Last week’s column described how pesticide resistance develops. Today describes how it can be prevented and next week how to manage it once it occurs. But first a brief review of how this problem arises. For more detail see last week’s column.
Whether a pesticide or an antibiotic, the chemistry affecting the target organism has a mode of action (the way it attacks the organism). Genetic variation of the pest population means susceptibility to the pesticide is not uniform and some small number are either less susceptible or immune to the chemistry. If the same mode of action is used over a period of time and not in combination with other modes of action, the susceptible individuals are eliminated, don’t reproduce, and their genes eliminated while the few resistant or immune individuals reproduce and their genetics win out – they are selected for. First, how can producers stop resistance from developing?  Remember the term pest refers to weeds, insects and diseases.
• Perhaps the single most important tool is the development of as diverse a crop rotation as practical integrating both grass and broadleaf crops. This is especially true as tillage is eliminated since it disrupts the habitat for pests.  It also allows more pesticide options.
• As important as the previous point is to read and follow the label. Don’t skimp on rates of pesticide, carrier, or adjuvant. Careful reading of the label with all its ifs, ands, and buts insures the greatest chance of successful pest control.
• Where monoculture or severely restricted rotations are necessary, manage the residue to eliminate habitat through tillage or burning. If not using conservation tillage, control pests through tillage. This isn’t a preferred option but may be necessary under certain circumstances.
• Use of weed free seed and if fields have resistant pests manage fields free of resistant pests first and eliminate possible sources of contamination through proper sanitation of equipment between fields.
• Rotate pesticide modes of action. By targeting different aspects of a pest’s physiology it is less likely for resistant individuals to survive. While there are literally hundreds of pesticides out there by various companies, it can be very difficult to figure out if modes of action are different.
• If not using conservation tillage, eliminate residue and pests as soon as possible through tillage. Again this isn’t the best or preferred option.
• Maintain the pool of susceptible individuals in the population through refuges so they can reproduce with resistant individuals.
• Eliminate pests at their most susceptible stage. Pests are typically must vulnerable when very young and the ability to control them decreases as they mature. Also make sure they are controlled before they can reproduce.
• Monitor pests for both species and the possible development of resistance.
• Keep right-of-ways, buffer strips, and ditches as free of pests as possible.
• Pesticide manufacturers are also combining modes of action either through product formulations or through tank mixes. Price often determines which producers use.
Next week, managing resistance once you have it.