Environmental Engineering Reference
In-Depth Information
Dormancy
Above-ground
growth
Above-ground
senescence
Flowering
Spring
Summer
Fall
Winter
Time of year
Fig. 9.1
Seasonal progression of stored carbohydrates in roots and below-
ground shoots of perennial plants. Reproduced with permission from Holt J.S.
and Radosevich S.R. (1989). Plants. In California Weed Conference (ed.)
Principles of Weed Control in California
, p. 20. Thomson Publications, Fresno, CA.
carbohydrate storage and in direction of carbohydrate translocation can determine
whether a control method will be successful. For example, shoot removal from a
perennial plant in spring using physical or chemical means is unlikely to kill the
plant since the majority of carbohydrates are being mobilized upwards to produce
new shoots at that time (Fig. 9.1).
Plants are also classifi ed in terms of undesirability. Legally, a noxious weed is
any plant designated by a Federal, State, or County government as injurious to
public health, agriculture, recreation, wildlife, or property (Sheley
et al
. 1999;
Radosevich
et al
. 2007). Many states, provinces and countries maintain at least one
o
cial list of such weeds so that their introduction can be prevented or restricted.
Noxious weeds usually create a particularly undesirable condition in crops, forest
plantations, grazed rangeland, or pastures. h erefore, both the identity and legal
status of a particular species should be considered when developing a management
programme.
Plants are characterized by growth and development from regions of cell division
(meristems) located at the apices of shoots and roots, which result in a repetitive
modular structure in the plant body. A unique feature of the plant body is roots
and, in many cases, reproductive structures (such as rhizomes, tubers, etc.) below
ground, which possess vegetative buds that can develop into new plants. Even
shoots can develop roots adventitiously in response to various environmental cues
