Agriculture Reference
In-Depth Information
Figure 1.3 Relationship between the number ofsulfonylurea herbicide
applications made to individual fields and the percentage of Lolium rigidum
populations with detectable resistance to sulfonylurea compounds.Plant
collections were made in Western Australia in 1992 and 1993.(After Gill,1995.)
(Warwick, 1991; Holt, 1992). Since that time, however, herbicide resistance
has been reported for 145 weed species in 45 countries throughout the world
(Heap, 1999). Herbicide resistance is appearing in additional weed species at a
rate equal to that observed for insecticide and acaricide resistance in arthro-
pod pests (Holt & LeBaron,1990),and weed biotypes now exist with resistance
to one or more herbicides in at least 16 different chemical classes, including
the arsenical, aryloxyphenoxyproprionate, benzonitrile, bipyridilium,
chloroacetamide, cyclohexanedione, dinitroaniline, dithiocarbamate, imida-
zolinone, phenoxy, substituted urea, sulfonylurea, triazine, and uracil com-
pounds (Heap, 1999).
Under field conditions in which the same herbicide or chemical class of
herbicides is applied repeatedly,herbicide resistance may evolve in four to five
years (Holt, 1992). As shown in Figure 1.3, resistance to sulfonylurea herbi-
cides was detected in all populations of the grass weed Lolium rigidum collected
from Western Australia wheat fields that had been treated with those com-
pounds only four times (Gill, 1995). Evolved resistance to glyphosate, which
was thought unlikely to occur,was reported in 1998 for a L.rigidum population
collected from an Australian orchard that had been treated with glyphosate
two or three times a year for 15 years (Powles et al ., 1998).
Suggested strategies for preventing or delaying the evolution of herbicide
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