Introduction
Many grass weeds are considered
among the most troublesome weeds allover the world. They cause - in heavy infestation
- great losses of crop yield. Chemical control is widely practiced to get rid
of these noxious pests. However, in many situations, a herbicide resistance
evolved with its drawbacks in herbicide activity. Wild oat (Avena fatua L.), an
annual erect grass in fields and orchards, exists in Mediterranean, Africa,
Europe, Asia, North and South America (Boulos and el-Hadidi, 1984), is one of
outstanding examples of this phenomena. This weed grows as a weed throughout
most wheat (Triticum aestivum L.) growing regions of the world (Thurston
and Phillipson, 1976). In Egypt, it can be found in wheat fields, representing
the dominant grass weed, and can be noticed easily in wheat fields, especially
in late season, with its long culm and characteristic panicle.
Control measures being taken for
this weed include mechanical and chemical control. Hand control is usually
practiced in developing countries in the early season but facing some
difficulties concerning distinguishing the plant from wheat plants and
threatening the crop through walking inside the field, therefore, chemical
control is usually recommended.
In Egypt, the herbicide benzoylprop-ethyl (Suffix) is
recommended for wild oat control at the rate of 1.25 lit./feddan as overall
application at 4-5 wheat’s seedling stage. In addition, the herbicides fenoxaprop-ethyl (Puma) an clodinafop (Topik) are also recommended in Egypt for the
control of Italian ryegrass
(Lolium multiflorum) (Ministry of Agriculture, Egypt, 2001). All these
herbicides are belonging to the chemical group aryloxyphenoxy-propanoate (APP)
of which different herbicides are commonly used, beside others of
cyclohexanedione (CHD) group for the control of wild oat allover the world
(Devine and Shimabukuro, 1994).
Different reports have been
published in the last two decades concerning herbicide resistance in weeds
including wild oat. This presentation sheds some light on herbicide resistance
in grass weeds especially toward the two commonly used herbicide groups against
these weeds, i.e. APP and CHD herbicides. It includes the following:
1.
Herbicide resistance in
weeds with focus on grass weeds especially wild oat.
2.
APP and CHD herbicides:
a.
. Chemistry and mode of
action.
b.
. Mechanisms endowing
selectivity in resistant species.
c.
. Evolution and
development of resistance.
d.
. Mechanism of
resistance in weeds.
3.
Detecting herbicide
resistance.
4.
The cost of herbicide
resistance.
5.
Management of resistant
populations.
a.
. Guideline to the
management of herbicide resistance.
b.
. The situation in
Egypt.
6.
Important figures
dealing with herbicide resistance.
7.
Classification of
herbicides according to mode of action.
8.
Herbicide Resistance
Action Committee (HRAC).
9.
Photos of wild oat
infestation in Assiut area.