Introduction

• Weeds are plants that are unwanted in a given situation and may be harmful, dangerous or economically detrimental.
• According to Crafts and Robbins (1973), “Weeds are those plants which are out of place, unwanted, non-useful, often prolific and persistent, competitive, harmful, even poisonous which interfere with agricultural operation, increase labor, add to costs, reduce yields and detract from comforts of life”.
• The term ‘weed’ for the plants other than crop in the field, first time was given by Jethro Tull in his book ‘Horse Hoeing Husbandry’.
• Plants, that come up in any land, of a different kind from the sown or planted crop, are weeds (Jethro Tull, 1731).
• In other words, weeds are the plants, which grow where they are not wanted. In 1967 the Weed Science Society of America defined a weed as “a plant growing where it is not desired” (Buchholtz, 1967).
• In 1989 the Society’s definition was changed to define a weed as “any plant that is objectionable or interferes with the activities or welfare of man” (Humburg, 1989, p. 267; Vencill, 2002, p. 462).
• The European Weed Research Society defined a weed as “any plant or vegetation, excluding fungi, interfering with the objectives or requirements of people” (EWRS, 1986).
• Harlan and de Wet (1965) assembled several definitions to show the diversity of definitions of the same or similar plants (Zimdahl 2007). The array of definitions emphasizes the care weed scientists and vegetation managers must take in equating how something is defined with a right or privilege to control.