Every potato grower understands the challenge of controlling fungal diseases. Although fungicide applications are the most effective strategy for disease management, the rise of fungicide resistance poses a significant risk to efficacy.
Growers are often unaware they have a fungicide resistance issue until devastating diseases, such as alternaria brown spot, early blight, late blight, powdery mildew, white mold and pink rot, have caused substantial and irreversible damage to their crops. To protect potato health and maximize yield, growers should consider implementing proactive strategies to address fungicide resistance.
Understanding Fungicide Resistance
Fungicide resistance, as defined by the Fungicide Resistance Action Committee (FRAC), is an acquired reduction in sensitivity of fungi to specific fungicides. The key challenge is the genetic variability of fungal populations, which leads to fungicide resistance in certain fungi within the population.
Spotting the Signs
Fungicide resistance is generally not found until there is an issue in the crop, but staying alert during the growing season can help potato growers spot signs of resistance. Avoid repeated use of fungicides from the same FRAC group, talk with neighbors about their treatment outcomes for different diseases and stay informed on resistant strains to avoid ineffective treatments.
Effects on Potato Growers
It is well known that the late blight pathogen (Phytophthora infestans), in favorable weather conditions, can destroy potato leaves in 10 to 15 days and reduce yield from 50 to 70 percent.(1) With such a narrow window for disease detection and intervention, implementing a proactive plan at the beginning of the growing season becomes crucial. The effective control of late blight is often achieved by integrating partially resistant potato varieties with fungicide applications. However, late blight resistance to commonly used fungicides has been a major concern to its successful management.
Studies also show that early blight and brown leaf spot are becoming major disease threats to potato production due to their growing resistance to fungicides. In a study with isolates collected from the field, 63 percent showed resistance to various fungicides with multiple modes of action.(2)
Potato growers should implement a proactive plan at the beginning of the growing season to help prevent resistance.
Best Management Practices
To combat fungicide resistance, consider these best management practices:
- Rotate fungicides with different FRAC groups to reduce the selection pressure on the fungi population.
- Scout fields daily for signs of disease development.
- Implement integrated disease management strategies.
- Apply the recommended label rates with adequate coverage.
- Apply fungicides preventively — prior to disease development.
- Select varieties with resistance to common potato diseases.
Defending potato fields from fungicide resistance starts with informed decisions and proactive strategies.
For more information, visit Corteva.us/FungicideResistance.
(1) Sedláková, V., et al 2011. Effect of Phytophthora infestans on potato yield in dependence on variety characteristics and fungicide control. https://pse.agriculturejournals.cz/pdfs/pse/2011/10/07.pdf
(2) Fairchild, K. L., Miles, T. D., and Wharton, P. S. 2013. Assessing fungicide resistance in populations of Alternaria in Idaho potato fields. https://doi.org/10.1016/j.cropro.2013.03.003