: Mechanical methodsDisrupt seed germination and destroy plant tissue

Hand pull weeds and discard in trash, not in compost Cut weeds at the base of the plant before they set

seeds if pulling is not an option Cultivate with a hoe or lightly till every 2 to 3 weeks to

disturb weeds and discourage further growth; this kills many weeds in 2 or more years

Mow lawn at a height of 3.0" to 4.0" and leave grass clippings on the lawn

With large areas of weeds, cover the area with 2 sheets of newspaper (forget using glossy sales ads, coupons, advertising inserts), dampen the newspaper with water to keep it from blowing away, add 2” of preferred mulch on top of the newspaper then water again

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Suppression: Biologic methodsUse living organisms to target weeds

Biologic control tactics are the least used by homeowners, yet this is the area in which the most research is currently focused.

Biologic methods employ bacteria, fungi, insects, and animals to target and destroy specific weed species Biologic agents are highly selective; their effectiveness relies on

matching organism to weed. For example, Yellow nutsedge can be controlled using an indigenous rust fungus, Puccinia canaliculate In some areas, goats can be rented to clear vegetation from

large spaces under specific conditions

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Suppression: Chemical methodsThe last resort

Select the right chemical method for your weeds based on life cycle. Consider Timing

• Preemergent• Postemergent

Mode of action• Contact• Systemic

Scope of plant or area to be treated• Selective• Nonselective

Always apply the appropriate herbicide at the correct rate and at the correct time for desirable results.

Timing a chemical applicationFor Lawns

Preemergent treatments are applied to the soil before weeds germinate• Water after application according to label instructions• May need second application• Label will specify waiting period before new seed can be sown

Postemergent treatments are applied directly to plants after they are growing

• Apply when temperature is between 65 and 85 degrees• Do not apply if rain is expected within 24 hours• See label for information on when to mow or plant new lawn

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Mode of action and scope of area Contact chemicals kill treated plant parts on contact

• Only effective on annual weeds Systemic chemicals are absorbed through foliage and move within

the plant to the roots, killing the entire plant FFor example: Glyphosate (no soil residual)

• Best applied in late summer or fall when plant is drawing energy down into the roots for storage

• Full effect may take weeks Selective or nonselective

• Selective kills weeds while they are germinating or growing and will not harm other plantsFor Example, Dicamba (liquid, dust, granules) 1100 products

• Nonselective kills or damages all plant life within the treated area

Do not spray herbicides containing Dicamba over the root zone of trees and shrubs! Roots can absorb the product, potentially damaging plant. Read the product label for precautions.

Chemical application methods

Apply herbicides specific to your plants as directed on the label. Make sure the chemical won't harm desirable plants. Avoid spraying onto hard surfaces, as runoff will affect the Chesapeake Bay.

Granular chemicals are incorporated into fertilizer and applied by rotary or drop spreader

Liquid chemicals may be supplied in ready-to-use or concentrated form and are sprayed or painted onto the plant—be sure to read the label and dilute as directed

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For additional help:

• Visit extension.umd.edu/hgic to ID your weed • Take the weed sample (stored in a plastic ziploc bag) to an

Ask-a-Master Gardener Plant Clinic

To locate the nearest clinic, go to https://extension.umd.edu/anne-arundel-county/master-gardeners/ask-master-gardener-plant-clinics

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Conclusions

Identification is key to effective weed management Strive to prevent introduction of new weeds Remove weeds before they become well-established Treat weeds with cultural and mechanical means when possible Consider biologic treatment if available Use chemical herbicides as a last resort and always according to label

directions

This presentation was brought to you by University of Maryland Extension

Master Gardener ProgramAnne Arundel County

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Look-alikes

Many weeds have look-alikes: Purple deadnettle and henbit Dandelion and chicory Lesser celandine and marsh marigold Curly dock and common plantain Eastern poison ivy and Virginia creeper

To distinguish: Examine life cycle, growth habit, structure and arrangement of leaves, flowers

Consult https://extension.umd.edu/hgic or https://weedid.cals.vt.edu/select to determine which weed is yours.