Weed Science, PLS 4601c Section 7644
and Grad. – Prin. Of Weed Science AGR 6932 Section 9212
University of Florida - Davie
Philip Busey, firstname.lastname@example.org
May 14, 2009
Weed Science – Learning Concepts
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
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.
Weeds provide benefits
Dooryard weeds are useful potherbs and provide vitamins and minerals.
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.
weeds such as Madagascar periwinkle provide beneficial drugs.
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
Most of the weed losses are in row crops but the burden of weed