Agriculture Reference
In-Depth Information
Table 12.6
Classifi cation of herbicides commonly used in wheat production according to primary site of action.
Group
Site of Action
Chemical Family
Common Name
2 (B)
a
Inhibitors of acetolactate synthase (ALS), also called
acetohydroxyacid synthase (AHAS)
Imidazolinone
Imazamox
b
Sulfonylamino-carbonyltriazolinone
Flucarbazone-sodium
Propoxycarbazone
Sulfonylurea
Chlorsulfuron
Mesosulfuron
Metsulfuron
Prosulfuron
Sulfosulfuron
Thifensulfuron
Triasulfuron
Tribenuron
Triazolopyrimidine
Florasulam
Pyroxsulam
3 (K1)
Inhibitors of microtubule assembly
Dinitroaniline
Pendimethalin
Trifl uralin
4 (O)
Synthetic auxins
Phenoxy
2,4-D
MCPA
Benzoic acid
Dicamba
Carboxylic acid
Aminopyralid
Clopyralid
Fluroxypyr
Quinoline carboxylic acid
Quinclorac
6 (C3)
Inhibitors of photosynthesis at photosystem II site A
Nitrile
Bromoxynil
9 (G)
Inhibitor of 5-enolpyruvyl-shikimate-3-phosphate
synthase (ESPS)
None
Glyphosate
14 (E)
Inhibitors of protoporphyrinogen oxidase (Protox)
Triazinone
Carfentrazone-ethyl
27 (F2)
Inhibitors of 4-hydroxyphenyl-pyruvate-dioxygenase
(4-HPPD)
Pyrazole
Pyrosulfotole
Source:
Adapted from Mallory-Smith and Retzinger (2003).
a
Letter in parentheses is the classifi cation according to the international Herbicide Resistance Action Committee (Schmidt
1998).
b
Used in imazamox-resistant wheat cultivars only.
mixture strategy has the potential to increase her-
bicide load in the environment. Furthermore, the
cost of using more herbicide is immediate, while
the returns from delayed occurrence of herbicide
resistance will be realized in the future (Diggle et
al., 2003). A similar approach to population genet-
ics modeling has produced recommendations of
a judicious sequence of glyphosate followed
by paraquat (double knockdown) to decrease the
likelihood of glyphosate-resistance evolution
(Neve et al., 2003).
The development of imidazolinone-tolerant
wheat has provided producers with an effective
tool for the management of winter annual grass
weeds such as feral rye and jointed goatgrass,
which have been diffi cult to control in winter
wheat in the US and Canada (Geier et al., 2004).
The adoption of imidazolinone-tolerant wheat is
also increasing rapidly in southern Australia, pri-
marily for the control of rigid brome (
Bromus
rigidus
Roth). However, concerns arise about
imidazolinone residues affecting performance of
subsequent crops grown in the rotation. Further-
more, Group 2 herbicides have been repeatedly
shown to be prone to resistance development in
weeds and thus need to be integrated with other
herbicide groups and nonchemical methods of
weed control. It is possible that genetically modi-
fi ed wheat cultivars resistant to herbicides such as
glyphosate or glufosinate could become available
for production in the future. Considering the
high value of glyphosate to the wheat industry, it
