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Weed life cycles. Types of reproduction in plants. 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 - PowerPoint PPT Presentation
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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