Environmental Engineering Reference
In-Depth Information
plant species. Herbicides can be “contact” or “systemic” (Table 17.2). Contact herbicides act imme-
diately on the tissues contacted but do not affect the areas not contacted, such as root crowns, roots,
or rhizomes. Systemic herbicides are translocated throughout the plant, causing the mortality of the
entire plant. Herbicides can also be broad spectrum or selective. Examples of use recommendations
for these herbicides are provided in Table 17.3.
17.5.7 b IoLoGIcaL c ontroLS
Biological controls usually focus on plant-eating organisms, such as the grass carp. In addition,
varieties of organisms have been introduced that impact the growth or reproduction of speciic nox-
ious host plants. The goal, of course, is to identify biological controls that are economical, relative,
for example, to mechanical or chemical controls, that provide long-term beneits, and are targeted at
speciic noxious plants, while not harming native species. The goal, typically, of biological controls
is not to eradicate the noxious species, but to obtain a dynamic equilibrium between the control and
the plant, at an acceptable level of plant biomass (Cooke et al. 2005). Some examples of biocontrols
are briely introduced in the following sections.
17.5.7.1 Triploid Grass Carp ( Ctenopharyngodon idella )
Grass carp, also called white amur, are plant-eating ish native to Asia and were introduced into the
United States to control aquatic vegetation. They were irst introduced in 1963 to aquaculture facili-
ties in Auburn, Alabama, and Stuttgart, Arkansas. They may grow rapidly, reaching weights of up
to 80-100 pounds, and they may eat up to three times their body weight per day, with submerged
plants such as hydrilla typically being their preferred food (Chilton 2004).
The grass carp introduced to control vegetation are most commonly triploid grass carp, which
are sterile, so the goal is, typically, to introduce only sterile carp to a conined area (e.g., lakes with
no or a controlled inlet or outlet) so they may not escape and ensure that they do not reproduce.
TABLE 17.2
Examples of Approved Herbicides
Half-Life in Water
(Aerobic
Conditions) (Days)
Compound
Formulation
Mode of Action
Contact
Diquat
Liquid
1-7
Disrupts plant-cell membrane integrity
Endothall
Liquid or granular
4-7
Inactivates plant protein synthesis
Systemic
2,4-D
BEE salt
DMA liquid
7-48
Selective plant-growth regulator
Fluridone
Liquid or granular
20-90
Disrupts carotenoid synthesis
Glyphosate
Liquid
14 days; used over but
not in water
Disrupts synthesis of amino acids
Triclopyr
Liquid
1-10
Selective plant-growth regulator
Source: Data from Getsinger, K.D., Poovey, A.G., Glomski, L., Slade, J.G., and Richardson, R.J., Utilization
of herbicide concentration/exposure time relationships for controlling submersed invasive plants on
Lake Gaston, Virginia/North Carolina, U.S. Army Corps of Engineers, Aquatic Plant Control Research
Program, Vicksburg, MS, 2011; Cooke, G.D., Welch, E.B., Peterson, S.A., and Nichols, S.A.,
Restoration and Management of Lakes and Reservoirs , 3rd ed., CRC Press, New York, 2005.
 
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