J. Boyd Carey, James J. Kells, Karen A. Renner
Department of Crop and Soil Sciences
MSU Contact: James J. Kells kellsj@msue.msu.eduExtension Bulletin E-1363, Major Revision, December 1993
Michigan State University Extension
Foreword
Accurate weed identification is the first step in a successful weed control program. Various weed species respond differently to different methods of control. Whether you choose chemical, cultural or mechanical control measures, you need to know what weed species are present. Failure to identify the weed problem accurately may lead to wasted time and money or excess pesticide applied to the environment.
Because weeds are most effectively controlled at a very young stage, it is important to identify them as early as possible. Unfortunately, many weeds look very similar at a young stage. This guide is designed to help identify seedling weeds while there is still time to control them.
This guide includes 33 of the most common problem weed species in Michigan. It is divided into two main sections grass and grasslike weeds and broadleaf weeds.
Grass weeds are especially difficult to distinguish, so an identification key is included at the beginning of the grass and grasslike weeds section. This key gives you a step-by-step progression of questions that will help you identify species correctly.
An illustrated guide to broadleaf weed characteristics is included at the beginning of the broadleaf weeds section. There is also a glossary of terms at the back of the guide. Referring to these sections will help you understand many of the terms used in the written descriptions of each species. An alphabetical index of the weed species is included in the back of the manual for quick reference.
Grass and Grasslike Weeds
Identification Key for Grass and Grasslike Weeds
Click on the species you wish to view:
1. Barnyardgrass (Echinochloa crus-galli) Summer
annual. Leaf sheath and blade hairless. No ligule. No auricles. Stem flattened.
Back to key Index Glossary Broadleaf weeds Top of page
2. Yellow Nutsedge(Cyperus esculentus) Perennial.
Not a grass species. Stem is triangular. Leaves are smooth, hairless and
deeply keeled. Whole plant is yellowish to pale green. Tubers (nutlets)
usually present at tips of rhizomes.
Back to key Index Glossary Broadleaf weeds Top of page
3. Quackgrass (Elytrigia repens) Perennial. Leaf
sheath and blade hairless or sparsely hairy. Clasping auricles present.
Short membranous ligule. Rhizomes usually present.
Back to key Index Glossary Broadleaf weeds Top of page
4. Johnsongrass (Sorghum halepense) Perennial.
Leaf sheath and blade hairless. No auricles. Prominent, jagged, membranous
ligule. Rhizomes usually present.
Back to key Index Glossary Broadleaf weeds Top of page
5. Large Crabgrass(Digitaria sanguinalis) Summer
annual. Leaf sheath and blade (both surfaces) densely hairy. Membranous
ligule. No auricles. Leaf blade is short and wide compared with blades
of most other grasses.
Back to key Index Glossary Broadleaf weeds Top of page
6. Smooth Crabgrass (Digitaria ischaemum) Summer
annual. Leaf sheath and blade hairless or sparsely hairy. Membranous ligule.
No auricles. Similar in appearance to large crabgrass.
Back to key Index Glossary Broadleaf weeds Top of page
7. Giant Foxtail (Setaria faberi) Summer annual.
Entire upper side of leaf covered with dense, short hairs. Sheath margin
hairy. Hairlike ligule. No auricles.
Back to key Index Glossary Broadleaf weeds Top of page
8. Yellow Foxtail (Setaria glauca) Summer annual.
Leaf blade hairless except for long, wiry hairs on upper side near base.
Sheath is hairless. Hairlike ligule. No auricles.
Back to key Index Glossary Broadleaf weeds Top of page
Back to key Index Glossary Broadleaf weeds Top of page
10. Fall Panicum (Panicum dichotomiflorum) Summer
annual. Leaf sheath and blade hairless. Hairlike ligule. Leaf midrib prominent
and somewhat white on older plants. No hairs on sheath margin. No auricles.
Back to key Index Glossary Broadleaf weeds Top of page
11. Wild-Proso Millet (Panicum miliaceum) Summer
annual. Leaf blade (both surfaces) and sheath densely hairy. Back of midrib
often with a row of hairs protruding at a 90-degree angle. Hairlike ligule.
No auricles. A large, oval-shaped, shiny, dark brown to black seed often
persists on the root system.
Back to key Index Glossary Broadleaf weeds Top of page
12. Witchgrass (Panicum capillare) Summer annual.
Leaf blade (both surfaces) and sheath densely hairy. Hairlike ligule. Leaf
midrib prominent. No auricles. Seed smaller and less persistent than that
of wild-proso millet.
