Agriculture Reference
In-Depth Information
e.
Benzonitrile Herbicides
Dichlobenil, bromoxynil, and ioxynil are contact herbicides used to con-
trol hard-to-kill weeds.
Mode of Action
The modes of action of this group are not similar. Dichlobenil is applied
to the soil as granules and prevents the germination of annual weeds and shoot
growth in perennials. Bromoxynil and ioxynil induce foliar chlorosis and ne-
crosis. The degradation products of these herbicides also inhibit other complex
cellular processes, and their precise modes of action are unknown.
Table 5.13
Commercial products containing benzonitriles.
Active Ingredients
Trade Names
Dichlobenil
Barrier, Casoron, Dyclomec, Norosac
Bromoxynil
Bromotril, Buctril, Certrol, Combine Emblem, Koril, Korilene,
Merit, Pardner, Sabre, Sanoxynil
Ioxynil
Not available in the U.S.
f.
Chlorophenoxy Herbicides
These herbicides are highly selective for broadleaved weeds. 2,4-D was
the first chlorophenoxy acid herbicide developed. There are several compounds
that belong to this group in addition to 2,4-D and they include 2,4-DB, Di-
chlorprop, MPCA, MPCB, MCPP, 2,4,5-T, and 2,4,5-TP (Silvex).
Mode of Action
These herbicides cause auxin-like responses (hormone-induced growth) in
broadleaf plants. They cause rapid cell division, resulting in unusual growth,
activated phosphate metabolism, and increased RNA and protein synthesis.
The mode of action thus appears to consist of a large number of structural and
biochemical reactions causing prolonged abnormal growth and the failure of
the plant to undergo changes characteristic of maturity and senescence.
Typical symptoms of the action of growth regulators manifest themselves
as crookedness, deformation, leaf or stem malformations, and adventitious root
formation. Increased distension as well as signs of wilting can appear. The
weed's growth is arrested, and it dies as a result of generalized damage. The
extent and length of time within which these effects occur are dependent on the
type of plant, the dose adsorbed, and also on environmental conditions.
Commercial Products
Several hundred commercial products contain chlorophenoxy herbicides in
various forms, concentrations, and combinations. Following are names of
