Potatoes in Canada

News Diseases
Ontario disease pressure kept at bay

August 20, 2019
By Stephanie Gordon

Late blight on tuber.

Potato harvest in underway in Ontario, and while some diseases have been reported in fields, Ontario has been spared from outbreaks of late blight, according to Ontario potato specialist Eugenia Banks’ latest crop update.

Late blight continues to be the number one disease of concern because of its ability to spread rapidly and devastate a crop. However, late blight has not been reported in the province, despite spore traps continuing to catch spores of the disease in Dufferin, Simcoe and Norfolk counties.

Banks emphasized that A&L Laboratories – who conduct the PCR (polymerase chain reaction) tests for the spore traps – have “state of the art PCR equipment capable of detecting very small amounts of late blight DNA,” even a couple of spores per filter. Despite the sensitivity of the spore trap testing equipment, growers should still be diligent in their disease management.

There is another type of spore trap that spins glass rods coated with a gel in the air above a crop canopy, Banks adds. The rods are removed and checked under the microscope to identify spores of late blight. To date, these Rotorod sampler spore traps have only found late blight spores in tomato fields near Ridgetown, Ont., but they also cannot detect spore as early the the PCR methods.

Earlier this season, late blight was found in potatoes in Wisconsin and recently, more outbreaks have been reported from Wisconsin. Across the Great Lakes, late blight has been detected in Cattaraugus, Allegany and Genesee counties in New York on August 16, according to the Cornell Cooperative Extension.

Harvesting is underway for crop planted in early May near the Simcoe, Delhi, and Waterdown, Ont. areas. Banks reports that quality is good but yields are variable.

For fields planted near the end of May, Banks sees crop yellowing and some common diseases, such as early blight and brown spot, starting to become noticeable. In some irrigated fields, white mold and grey mold was reported.