Growers asked to join the fight against late blight

Whether you grow potatoes and tomatoes in your garden or commercially, don’t give late blight a chance

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Potato and tomato growers are being asked to help the effort to restore Alberta’s status of being free of late blight.

“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,” said Robert Spencer, commercial horticulture specialist with Alberta Agriculture and Forestry.

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Late blight was largely responsible for the Irish Potato Famine in the 1840s, which resulted in the death and mass emigration of millions of people. Each year, late blight reduces the yields of potatoes and tomatoes in the field and can cause major losses in potato tubers in storage.

Monitoring of spore levels found increases in some regions, but no cases of late blight had been confirmed in Alberta as of late August.

However, it is recommended all potato or tomato growers — both commercial operations and home gardeners — take steps to reduce the threat of the disease overwintering. This includes ensuring plants die down quickly by using a desiccant (diquat) or mechanical treatments and then disposing of stems and foliage, either by burial, freezing, or composting, said Spencer.

“Avoid placing infected materials in uncovered compost piles as spores may be produced and spread the disease to nearby plantings of susceptible crops,” said Spencer. “Piles may be covered with a tarp until the materials have frozen and are completely dead.”

Potato tubers are most likely to harbour the disease and so should be carefully graded to remove infected tubers.

“Commercial seed growers should be prepared to further grade seed tubers in the spring, and mancozeb-based seed treatments should be applied to try and protect developing crops from seed-borne late blight,” said Spencer.

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.

“The late blight pathogen normally cannot survive away from living tissues,” said Spencer. “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 reinfection 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 buildup 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 reinfection that they will face for the next growing season,” said Spencer. “Determine where disease might have come from and put preventive measures in place to protect against infection. It is in everyone’s best interest to manage late blight, as this is a community disease.”

For more information, search for ‘late blight’ at agriculture.alberta.ca.

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