learning_concepts - Weed Science PLS 4601c Section 7644 and...

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Weed Science, PLS 4601c Section 7644 and Grad. – Prin. Of Weed Science AGR 6932 Section 9212 University of Florida - Davie http://grove.ufl.edu/~turf/weedscience/ Philip Busey, [email protected] 954-579-3932 (cell) May 14, 2009 Weed Science – Learning Concepts A. Introduction 1. There is a useful biological definition of “weed” A weed is a plant that is adapted to disturbed habitats. Weeds occur in nature as first stage colonists after cataclysms such as earthquakes and landslides, they invade dung patties and grow along cattle paths, and they follow the trail of human settlement and disturbance. A commonly used definition, “a weed is a plant that is not desired,” does nothing to advance scientific understanding. The official Weed Science Society of America (WSSA) definition of a weed is unclear, “a plant originating under natural conditions and in response to imposed environments that interferes with human activity.” What is an imposed environment? How do invasive exotic in natural areas interfere with human activity? As weeds continue to evolve under selection pressure for reproduction in disturbed habitats, particularly farmers’ fields, it is likely that weeds will originate under the artificial conditions imposed by people. 2. Weeds provide benefits Dooryard weeds are useful potherbs and provide vitamins and minerals. Weeds are sometimes progenitors or sister ecotypes of useful cultivated species, and weeds provide reservoirs of genes for pest resistance in the crops. Many of the useful ground cover species including some turfgrass species are weeds or weedy. Other weeds such as Madagascar periwinkle provide beneficial drugs. 3. Weeds harm public health and safety, agriculture, and the environment Ragweed and other pollen producing species can be allergenic to humans, causing “hayfever,” and loss of work productive, rashes, and some are poisonous especially to children, pets, and animals raised for food. Crop yield losses, loss of quality, loss of harvest efficiency, difficulties in processing, and the cost of herbicides and other practices for reducing weed infestation account for billions of dollars per year in U.S. agriculture. Most of the weed losses are in row crops but the burden of weed
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Page 2 Weed Science–Univ. Florida, Davie–Learning Concepts control is great on human cultivators. Much of the expense of fertilizer goes to grow weeds and is unavailable to crops because the weeds are competing for fertilizer and other resources. Some weeds such as witchweed (Striga) have no chlorophyll and are obligate parasites often attached by haustoria; other weed parasites have chlorophyll. Weeds are nuisances that affect driver visibility; clog canals needed to prevent flooding and reduce damage. Weeds can have thorns and other structures to attach to people and their clothing, and be alternate hosts for plant disease organisms, such as the virus maize dwarf mosaic which can move from johnsongrass to maize. Weeds reduce property values and harm the environment.
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learning_concepts - Weed Science PLS 4601c Section 7644 and...

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