Herbicide resistance Subject

Problems and Model If the development of herbicide resistance continues, the lifespan of several herbicides will probably be shortened, leaving farmers to face several impossible weed control problems. Moreover, weeds resistant to herbicides are costly because alternative herbicides are not always available. In some cases, supplementary treatments must be applied in addition to the standard treatment that remains efficient for controlling numerous "ordinary" weeds. Of the 3 million hectares of corn grown in France, 1.2 million hectares are now subjected to a postemergence treatment (e.g., pyridate) specifically directed against triazine resistant weeds. Thus, this so-called "remedial treatment" is becoming a standard treatment that is carried out after the preemergence atrazine treatment. This creates a four-fold increase in the cost of weed control in these corn fields. 

ACC was extracted from hydroponically-grown susceptible and resistant biotypes of Lolium. The extracts were subjected to (NH)2S04 fractionation followed by gel filtration. The ATP-, acetyl Co-A- and protein- dependent incorporation of radioactivity from H14C03 into acid-stable products was monitored. The sensitivity of ACC from both biotypes to diclofop-methyl, diclofop-acid, fluazifop-acid, sethoxydim and tralkoxydim was similar (Table I). The small differences observed are unlikely to account for resistance at the whole plant level. ACC was not affected by either chlorsulfuron or trifluralin, two herbicides against which there is resistance but which have different modes of action. 

To date, detection and management of resistance has predominantly been carried out with bioassays. These are essentially based on comparative growth of seedlings or plants of suspected resistant and sensitive weed biotypes subjected to different herbicide treatments [51-53]. Such bioassays are simple, but do not differentiate between target site and metabolic resistance mechanisms. 

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