Weed life cycles

Vegetative reproduction Production of new plants from vegetative structures Clones=daughter plants=ramets Genetically identical to the parent plant

Sexual reproduction Production of new plants from seeds Allows for genetic mixing/diversity in offspring (genets)

Types of reproduction in plants

Summer annual Germinate in spring and summer and mature before winter Problems in spring and early summer planted crops, open sites, winter

cereal crops, edges of natural areas Lambsquarter, redroot pigweed, bedstraw, wild buckwheat, green foxtail,

wild oat

Winter annual Germinate in the late summer, fall, and winter (in warmer regions) Mature in spring or early summer Problems in late summer and fall planted crops, open sites, bare spots in

pastures In colder regions, winter annuals may be summer annuals Shepherd’s purse, field pennycress, downy brome

Five life cycle categories for weeds

Biennial Live for two growing seasons

Seeds germinate and plants grow vegetatively as rosettes the first year Exposure to cold in winter causes the rosette to bolt in the spring The biennial then flowers, matures its seed, and dies during the summer or fall

of the second growing season Usually a problem in perennial fields; not in fields that are disturbed in fall Henbit, houndstongue

Perennial Survive indefinitely (3+ years) Flowering doesn’t trigger senescence

Underground structures continue to live

Five life cycle categories for weeds

Simple perennials Start from seed, grow vegetatively

Form a crown of tissue at or below the soil surface on the upper end of a taproot Root and crown survive indefinitely Shoots periodically produce flowers and seeds

What is the purpose of seeds? Found in perennial crops, undisturbed areas, no-till fields Spotted knapweed

Creeping perennials Reproduce from vegetative structures and seed Vegetative reproductive structures are the major means of localized spread, competition,

and survival Creeping roots, rhizomes, stolons, bulbs, tubers

Have large amounts of stored food and numerous buds Field bindweed, quackgrass, Canada thistle

Five life cycle categories for weeds

Vegetative reproductive structures

Rhizomes Elongated horizontal underground stems

with nodes, internodes, and modified leaves Root and new shoot growth always

originates from buds at the nodes

Tubers Thickened underground stems borne on

rhizomes Internodes are shorter than those on a

rhizome Root and new shoot growth always

originates from buds at the nodes

Vegetative reproductive structures

Bulbs Modified leaf tissue borne on a small

stem plate Roots and new bulbs develop from this

stem plate

Stolons Horizontal aboveground stems Leaves produced at the nodes are

green Food storage not a major function

Vegetative reproductive structures

Creeping roots No leaves, nodes, or internodes Can grow downward and

horizontally Can produce shoots along their

length Tend to penetrate deeper than

other vegetative reproductive structures and are harder to control

Shoot Regeneration in Weed Species

Shoot regeneration

All plants have a growing point from which they can regenerate shoots Any practice that destroys the plant below the lowest growing point will

kill the plant The position of shoot regeneration on a plant and the resistance of a

plant to destruction depends on the life cycle

Annuals Broadleaves

The bud in the axil of the cotyledons in the lowest point from which an annual broadleaf can regenerate a new shoot

Any action that destroys the weed below that point should kill it Grasses

The growing point, or crown, is just below the soil surface Annual grasses need to be damaged under the soil surface for complete kill

Shoot regeneration

Biennials Rosette stage difficult to control As the seed stalk begins to elongate (bolt) the meristems raise aboveground

Simple Perennials Crown is 1 to several inches below soil surface Crown and taproot survive and generate new shoots even after substantial damage How would you go about trying to control a simple perennial (mechanically?)

Creeping Perennials Numerous well-protected buds capable of generating new shoots Large amounts of stored food and many buds Usually 6 in belowground, sometimes several feet Severe disturbance usually helps them regenerate Need repeated action to deplete the plant of energy reserves

Growing points

Questions!

1. Summer and winter annuals germinate in spring and summer and mature before winter. True or False?

2. _______________ weeds are most troublesome in perennial and no-till cropping systems.

a. Perennialb. Annualc. Bienniald. Centennial

3. What stage of a biennial weed is most difficult to control? Why?

Field pennycress Scientific name: Thlaspi arvense Family: Brassicaceae Life cycle: Annual Where found: Cropland Physical description:

Seed: fingerprint pattern Cotyledon: oval with long petiole True leaves round to spatulate, then oblong to oval

Forms a basal rosette at first, then alternate when flowering Early leaves have long petioles; later stem leaves are

sessile, clasping around stem Leaves without hair, in contrast to shepherd’s purse Growth habit: erect

Interesting facts: Seed pods are disc-shaped with a distinct notch at tip Distinct, garlic-like odor when brushed Latin name describes flat pod

Thlas=to crush or flatten

Shepherd’s Purse Scientific name: Capsella bursa-pastoris Family: Brassicaceae Life cycle: Annual Where found: Cropland Physical description: highly variable

Seed: small, sticky when wet Cotyledon: ovate, apex may be indented Growth habit: basal rosette; flowering stem alternate True leaves oval, then elliptic to oblanceolate, most

becoming pinnately divided Stem leaves lanceolate Early leaves have long petioles; later stem leaves are

sessile, clasping around stem Leaves are sparsely hairy

Interesting facts: Seed pods heart-shaped, flattened Latin name describes seed pods

caps=small box bursa= purse, pastor=shepherd