Weed Ecology, Biology, and Identification

Understanding weed ecology can help in designing management systems to minimize their impact.
Weed Ecology, Biology, and Identification - Articles

Updated: August 24, 2017

Weed Ecology, Biology, and Identification

Weed Ecology

Weed ecology might be described as the weed's lifestyle - where does it tend to thrive, what are its particular needs and adaptations to its environment? People have a major influence on weed ecology such as weed transport/spread and creating various cropping and management techniques that favor a particular weed species. Also, weedy plants have the capability to survive under adverse conditions and use adaptive mechanisms that enable them to thrive under conditions of extreme soil disturbance. Understanding weed ecology can help in designing management systems to minimize their impact.

Weed Biology

Effective weed management is dependent upon the biology of the weed including type and lifecycle. Weeds are more easily identified and/or managed at certain times during their lifecycle.

Life cycles

Summer annuals

Seeds germinate in spring, vegetative during spring/summer, and flowers and sets seed in mid to late summer, die in fall

Examples:

  • common lambsquarters
  • pigweed
  • hairy galinsoga
  • velvetleaf
  • large crabgrass
  • common ragweed
  • giant foxtail
  • common purslane
  • smartweed

Winter annuals

Seeds germinate in fall and winter, vegetative during spring, and flowers and set seed in late spring/early summer before it dies

Examples:

  • common chickweed
  • downy brome
  • shepherdspurse
  • henbit

Biennials

Plants live more than one year over two growing seasons; seeds germinate and overwinter in a rosette stage, then complete life the following year

Examples:

  • wild carrot
  • common teasel
  • bull thistle
  • common burdock

Perennials

Simple: generally spread by seed; large root but no spreading horizontal roots

Examples:

  • dandelion
  • common pokeweed
  • dock
  • plaintain

Creeping: reproduce by rhizomes and stolons; some seed reproduction

Examples:

  • Canada thistle
  • poison ivy
  • multiflora rose
  • quackgrass
  • ground ivy
  • hemp dogbane
  • yellow nutsedge
  • Japanese knotweed
  • groundcherry

Weed Identification

Effective weed management requires proper identification of weeds - otherwise tactics chosen may not work and end up costing money and frustration. Below are some of the key features to look at when identifying a plant accused of being a weed! Many good books, fact sheets and websites now feature photo galleries of weeds at various stages to help with identification (see end of section).

Botanical Review

Grassy weeds and sedges

  • monocots, one cotyledon (coleoptile in seedling grasses)
  • parallel veins
  • grasses-round, oval, or flat stems with hollow internodes
  • sedges-generally, triangular, solid stem