Back to key Index Glossary Broadleaf weeds Top of page
Broadleaf Weed Characteristics
13. Ladysthumb (Polygonum persicaria) Summer
annual. Cotyledons are lanceolate with rounded tips and smooth on both
surfaces. True leaves are alternate, smooth and lanceolate with smooth
edges. May or may not have a purplish mark (watermark) near the center
of the leaf. Nodes are surrounded by an ochrea with hairlike projections
extending up the stem. Similar to Pennsylvania smartweed.
Index
Glossary To
top Grass Key Top
of page
14. Pennsylvania Smartweed (Polygonum pensylvanicum)
Summer annual. Cotyledons are lanceolate with rounded tips and smooth on
both surfaces. True leaves are alternate, smooth and lanceolate with smooth
edges. May or may not have a purplish mark (watermark) near the center
of the leaf. Nodes are surrounded by an ochrea. Very similar to ladysthumb,
but Pennsylvania smartweed does not have hairlike projections extending
from the ochrea up the stem.
Index
Glossary To
top Grass Key Top
of page
15. Wild Buckwheat (Polygonum
convolvulus) Summer annual. Cotyledons are linear and hairless. Stems
are reddish and hairless. Nodes are surrounded by an ochrea. First true
leaf is arrow-shaped.
Index Glossary To top Grass Key Top of page
16. Common Lambsquarters (Chenopodium album)
Summer annual. Small seedling with linear cotyledons. First two true leaves
are opposite and ovate with smooth edges. Later emerging leaves are alternate
and triangular with unevenly toothed edges. Cotyledons and true leaves
are covered with white, mealy granules that look like frost.
Index
Glossary To
top Grass Key Top
of page
17. Redroot Pigweed (Amaranthus retroflexus)
Summer annual. Cotyledons linear and hairless. True leaves are alternate
and ovate with a small notch or indentation at the tip. This notch helps
differentiate redroot pigweed from eastern black nightshade. Leaves also
have purple petioles.
Index Glossary
To top Grass
Key Top of page
18. Eastern Black Nightshade (Solarium ptycanthum)
Summer annual. Cotyledons small, ovate and green on both surfaces. First
true leaves are ovate and simple with a wavy edge and petioles. First leaves
have purple undersides. May look like redroot pigweed when very small,
but does not have notch at leaf tip as redroot pigweed does.
Index Glossary To top Grass Key Top of page
19. Common Cocklebur (Xanthium strumarium) Summer
annual. Cotyledons are smooth, waxy and lanceolate and may be protruding
from the bur. True leaves are alternate and triangular to ovate with a
rough, sandpapery feel.
Index Glossary To top Grass Key Top of page
20. Jimsonweed (Datura stramonium) Summer annual.
Cotyledons smooth and lanceolate. Hypocotyl is often hairy. True leaves
are smooth and alternate with petioles. Seedling has an unpleasant odor
when crushed.
Index Glossary To top Grass Key Top of page
21. Common Purslane (Portulaca oleracea) Summer
annual. Cotyledons linear and hairless. True leaves are opposite with each
pair rotated around the stem 90 degrees from the previous pair. Leaves
are wedge- shaped, tapering toward the base. Leaves are thick, fleshy and
glabrous. Stems are prostrate and reddish.
Index Glossary
To top Grass
Key Top of page
22. Common Ragweed (Ambrosia artemislifolia)
Summer annual. Cotyledons are thick and oval to spatulate with grooved
petioles. Adult leaves are pinnatifid with a lacy appearance. Small seedling
very similar to giant ragweed, but common ragweed cotyledons are much smaller
with purple undersides.
Index
Glossary To
top Grass Key Top
of page
23. Giant Ragweed (Ambrosia trifida) Summer
annual. Cotyledons oval to spatulate with grooved petioles. Early leaves
covered with dense hair. Small seedling very similar to common ragweed,
but giant ragweed cotyledons are three to four times larger and green underneath
instead of purple. Adult leaves are deeply three-lobed (occasionally five-
lobed) with a rough surface.
Index Glossary To top Grass Key Top of page
24. Velvetleaf (Abutilon theophrasti) Summer
annual. Cotyledons have slightly different shapes--one is nearly round;
the other, more heart-shaped. Both cotyledon margins are entire, and cotyledons
are covered on both surfaces with short hairs. The stem is densely hairy.
True leaves are heart-shaped and alternate with serrated margins and velvety,
hairy surfaces.
Index
Glossary To
top Grass Key Top
of page
25. Common Chickweed (Stellaria media) Summer
or winter annual. Seedling is small, pale green and only sparsely hairy.
First leaves have very pointed tips and petioles. Hypocotyl is slender
and often reddish.
