Late blight reduction forms focus of Ontario Potato Conference.
THE REDUCTION of late blight risk was the focus of a panel discussion at the Ontario Potato Conference held in Guelph in late February.
With increasing incidents over recent years, Gary Secor, a professor of plant pathology with North Dakota State University, said it was now widely accepted that it could not be completely conquered, but the aim should be to reduce it to ‘a dull roar’.
Ontario has no late blight-resistant potato varieties, and even resistant varieties in the United States don’t last long because late blight has evolved quickly, he said.
High humidity, rain and high harvest pulp temperatures leading to soft rot and leak played a part in Ontario’s 2023 outbreak, but so did volunteers, culls and seed potatoes by providing hosts.
Removing those hosts can disrupt transmission, Gary said.
“Because seed is not washed, it’s hard to see those external symptoms. One to three per cent of the time, you can get transmission during the cutting operation. It’s enough to start an epidemic,” he said, stressing that one lesion can produce up to 10,000 spores.
The US government removed the use of mancozeb after the 2023 growing season and Gary recommended producers develop integrated multi-tactic management protocols before, during and after the season.
Hot, dry weather and ultraviolet light can kill spores or limit leaf presence, but reintroduction of moisture results in a resurgence, the conference was told.
New Brunswick potato growers use spore monitors for late blight three times a week, and share data with neighbouring Maine for improved disease management. The optical microscopy monitoring of spores provides five to seven days of early disease detection, giving growers sufficient lead time for preventive measures.
Mark VanOostrum, WD Potato Ltd Supply Manager, said Ontario spore traps failed to report any cases in 2023, despite being near fields with confirmed infection.
“We don’t have a provincially-funded late blight monitoring system,” he said, adding that growers should share information and eliminate potential avenues for disease spread.
In the absence of resistant varieties, producers should increase scouting, use 100% quarantine measures to control suspect seed, cull piles and volunteers, and manage harvest to prevent late blight development, said Mark.
Fields and bins that were not treated with Orondis or phosphorus acid have contributed to later problems in potato storage.
Source: Farmtario
