Spring weather in 2018 was favorable for late blight development. Be sure you are taking steps to protect your potato crop.

The spring weather experienced in southern Idaho was optimum for the development of late blight. With no late blight reported in the state in 2017, it is not likely that cull piles or volunteers would be a source of an epidemic in 2018. However, it is possible that late blight could be brought in on infected seed. The early season weather was favorable for the late blight organism to get established and spread.

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:

  • $1·         The center span of pivots
  • $1·         Areas of irrigation overlap
  • $1·         Along mainlines where water leaks
  • $1·         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 rates.

I have recommended that growers begin fungicide programs just prior to row closure and continue on a two-week interval. I have also recommended that a protectant fungicide always be included in the tank mix. These protectant fungicides are active against the late blight pathogen and will provide protection if applied preventatively. Protective fungicides include those based on chlorothalonil (e.g. Bravo, Echo, etc.) and EBDC (e.g. Dithane, Penncozeb, Koverall, etc.) For the time being, this approach should be effective. If the weather changes or if blight is found, then the recommendations may change.

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.