IDENTIFICATION AND DOCUMENTATION OF HERBICIDE RESISTANCE

Proactive herbicide resistance management programs rely upon early det ection of resistant populations and knowledge of which combinations of weed and herbicide are prone to the development of resistance. Annual weeds that are prolific seed producers, genetically diverse, and repe atedly exposed to a single herbicide mode of action, are prone to rapi d development of resistance. When resistance is suspected, seed sample s are collected and evaluated using a whole plant bioassay. Whole plan t bioassays are conducted under field, growth room, or Petri dish cond itions. Complete dose response curves for the suspected resistant and a reference susceptible population are used to verify resistance. Bioa ssay, conducted in growth rooms, is the most reliable method for ident ification of new cases of herbicide resistance. Bioassays, based on th e biochemical detection of a single mechanism of resistance, are not r eliable for screening for new occurrences of resistance.