End-of-Season Checklist for Managing Late Blight

  Hort Snacks - September 2018
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 In recent years, late blight has, at times, been confirmed in parts of Alberta and has then spread through various regions. With the intent of returning to late blight-free status, increased awareness efforts have been instituted in both the industry and the public. Everyone was encouraged to increase early and season-long monitoring of fields, gardens and greenhouses in order to protect crops from late blight, as well as have a quicker response to any perceived infections.

As the 2018 season wraps up, it seems like the hot and dry conditions that prevailed over much of Southern and Central Alberta throughout the summer appear to have helped keep late blight in check, as there were no samples submitted for testing. As always, it is recommended that all growers of potato or tomato (commercial or home garden) take specific steps to prevent the carryover of disease into future years, as a number of valuable crop industries in Alberta could be impacted by repeated outbreaks.

In the late parts of the growing season, ensure that plants die down quickly using top-killing treatments such as chemical desiccant (diquat) or mechanical treatments.

At the end of the growing season, gardeners should dispose of all above-ground plant materials (stems and foliage), whether infected or not, either by burial, freezing or composting. The purpose is to ensure that living tissues do not survive the winter and will break down completely, thus preventing carryover of the late blight pathogen. Avoid placing infected materials in uncovered compost piles as spores may be produced and spread the disease to nearby plantings of susceptible crops. Piles may be covered with a tarp until the materials have frozen and are completely dead.

Since tubers represent the primary method of disease carryover in potatoes in Alberta, every effort should be made to prevent the survival of infected tubers. Recognize that some of the recently prevalent strains of the late blight pathogen are more aggressive on tubers. Carefully grade and sort harvested potato tubers in an effort to remove any infected tubers. Commercial seed growers should be prepared to further grade seed tubers in the spring, and mancozeb-based seed treatments may be applied to try and protect developing crops from seed-borne late blight.

Culled tubers should be disposed of in such as way at to encourage them to breakdown over winter. Culled tubers can be fed to livestock or may be chopped, incorporated and buried, or can be placed in covered piles until they freeze completely. Ensure that potatoes do not volunteer (grow in another crop).

The late blight pathogen normally cannot survive away from living tissues. While the disease can survive for a time on tomato fruit, spores will not carry over on tomato seed. The disease can be introduced on living tomato transplants that are brought in from areas where late blight survives the winter.

In Alberta, the late blight pathogen does not survive or overwinter in the soil, so growers should not worry about re-infection by planting in or adjacent to a field where late blight has occurred, provided there are NO surviving tubers that could reintroduce the disease through infected volunteer plants. However, rotating between locations is always recommended, whenever possible, to prevent the build-up of other diseases.

All growers should take the time to assess the past growing season and the level of risk of late blight infection or re-infection that they will face for the next growing season. Determine where disease might have come from and put preventative measures in place to protect against infection. It is in EVERYONE’S best interest to manage late blight, as this is a community disease. It is also critical that everyone take an active role in submitting suspect material to improve detection and management.

If you have questions regarding identifying or dealing with late blight, or wish to submit a sample for testing, please contact 310-FARM (3276) for assistance. For more information on late blight, consult the following document – FAQ – Late Blight of Potatoes and Tomatoes.

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For more information about the content of this document, contact Robert Spencer.
This information published to the web on August 30, 2018.