weed.pdf - WEED BIOLOGY PART 1 PROF DR ISA IPOR What is weed science \u2013 Weed science is the discipline that investigates the biology and ecology of

weed.pdf - WEED BIOLOGY PART 1 PROF DR ISA IPOR What is...

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WEED BIOLOGY PART 1 PROF DR ISA IPOR
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What is weed science? Weed science is the discipline that investigates the biology and ecology of weeds and how best to manage these plant species for the betterment of mankind.
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What is a weed? The term “weed” is defined by man. A weed is often defined as “a plant out of place”, or “a plant growing where it is not wanted”. These definitions are overly simplistic. Designating a plant as a weed simply by its physical location does not take into account problems caused by weeds nor certain characteristics of plants that contribute to their potential to be weeds. These simple definitions do not distinguish plants that possess truly weedy characteristics from those that are only an occasional nuisance. Weeds possess certain definable characteristics that set them apart from other plant species. The Weed Science Society of America defines a weed as “any plant that is objectionable or interferes with the activities or welfare of man.” Weeds are perhaps best defined as “plants that are competitive, persistent, and pernicious, and are undesirable because they interfere with human activities.”
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Characteristics of weedy plants: A. Ability to colonize disturbed environments; rapid population establishment B. High reproductive capacity (sometimes multiple methods of reproduction) C. Short time to reproduction (short time to flowering or between flowering and seed maturity) D. Germination and reproduction over a wide range of environmental conditions E. Seed dormancy, discontinuous germination, longevity of seed F. Presence of vegetative reproductive structures G. Adaptations for propagule dispersion H. Ability to compete well with crops
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1. Growth and resource capture: Success of plants grown in mixture (such as weeds in a crop) is associated with early and rapid establishment, rapid canopy development, and rapid root growth. In general, a species that grows faster than its neighbors will use a disproportionate share of the available resources, to the detriment of its neighbors. Several studies have shown that growth parameters related to plant size and leaf area are the best predictors of competitiveness in mixtures of plant species. Weeds often have more rapid root elongation and/or deeper, more extensive root systems than crops.
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2. Photosynthetic pathways: Basically referring to C3 vs C4 plants. C4 plants are generally considered to be more efficient at “fixing” carbon. C4 plants have a higher temperature optimum for photosynthesis, a higher light optimum for photosynthesis, higher photosynthesis rates per unit leaf area, higher growth rates under optimum conditions for photosynthesis, and greater dry matter production per unit of water used. Most of the world’s flora (> 99%) are C3 plants. However, the C4 pathway is well represented in agricultural weeds; many of the world’s worse weeds are C4 plants. C4 photosynthesis does not confer an intrinsic advantage to the plant in competition with a C3 species; rather the advantage depends heavily upon environmental conditions. In
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