Late blight has been confirmed in Minidoka County. It is critical for growers to manage the potato crop for late blight until the tubers are in the storage.

The spring weather experienced in southern Idaho in 2019 was optimal for the development of late blight. Late blight was confirmed in southwestern Minidoka County on August 19. If thundershowers come through the area, there is a risk of the pathogen spreading to a much wider area.

Growers and consultants need to be thorough in scouting. Areas which remain wet for long periods of time should be monitored regularly. These areas include:

  • The center span of pivots
  • Areas of irrigation overlap
  • Along mainlines where water leaks
  • The western side of tree or hedgerows where shadows allow for longer morning dew periods.

It is also important to scout in areas where fungicide coverage may not be optimal. Small field extensions and areas near houses may be missed or receive lower fungicide rates.

Luna Tranquility and Endura are two fungicides commonly used to manage early blight and white mold. These fungicides do not have activity against late blight. This is one reason I recommend tank-mixing a protectant fungicide with these products whenever they are applied. A second reason is that the inclusion of the protectant will help manage the development of fungicide resistance in the early blight pathogen population.

See the attached article for a more in-depth discussion of the various fungicides labeled for managing late blight, and how these fungicides work against other diseases.