Lecture 02 2010

Lecture 02 2010 - Weed Biology 1 PLS 176 Winter 2010 Weed...

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Unformatted text preview: Weed Biology 1 PLS 176 Winter 2010 Weed Biology life cycles methods of reproduction mating systems/genetics seed production seed dispersal soil seed bank seed germination seed dormancy Life Cycle A weed’s life cycle determines what kinds of cropping situations the weed might be a problem in and what management methods are likely to succeed. • annuals, • biennials, and • perennials 1. Annuals • From germination to seed in one year or less • Grow fast, lots of seed early • Spread by seed, soil seed bank is a problem • Early colonizers, ruderals, typical crop weeds a.sum m er annuals Emerge in spring, grow in summer, seed in fall Usually most troublesome Problem in summer crops b. w inter annuals Fall emergence, winter as rosette, in spring they grow & set seed Often have summer dormancy Problem in fall-seeded crops Summer Annuals – Broadleaf Weeds Amaranthus retroflexus, redroot pigweed Chenopodium album, lambsquarters Xanthium strumarium cocklebur Summer Annuals – Grass Weeds Digitaria sanguinalis, crabgrass Echinochloa crus-galli, barnyardgrass Winter Annuals – Broadleaf Weeds Centaurea solstitialis, yellow starthistle Capsella bursaPastoris, shepherd’s purse Lamium amplexicaule, henbit Winter Annuals – Grass Weeds Bromus tectorum, downy brome, cheatgrass 1. Annuals 2. Biennials • Need two growing seasons to complete their cycle • Spread by seed Year 1: Usually emerge in spring, grow in summer, and overwinter as rosette Year 2: After the preceding cold period resume growth in Spring 2 bolt, seed set and die Biennial Weeds Silybum marianum, milk thistle Carduus nutans, musk thistle Verbascum thapsus, common mullein 1. Annuals 2. Biennials 3. Perennials live longer than 2 years and may reproduce several times before dying yearly regrowth from same root system late successionals a. sim ple perennials • reproduce and spread only by seed • vegetatively: for plant regeneration only b. creeping perennials • vegetative spread, also by seed over long distances Simple Perennials Rumex crispus, curly dock Taraxacum officinale, common dandelion Plantago major, broadleaf plantain Creeping Perennials Cyperus esculentus yellow nutsedge Cirsium arvense Canada thistle Sexual Reproduction Weed Seed Production • Role of seeds: multiplication dispersal (long distance), stress avoidance (coat, reserves, dormancy) Sexual Reproduction Genetic diversity from cross fertilization and recombination; crossing over during meiosis Genetic flexibility • adaptation to uncertain conditions • favored in disturbed environments Weeds: usually rapid growth to maturity large number of small seeds Sexual Reproduction Weed Seed Production • Primary means of spread for annuals, biennials & simple perennials • Weed control depends on prevention of seed production Asexual Reproduction • New clones (ramet) from a genet • restricted, local dispersal • more vulnerable to habitat disturbance prefer stable environments (climax, no till) tillage can disperse propagules • genetically uniform populations less adaptability to environmental changes but there are usually means for clonal variability Asexual Reproduction • High survival chance storage, quick start once established occupy the mother’s safe site clones are successful genotypes • dependable reproduction: no pollinators needed Asexual Reproduction Difficult to control • need to destroy vegetative organs, (often underground) • must deplete reserves • creeping perennials among world’s worst Perennial spp. differ in Sex/Asex balance: • Trade-off in resource allocation vegetative allocation: more competitive • Sexual repro.: allows seizing a new opening Asexual Reproduction: Structures creeping roots (buds) Canada thistle creeping underground stems: rhizomes quackgrass creeping stems: stolons bermudagrass Tubers (swollen stems) yellow nutsedge 4. Reproduction 3. Development to adulthood Life Cycle 5. Seed That Dispersal Doesn’t Migrate 6. Survival 2. Seedling Establishment 1. Germination Weed Seed Dispersal • Gain or loss from current habitat • Is the mobile phase of a life cycle • Seeds, propagules (vegetative) • In space and/or time (dormancy) • Plant invasions ...
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This note was uploaded on 03/05/2010 for the course PLS 176 taught by Professor Fischer during the Winter '10 term at UC Davis.

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