Environmental Engineering Reference
In-Depth Information
in wildlands is relatively recent by comparison. Herbicides
are organic, synthetic
chemicals used to kill or suppress unwanted vegetation. There are many advantages
to the use of herbicides as tools for weed control in agricultural and wildland eco-
systems, including control of weeds where other methods are diffi cult or imprac-
tical; reduction in the number of mechanical operations needed; reduction in the
amount of human effort and cost expended for hand and mechanical weeding; and
greater fl exibility in the choice of management systems (Ross and Lembi 1999;
Radosevich
et al
. 2007). There are potential problems associated with herbicide
use, however, including injury to non-target plants; residues in soil or water; tox-
icity to other non-target organisms; and concerns for human health and safety. The
increased legal and regulatory requirements for herbicide application and worker
safety are other concerns associated with the use of herbicides. In many cases, these
problems or disadvantages can be overcome by proper selection, storage, handling,
transportation, and application of the chemical (Vencill 2002).
If herbicides are found to be necessary or indicated, specifi c sites for application
should be identifi ed and the application should be restricted to specifi c plants or
stands. h e criteria for such site selection would be a quantifi able risk assessment
of weed impacts to desirable species and potential herbicide impacts to non-target
plants, animals, and their habitats. Adequate buff er zones should be allowed to
minimize herbicide drift, runoff , or leaching to riparian areas, waterways, or areas
of human habitation. Indigenous and recreational food sources in the vicinity of
the area to be treated should be avoided or alternatively, established residue toler-
ances should not be exceeded. Herbicides are only one type of tool available for
weed or invasive plant control and not all vegetation management problems can be
controlled eff ectively by chemical means.
Over the past several decades, concerns about the environmental and health haz-
ards of pesticides, soil erosion and degradation, and pest adaptation to control
methods, such as population shifts and pesticide resistance, have led to the devel-
opment of the concepts of integrated pest management (IPM) and integrated
weed management (IWM) as alternatives to sole reliance on pesticides (Kogan
1986, 1998). In contrast to using single weed control tools at the fi eld scale, IWM
uses multiple control tools at the fi eld, farm, landscape, or regional scale within the
context of a management system (Buhler
et al.
2000; Liebman 2001). IWM also
considers other organisms besides weeds, such as insects and other plants, to be
integral parts of the system that are not necessarily detrimental. These broader spa-
tial scales and higher complexity represent the levels at which impacts of invasive
species often occur. Perhaps because invasive plants often occur in proximity to
native species and/or in sensitive or endangered habitats, integrated programmes
in which chemical and mechanical control tools and tactics are used in conjunc-
tion with other approaches for vegetation management are particularly promising
for the management of invasive species (Hobbs and Humphries 1995; Sakai
et al
.