Index Glossary To top Grass Key Top of page
26. Shepherd's-purse (Capsella bursa-pastoris)
Summer or winter annual. Cotyledons and early true leaves are oval to spatulate
and are borne on long stalks or petioles. Older rosette leaves are variable
in shape and variously lobed with toothed or undulating edges.
Index
Glossary To
top Grass Key Top
of page
27. Horseweed (Marestail) (Conyza canadensis)
Summer or winter annual. Cotyledons are smooth and green. Early leaves
are entire. Later leaves are alternate, sessile, crowded around the stem,
entire or toothed, and often hairy.
Index
Glossary To
top Grass Key Top
of page
28. Prickly Lettuce (Lactate serriola) Summer
or winter annual or sometimes a biennial. Seedling is a rosette. First
leaves are pale green and spatulate. Later emerging leaves have spiny edges
and prickly spines along the underside of a prominent midrib. Stem is hollow
with milky juice.
Index
Glossary To
top Grass Key Top
of page
29. Wild Mustard (Brassica kaber) Summer or
winter annual. Cotyledons are kidney-shaped and smooth. True leaves are
alternate and hairy and vary considerably in size and shape. Stem also
hairy, especially near base.
Index Glossary
To top Grass
Key Top of page
30. Yellow Rocket (Barbarea vulgaris) Winter
annual or biennial. Cotyledons and early true leaves are round to ovate
and are borne on long stalks or petioles. Cotyledons have a slight notch
at the tip. Older leaves are pinnately lobed with a large terminal lobe.
Index Glossary To top Grass Key Top of page
31. White Campion (Silene alba) Biennial or
short- lived perennial. Cotyledons are spatulate and hairy. First true
leaves are also hairy and narrowly oval.
Index Glossary To top Grass Key Top of page
32. Wild Carrot (Daucus carota) Biennial. Cotyledons
are linear, long and smooth. The first emerging true leaf and subsequent
leaves are compound, lacy and pinnatifid. Seedling similar in appearance
to cultivated carrot.
Index
Glossary To
top Grass Key Top
of page
33. Bull Thistle (Cirsium vulgare) Biennial.
Cotyledons are round to spatulate, glabrous and fleshy. First true leaves
are oval to spatulate with spines and a rough, bumpy surface. Forms rosette
with adult leaves becoming pinnatifid and with dense hairs on undersurfaces.
Index Glossary To top Grass Key Top of page
Barnyardgrass (Echinochloa crus-galli)
Buckwheat, Wild (Polygonum convolvulus)
Campion, White (Silene alba)
Carrot, Wild ("Daucus carota")
Chickweed, Common (Stellaria media)
Cocklebur, Common (Xanthium strumarium)
Crabgrass, Large (Digitaria sanguinalis)
Crabgrass, Smooth (Digitaria ischaemum)
Foxtail, Giant (Setaria faberi)
Foxtail, Green (Setaria viridis)
Foxtail, Yellow (Setaria glauca)
Horseweed (Marestail) (Conyza canadensis)
Jimsonweed (Datura stramonium)
Johnsongrass (Sorghum halepense)
Ladysthumb (Polyponum persicaria)
Lambsquarters, Common (Chenopodium album)
Lettuce, Prickly (Lactuca serriola)
Millet, Wild-Proso (Panicum miliaceum)
Mustard, Wild (Brassica kaber)
Nightshade, Eastern Black (Solanum ptycanthum)
Nutsedge, Yellow (Cyperus esculentus)
Panicum, Fall (Panicum dichotomiflorum)
Pigweed, Redroot (Amaranthus retroflexus)
Purslane, Common (Portulaca oleracea)
Quackgrass (Elytrigia repens)
Ragweed, Common (Ambrosia artemisiifolia)
Ragweed, Giant (Ambrosia trifida)
Rocket, Yellow (Barbarea vulgaris)
Shepherd's-purse (Capsella bursa-pastoris)
Smartweed, Pennsylvania (Polygonum pensylvanicum)
Thistle, Bull (Cirsium vulgare)
Velvetleaf (Abutilon theophrasti)
Witchgrass ("Panicum capillare")
Glossary Grass Key Broadleaf Weeds Top of page
glabrous - hairless, smooth.
midrib - the central vein running lengthwise along the underside of a leaf or cotyledon; underside of midvein.
rosette - a cluster of leaves growing from a common point at the soil surface, without a stem.
sessile - describes a leaf that lacks a petiole, attached directly to the stem.
rhizome - an underground stem from which new plants may emerge, appears to be a root.
tuber - underground nutlike storage organ located at tips of rhizomes.
