Horticulture Principles and Practices

occurs in nutsedges and johnsongrass. They are relatively less toxic than inorganic chemicals
and are salts of arsenic and arsenic acid derivatives.
Phenoxy Herbicides Phenoxy herbicides are also referred to as hormone weed
killers. One of the most common phenoxy herbicides is 2,4-D. Another is 2,4,5-
trichlorophenoxy acetic acid, which is used in the control of woody perennials and is associated
with the Agent Orange episode in Vietnam, where it was used to defoliate large
forest areas. The latter has been banned by the EPA.
Diphenyl Ethers
An example is Fusilade.
Substituted Amide These herbicides are readily biodegradable by plants and in the
soil. An example is Diphenamid.
Substituted Ureas Selective preemergence herbicides, substituted ureas have strong
residual effects in the soil. An example is Siduron.
Carbamates This class of herbicides is formulated generally for preemergence
application. An example is EPTC.
Triazines An example of this class of herbicides is Simazine. It is used in driveways
and around patios.
Aliphatic Acids
An example is Dalapon, used to control grasses.
Arylaliphatic Acid
An example is DCPA.
Substituted Nitriles These herbicides are fast acting and also have broad action. An
example is Dichlobenial.
Bipyridyliums
Examples are diquat and paraquat, called contact herbicides.
Inorganic Herbicides
Inorganic herbicides have great residual effects and thus are strictly regulated by the
EPA. They are not recommended for use around the house.
8.13 FORMULATIONS
Herbicides are formulated to be applied as either liquids or granules.
8.13.1 LIQUIDS
Liquid formulations are applied as either wettable powders or water-dispersible granules in
water. Most herbicides are applied as sprays, making the sprayer the most important implement
in herbicide application. Sprayers come in a variety of designs and may be hand or
power operated. Sprayers may be mounted on trucks or tractors. Sprayer application may also
be at low volume (high herbicide concentration delivered in small amounts per unit area) or
high volume (low concentration of a herbicide applied in large amounts per unit area).
8.13.2 GRANULES
When granules are used, they may be applied at low or high rates. When applying at low
rates (small amounts of granules), a carrier material such as sand may be mixed with the
granules to increase the bulk for more effective and uniform application. Granular formulations
are more expensive than others because of the bulk and shipping costs.
272 Chapter 8 Principles and Methods of Disease and Pest Control