Survival of the fittest – fighting fungicide resistance

The use of fungicides is an essential agronomic practice that is critical in ensuring healthy crops, protecting yields, and improving their quality. Like most living organisms, pathogens need to adapt to survive. Surviving control by fungicides is done through a process of mutation resulting in resistance against fungicides. To mitigate and manage the risk of resistance the Fungicide Resistance Action Committee (FRAC), an inter-company organisation affiliated with CropLife International, was established to define fungicide resistance prevention measures. This involves regular reviews of the status of resistance as well as defining testing procedures. In South Africa, a working group also exists under the auspices of CropLife South Africa. 

Resistance (also known as a shift in sensitivity) can develop against a particular mode of action of a fungicide and is attributed to the following scenarios:

• Repeated applications of a specific fungicidal mode of action.
• The rate of the fungicide used may influence risk. For example, sublethal dose rates can aggravate the risk.
• The population of pathogen exposed to the fungicide; if disease incidence is relatively low the occurrence and selection of possible resistant mutants are reduced.
• When a large area is treated uniformly and continuously with a specific fungicide it will pose a greater risk of resistance.
• The use of integrated disease management including the use of non-chemical methods, such as disease-resistant varieties, rotation of crops, or hygienic practices will lower the disease pressure and fungicide selection pressure.

How to avoid resistance

• Avoid sole use of a single mode of action fungicide.
• Alternate fungicidal modes of action.
• Stick to the approved rate, sub-lethal rates will aggravate resistance.
• Introduce cropping methods to reduce disease incidence which includes:
  • Disease tolerant varieties
  • Manipulating the crop environment (through pruning and improved airflow)
  • Optimising the crop health

The prevention of fungicide resistance is extremely important for the sustainability of your farming practice. By implementing the correct risk management strategies, you can safeguard your crops this season. 

For more information about this topic visit Bayer Crop Science’s website at www.cropscience.bayer.co.za.