Features Agronomy Diseases
Alberta potatoes at risk of late blight

Photo is courtesy of Khalil Al-Mughrabi.

May 14, 2014, Alberta – Over the last few years, there has been a great deal of concern in Alberta surrounding late blight, which is a serious disease that affects potatoes. This year appears to be no different.

“This disease is caused by a fungal pathogen called Phytophthora infestans,” says Robert Spencer, commercial horticulture specialist, Alberta Ag-Info Centre, Stettler. “The favourable conditions for disease development, combined with the presence of the pathogen, have resulted in multiple outbreaks of late blight in commercial, market garden and urban potato and tomato crops throughout parts of Alberta. For 2014, this disease continues to be a risk for all solanaceous crops (potato/tomato family) grown in Alberta.”

When the pathogen is present and weather conditions are favourable for disease development, commercial potato and market garden crops are at risk from late blight, as are all other plantings of potatoes and tomatoes, including greenhouse tomato operations. The risk of introduction comes from either infected transplant material (tomatoes or other host crops) or infected seed potato stock (either imported or carried over). During the season, if spore loads build up, there is a risk of introduction of the pathogen via wind-blown/storm carried transfer.

Potato tubers may be infected by spores produced on the foliage which are subsequently washed into the soil. Infected tubers may have irregular, sunken lesions that are often first found around the eyes. The pathogen can penetrate into skin of the fruit or tubers, causing rot and discolouration of the internal tissues. The rot often has a reddish-brown colour. Late blight can spread from diseased to healthy tubers in potato piles in storage and on seed potato pieces.

On the Prairies, late blight does not form an overwintering spore. Rather, the pathogen overwinters on living tissues, carrying forward from one season to another on infected seed potatoes, cull piles or volunteer potatoes.

In-season spread is by spores (sporangia) produced on infected tissues (infected transplants, volunteers, weeds and diseased crop debris). Spores spread within the fields by rain or water splash. Sporangia may also move short distances in soil water and spores may move between fields on equipment. Spores can move considerable distances on the wind.

“In early spring and into summer, the priority is for regular scouting and monitoring of emerging plants, and new plant material,” says Spencer. “Early detection is critical for minimizing the impact of the disease and preventing further spread and significant outbreaks.”

For more information, go to Alberta Agriculture’s Late Blight of Potatoes and Tomatoes - Frequently Asked Questions or call 310-FARM (3276).

May 15, 2014  By Alberta Agriculture and Rural Development