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Home > Protecting Our Lands & Waters > Best Management Practices > Timing of Pesticide Use: Before or After Infestation

Timing of Pesticide Use: Before or After Infestation


Pesticides are one of many tools available to us for effective protection of crops from weeds, insects and diseases. Pesticides require special care and handling. The following practices outline safe, responsible and effective procedures for pesticide use and handling that can help protect our environment, our water supplies - and ourselves.

Consider the following voluntary Best Management Practices (BMPs) when making pesticide application and handling decisions.

  • When planning pesticide use, both preventive and post-infection management can be used in appropriate situations.
  • Preventive pest management is defined as applying control measures before the type or level of pest infestation has become apparent. Example: Using soil-applied herbicides before weeds have emerged.
  • Post-infestation pest management is defined as applying control measures after the pest is apparent and can be assessed as to what it is and how much damage it can do. Example: Waiting for weeds to emerge, identifying the weed species and population present, assessing whether control is needed, and, if needed, choosing the most appropriate control.
  • The most appropriate control can be determined from available options once the pest has become apparent. Thresholds, when available, can be used to determine the need to apply control measures.

Preventive pest management is most appropriate for situations where...

  • High annual weed populations are known to exist. (Use pre-emergence or preplant-incorporated herbicides.)
  • Potential for high levels of an insect pest are known to exist. (Use soil-applied insecticides.)
  • Protecting the host plant prior to infection is desired when conditions are conducive for infection. (Use appropriate fungicides.)
  • Seed treatments are appropriate.

Post-infestation pest management is most appropriate for situations where...

  • Potential weed pressures are uncertain, and decisions can be made after weeds emerge. (Use post-emergence herbicide applications.)
  • High annual weed populations are known to exist, and decisions can be made after weeds emerge. (Use post-emergence herbicide applications.)
  • Insect pest and economic injury levels can be assessed prior to making application decisions. (Use appropriate insecticides.)
  • Fungi (plant diseases) can be controlled shortly after appearance. (Use appropriate fungicide.)

Minnesota Department of Agriculture • University of Minnesota Extension • USDA Natural Resources Conservation Service
Working cooperatively to balance pest management and water quality protection. October 2008


MDA Contact

Ron Struss
Ron.Struss@state.mn.us
651-201-6269
Pesticide & Fertilizer Management Division