Integrated chemical pest management

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Reliance solely on fungicides, bactericides or viricides for control of pathogens often results in unforeseen problems such as build up of chemical-tolerant or resistant races of the pathogen and displacement of one pathogen by another. Often expectations for the efficacy of chemicals are too high. Chemicals should therefore be used with caution and lowered expectations. Once a disease has appeared on a plant it is difficult to eradicate. To get the best from chemicals, they should be applied as part of an integrated disease management strategy. Routine spray programs should only be used when for example seed or propagation materials are known to be infected. Areas that are historically at risk should also be routinely protected rather than utilizing a non-planned emergency program after the appearance of symptoms of an expected disease. It is easier to prevent disease than to cure disease on plants. To help predict when diseases infect, it is useful to have prior knowledge of the conditions that enhance infection periods.

For example, if leaf wetness is persistent or there are extended periods (14-24 hours) of relative humidity greater than 90 percent, it would be prudent to apply a protectant fungicide to known susceptible species. During extensive dry and low humidity periods it would not be necessary to apply protectant chemicals frequently; however in Michigan a minimal protectant chemical barrier on susceptible species should be maintained. On species not known to be susceptible to diseases, routine spray programs should be discontinued and pesticides applied only when needed.

The farm or nursery should be well mapped to document plant locations. Susceptible species should be highlighted on maps and inspected regularly. A record of symptoms should be kept and correlated with weather records to determine if the appearance of irregularities is associated with abiotic conditions. Specific pest problems should be identified to determine appropriate control options. Determine if there are action thresholds based on acceptable levels of disease to decide when to treat. Not all diseases are lethal and some may cause only temporary blemishes which may be tolerable. If it is decided that chemical control is warranted always use the appropriate chemical for the species and disease and always read the label and always use chemicals in compliance with the safety recommendations. Consider using biopesticides or softer pesticides that are less toxic to the environment, e.g., horticultural oils or soaps. However, be careful with methylated oils as they can cause cuticle disruptions and allow further infections to occur.
When conditions are less conducive for disease development, reliance on chemical control may be reduced. These conditions can be manipulated and their impact minimized by reducing plant exposure to high risk environments e.g. avoiding early planting into cool wet soil, avoiding late fall harvest when plants are again exposed to a cool wet climate, avoiding inappropriate irrigation which can increase soil moisture, extend duration of leaf wetness and canopy humidity.

In summary:

  • Start with clean seed/stock and appropriate rotation.
  • Plan a preventative spray program.
  • Initiate a timely program with the use of seed treatments where appropriate.
  • Spray programs with a mixtures of fungicides with different modes of action.
  • Scout fields for pest occurrence.
  • Follow guidelines on maximum usage of high resistance risk fungicides.
  • Minimize exposure to high risk environments, e.g., early planting, late fall harvest, unnecessary or over/under irrigation.

Dr. Kirk's work is funded in part by MSU's AgBioResearch.

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