Similar to herbicide resistance, the development of fungicide resistance is a growing concern for U.S. farmers. Although currently less prevalent than herbicide resistance, fungicide resistance will develop if proper care is not taken to retain fungicide efficacy.

Implement these practices to keep fungicides effective and reduce the chance of developing fungicide resistance on your farm:

Scouting and Identification

Scouting before fungicide application allows for the correct timing of application at the correct growth stage. Even more than timing, proper identification of which diseases are present is imperative. Misidentification leads to improper fungicide recommendations and opens the door to resistant pathogens spreading.

Disease Development

Fungicides are most effective when applied just before or as disease symptoms begin to appear in soybeans. First, it is important to understand how environmental factors interact with hosts and pathogens to know if conditions are ripe for disease.

In order for a soybean disease to develop:

  • Environmental conditions must be favorable for disease development.
  • The plant must be a susceptible variety that isn’t completely resistant to a particular disease.
  • A bacterial, fungal or viral organism that can cause a disease is present in the host.

Cultural Practices

When managing soybean diseases, consider how nonchemical control methods diversify your ability to control diseases and reduce the need for fungicides. Planting disease-tolerant soybean varieties and rotating between non-host crops are two examples of effective, nonchemical control methods.

Economic Thresholds

Before you apply fungicide, confirm the disease you want to control threatens your crop yield. Only make applications if economic thresholds have been met and the risk of yield loss is greater than the cost of application. In order to make economically wise applications, understand the risk for disease development in your fields and use fungicides that have high efficacy ratings for pathogens that pose a threat to your soybean yield.


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