Broadleaf weeds

  • dicots, two cotyledons (seed leaves)
  • usually have wider leaves than grasses or sedges
  • netted veins
  • branched stem
SpeciesDistinguishing Features
smooth crabgrassmembranous ligule, no to few hairs around collar otherwise hairless, bluish color
large crabgrassmembranous ligule, hairy blade and sheath
barnyardgrassno ligule, flat stem
goosegrassmembranous ligule, flat stem, few hairs near collar, distinct parallel veins, "flattened"
quackgrassclasping auricles, white rhizomes
wirestem muhlytoothed membranous ligule, scaly rhizomes, bushy appearance
nimblewilltoothed membranous ligule, scaly rhizomes, bushy appearance
witchgrasshairy ligule, very hairy sheath and blade (otherwise similar to fall panicum)
fall panicumhairy ligule, prominent white mid-rib in blade
annual bluegrassslightly pointed membranous ligule, light green, folded leaves, boat-shaped tips
giant foxtailhairy ligule, fine hairs on upper blade
yellow foxtailhairy ligule, long straggly hairs near collar, flat stem, purplish near base
green foxtailhairy ligule, no hairs (smooth on blade)
shattercanemembranous ligule, prominent mid-rib, shiny black seed
johnsongrassmembranous ligule, prominent mid-rib, reddish-brown seed or rhizomes
yellow nutsedgetriangle stem, shiny, V-shaped leaves, rhizomes and tubers (nutlets)
prostrate knotweedelliptic, dull blue-green, leaves, ochrea, flowers in leaf axils
wild buckwheatrounded arrow shape leaves, ochrea at petiole base, triangular seeds
Pa. smartweed/ladysthumbtrue leaves have purple blotches, stems are reddish-purple, ochrea has no hairs vs. ladysthumb ochrea which has hairs, otherwise smaller plant but similar
mile-a-minutetriangular leaves, waxy-look, prominent ochrea, recurved spines
red sorrelarrow/spade shaped leaves with lobes at base, ochrea, long slender seed stalk, sour taste
curly/broadleaf dockwavy leaf edge vs. broad, flat heart-shaped base on broadleaf dock, ochrea
common lambsquartersgreyish cast, frosted appearance (esp. on new leaves)
tumble pigweedlight green, bushy, small wavy leaves, flowers clusters in leaf axils
redroot/smooth pigweednotch on end of first true leaves, reddish hue on under leaf, red stem, both can have hairs on stems, look similar until mature---rr pig. has long spike seed heads, sm. pig. has shorter spikes w/ finger-like projections
common pokeweedreddish-purple stem, dark purple berry clusters, large poisonous taproot
common purslanereddish-purple stem, dark purple berry clusters, large poisonous taproot
chickweedspp.common: broadly ovate leaves, single row of hairs on stem, winter annual; mouse-ear: very hairy stems and leaves, perennial
mustard spp.most have heart to kidney-shaped cotyledons, most have long narrow seed pods, variable features for each species
yellow rocket-winter annual, smooth dark green leaves,
lobes at base
wild mustard-w.annual, may have hairs on leaf, wavy. loby
leaves
shepherdspurse- w. annual, rosette at base, coarsely lobed leaves that clasp around stem, triangular, heart-shaped seed pod
f. pepperweed-finely toothy basal leaves, leaves up the
single stalk, seed head branched with small boat shaped
seed pods
Va. pepperweed-similar to field pep. but smooth leaves and stem, branches lower on stem
wild radish-deeply lobed/cut wavy leaves, coarse hairs on
leaves
f. pennycress-large flat round, notched seed pods, plant can look similar to pepperweed
multiflora roselike garden rose, 5-9 leaflets of compound leaf, feathery stipules at base, white flowers
black mediclooks like spindly alfalfa, 3-leaflets, yellow flowers and black seed clusters
white clovertrifoliate leaves w/ V-shaped, greenish-white leaf blotch, white flowers
prostrate spurgeprostrate to ground, pink stems and green leaves with purple blotches, milky sap
velvetleafheart-shaped, toothed leaves and cotyledons, stem and true
leaves densely hairy
spurred anoda3-lobed leaves, triangular-ovate w/purple veins, hairy, 6-pointed seed pods, in south
common mallowround, wavy leaves w/base near center, white flowers, fruits like button or "cheese"
prickly sidatoothed oblong leaves, small spines at leaf base, yellow flowers, seedling-like velvetleaf
poison hemlocklacy leaves, large plant, white flowers in umble, purple spots on hollow stalk, hairless
wid carrotlacy leaves like garden carrot, white flowers clusters, biennial
hemp dogbaneelliptical leaves, purple stems, branchy, rhizomes, milky sap
common milkweedoblong leaves with parallel veins that connect near the outer edge, hairy on under side of leaf, milky sap, larger in stature than dogbane
bindweed spp.field: rounded tips and pointed lobes;
hedge: arrow-shaped (triangular) and squared off lobes (i.e., hedge has edge), both have large trumpet-like white/pink flowers
morning glory spp.tall: hairy heart-shaped leaves, butterfly shape cotyledons; ivyleaf: hairy, three-lobed leaves, butterfly shape cotyledons;
pitted: smooth heart-shaped leaves, purple edges, deeply indented butterfly shaped cotyledons;
all may have purple, white, pink flowers
ground ivycreeping, square stem, toothed kidney/rounded leaves, common in lawns
henbitround, hairy, toothed leaves, square, branched stem, flowers in whorl of upper leaves, winter annual
purple deadnettleresembles henbit but leaves are more triangular and crowed at top, top leaves purple
jimsonweedsmooth leaves, prominent mid-rib, purple stem, unpleasant
odor when crushed
smooth groundcherrysimilar to EBNS but flower petals are fused, lantern-type seed pod and is perennial
horsenettletoothed leaves, yellow spines on petiole, mid-rib and veins,
grape sized fruits
eastern black nightshadesome hairs on stem and leaf margins, toothed edges, purplish color on under leaf, flowers star shaped with five petals, green berries turning black at maturity, annual
creeping speedwellopposite, rounded/kidney shaped leaves w/ toothed edges, prostrate, stolons, in lawns
plantain spp.buckhorn: long narrow leaves, tall, slender seed stalk,
broadleaf: large oval leaves
wild cucumber5-7 lobed leaves (star shape), large egg shaped seed pod
burcucumber3-5 lobed leaves (pentagon shape), fruits in seed cluster
ragweed spp.common: spoon-shaped cotyledons, finely lobed and hairy leaves;
giant: large, spoon-shaped cotyledons, first leaves irregularly toothed or lobed, older leaves 3-5 lobed, 5-10+ft. tall
mayweed chamomilelacy leaves, daisy like flower, strong unpleasant odor
common burdocklarge, heart-shaped base leaves, stem and leaves w/ whitish hairs, spiny seed pod, biennial
musk thistlelobey leaves and stems spiny, spiny "wings" down stalk, pretty, dense flower head
Canada thistlecrinkled leaf edges with spiny margins, horizontal roots, perennial
bull thistledeeply cut, hairy leaves with large spines, biennial
horseweed (marestail)many leaves (w/ scattered white bristles) around and up the stalk, branchy seed head
hairy galinsogaleaves egg shaped to rounded triangle, hairy, yellow w/ white petal flowers, in gardens
common groundselirregular, long loby leaves, yellow flower clusters, in flower beds
dandeliondeeply toothed leaves, yellow flowers, milky sap (need I say more?!?)
common cocklebursmooth, waxy cotyledons, true leaves wavy, large triangle, rough, sandpaper feel, purple specks on stem, spiny seed pod