Among other hormone herbicides available, picloram has been found to be
extremely effective in killing trees and is probably the most persistent and most
active of the herbicides. In contrast with most other pesticides, the hormonal
herbicides have a very low toxicity to animals because of their specific effect on
plant metabolism. This is also apparently true for the nonhormone substituted ureas
and triazines that act by inhibiting the photolysis step in photosynthesis. Of this
group atrazine and simazine have been widely used for massive weed killing programs, and are unusually nontoxic toward corn crops and slightly to moderately
toxic to humans.
A widely used herbicide is glyphosate. It operates by interfering with key plant
enzymes. Since introduction in the 1970s, its use has increased significantly for both
home and agriculture.
Among nuisance plants, one must mention again the fungi, but this time as agents
that produce tremendous damage to wood and wood products. In general, damage
can be lessened through various treatments. Polymerizing chemicals applied to
lumber reduce porosity and water adsorption and mimic the lignification process
in nature. Heartwood, which is more widely lignified, is more resistant to fungal
attack than sapwood. Lumber can also be treated by pressurized or brush application
of various fungicides.
Most preservatives have been developed to be applied in an oil base to facilitate
penetration and prevent warping. There are various wood preservatives of low
volatile organic compounds (VOCs) content and toxicity, and are water based or
whey based that have undergone USEPA registration. For outdoor and commercial
purposes only, creosote, which is a crude mixture of aromatic hydrocarbons, is
permitted for railroad ties away from drinking water sources. Creosote has no
registered residential uses. Pentachlorophenol is a restricted use pesticide that is
only used for commercial purposes such as utility poles, railroad ties, and wharf
piling.
Wood preservatives containing chromated arsenicals include preservatives
containing chromium, copper, and arsenic (i.e., CCA treatments). Effective
December 31, 2003, chromated arsenical manufacturers voluntarily canceled virtually all residential uses of CCA, and wood products treated with CCA are no longer
used in most residential settings, including decks and children’s playsets. Newer
arsenic-free options rely on copper as their primary biocide.
7.2 Aquatic Plants
Aquatic plants are valuable as food and shelter for aquatic animals. Floating or
emergent vegetation is rarely desirable, however, when the body of water is used for
recreation. Excessive algal growths severely restrict the use of the water for drinking,
cooling, or recreation. They compete with the aquatic fauna for oxygen during low
light intensity and, upon death, products of their decomposition produce objectionable tastes and odors in the water.
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extremely effective in killing trees and is probably the most persistent and most
active of the herbicides. In contrast with most other pesticides, the hormonal
herbicides have a very low toxicity to animals because of their specific effect on
plant metabolism. This is also apparently true for the nonhormone substituted ureas
and triazines that act by inhibiting the photolysis step in photosynthesis. Of this
group atrazine and simazine have been widely used for massive weed killing programs, and are unusually nontoxic toward corn crops and slightly to moderately
toxic to humans.
A widely used herbicide is glyphosate. It operates by interfering with key plant
enzymes. Since introduction in the 1970s, its use has increased significantly for both
home and agriculture.
Among nuisance plants, one must mention again the fungi, but this time as agents
that produce tremendous damage to wood and wood products. In general, damage
can be lessened through various treatments. Polymerizing chemicals applied to
lumber reduce porosity and water adsorption and mimic the lignification process
in nature. Heartwood, which is more widely lignified, is more resistant to fungal
attack than sapwood. Lumber can also be treated by pressurized or brush application
of various fungicides.
Most preservatives have been developed to be applied in an oil base to facilitate
penetration and prevent warping. There are various wood preservatives of low
volatile organic compounds (VOCs) content and toxicity, and are water based or
whey based that have undergone USEPA registration. For outdoor and commercial
purposes only, creosote, which is a crude mixture of aromatic hydrocarbons, is
permitted for railroad ties away from drinking water sources. Creosote has no
registered residential uses. Pentachlorophenol is a restricted use pesticide that is
only used for commercial purposes such as utility poles, railroad ties, and wharf
piling.
Wood preservatives containing chromated arsenicals include preservatives
containing chromium, copper, and arsenic (i.e., CCA treatments). Effective
December 31, 2003, chromated arsenical manufacturers voluntarily canceled virtually all residential uses of CCA, and wood products treated with CCA are no longer
used in most residential settings, including decks and children’s playsets. Newer
arsenic-free options rely on copper as their primary biocide.
7.2 Aquatic Plants
Aquatic plants are valuable as food and shelter for aquatic animals. Floating or
emergent vegetation is rarely desirable, however, when the body of water is used for
recreation. Excessive algal growths severely restrict the use of the water for drinking,
cooling, or recreation. They compete with the aquatic fauna for oxygen during low
light intensity and, upon death, products of their decomposition produce objectionable tastes and odors in the water.
402
L. S. Clesceri and E. J. Clesceri